i

A GUIDE TO WASTEWATER TREATMENT

Case studies Included

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CONTENTS

SECTION PAGE

1  INTRODUCTION ......................................................................................................... 0 

1.1  Wastewater sources, composition and flow rate estimation ................................................................. 1

1.1.1  Domestic wastewater ........................................................................................................ 1 

1.1.2  Industrial Wastewater ....................................................................................................... 2 

1.2  Water Quality Standard-Measures of Water Quality- When is water contaminated ............................ 3

1.2.1  Dissolved oxygen .............................................................................................................. 3 

1.2.2  Biochemical oxygen demand ............................................................................................ 4 

1.2.3  Solids ................................................................................................................................. 5 

FIGURE1  CLASSIFICATION OF TOTAL SOLIDS (BASED ON FILTRATION) (VESILIND & ROOKE, 2003) ............................................................................................. 5 

1.2.4  Nitrogen ............................................................................................................................. 5 

1.2.5  Phosphorous ...................................................................................................................... 6 

1.2.6  Bacteriological measurements .......................................................................................... 6 

1.3  Wastewater characteristics .................................................................................................................... 7

1.3.1  Physical characteristics of wastewater ............................................................................. 8 

1.3.2  Chemical wastewater characteristics ................................................................................ 9 

1.3.3  Biological Characteristics of Wastewaters ..................................................................... 11 

1.4  Effects of Untreated liquid effluents ................................................................................................... 12

1.4.1  Health effects .................................................................................................................. 12 

1.4.2  Increase in the B.O.D. & C.O.D. content of water bodies ............................................. 13 

1.4.3  Increase in nutrient content ............................................................................................. 13 

1.4.4  Increase of soil deposition .............................................................................................. 14 

1.4.5  Effects of odours ............................................................................................................. 14 

1.4.6  Effects of Increased Temperatures ................................................................................. 14 

1.5  Wastewater collection systems ........................................................................................................... 15

1.5.1  Sanitary sewer systems ................................................................................................... 16 

1.5.2  Storm sewer systems ....................................................................................................... 16 

1.5.3  Combined sewer systems ................................................................................................ 17 

1.5.4  Collection System Components...................................................................................... 17 

FIGURE2  (A) JUNCTION BOXES (B) INTERCEPTOR PIPES (DRINAN & WHITING, 2001) ................................................................................................................. 18 

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2  WASTE WATER TREATMENT METHODS ........................................................ 18 

FIGURE3  TYPICAL STAGES IN THE CONVENTIONAL TREATMENT OF SEWAGE 19 

FIGURE4 .............................................................................................................................. 20 

constituent .................................................................................................................................................... 20Unit operation or process ............................................................................................................................. 20Suspended Solids ......................................................................................................................................... 20

3  INDUSTRIAL WASTE WATER TREATMENT METHODS .............................. 22 

3.1  Physical/chemical treatment methods ................................................................................................. 23

3.1.1  Screening ......................................................................................................................... 23 

FIGURE5  INCLINED BAR SCREEN ........................................................................... 24 

FIGURE6  CURVED BAR SCREEN .............................................................................. 25 

FIGURE7  RADIAL BAR SCREEN ............................................................................... 25 

FIGURE8  STEP TYPE SCREEN ................................................................................... 25 

FIGURE9  BRUSH TYPE SCREEN ............................................................................... 26 

3.1.2  Sedimentation.................................................................................................................. 26 

FIGURE10  CIRCULAR AND RECTANGULAR SETTLING TANKS .................. 26 

FIGURE11  PRIMARY CLARIFIER ELEVATION VIEW ...................................... 27 

FIGURE12  PRIMARY CLARIFIER PLAN VIEW ................................................... 27 

FIGURE13  SUCTION TUBE CLARIFIER ELEVATION ....................................... 27 

FIGURE14  PICKET FENCE SLUDGE THICKENER ............................................. 28 

3.1.3  Flotation and Skimming ................................................................................................. 28 

FIGURE15 ............................................................................................................................ 29 

3.2  Chemical treatment methods ............................................................................................................... 29

3.2.1  Chlorination .................................................................................................................... 30 

FIGURE16  CHLORINATOR ....................................................................................... 30 

3.2.2  Ozonation ........................................................................................................................ 31 

FIGURE17  OZONE WATER TREATED AREA ...................................................... 31 

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FIGURE18  OZONATOR .............................................................................................. 32 

3.3  Biological treatment methods ............................................................................................................. 32

3.3.1  Activated-sludge Process ................................................................................................ 34 

FIGURE19  AN AERATION BASIN (PEPPER, GERBA, & RUSSEAU, 2006) ...... 35 

FIGURE20  DENITRIFICATION SYSTEMS: (A) SINGLE-SLUDGE SYSTEM. (B) MULTISLUDGE SYSTEM (PEPPER, GERBA, & RUSSEAU, 2006). ................... 36 

FIGURE21  DENITRIFICATION SYSTEM: BARDENPHO PROCESS (PEPPER,

GERBA, & RUSSEAU, 2006). ............................................................................................ 37 

3.3.2  Trickling Filters .............................................................................................................. 38 

FIGURE22  (A) A UNIT OF PLASTIC MATERIAL USED TO CREATE A

BIOFILTER. THE DIAMETER OF EACH HOLE IS APPROXIMATELY 5 CM. (B) A TRICKLING BIOFILTER OR BIOTOWER. THIS IS COMPOSED OF MANY PLASTIC UNITS STACKED UPON EACH OTHER. DIMENSIONS OF THE BIOFILTER MAY BE 20 M DIAMETER BY 10–30 M DEPTH (PEPPER, GERBA, &

RUSSEAU, 2006).................................................................................................................. 39 

3.3.3  Oxidation Ponds .............................................................................................................. 40 

FIGURE23  AN OXIDATION POND. TYPICALLY THESE ARE ONLY 1–2

METERS DEEP AND SMALL IN AREA. ....................................................................... 40 

3.3.4  Aerobic ponds ................................................................................................................. 40 

FIGURE24  AEROBIC WASTE POND PROFILE (PEPPER, GERBA, & RUSSEAU, 2006).................................................................................................................. 41 

3.3.5  Anaerobic ponds ............................................................................................................. 41 

FIGURE25  ANAEROBIC WASTE POND PROFILE (PEPPER, GERBA, & RUSSEAU, 2006).................................................................................................................. 41 

3.3.6  Facultative ponds ............................................................................................................ 41 

FIGURE26  MICROBIOLOGY OF FACULTATIVE POND (PEPPER, GERBA, & RUSSEAU, 2006).................................................................................................................. 42 

3.3.7  Aerated lagoons or ponds ............................................................................................... 42 

4  INTRODUCTION ....................................................................................................... 44 

4.1  Fibers Categorization .......................................................................................................................... 44

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FIGURE27  SCHEMATIC DIAGRAM OF DIFFERENT PROCESSING SECTORS IN TEXTILE INDUSTRY (RAMESH BABU, 2007) ....................................................... 45 

4.1.1  Cultivating and harvesting .............................................................................................. 46 

4.1.2  Preparatory Processes ..................................................................................................... 46 

4.1.3  Spinning- Yarn manufacture .......................................................................................... 46 

4.1.4  Weaving- Fabric manufacture ........................................................................................ 47 

4.1.5  Finishing- Processing of Textiles ................................................................................... 47 

4.2  Textile Industry Chemicals ................................................................................................................. 49

Hydrophobic/ Oleophobic Agents ............................................................................................ 52 

1.5.5 ............................................................................................................................................... 52 

1.5.6  Antistatic    Agents .......................................................................................................... 52 

1.1.1 ............................................................................................................................................... 52 

1.5.7  Oxidative compounds ..................................................................................................... 52 

4.3  The origin of textile effluents ............................................................................................................. 53

4.3.1  Colour .............................................................................................................................. 53 

4.3.2  Persistent Organics.......................................................................................................... 53 

4.3.3  AOX and heavy metals ................................................................................................... 54 

4.3.4  Toxicants ......................................................................................................................... 54 

4.3.5  Surfactants ....................................................................................................................... 54 

4.3.6  Temperature .................................................................................................................... 55 

4.4  Waste disposed from each section ...................................................................................................... 574.5  Treatment Methods ............................................................................................................................. 57

4.5.1  Primary treatments .......................................................................................................... 58 

FIGURE28  MECHANICAL WASTEWATER SCREENING (HH AG, 2005) ....... 58 

4.5.2  Secondary treatments ...................................................................................................... 60 

FIGURE29 ............................................................................................................................ 61 

FIGURE30  COMPACT CHEMICALLY ENHANCED-TRICKLING FILTER SYSTEM (AHMED, 2006) .................................................................................................. 63 

FIGURE31  ACTIVATED SLUDGE (BABU B.V., 2008) ........................................... 64 

FIGURE32 ............................................................................................................................ 64 

FIGURE33 ............................................................................................................................ 67 

FIGURE34  SCHEMATIC DIAGRAM OF THE EXPERIMENTAL APPARATUS FOR PHOTOCATALYTIC REACTION ......................................................................... 70 

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FIGURE35  ADSORPTION COLUMN ........................................................................ 71 

FIGURE36  SCHEMATICS OF A THERMAL EVAPORATOR ............................. 71 

4.6  Example 1 - WASTEWATER CHARACTERISTICS IN TEXTILE FINISHING

MILLS ......................................................................................................................................................... 71

FIGURE37  SCHEMATIC DIAGRAM OF THE TEXTILE FINISHING MILL SHOWING DIFFERENT SECTIONS .............................................................................. 72 

4.7  Example 2- Textile Wastewater Treatment Plant ............................................................................... 74

4.7.1  Plant operation ................................................................................................................ 75 

FIGURE38  AMARAVATHI COMMON EFFLUENT TREATMENT PLANT ..... 78 

5  INTRODUCTION ....................................................................................................... 79 

5.1  EFFLUENT SOURCE ........................................................................................................................ 80

FIGURE39  OIL STORAGE TANK ............................................................................. 81 

5.3  EFFLUENT PARAMETERS ............................................................................................................. 81

5.4  EFFLUENT TREATMENT ............................................................................................................... 83

5.4.1  PRE TREATMENT ........................................................................................................ 83 

5.4.2  PRIMARY TREATMENT ............................................................................................. 84 

FIGURE40  PROCESS DIAGRAM OF TREATMENT METHODS SOURCE:

STEFAN T. O, 2008 ............................................................................................................. 84 

5.4.3  SECONDARY TREATMENT....................................................................................... 84 

5.4.4  TERTIARY TREATMENT ........................................................................................... 84 

5.5  LEGISLATION .................................................................................................................................. 85

FIGURE41  FIG. 1 DISSOLVED AIR FLOTATION SYSTEM ................................ 87 

FIGURE42  FIG. 2 HYDRO-CYCLONE SEPARATOR ............................................ 88 

FIGURE43  API OIL-WATER SEPARATOR ............................................................ 89 

FIGURE44  A TYPICAL BIOLOGICAL TREATMENT PLANT ........................... 90 

5.7  LIQUID EFFLUENT MONITORING ............................................................................................... 90

FIGURE45  WASTE WATER ANALYSIS LABORATORY .................................... 91 

6  LEGISLATIONS ON TEXTILE INDUSTRY CASE STUDY: .............................. 95 

7  LEGISLATIONS ......................................................................................................... 96 

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8  REFERENCES ............................................................................................................ 99 

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1 INTRODUCTION

Liquid effluents refer to water discharged from a community after it has been contaminated by various uses. It is often referred to as wastewater and it is combination of water removed from residences, institutions, industrial establishments, and surface and ground waters (Metacalf & Eddy Inc, 1991). It consists of 99.94 percent water by weight and the remaining 0.06 percent is suspended or dissolved material (Shun & Lee, 2000). In the United States in the early 19th century, liquid effluents from residences, commercial premises and industries were generally discharged in to large bodies of water on to land directly without treatment. However, as the cities got larger, population increased and the demand for land became higher. Waste could no longer be dumped into the land untreated. A similar method was also being applied in the UK. Most settlements of old were located where there was easy access to water supply. However, as the clean water was used up, it was replaced by used dirty water. The polluted water was then sent back into the homes for use. Population explosion of urban areas produced massive outbreak of cholera and in 1848 and 14,000 people died of the disease. However, at this time there was no link between polluted water and disease. It was not until 1852 that a link was made between the polluted water and disease. Soon after this, laws were then enacted and certain actions were carried out. For instance in the London, efforts were made to clean up the river Thames which was regarded as biologically dead. Water from the Thames was first treated before being sent to homes for use. The water was also treated after use before being discharged back into the Thames. Today, the river Thames is considered as one of the cleanest rivers to run through a city (Read & Vickridge, 1997). Today, in most modern cities, wastewater is treated before being discharged in to natural water bodies. In the US, 15,000 wastewater treatment plants treat approximately 150 billion liters of wastewater per day (Pepper, Gerba, & russeau, 2006). In this chapter, a brief introduction into wastewater, its sources, water quality standards, its effect and collection mechanism is described. Brief notes are also given to describe some references that can be consulted for more detailed information.

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Wastewater sources, composition and flow rate estimation

Wastewater is usually generated from residences, institutions and commercial houses, industries, farms, and run-offs from storms. Waste waters from residences, institutions, commercial houses, and farms are referred to as domestic wastewaters. However, recently farmers are required to set up on-site treatment systems for animal waste (Ministry for the Environment of Manatu Mo Te Taiao, 2009). Industrial wastewaters are sometimes treated separately but this depends on the type of industry and the size of the community. Most communities collect and treat both domestic and industrial wastewaters together in municipal wastewater treatment plants. Below is a brief introduction into some of the sources of wastewaters, their composition and flow rate.

1.1.1 Domestic wastewater The components of domestic wastewater are; wastewater from homes, commercial places,

water from rain runoff and infiltration wastewater (Kiely, 1997). Residential wastewater

usually comprises of water from toilets, laundry, washing dishes etc and they are usually

referred to as sewage. They can also be divided into two groups; Black water-which is

basically water from toilets and Grey water which is water from every other source like

kitchen sinks. Humans excrete 100–500 grams wet weight of faeces and 1–1.3 Liters of urine

per person per day.

The composition and concentration of domestic water varies depending on the time of the

day, the day of the week, the month of the year and other conditions (Metacalf & Eddy Inc,

1991). Table 1 gives a data of typical composition of domestic wastewater. The composition

refers to the amount of physical, chemical, and biological pollutants present1.

To reduce the load of water in the treatment plant, some countries separate the pipe network for rain runoff from the main sewer water body. However, some countries do not have such and it will be too expensive to embark on the project of creating new sewer networks

1 For details on the composition of domestic wastewater further reading can be carried out in the book by (Metacalf & Eddy Inc, 1991) 

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TABLE 1 Typical composition of untreated domestic wastewater (Pepper, Gerba, &

russeau, 2006).

CONTAMINANTS

CONCENTRATION (mg/l) LOW MODERATE HIGH

Solids, total 720 1200 350 720 1200 Dissolved, total 250 500 850

250 500 850

Volatile 105 200 325 105 200 325 Suspended solids 100 220 350

100 220 350

Volatile 80 164 275 80 164 275 Settleable solids 5 10 20

5 10 20

Biochemical oxygen demanda 110 220 400

110 220 400

Total organic carbon 80 160 290

80 160 290

Chemical oxygen demand 250 500 1000

250 500 1000

Nitrogen (total as N) 20 40 85

20 40 85

Organic 8 15 35 8 15 35 Free ammonia 12 25 50

12 25 50

Nitrites 0 0 0 0 0 0 Nitrates 0 0 0 0 0 0 Phosphorous (total as P) 4 8 15

4 8 15

Organic 1 3 5 1 3 5 Inorganic 3 5 10 3 5 10 5-day, 20°C (BOD, 20°C).

1.1.2 Industrial Wastewater

This is wastewater generated from industrial processes. The wastewater generated from

industries varies in flow and composition depending on the type of industries. Metacalf &

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Eddy Inc. (1991) suggest that for industries with little or no wet processes, the estimated flow

is about 1000 – 1500 gal/acre.d (9-14 m3/ha . d) for light industries and 1500-3000 gal/acre . d

(14-28m3/ha . d) for medium industrial development. Generally, to determine the wastewater

flow from an industry, a flow duration curve is created by taking measurements from the

wastewater streams continuously using automatic continuous flow recorders. However, as this

is expensive and time consuming, adequate measurements can also be obtained by using

autosampling-autoanalytical equipments (Kiely, 1997).

As mentioned earlier, wastewater composition from industries vary and before treatment

processes can be set up, waste flow diagrams or mass balance of waste flows and

characteristics have to be carried out. Kiely, (1997) identifies five major steps required in the

survey;

• Identifying the unique process from start to finish

• Identifying the liquid waste streams

• Calculating flows of all wastewater streams

• Determining the pollutant load of all wastewater streams

• Analysing the pollutant load for the most suitable parameter to identify the waste

stream

Water Quality Standard-Measures of Water Quality- When is water contaminated

The quality of water is relative to its use. What may be considered as a pollutant for a particular water use may be of importance in another application. For example, organics in water help to support plant and animal life. However, organics in water will have an adverse effect if the water were to be used in a cooling tower (Vesilind & Rooke, 2003). The standard reference for water quality based on physical, chemical and biological characteristics is “Standard Methods for Examination of water and wastewater” The book is a compilation of test methods for measuring water quality. Some of the parameters measured are discussed below.

1.1.3 Dissolved oxygen

This is a very important parameter in the determination of water quality. Water devoid of oxygen will have odours and facilitate anaerobic conditions which will also result in odours

4

and loss of aquatic life. The oxygen content can be measured using an oxygen probe and meter (Vesilind & Rooke, 2003). 1.1.4 Biochemical oxygen demand

This is another very important parameter. It is a measures of both the rate at which oxygen is

used up by microorganisms to break down organic matter and the amount of organic matter

present in the water. In wastewater treatment, removal of BOD is essential as if left untreated

and the rate of oxygen consumption is greater than re-oxygenation from the atmosphere

unfavourable conditions will develop in the water body the wastewater is being discharged

into.

The BOD in wastewater can be detected using the standard BOD test known as the 5-day

BOD test which is run at 20°C for five days. The test is also carried out in the dark to prevent

algae from producing oxygen. However, the test is not accurate as it depends on the use of

oxygen by microorganisms. Other tests that have been employed are determination of

chemical oxygen demand (COD test) and Total Oraganic Carbon (TOC test). The COD test

makes use of strong oxidants to destroy the organic compounds present in the wastewater. It

is based on the assumption that all the organics are destroyed. The organics present can then

be estimated from stoichiometry. The TOC test measures the total carbon content of the

wastewater. This is done by injecting the sample wastewater into a heating coil and measuring

the amount of carbon dioxide gas produce and relating it stoichiometrically to the amount of

carbon. Since the test does not measure the organic food material alone, the %5 day test is

still used for the determination of BOD (Vesilind & Rooke, 2003).

The BOD content for most domestic wastewater discharge is approximately between 150 and

250 mg/L but that of industrial wastewater maybe as high as 30,000mg/L (Vesilind & Rooke,

2003). The BOD test carried out to;

• To determine the amount of oxygen that will be required for biological treatment of

the organic matter present in a wastewater

• To determine the size of the waste treatment facility needed

• To assess the efficiency of treatment processes, and

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• To determine compliance with wastewater discharge permits.

1.1.5 Solids In wastewater, anything other than water or gas is classified as solids. However, the basic

definition for solids is anything that remains after evaporation at 103°C (Vesilind & Rooke,

2003). These solids are often referred to as Total solids. They can be classified into two

groups based on filtration; suspendes solids and dissolved solids( as shown on figure 1.1). If

left untreated, these solids can serve as serious pollutants leading to several effects which will

be discussed later.

FIGURE1 CLASSIFICATION OF TOTAL SOLIDS (BASED ON FILTRATION)

(VESILIND & ROOKE, 2003)

To determine the amount of total solids present, a known volume of wastewater is placed on

an evaporating dish until all the water has evaporated. The total solids is expressed in

milligrams per liter. As the name implies, dissolved solids are those components that dissolve

in the water and will crystallize upon evaporation. Solids can also be classified in another

way based on combustion into; volatile suspended solids and fixed suspended solids. Volatile

suspended solids are generally organic in nature and a considered to combust at about 600°C.

1.1.6 Nitrogen The presence of Nitrogen in wastewater being discharged untreated into a water body can

cause euthrophication (presence of excess nutrients leading to the increase in microbial life).

Nitrogen is an important element in biological reactions and is present in the organic form (i.e

as amino acids and amines) and in ammonia form. It oxidises to nitrate reducing the oxygen

levels in the stream.

Nitrogen presence can be detected analytically by calorimetric techniques. A known sample

of wastewater can be reacted with Nessler reagent (a solution of potassium mercuric iodide).

A yellow-brown colloid is formed and then it indicates the presence of Nitrogen. The precise

amount can’t be determined from photometric analysis of the colloid.

Total

Suspended Dissolved

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1.1.7 Phosphorous

Phosphorous is the limiting nutrient that prevents euthrophication and limits the rate of

metabolic activity. If allowed to exceed natural limits can disrupt the ecological balance of the

water body (Vesilind & Rooke, 2003).

1.1.8 Bacteriological measurements

Pathogens are organisms that cause illness and their determination is very important.

However, the detection of pathogens is challenging for some reasons: Each pathogen has a

specific detection procedure. Also, their concentration is so small as to make detection

difficult. Yet, the presence of one or two of these organisms in water may be sufficient to

cause infection (Vesilind & Rooke, 2003). In the United states pathogens of importance

include Salmonella, Shigella, the hepatitis virus, Entamoeba histolytica, Giardia lambilia,

Crptosporidium, and Escherichia coli H57 strain2. Some of these pathogens cause gastro

intestinal disease and sometimes can lead to death. As mentioned earlier, it is impossible to

measure all the pathogens carried by wastewater hus an indicator is used to define the

bacteriological water quality. The most commonly used indicators are a group of microbes

called coliforms (Vesilind & Rooke, 2003). Coliforms have five important attributes which is

why they have become universal indicators;

• They are normal inhabitants of the digestive tracts of warm-blooded animals;

• They exist in abundance and thus are not difficult to find

• They are easily detected

• They are generally harmless except in unusual circumstances

• The can survive longer than most known pathogens

The amount of coliforms in water can be measured by passing a known amount of water

through a sterile filter, then placing the filter in a Petri dish and soaking it with sterile agar

solution that promotes the growth of coliforms alone. The number of dark blue-green dots

formed after 24 or 48 hours indicates the coliform colonies present and it is expressed as

coliforms/100mL. The removal of coliforms has become perfected by most wastewater

treatment plant and the US EPA is tending towards the use of enterococci as an indication for

2 For more information on the disease caused by each pathogen consult (Vesilind & Rooke, 2003). 

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contamination. Table 2 below shows some of the pathogenic organisms found in water and

their typical concentration.

TABLE 2 Types and numbers of microorganisms typically found in untreated

domestic wastewater (Pepper, Gerba, & russeau, 2006)3.

ORGANISM CONCENTRATION (per ml)

Total coliform 105–106

Fecal coliform 104–105

Fecal streptococci 103–104

Enterococci 102–103

Shigella Present

Salmonella 100–102

Clostridium perfringens 101–103

Giardia cysts 10_1–102

Cryptosporidium cysts 10_1–101

Helminth ova 10_2–101

Enteric virus 101–102

The objective of wastewater treatment is to prevent the receiving water body from being

contaminated by reducing;

• Biochemical oxygen demand (BOD)

• Total suspended solids (TSS)

• Nitrogen and Phosphorous

• Faecal coliforms

However, other objectives may be set depending on the country and the legislation set up

regarding the disposal of wastewater.

Wastewater characteristics

A combination of domestic and industrial wastewater is often referred to as municipal

wastewater. Some countries have separate sewer networks for domestic and industrial

effluents. However, in most countries the sewer systems are combined. In order to ensure that

3 (Pepper, Gerba, & russeau, 2006) this book contains detailed information on test that are used to detect amount of BOD, COD and TOD. It also contains detailed calculations and example. The book generally looks into all forms of environmental pollution with a chapter dedicated to water pollution. 

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toxic substances are not released into the municipal wastewater system, industrial wastewaters

have to be pre-treated to a certain standard depending on the country (Hammer, 1986).

In order to effectively collect, treat and dispose of wastewater an understanding of the basic

characteristics of wastewater is essential. Wastewater is characterised in terms of;

• Physical

• Chemical

• Biological

However, some of these characteristics are interrelated. For example, temperature is a

physical property but affects both the biological activity and the solubility of gases in

wastewater (Metacalf & Eddy Inc, 1991). A summary of the characteristics is shown on Table

1.2. However some properties will be discussed briefly below.

1.1.9 Physical characteristics of wastewater 1.1.9.1 Solids in wastewater

Solids can exist in water either as suspended or dissolved solids as mentioned earlier. They

are made up of organic or inorganic particles or immiscible liquids like oils and grease. The

total solid content in wastewater is regarded as the residue upon evaporation at 103 to 105°C

(Metacalf & Eddy Inc, 1991). They are often characterised by their size distribution, state and

chemical characteristics. Solids are of importance in wastewater treatment as they serve as

adsorption sites for micro organisms and chemicals and thus reduce the efficiency of

treatment (Drinan & Whiting, 2001). Domestic wastewaters usually contain suspended solids

that are organic in nature while industrial wastewaters contain a diverse variety of both

organic and inorganic pollutants. Solids can be removed by primary sedimentation. However

for particles of size 0.001 to 1 µm, secondary methods can be used to remove the solids

(Metacalf & Eddy Inc, 1991). The TSS standards for primary and secondary effluents are

usually set at 30 and 12 mg/L (Shun & Lee, 2000)4

1.1.9.2 Colour

The colour of waste water indicates how septic the waste is. At the initial stages, the

wastewater is brownish or light grey in colour. As it flows further down the collection system,

anaerobic reactions occur and it becomes dark grey or black in colour (Drinan & Whiting,

4 Shun & Lee, 2000 gives more detials on how to measure total suspended solids in wastewater and it also includes detailed calculations and examples. 

9

2001).

1.1.9.3 Odour Treatment basins, clarifiers, aeration basins, and contact tanks are some of sources where bad odour is generated in a wastewater treatment plant. Odours are generated from the anaerobic decomposition of organic compounds in wastewater. The units are normally covered to prevent the odours from escaping. However explosive gases may ensue and cause problems. Thus the units are vented to a scrubber to prevent that (Drinan & Whiting, 2001). Odours can be detected using olfactory systems. (Koe & Tan, 1998) in their work came up with a method to quantify wastewater odour strength using an olfactometer and a first order model5. Although there are four independent factors for the characterisation of odours: intensity, character, hedonics and detectability, the only factor commonly used in statutory development is detectability (Metacalf & Eddy Inc, 1991). 1.1.9.4 Temperature

The temperature of the wastewater is a very important parameter as it affects the rate of both

the chemical and biological treatment. If temperatures are high, the solubility of the chemicals

for treatment increases and microbial action is more effective. However if temperatures are

low, microbial activity is slow and more chemicals will be required (Drinan & Whiting,

2001).

1.1.10 Chemical wastewater characteristics

The chemical characteristics of wastewater refers to the total dissolved solids (TSD) which

comprises majorly of alkaline minerals, organics, PH, chlorides and nutrients. They are

related to the solvent capabilities of the wastewater (Drinan & Whiting, 2001).

1.1.10.1 Total dissolved solids

These are the solid compounds that remain as residue after the wastewater has been filtered

and has undergone evaporation. They can be removed from wastewater by filtration and

evaporation, and also by electrodialysis, reverse osmosis, or ion-exchange (Drinan & 5 A method of quantifying the odor strength of wastewater samples has been investigated. Wastewater samples from two locations of a wastewater treatment plant were collected and subjected to air stripping. The off‐gas odor concentration was measured by a dynamic olfactometer at various time intervals. Applying a first order model to the decay of odorous substances in the wastewater under air stripping, the initial odor strength of the wastewater was determined. The model was found to be acceptable under five different air‐stripping rates studied. (Koe & Tan, 1998) 

10

Whiting, 2001). As discussed earlier they can be grouped into total suspended solids(TSS)

and total dissolved solids(TDS). Each group can then be further divided into volatile and

fixed fractions (Shun & Lee, 2000).

1.1.10.2 Metals

Metals such as cadmium, copper, lead, zinc,mercury, and others are of great concern in

wastewater treatment because they are very toxic. And if discharged untreated can lead to

severe complications and even death. Not only are they toxic, but the can greatly reduce the

removal efficiency of some biological process (e.g. activated sludge process). The can be

removed via chemical treatment and their presence in wastewater streams often increase the

cost of the wastewater treatment plant. Their major source are from industrial wastes (Drinan

& Whiting, 2001).

1.1.10.3 Organic Matter

Wastewater contains organic compounds which have their roots from both the plant and the

animal kingdom. According to Metacalf & Eddy Inc, 1991, "In wastewater of medium

strength, about 75% of the suspended solids and 40% of the filterable solids are organic in

nature," Also organic compounds synthesised by man are found in wastewater. The

compounds are usually made up of carbon, hydrogen, and oxygen. Compounds like sulphur,

phosphorous,nitrogen and iron. The major organic compounds found in wastewaters are;

proteins, carbohydrates, urea, fats and oils. The manmade compounds found are pesticides,

surfactants and volatile organic compounds. As a result of industrialisation the amount of

synthetic organic compounds in wastewaters are rapidly increasing. However, these

compounds are not easily removed from wastewaters by biological treatment. Detailed brief

description of some of these compounds can be found in (Metacalf & Eddy Inc, 1991) and

(Drinan & Whiting, 2001)6.

1.1.10.4 pH

This is an indication of the hydrogen ion concentration present in the wastewater. The PH

affects the chemical and biological processes in wastewater treatment. For instance, if the pH

is high, the amount of chlorine required for the disinfection process will be greatly increased

6 (Metacalf & Eddy Inc, 1991) contains more details on types of organic compounds and the measurement of these organic constituents. 

11

(Drinan & Whiting, 2001).

1.1.10.5 Nutrients

These are inorganic compounds that are essential to the growth and reproduction of plants and

animals. The nutrients of greatest concern in wastewater treatment are nitrogen and

phosphorous. Other nutrients include carbon, sulfur, calcium, iron, potassium, manganese,

cobalt, and boron. The presence of nitrogen and phosphorous in surface waters is an

indication of wastewater contamination. Their presence can lead to the growth of unwanted

plants like algae and euthrophication. Typical ranges of nitrogen concentration in domestic

raw wastewater are 25-85 mg/L for total nitrogen (the sum of ammonia, nitrate, nitrite, and

organic nitrogen) and for phosphorus its 2 - 20 mg/L, which includes 1-5 mg/L of organic

phosphorus and 1-15 mg/L of inorganic phosphorus (Shun & Lee, 2000).

1.1.11 Biological Characteristics of Wastewaters Wastewater contains millions of microorganisms per milliliter. However many or these

organisms are harmless. The water becomes contaminated with dangerous pathogens from

waste discharged from people who are infected with them. Although micro organisms are

used in various treatment processes, the final effluent discharge most not carry dangerous

levels of pathogens. Basic orgfanisms of interest are bacteria, parasitic worms, protozoa,

viruses and algae (Drinan & Whiting, 2001). Below is a brief description of these organisms.

1.1.11.1 Bacteria

Bacteria is common place in wastewater treatment procrsses. However the presence of some

type of bacteria may cause gastrointestinal disorders.

1.1.11.2 Protozoa

These are single celled organisms that are widely distributed and highly adaptable. They are

active participants of the activated sludge process. However they have to be revoved either by

sedimation or filtration. Although most protozoans are harmless, two categories Entamoeba

12

histolytica (amebiasis), and Giardia lamblia (giardiasis) are considered as very harmful. The

levels of protozoa should be kept minimal in effluents.

1.1.11.3 Viruses

The presence of virus in wastewater is of great concer. This is because viruses are very small

and cannot be easiliy removed by filtratio. Also, viruses remain inactive until they find a host

and can reenter the water supply further downstream. Finally, testing for viruses is limited as

there are limited methods available.

1.1.11.4 Algae

Algaes grow in fresh water, saltwater and ppolluted water. They are usually found at the

surface as they require light for they metabolism. They are often used in waste water

treatments like fluculative and aerobic ponds to generate oxygen. However, their growth is

not easy to control, they encourage the formation of suspended solids and die of when the

wheather is cold

1.1.11.5 Worms (Helminths)

These are organisms that metabolise organic compounds aerobically. They are indicators that

a water body has been contaminated by wastewater. Parasitic worms like helminths are

transmitted to humans via contact with untreated wastewater.

Effects of Untreated liquid effluents The discharge of untreated effluents into local water may lead to several unwanted situations

like the destruction of aquatic life, contaminations of drinking water which will lead to illness

or even death, bad odours etc. Below some of the effects of untreated wastewater will be

discussed.

1.1.12 Health effects

Of all the effects the health effects of untreated wastewaters are one of the most important

ones. The first set of legislations on wastewater effluent discharge was focused towards their

effect on human health. Wastewater contains millions of bacteria that originate from human

13

faeces. However most are harmless. The organisms that may cause diseases are called

pathogens. Contact with the contaminated water may lead to disease such as typhoid, cholera

and gastrointestinal problems. The main class of viruses of concern are enteric viruses, which

cause gastro-enteritis; for example, calcivirus (Norwalk virus), rotavirus, enterovirus (polio

and meningitis) and hepatitis (Ministry for the Environment of Manatu Mo Te Taiao, 2009).

Asides from bacteria and viruses, other substances present in wastewater may lead to bad

health or even death. For instance, compounds like mercury, volatile organic compounds,

zinc, pesticides and other chemicals. Some of these compounds exist naturally but human

activities have increased their concentration in natural water systems. They may not have

immediate effects but may bio-accumulate in food and cause complications. According to the

Ministry for the Environment of Manatu Mo Te Taiao, some ivestigations are being carried

out to investigate the ability of some of these compounds to act as endocrine disruptor.

Endocrine distruptors are chemicals that when absorbed into the body mimics or hinders the

normal functions of hormones in the body.

1.1.13 Increase in the B.O.D. & C.O.D. content of water bodies

The discharge of untreated wastewater into springs, rivers and lakes will cause the BOD and

COD to rise. This will reduce the amount of oxygen available to aerobic (oxygen demanding)

aquatic animals like fish. Also this will encourage the growth of plants like algae and other

anaerobic organisms. Eventually, this will render the water body septic and biologically dead

(Weiner & Matthews, 2003)

1.1.14 Increase in nutrient content

Increased nutrient content (that is, organics from wastewater) will lead to algal bloom and

eutrophication. Nitrogen in the form of nitrate (NO3) in surface waters indicates

contamination with sewage and is an immediate health threat to both human and animal

infants (Drinan & Whiting, 2001). Excessive nitrate concentrations in drinking water can

cause death. The limiting factor for accelerated growth or some organisms is the absence of

nutrients nitrogen and phosphorus in the water body. These compounds exist in water

naturally but in limited quantities. An increased amount of these nutrients will cause the

accelerated growth of some toxic organisms like algae which will slowly lead the water body

to become septic.

14

1.1.15 Increase of soil deposition

Solids in water can have several harmful effects some of which are listed below

• Solids can cause unsightly floating scum

• They can sink to the bottom of the stream or river and form potentially hazardous mud

banks

• Most solids are organic in nature and upon decomposition create a demand for oxygen

• Floating solids serve as sites where pathogenic organism can hide and pose a threat to

human health.

1.1.16 Effects of odours

Odours although cause no direct physical harm to humans have great psychological effects

that may eventually lead to social and economic collapse in a community. Odours from

wastewater treatment plant can cause; loss of appetite, water intake, impaired respiration,

nausea, vomiting and mental perturbation. Offensive odours can also discourage capital

investment and lower socio-economic status of the community if left untreated. In a paper

prepared by Schiffman, et al., 2000, they proposed three paradigm which ambient odors may

produce health symptoms in communities with odorous manures and biosolids7. Many

communities have opposed the several wastewater treatment plant projects as a result of

public perception of odours.

1.1.17 Effects of Increased Temperatures

The temperatures of wastewater is usually higher than the atmospheric temperature and the

receiving water. High temperature decreases the solubility of oxygen. This combined with

7 Schiffman, et al., 2000, proposed three paradigm by which ambient odors may produce health symptoms in communities with odorous manures and biosolids. This site summarises the three paradigms  

15

increased biochemical oxygen demand can greatly affect the oxygen content of the receiving

water body. Eventually this will affect the aquatic life of the waterbody. Decreasing fish

lifand supporting the growth of unwanted organisms.

Below shows a summary of some of the effects of pollutants contained in wastewater. TABLE 3 Effects of pollutants in wastewater (Kiely, 1997)

Pollutants Effects

Soluble organics Deplete dissolved oxygen

Suspended solids Deplete dissolved oxygen and

release undesirable gases

Trace organics Affects taste odours and toxicity

Heavy metals Toxic to aquatic and human life

Colour and turbidity Affects aesthetics

Nutrients (N and P) Cause eutrophication

Refractory substances resistant to

biodegradation

Toxic to aquatic life

Oil and floating substances Unsightly

Volatile substances e.g H2S and

VOC

Air pollution

http://www.woodlands-junior.kent.sch.uk/riverthames/pollution.htm

dirty river thames

http://www.metrovancouver.org/services/wastewater/treatment/Pages/default.aspx

Wastewater collection systems

Wastewater collection systems are employed to transport wastewater form source to treatment

plant before disposal (Read & Vickridge, 1997). Collection systems are made up of a series of

network of pipes and pumping systems. In designing a collection system one must consider;

16

1. Health and Environmental aspect. That is the proposed collection system must not

pose a risk to human health and to the environmental.

2. The area the sewer network is going to service. The treatment plant must be adequate

in serving the allocated region.

3. The natural topography and drainage. Collection systems must be designed to take

advantage of the natural systems and thus reduce cost of installing pumps.

There are three main types of sewer networks (Kiely, 1997);

1. Sanitary sewer systems

2. Storm sewers

3. Combined sewer systems

Below is a description of each of these systems.

1.1.18 Sanitary sewer systems

For these systems, wastewaters generated from both domestic and industrial sources are

carried by separate systems of sewers to treatment plants while surface runoffs are carried of

by another set of systems to natural watercourses. This type of system is mostly adopted in

newer towns and cities (Read & Vickridge, 1997). Rain water washes contaminants from

roofs, streets and other areas, however the contaminant load is considered insignificant

compared to wastewater discharges from domestic and industrial sources (Hammer &

Hammer, Water and Wastewater Technology, 2008). Sanitary contains majorly human waste

as a result of the most important aspect of sanitary sewer design is the prevention of sewage

overflow (as they contain pathogens dangerous to human health) (Drinan & Whiting, 2001).

1.1.19 Storm sewer systems

These systems handle wastewaters generated from run-offs as a result of rainfall or melting

snow. They are becoming very important in developed and populated areas. This is because in

such areas, the ground is paved and this prevents water from naturally percolating and

17

recharging ground water. Instead, heavy run-offs result which carry large amounts of

contaminants (Drinan & Whiting, 2001).

Storm drains should be designed to handle contaminants like sand, silt and also sudden heavy

flows. Since they do not contain sewage, they can be discharged directly into the natural

environment although sometimes, primary treatment may be required (Hammer & Hammer,

2008).

1.1.20 Combined sewer systems

These are the oldest and most common type of collection system. For this type of system,

both surface runoffs and municipal wastewater are transported by the same pipe networks to

sewage treatment plants. This type of system is mostly found in older cities and towns (Read

& Vickridge, 1997)8. The systems are designed to accommodate large flows, especially those

resulting from heavy rain falls. However during storms, the system overflows and excess flow

above the plant capacity is bypassed into natural water bodies. This may become a health

hazard especially if water is used as supply for drinking water (Hammer & Hammer, 2008).

Typical storm water contains a BOD of 30mg/l while overflow from a combined sewer

contains contains 120mg/liter of BOD. Combined sewer overflows (CSO) are of great

concern. However, it is very expensive to change the entire sewer network and other methods

such as storage for later treatment are being explored (Shun & Lee, 2000).

1.1.21 Collection System Components

Most components of collection systems are built under streets easements, and right of way

and they are designed to meet considerations of population size, estimated flowrates,

minimum and maximum loads, velocity, slope depth, and need for additional system elements

8 This book contains detailed information on the history, construction, hydraulics and design of sewer systems. Focusing mainly on sewer rehabilitation, repair, and management. 

to ensure

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19

Preliminary: this includes simple processes such as screening (usually by bar screens) and

grit removal. (through constant velocity channels) to remove the gross solid pollution.

Primary: usually plain sedimentation; simple settlement of the solid material in sewage can

reduce the polluting load by significant amounts.

Secondary: for further treatment and removal of common pollutants, usually by a biological

process.

Tertiary: usually for removal of specific pollutants e.g. nitrogen orphosphorous, or specific

industrial pollutants

FIGURE3 TYPICAL STAGES IN THE CONVENTIONAL TREATMENT OF

SEWAGE

20

FIGURE4

Shown in table1 are some constituents found in wastewater and conventional water treatment

methods used to purify the water.

TABLE 4

CONSTITUENT UNIT OPERATION OR PROCESS

Suspended Solids Screening

21

Grit removal

Sedimentation

High-rate clarification

Flotation

Chemical Precipitation

Depth Filtration

Surface Filtration

Biodegradable organics Aerobic suspended growth

variation

Aerobic attached growth variation

Aerobic suspended growth

variation

Aerobic attached growth variation

Lagoon variation

Physical chemical systems

Chemical oxidation

Advanced oxidation

Membrane filtration

Nitrogen Chemical oxidation

Suspended-growth nitrification and

denitrification variations

Fixed-film nitrification and

denitrification variations

Air stripping

Ion exchange

Phosphorous Chemical treatment

Biological phosphorous removal

Nitrogen and phosphorous Biological nutrient removal

variations

Pathogens Chlorine compounds

Chlorine dioxide

Ozone

Ultraviolet radiation (UV)

Colloidal and dissolved solids Membranes

Chemical Treatment

22

Carbon adsorption

Ion exchange

Volatile organic compounds Air stripping

Carbon adsorption

Advanced oxidation

Odours Chemical scrubbers

Carbon adsorption

Bio filters

Compost filters

3 INDUSTRIAL WASTE WATER TREATMENT METHODS

The same way that you would know the steps of the process that you would be running in

industry, a critical study should be carried out to familiarize yourself with the wastewater to

find ways that the wastewater is generated in the plant.

Treatment methods can be divided into three general cases

- Physical/Chemical treatment methods

- Thermal Treatment methods

- Biological treatment methods

Physical

Waste water treatment methods

Biological Chemical

Aerobic

Septic tanks

Lagoons

Anaerobic

Trickling Filtration

Lagoons

Chlorination

Ozonation

Neutralization

Coagulation

Screening

Sedimentation

23

3.1 Physical/chemical treatment methods

After its biological treatment the waste water is almost clean and fresh again. However, the

micro-organisms responsible for cleaning should now be kept in their individual basins and

not run off with all the rest. Physical chemical treatment methods encompass a wide variety of

technologies, including gravity separation, filtration, chemical precipitation, evaporation,

oxidation, reduction, air stripping, carbon adsorption, ion exchange, adsorption on other

media, electrolytic recovery and membrane separation.

Gravity separation is used to extract clean water when the waste is settled in the bottom of the

tank. There are three types of separation methods which uses the same principal. Clarifiers,

Oil water separators and catch basins and sumps.

3.1.1 Screening

Mechanical treatment is indispensable as the first process step of preliminary treatment for

both municipal and industrial wastewater applications. It removes the bulk of the non

biodegradable matter such as plastic, women materials, metallic items so that the subsequent

treatment stages are protected against damage/pollution or to relieve them. There are many

different types of screens in industry at present designed to suit different needs. Some

examples as stated in EPCO, Australia are Inclined bar, curved bar, radial bar, step type,

brush type, back-raked and static screens.

Equalization

Degassification

Flotation & skimming

24

In operation in all these types, the sewage flows through the screen which approaches it from

the upstream side and after passing through exits from the downstream side. A mechanized

comb system is attached between the two side chains and is driven through a head shaft and

sprockets, to rake the screen periodically and the screenings collected are removed by a doctor

blade at the top of the comb travel as stared in [Epco, Australia]. These screenings are

dropped onto a skid plate which transports the screening down to a container.

FIGURE5 INCLINED BAR SCREEN

25

FIGURE6 CURVED BAR SCREEN

FIGURE7 RADIAL BAR SCREEN

FIGURE8 STEP TYPE SCREEN

26

FIGURE9 BRUSH TYPE SCREEN

3.1.2 Sedimentation

Sedimentation, a fundamental and widely used unit operation in waste-water treatment,

involves the gravitational settling of heavy particles suspended in a mixture, sedimentation

tanks are also known as clarifiers in the wastewater treatment industry. This process is used

for the removal of grit, particulate matter in the primary settling basin, biological floc in the

activated sludge settling basin, and chemical flow when the chemical coagulation process is

used.

FIGURE10 CIRCULAR AND RECTANGULAR SETTLING TANKS

Circular sedimentation tanks are preferred over rectangular tanks due to the ease of

maintenance, faster sludge removal and higher removal efficiencies. There is a scraper

mechanism adopted inside the tank which is used to collect the settled solids out of the tank

with the use of a pump. As stated by [Hammer 2004, pg 370] the scraper mechanism takes

different forms depending on which part of the treatment it is used for, i.e. primary, secondary

or tertiary. As further stated in circular sedimentation tanks these sludge scrapers are attached

to the rotating arm which scrapes the sludge towards the centre hopper where as in rectangular

tanks the scrapers are carried along in the tank bottom which collects the sludge into a hopper

which is situated at the influent end of the tank. There are 3 types of clarifiers which are

named as primary, secondary and tertiary tanks.

Primary tanks

The point at which the coarse solids and the grit are removed from the sewage stream is the

27

beginning of the primary process. The scraper mechanism as stated in [Epco] for primary

tanks would also be fitted with scum removal equipment to remove the floating matter and in

the primary stage as further stated approximately 65% of the organic solids and 35% pr the

BOD in the sewage is removed.

FIGURE11 PRIMARY CLARIFIER ELEVATION VIEW

FIGURE12 PRIMARY CLARIFIER PLAN VIEW

Secondary Tank

The water from the primary stage goes through some biological treatment and then enters the

secondary sedimentation which separates the mixed liquids and suspended solids and humus

sludge. The secondary clarifiers are fitted with scraper blades like in primary systems but

could also adapt a suction tube system as shown in the picture below. These systems also are

equipped with scum skimming systems.

FIGURE13 SUCTION TUBE CLARIFIER ELEVATION

Tertiary Tank

28

These systems often adapt simple sweeper chains but could also be fitted with the same

mechanisms as the primary and the secondary treatments. The final clarifiers are designed to

use with biological aeration. Activated sludge is withdrawn through suction pipes located

along the collector arm for rapid return to the aeration basin. Sludge thickeners and fermenters

are also used to scrape heavier sludges as shown in the figure.

FIGURE14 PICKET FENCE SLUDGE THICKENER

3.1.3 Flotation and Skimming

EffluentEffluent

Settled solids discharge

Float Discharge

29

FIGURE15

Dissolved air flotation is achieved by releasing fine air bubbles that attach to sludge particles

and cause them to float. Small units tend to be rectangular for and fabricated using steel.

Larger units are circular and manufactured in steel or concrete. Waste activated sludge enters

the bottom of the flotation tank, where it is merged with recirculated flow that contains

compressed air. A portion of the clarified effluent is pressurized in a separate retention tank

under an air pressure of approximately 60 psi to force air into solution. On pressure release,

the air dissolved in the recirculated flow forms fine bubbles to the suspended solids. The

process underflow is returned to wastewater treatment, and the overflow, discharge by

3.2 Chemical treatment methods

This treatment method uses burning or exposure of wastewater to high temperatures to

destroy the waste. Some waste that is burned could be used to recover energy in industrial

furnace or cement kiln on site. Treatment facilities such as hazardous waste incinerators are

another mean of for wastewater treatment but isn’t cost effective if used in small businesses

as they are quite expensive, unless the facility generates a large amount of waste. Some

industries tend to use off site facilities to treat wastewater but it is among the last choices to

use such means. Wet air oxidation is another method used to treat waste water which is

difficult to treat by other means. But this demands a huge amount of energy which in the long

run is more cost effective if the wastewater is treated off site.

30

3.2.1 Chlorination Chlorination is basically the process of adding liquid or gaseous chlorine in order to purify

water. This process isn’t solely used for disinfection; it is also used for odor control and

prevention of septicity, ammonia removal, destroying cyanides and phenols etc as stated by

the water quality and health council. The liquid form of chlorine which is generally more

expensive comes in the form of soluble salts (hypochlorites) while the gaseous form first

needs to be dissolved in water before it is used in the waste water industry.

There are a few reactions that occur in chlorination when used in the waste water industry.

When the chlorine is dissolved in water it firstly forms hypochlorous acid and hypochlorites.

Cl2 + H2O HOCl + H + Cl

HOCl OCl + H

As chlorine is an active oxidizing agent when added into waste water even in small amounts it

would react rapidly firstly with H2S, ferrous iron etc which are all compounds capable of

reducing. After all inorganic reducing matter is converted chlorine subsequently reacts with

the organic matter, ammonia or other nitrogeneous compounds to produce chloramines.

The device used for the control of the chlorine added is called the chlorinator.

FIGURE16 CHLORINATOR

http://www.backyardcitypools.com/chemicals/feeders/Hydrotools-Automatic-Chlorinator.htm

31

3.2.2 Ozonation

Before After

FIGURE17 OZONE WATER TREATED AREA

It is one of the modern methods used in wastewater treatment with a growing popularity. A

device known as the ozone generator is used to break down pollutants in the wastewater. The

ozone generator uses up the oxygen in the environment to produce ozone with the air of

ultraviolet radiation which is discharged by an electric field. This ozone which is known to be

highly reactive oxidise the bacteria, moulds and other pollutants in the wastewater.

As stated in the water pollution guide there are many advantages and disadvantages in using

ozone in wastewater treatment.

• Advantages:

o Effective killing of bacteria.

o Ease of extracting irons and sulphur compounds as they are oxidised.

o No nasty odours or residues hence precautions or measures for residue

treatment is not needed.

o As the oxygen to ozone conversion is a reversible reaction and the backward

reaction is fast the ozone converts back to oxygen instantly leaving no traces of

an oxygen use up.

• Disadvantages:

32

o This method is unreliable as it needs electricity to run and would not run

during an electric shortage and also costs money due to its power requirement.

o The treatment cannot remove dissolved minerals and salts.

o Ozone treatment can sometimes produce by-products such as bromate that can

harm human health if they are not controlled.

FIGURE18 OZONATOR

3.3 Biological treatment methods

Biological processes aid in the removal of non-settleable colloidal solids, inorganic

compounds and some organic matter with the aid of micro organisms. Biological processes

are often referred to as secondary wastewater treatment method as they aid in the removal of

biodegradable organic matter that could not be removed during primary treatment (Kiely,

1997). In wastewater treatment, the main objectives is the reduction of organic contents and

nutrients like nitrogen and phosphorus and also the removal of toxic organic compounds such

that the discharge to a water body should lead to little or no removal of oxygen in it by

bacterial action. During biological processes, organic pollutants are converted to less harmful

compounds like water and cell tissues. These can then be removed by gravity settling.

The commonly used biological treatment processes:

• Activated-sludge process

33

• Aerated lagoons

• Trickling filters

• Rotating biological contactors

• Stabilization ponds

Fundamentals of Biological wastewater treatment process

Biological treatment processes all take place in a vessel called a reactor and designers are

interested in the rate at which biodegradable compounds are removed from the inflow and

also, the rate of growth of the biomass in the reactor. (Benefield & Randal, 1980). The

biomass refers to the microbial body responsible for breaking down the pollutants. In

designing a biological process, it is very important to understand the nature and biochemical

activities carried out by the micro organism. Below, the types of micro organisms used and

their nutritional requirements will be mentioned briefly.

Important microorganisms

The important microorganisms in biological treatments are; Bacteria, Fungi, Algae, Protozoa

and Rotifiers.

Bacteria are single- celled organisms that reproduce mainly by binary fission although some

species can produce asexually or by budding. They are made up of 80% water and 20% dry

material. They also vary widely in size and their growth is greatly affected by the conditions

of temperature and pH (Metacalf & Eddy Inc, 1991).

Fungi are multicellular organisms. Example of this is yeast. They can reproduce sexually or

asexually. They have the ability to withstand lower pH and Nitrogen levels than bacteria and

this makes them very important in wastewater treatment.

Algaes are unicellular or multicellular compounds. They are very important in wastewater

treatment processes because of their ability to generate oxygen from photosynthesis.

However, excess algae growth can lead to the biological death of a water body.

Protozoa and Rotifiers are single celled motile protists. Most protozoa are aerobic and are

generally larger than bacteria and alsoeat bacteria as an energy source. Thus are used to polish

effluents from biological waste treatments.

Rotifiers generally perform the same duties as protozoas in wastewater treatment. Their

34

presence indicates a highly efficient biological process (Metacalf & Eddy Inc, 1991).

Nutritional requirements

For micro organisms grow, reproduce and function efficiently they must have;

1. A source of energy

2. Source of carbon for synthesis of new cellular material

3. Source of inorganic nutrients such as Nitrogen, phosphorous, sulphur, potassium

calcium and magnesium (Metacalf & Eddy Inc, 1991).

The carbon and energy sources are considered as substrate

3.3.1 Activated-sludge Process This is one of the most popular biological treatments adopted in most countries and it is also

known as aeration-tank digestion. In this process, wastewater that has undergone primary

treatment is pumped into a large tank and mixed with bacteria rich slurry known as activated

sludge (Pepper, Gerba, & russeau, 2006). To encourage bacterial growth and decomposition

of the organic materials present, air or oxygen is pumped into the tank. The mixture is then

sent to a secondary settling tank where water is removed from the top and the bacteria rich

sludge is removed from the bottom. About 20 percent of the sludge is recycled back into the

primary aeration tank as inoculums while the remainder known as secondary sludge is

removed (Kiely, 1997). Fig below shows an aeration basin.

The activated sludge culture is made up of bacteria, protozoa, rotifiers and fungi. The bacteria

is mostly responsible for the break-down of organic material while the protozoa and rotifiers

remove the bacteria.

35

FIGURE19 AN AERATION BASIN (PEPPER, GERBA, & RUSSEAU, 2006)

The content of the aeration tank is referred to as the mixed-liquor suspended solids (MLSS)

and the organic part of the MLSS is called the mixed-liquor volatile suspended solids

(MLVSS), which consists of the non-microbial organic matter as well as dead and living

microorganisms and cell debris (Kiely, 1997). The activated sludge process must be

controlled to maintain a proper ratio of substrate (organic load) to microorganisms or food-to-

microorganism ratio (F/M) (Pepper, Gerba, & russeau, 2006). This is expressed as BOD per

kilogram per day. It is expressed as:

/ [1]

where:

Q -flow rate of sewage in million gallons per day (MGD)

BOD5 - 5-day biochemical oxygen demand

MLSS - mixed-liquor suspended solids (mg/L)

V - volume of aeration tank (gallons)

It can thus be observed that the higher the wasting rate, the higher the food-micro organism

ratio. A low F/M ratio indicates that the micro organisms are starved and will tend to have

higher removal efficiencies. In conventional aeration tanks, the F/M ratio is 0.2–0.5 lb

BOD5/day/lb MLSS, but it can be higher (up to 1.5) for activated sludge when high-purity

oxygen is used (Hammer, 1986). The parameters that controll the operation of an activated

sludge process are;

• organic loading rates

• oxygen supply

• control and operation of the final settling tank

An important parameter to consider is the sludge settleability in the sludge tank. The biomass

must settle well in order for it to be returned to the aeration tank. The best conditions for

settling are achieved when carbon and energy sources are limited and the specific microbial

growth rate is local. Conditions that hinder effective settleability are sudden changes in

temperature, pH, absence of nutrients, and presence of toxic metals and organics. Another

36

important factor is the presence of filamentous bacteria. For effective settling, a residence

time of three or four days is required (Metacalf & Eddy Inc, 1991).

Removal of Nitrogen and Phosphorous by activated sludge process

Activated sludge process can be modified such that they not only remove organic compounds

but can also remove nutrients like nitrogen and phosphorous.

Nitrogen Removal

For nitrogen removal, the sludge is left to age for over four days to encourage nitrification of

ammonia to nitrate by nitrifying bacteria. The nitrogen is then removed via denitrification

process. Examples of avtivated sludge systems that have been modified for nitrogrn removal

are:

• Single sludge system

• Multisludge system and

• Bardenpho process

Figure below shows a schematic diagram of these processes9

FIGURE20 DENITRIFICATION SYSTEMS: (A) SINGLE-SLUDGE SYSTEM. (B) MULTISLUDGE SYSTEM (PEPPER, GERBA, & RUSSEAU, 2006).

9 Pepper, Gerba, & russeau, 2006 can be consulted for more detailed information on each process. 

37

Phosphorous removal

Phosphorous can also be removed by modifying the activated sludge process. The process

involves an uptake of the phosphorous during the aerobic stage and the release during the

anaerobic stage. Two processes used are;

A/O (anaerobic/toxic) process: This process consist of and anaerobic zone upstream the

conventional aeration tank. In the aerobic phase, soluble phosphorus is taken up by bacteria

and is synthesised to polyphosphates and during the anaerobic stage, the phosphorus is

released by the hydrolysis of the polyphosphates formed.

Bardenpho process: This process can also be used for the removal of nitrogen

A schematic diagramof these process are shown on fig below

FIGURE21 DENITRIFICATION SYSTEM: BARDENPHO PROCESS (PEPPER, GERBA, & RUSSEAU, 2006).

Design of an activated sludge process

In designing an activated sludge process, the following conditions are considered;

• Mixing regimes

• Load criteria

• Sludge viability

• Oxygen requirement

• Nutrient requirement

• Temperature

• Solid-liquid separation

• Effluent quality

38

Another very important consideration is the choice of reactor as this will define the geometry

of the reactor, the bath of effluent into the reactor and the mixing regime. There are two

mixing regimes applicable in the activated sludge process

(1) Plug-flow: in this type of regime, the wastewater flows into the reactor

(aeration tank) in an orderly fashion with no element of mixing.

(2) Complete mixing flow: Here, the reactor is constantly stirred and kept

uniform. This type of mixing is often referred to as steady state.

However, complete mixing or plugflow is not achieved in the reactor but the design has to

ensure that the conditions are almost met (Benefield & Randal, 1980)10.

3.3.2 Trickling Filters

This is one of the oldest biological treatment methods. However the main mechanism is not

filtration as the name suggest. Treatment is achieved by diffusion and microbial assimilation.

In the process, the effluent from the primary treatment is pumped through an overhead

sprayer onto a bed of stones or plastic where bacteria and other organism reside. As the

organic materials trickle past, the bacteria intercepts it and decomposes it aerobically. In

older trickling filter designs, the beds were made of stones. But these had the disadvantage of

limited depth of 3-10 ft, low void space, and requirement for structural design (Benefield &

Randal, 1980). However, in modern trickling filter designs, the bed is made up of plastic

units. Other materials that can be used are ceramic, hard coal. The most common type of

plastic bed used is polyvinyl chloride (PVC) because of their light weight. Other advantages

are the greater void space and larger specific area. The PVC are stacked in towers as shown

on fig below.

10 Details on the design of activated sludge process and the associated kinetics involved can be found in this text. 

39

(a) (b)

FIGURE22 (A) A UNIT OF PLASTIC MATERIAL USED TO CREATE A BIOFILTER. THE DIAMETER OF EACH HOLE IS APPROXIMATELY 5

CM. (B) A TRICKLING BIOFILTER OR BIOTOWER. THIS IS COMPOSED OF MANY PLASTIC UNITS STACKED UPON EACH

OTHER. DIMENSIONS OF THE BIOFILTER MAY BE 20 M DIAMETER BY 10–30 M DEPTH (PEPPER, GERBA, & RUSSEAU, 2006).

As the organic matter passes through the filter, it is converted to a microbial biomass that

forms a bio film called zooleal on the filter surface. With time, the film thickens and the lower

part has limited access to oxygen and as a result film sloughs off ( also called sloughing) and

a new bio film is formed. Effluents from a trickling filter are sent to a clarifier for further

removal of solid compounds. A typical trickling filter had a BOD removal efficiency of 85%

(Pepper, Gerba, & russeau, 2006).

Two important properties of the filter media are;

The specific area of the media

The percent void space

The greater the surface area, the greater the amount of biomass per unit volume. Also, the

greater the void space, the higher the hydraulic loading can be without restricting oxygen

40

transfer (Benefield & Randal, 1980)11.

3.3.3 Oxidation Ponds

These are often referred to as sewage lagoons or stabilization ponds. They are the oldest of the

wastewater treatment process requiring huge land space. Here, the wastewater is detained for

a period of 1-4 weeks( sometimes longer) while microorganisms degrade the organic matter

in them. A tyoical oxidation pond is shown below on fig

FIGURE23 AN OXIDATION POND. TYPICALLY THESE ARE ONLY 1–2 METERS DEEP AND SMALL IN AREA.

There are four categories of osidation ponds which are often used in series: aerobic ponds,

anaerobic ponds, facultative ponds and aerated ponds.

3.3.4 Aerobic ponds

Here, the wastewater is detained for 3-5 days at a depth of about 1.5m to encourage the

growth of algae which in turn promotes the generation of oxygen. A section of an aerated

pond is shown on fig below.

11 Detail design calculations for tricling filters can be found in Benefield & Randal, (1980) 

41

FIGURE24 AEROBIC WASTE POND PROFILE (PEPPER, GERBA, & RUSSEAU, 2006)

3.3.5 Anaerobic ponds

These are about 1-10m deep and have a longer detention time of about 20 – 50 days. They are

normally used to treat wastewater with high BOD content and do not requireany form of

mechanical aeration. They also generate comparably small amount of sludge. Fig shows the

profile of an anaerobic pond.

FIGURE25 ANAEROBIC WASTE POND PROFILE (PEPPER, GERBA, & RUSSEAU, 2006)

3.3.6 Facultative ponds

They are normally used for the treatment of domestic waste and they have a dentention time

of 5-30 days. These type of ponds range in depth from 1- 1.25 m and are is made up of three

sections: an upper aerated zone, a middle facultative zone, and a lower anaerobic zone as

shown on fig . The make use of both aerobic and anaerobic treatment.

42

FIGURE26 MICROBIOLOGY OF FACULTATIVE POND (PEPPER, GERBA, & RUSSEAU, 2006)

3.3.7 Aerated lagoons or ponds

These are usually about 1-2 m deep with a detention time of less than 10 days. The removal

efficiency depends on the aeration time and temperature as well as the source of the

wastewater.

Limitations of oxidation ponds

Although oxidation ponds are cheap and require minimum technology, they have several

draw backs. Biodegradable organic matter and turbidity are not as effectively removed when

compare to the activated sludge process. Also, they have a potential for short circuiting and

detectable levels of pathogens can be found in their effluents.

This method is used to remove organic compounds from wastewater. It is most suitable for

wastewater that contains a relatively constant source of biochemical oxygen demand (BOD)

and very low concentrations of toxic metals. A surge tank to equalize wastewater flow and

concentration variations can help the treatment system work effectively. This is commonly

used to treat domestic sewage.

43

CASE STUDY 1:

44

4 INTRODUCTION

The textile industry is a major industry involved in the manufacture of textiles as the final

product. Textiles refer to the finished products of a production process involving the

conversion of fibres to fabrics and the material fabricated into clothes or other artifacts. The

production process requires the use of several chemicals and a large volume of water at

various stages of the production. Textile production is simply based on the conversion of

three types of fibres into yarn, yarn into fabric and then fabric into textiles. Fibres can be

classified into two major groups, namely natural and artificial fibres (man-made fibres).

4.1 Fibers Categorization

Natural Synthetic (Artificial)

Vegetable fibres (Plant origin) Man-made fibres (Artificial)

• Flax Nylon • Hemp Polyester • Jute Polyamides

Protein fibres (Animal origin)

• Wool • Silk • Angora

The production stages in a typical textile company includes: fibre production, fibre

processing, spinning, yarn production, fabric production and finishing. Due to the nature and

applicable technology of the production process, a high amount of water is consumed in

manufacturing of textiles that is consequently generating a considerable amount of

wastewater (Nemerow, 1978). Textile industries are a major source of effluent in the

environment. (Ghoveishi and Haghighi,2003).The major pollutant in textile wastewater are

high suspended solid, chemical oxygen demand, heat, colour, acidity and other soluble

substances (Venceslau et al. 1999, World Bank, 2007). Most of these pollutants are produced

from the finishing section.

The impacts resulting from textile industry on the environment have been recognisable for

some time both in terms of discharge of pollutants and the consumption of water and energy

(Lacasses and Baumann, 2006). Some significant impacts the textile industry has on the

45

environment have been identified as primary water consumption (80 – 100m3/ton of finished

textile) and wastewater discharge (115 – 175Kg of COD/ton of finished textile) a large range

of organic chemicals, low biogradability, color and salinity. These pollutants resulting from

the production process differ greatly in composition due to several factors (Bisschop and

spanjer, 2003).

Cotton is one of the mostly used fibres in textile manufacturing. It is an important natural

fibre which posses unique characteristics. The production process of textile from cotton

involves the following processing steps:

FIGURE27 SCHEMATIC DIAGRAM OF DIFFERENT PROCESSING SECTORS IN TEXTILE INDUSTRY (RAMESH BABU, 2007)

46

4.1.1 Cultivating and harvesting

This refers to the preliminary production process carried out to attain the raw material. Cotton

plants are cultivated and harvested upon maturity. They are usually grown anywhere in long,

hot dry summers with plenty of sunshine and low humidity. Indian cotton, gossypium

arboreum is finer but the staple is only suitable for hand processing. American cotton,

gossypium hirsutum produces the longer staple needed for machine production. The cotton

bolls are harvested by stripper harvesters and spindle pickers that remove the entire boll from

the plant. The cotton boll is the seed pods of the cotton plant, attached to each of the

thousands of seeds are fibres about 2.5 cm long.

4.1.2 Preparatory Processes

• Opening and cleaning: The stage ensures the cleaning of the cotton bolls. A cotton

opener and picker are employed in the stage of preparation.

• Ginning: This refers to the process whereby the cotton seeds are separated from the

fibre and other contaminants such as leaves, in a Gin.

• Carding: the fibres are separated and then assembled into a loose strand (sliver or

tow) at the conclusion of this stage.

• Combing: this is used to remove the shorter fibres, creating a stronger yarn.

• Drawing: the fibres are straightened and it sliver form the combing process processed

into rovings

4.1.3 Spinning- Yarn manufacture

• Spinning: This is carried out in a spinning machine; the rovings are thinned, twisted

and wound onto the bobbin in preparation for fabric manufacture.

• Checking: This is the process where each of the bobbins is rewound to give a tighter

bobbin.

• Folding and twisting

Plying is done by pulling yarn from two or more bobbins and twisting it together, in

the opposite direction that that in which it was spun. Depending on the weight desired,

the cotton may or may not be plied, and the number of strands twisted together varies.

47

• Gassing

Gassing is the process of passing yarn, as distinct from fabric very rapidly through a

series of Bunsen gas flames in a gassing frame, in order to burn off the projecting

fibres and make the thread round and smooth and also brighter.

4.1.4 Weaving- Fabric manufacture

The weaving process uses a loom. The length-way threads are known as the warp, and the

cross way threads are known as the weft. The warp which must be strong needs to be

presented to loom on a warp beam. The weft, passes across the loom in a shuttle that carries

the yarn on a pirn. These pirns are automatically changed by the loom. Thus, the yarn needs to

be wrapped onto a beam and onto pirns before weaving can commence.

• Winding

After being spun and plied, the cotton thread is taken to a warping room where the

winding machine takes the required length of yarn and winds it onto warper’s bobbins

• Sizing

This is a process whereby starch is added to the wrap to strengthening it.

• Drawing in or Looming

The process of drawing each end of the warp separately through the dents of the reed

and the eyes of the healds.

• Pirning (Processing the weft)

Pirn winding frame was used to transfer the weft from cheeses of yarn onto the pirns

that would fit into the shuttle

4.1.5 Finishing- Processing of Textiles

48

The grey cloth, woven cotton fabric in its loom-state, not only contains impurities, including

warp size, but requires further treatment in order to develop its full textile potential.

Furthermore, it may receive considerable added value by applying one or more finishing

processes.

• Desizing

Depending on the size that has been used, the cloth may be steeped in a dilute acid and

then rinsed, or enzymes may be used to break down the size.

• Scouring

Scouring, is a chemical washing process carried out on cotton fabric to remove natural

wax and non-fibrous impurities (eg the remains of seed fragments) from the fibres and

any added soiling or dirt.

• Bleaching

Bleaching improves whiteness by removing natural coloration and remaining trace

impurities from the cotton; the degree of bleaching necessary is determined by the

required whiteness and absorbency.

• Mercerising

This is a further treatment process to improve the quality of the fabric. The fabric is

treated with caustic soda solution to cause swelling of the fibres. This results in

improved lustre, strength and dye affinity.

Singeing

Singeing is designed to burn off the surface fibres from the fabric to produce

smoothness. The fabric passes over brushes to raise the fibres, and then passes over a

plate heated by gas flames.

• Raising

49

During raising, the fabric surface is treated with sharp teeth to lift the surface fibres,

thereby imparting hairiness, softness and warmth, as in flannelette.

• Calendering

Calendering is the third important mechanical process, in which the fabric is passed

between heated rollers to generate smooth, polished or embossed effects depending on

roller surface properties and relative speeds.

• Shrinking (Sanforizing)

Finally, mechanical shrinking (sometimes referred to as sanforizing), whereby the

fabric is forced to shrink width and/or lengthwise, creates a fabric in which any

residual tendency to shrink after subsequent laundering is minimal.

• Dyeing

Finally, cotton is an absorbent fibre which responds readily to colouration processes.

Dyeing, for instance, is commonly carried out with an anionic direct dye by

completely immersing the fabric (or yarn) in an aqueous dyebath according to a

prescribed procedure. For improved fastness to washing, rubbing and light, other dyes

such as vats and reactives are commonly used. These require more complex chemistry

during processing and are thus more expensive to apply.

• Printing

Printing, on the other hand, is the application of colour in the form of a paste or ink to

the surface of a fabric, in a predetermined pattern. It may be considered as localised

dyeing. Printing designs on to already dyed fabric is also possible.

4.2 Textile Industry Chemicals

50

Process Basic chemicals

chemicals structure

Washing

detergent

Cationic

Anionic

Nonionic

Dying &

Printing

Dye

Acid Dye

Basic Dye

Direct Dye

Vat Dye

Mordant

Dye

Reactive Dye

51

Disperse

Dying &

printing

Dye

Azo Dye

Sulphur

Dye

Pigments

Anti foam

Silicon antifoam

Non-silicon antifoam

Thickener

Natural

Starch, Alginate, seeds such as acacia

Synthetic

CMC, PVA

Emulsion Oil in water (O/W)

Binders

Acrylate based CH2=CHCOO−

Butadiene acetate

Vinyl acetate

Fixing Agent

Melamine-

formaldehyde

52

Finishing

Bleaching Agent

Sodium hypochlorite

NaClO3

Calcium hypochlorite

Ca(ClO2)2

Hydrogen Peroxide H2O2

Softening

Agent

non‐ionic surfactants 

fatty acids, fatty esters and fatty amides 

cationic surfactants quaternary ammonium compounds, amido amines, imidazolines

paraffin and polyethylene waxes

oregano-modified silicones

Hydrophobic/ Oleophobic

Agents

Wax-based repellents zirconium- & aluminium-based salts

Resin-based repellents condensed fatty compounds (amines, alcohols or acids)

Silicone repellents polysiloxane-active substances

Fluorochemical repellents Fluoroalkyl- acrylates /methacrylates copolymers

Flame Retardants

Inorganic FR agents Zirconium , Aluminium and Titanium salts

Halogenated FR agents Cl/ Br compounds

Phosphor-organic FR agents

PO* radicals

1.1.22  

1.1.23 Antis

tatic 

   

Agen

ts 

quaternary ammonium compounds

phosphoric acid ester

derivatives

Sizing Agents

Natural Starch, cellulosic derivatives (CMC), glue, gelatine, albumen

Synthetic Poly acrelytes, poly vinyl alcohol (PVA), Styrene/Maleic acid copolymers

Desizing Agents

Enzymes Amylases

1.1.24 Oxidative 

compounds 

Sodium per sulphate, sodium bromite

Acidic Agents Sulphuric/Hydrochloric acids

53

4.3 The origin of textile effluents Based on both magnitude and complexity of the effluents composition, discharged from

textile industry, this sector is considered as one of the most polluting industries. Bleaching,

washing (or scouring) and those wet procedures undertaken within dyeing and finishing

sectors are at most responsible for the disposed effluents. Huge variety of dyes and chemicals

disposed in textile wastewater make it hard to be treated in conventional WWTPs. The nature

of textile wastewater is studied based on chemicals consumed and in terms of some general

parameters such as TS, TSS, BOD, COD, heavy metals, Phosphor and Nitrogen contents. The

main troublesome pollutants in textile waste can be categorized to dyes, persistent organics,

absorbable organic halogens (AOX), toxicants and surfactants (Vandevivere et al., 1998).

4.3.1 Colour

Chromagen is the central point of every dye that adheres to the fibre and absorbs the visible

light. There are about twelve different types of chromagens which are mainly (60-70%) azo

type and anthraquinone type. Dyes are basically resistant toward degradation; therefore,

majority of them are not biodegraded in aerobic activated sledges. Azo dyes stability under

aerated conditions strongly depends on the complexity of their chemical structure. Azo dyes

are readily reduced to amines that are amongst most carcinogenic chemical compounds.

Decolourization of reactive dyes is highly concerned because of three main reasons. First of

all reactive dyes have dominated the market by having about 20-30% of the total share,

because they are used for dyeing and printing cotton fibres. Secondly about 30% of reactive

dyes used is hydrolyzed and discharged into wastewater. At last the conventional wastewater

treatment plants that are mainly functioning based on aerobic degradation and sorption are

vulnerable in treating reactive and other anionic soluble dyes.

4.3.2 Persistent Organics

The persistent compounds exist in textile effluents are produced from different types of

chemicals; mainly include dyes, dyeing auxiliaries such as deflocculating agents

(naphtalenesulfunates or lignins), sequestering agents, phosphonates and polyacrylates,

antistatic agents for manmade fibres, preservatives (substituted phenol), fixing agents applied

in direct dyeing of cotton, carriers used in disperse dyeing of polyester and great amounts of

finishing chemicals applied for water-, moth- and fire- proofing. Although just small portions

of these chemicals are used in each stage, their great persistency against degradation makes

their treatment highly challenging.

54

4.3.3 AOX and heavy metals

Sodium hypochlorite has some priorities to H2O2 as a bleaching agent. It results in reasonably

better whiteness, lower cost and less structural damages caused by H radicals. However all

types of hypochlorite bleaching agents produce high amounts of absorbable organic halogens

(AOX)(in this case chloroform) that are highly toxic and carcinogenic. Also chemicals used

for moth proofing and shrink proofing of wools that contain chlorine in their structure

effectively contribute to AOX formation. There are also some reactive dyes that are basically

AOX.

Heavy metals present in textile wastewater causing another hardship in treating these waste.

Cr, Mg, Na, Zn, Cu, Ni and Ca are the most famous heavy metals that mainly exist in metal-

complex dyes and some chemical auxiliaries.

4.3.4 Toxicants

The heterotrophic activities are slowed down very slightly by textile wastewater in the

activated sludge; while the functioning of chemoautotrophic nitrifying bacteria is inhibited

significantly by these types of effluents. Therefore, inorganic compounds are hardly

biodegraded and oxidized and so several types of them remain as hazardous toxic matters in

the wastewater.

Moreover, great amounts of azo dyes, which can be easily reduced to aromatic amines,

metallic compounds remained from metal complex dyes and numerous finishing agents such

as cross linking, water and flame retardants and softeners that constitute aromatic compounds

in their chemical structures can be accounted as persistent toxic waste in the final textile

effluent.

4.3.5 Surfactants

Majority of textile wet processes such as washing and scouring, weaving, spinning, sizing,

desizing, printing, dyeing and most of the chemical finishing procedures consume great

amounts of surfactants. Alkyl phenol ethoxylates are the main non-ionic surfactants highly

used in different textile processes. These surfactants are biodegraded to alkyl phenols and

readily adsorbed to the sewage sludge, accumulate there and increase the regional sludge

55

concentration. The concentrations of up to 1000 ppm have been reported. Alkyl phenols are

much more hazardous and toxic than the ethoxylated compounds.

4.3.6 Temperature

The temperature of the wastewater obtained from textile wet processes is unusually higher

than what is disposed from other industries. Rinse waters used in dyeing and printing sectors

has temperatures of up to 90°c and result in high temperature wastewater of about 40°c.

Therefore a prior heat dissipation system is always necessary to reduce the effluent’s

temperature to 30°c or less before transferring the waste to the treatment cycle. This step can

significantly enhance the treatment efficiency.

The final textile wastewaters can be generally classified into three categories based on their

colour intensity and their COD content (Lin & Peng, 1993). The high strength wastewater has

a dark colour with very low transparency and COD concentration of more than 1600 mg/l.

The medium strength wastewater also has dark colour but with higher transparency and COD

concentration of between 800 and 1600 mg/l; while the COD concentration of the low

strength, light colour wastewater is mainly less than 800 mg/l.

TABLE 5 Characteristics of typical textile wastewater

56

Process  Wastewater  Residual wastes 

Fibre Preparation  little or none  Hard waste, packing waste, fibre 

waste 

Yarn Spinning  little or none  Sized yarn, packaging waste, 

cleaning and processing waste, 

fibre waste 

Slashing/Sizing  Size, metals, cleaning waste, 

BOD, COD 

Un‐used starch based sizes, 

packaging waste, fibre lint, yarn 

waste 

Weaving  little or none  Used‐oil, off‐spec fabric, yarn 

and fabric scraps, packaging 

waste 

Knitting  little or none  Yarn and fibre scraps, packaging 

waste,  off‐spec fabric 

Tufting  little or none  Yarn and fibre scraps, packaging 

waste,  off‐spec fabric 

Desizing  BOD from lubricants, synthetic 

size, water‐soluble sizes, anti 

static compounds and biocides 

Cleaning materials such as 

filters, rags, wipes; yarn waste, 

fibre lint, packaging waste,  

maintenance and  cleaning 

wastes containing solvents 

Scouring  Insecticide and disinfectants, 

NaOH, pectin, oil, fats, wax, 

detergent, knitting lubricants, 

spin finishes, spent solvents 

 

Little or none residual waste 

Bleaching  Sodium silicate or organic 

stabilizer, Hydrogen Peroxide, 

high PH 

 

Little or none residual waste 

Singeing  little or none  Little or none residual waste 

Mercerizing  NaOH, High PH  Little or none residual waste 

Heat setting  little or none  Little or none residual waste 

Dyeing  Surfactants, Salts, Metals, 

organic processing assistance, 

toxics, Sulphide, BOD, spent 

solvents, acidity/alkalinity. 

 

Little or none residual waste 

Printing  Urea, metals, colours, foam, 

BOD, heat, solvents, suspended 

solids 

 

Little or none residual waste 

Finishing (cross‐linking, water 

proofing, flame retardant 

BOD, COD, spent solvents, 

toxics, suspended solids, Urea 

Packaging waste, fabric scraps 

and trimmings 

57

Class BOD

(mg/l)

COD

(mg/l)

PH SS

(mg/l)

Temperature

(˚C)

Oil (mg/l) Conductivity

(μS cm-1)

High Strength 500 1500 10 250 28 50 2900

Medium

Strength

270 970 9 137 28 21 2500

Low Strength 100 460 10 91 31 10 2100

4.4 WASTE DISPOSED FROM EACH SECTION

List of the waste materials disposed from each sector in textile industry (Ramesh Babu, et al. 2007), (Yussuf,

2004)

4.5 Treatment Methods

processing) 

Product Fabrication  little or none  Fibre scraps 

58

The treatment methods applicable to the textile industry can be divided into three main

categories which are Primary, Secondary and Tertiary treatment methods. These treatment

methods are classified based on their simplicity and application in the industry

4.5.1 Primary treatments

4.5.1.1 Screening

Screening is an important but simple primary treatment that is applied for removing Coarse

suspended substances such as rib and rag parts, lints, yarns, fibres and pieces of fabric(Das,

2005). Mechanically cleaned fine screens and bar screens eliminate most of the fibres.

Preceding to the secondary treatments such as susceptible biological and oxidation processes

these suspended matters should be completely removed from the wastewater. Clog trickle

filters, carbon beads and seals are mainly used in this system.

FIGURE28 MECHANICAL WASTEWATER SCREENING (HH AG, 2005)

4.5.1.2 Sedimentation

The main goal of primary treatment (clarification or sedimentation) is removing floatable

solids and settling organics (Das, 2005). Sedimentation is considered as an efficient and

economic alternative to remove suspended material in textile effluent. Sedimentation and

clarification sectors are mostly capable of removing 25-35% BOD, 40-60% TSS and 90-95%

settling solids. Removing these great amounts of floatable, suspended and settling matters in

the primary treatment stages reduces the organic loading of wastewater transferred to other

treatment steps.

59

In this step the velocity of the wastewater is reduced by 1-2 ft/min rate, sedimentation and

floatation processes take place, and enhanced by slowing the wastewater flow (Ramesh Babu,

2008). In the sedimentation tanks floatable foam and grease and the settled sludge material

are collected respectively and then pumped to the disposal or transferred for further

treatments. Rectangular and centre-feed clarifiers are the most common types of equipments

used in this sector. In rectangular clarifiers the effluent flows horizontally from one side to the

other side and finally with help of a single bottom scrapper on a channel bridge or sets of

flights placed on parallel chains the settled sludge is transferred to a hopper. In the centre-feed

clarifiers the effluent is fed from the centre and flows outward. The sludge is collected from a

hopper in the middle of the tank bottom. In both types of clarifiers it is a surface skimmer that

is responsible for removing floatable matters (mainly oil and grease).

4.5.1.3 Equalization

Wastewater streams are gathered in a sump tanker. The rotating agitators and air compressors

are responsible for stirring the mixed effluents (Eswaramoorthi, 2009). In the case of using

compressed air flow the air is blown in high velocity from below of the sump tanker. The

conical bottom of the tanker enhances the efficiency of removing suspended solids which are

tiny fibres and accumulated colours, printing pastes and metallic compounds.

4.5.1.4 Neutralisation This is a process which entails the removal of excess acidity or alkalinity from the wastewater

by the treatment with a chemical of the opposite composition. The adjustment of the pH value

is the main criterion in the neutralisation process. Acidic wastewater i.e in the region of 0-6.9

can be neutralised with chemicals such as sodium hydroxide (NaOH), Sodium bi-carbonate

etc. A detailed table providing alternative chemicals suitable for neutralisation can be found in

Wastewater Engineering treatment and Reuse 4th edition, chapter 6)

In the textile industry, some of the chemicals used during production which may influence the

pH value of the wastewater are: Cationic Surfactant/Blend for Dyed Cellulosic fibres,

Polyester Acrylic and Blended fabrics these chemicals impart excellent soft feel on the

finished fabric. Anionic Surfactant /Strong Detergent the chemical acts as an emulsifier

/scouring and wetting Agent. Poly Vinyl Acetate Emulsion imparts handle stiffness with hard

60

feel on the finished fabric. A detailed source of textile chemicals their composition and

applications can be found in Textile processing chemicals available at

http://www.indiamart.com/atulitchemical/chemical.html

4.5.1.5 Mechanical Flocculation & Chemical Coagulation

Flocculation refers to the transport step which brings about the cohesion of destabilised

particles needed to form larger particles known as ‘flocs’. These are readily removed by

settling or filtration. The purpose of wastewater flocculation is the formation of flocs or

aggregates from finely divided particles which cannot be removed by simple sedimentation.

In the textile industry, the textile wastewater is passed through a tank under gentle stirring

addition of a chemical coagulant might be necessary to aid the floc formation. The resultant

effluent is usually a clear and free from colloidal particles such as sizing agents; suspended

particles etc. 80-90% removal of Total suspended solids can be achieved via this process. 40-

70% BOD removal can be achieved over a period of five days while COD removal can be up

to 60%. Das S. (Textile Effluent Treatment – A Solution to the Environmental Pollution)

4.5.2 Secondary treatments

Secondary treatments are used in succession to the primary treatment methods in the textile

industry. These methods are basically suitable for the removal of organics, BOD, COD, which

have not the removed by the primary methods

4.5.2.1 Aerated Lagoons

Lagoons are relatively shallow earthen basins with varying dept in the range of 2 – 5m.

Mechanical aerator provides oxygen for the biological treatment of the wastewater and to

keep the biological solids in suspension. These aerators are either floats or fixed platforms.

Aerated lagoons are operated on a flow-through basis or with solid recycles and three

principle types can be identified based on the manner in which the solids are handled.

These are:

1. Facultative partially mixed

2. Aerobic flow through with partial mixing

3. Aerobic with sold recycle and nominal complete mixing

The differences in the manner in which the solids are handled affect the treatment efficiency,

61

power requirement, hydraulic solid retention time, sludge disposal and environmental

consideration. An in-depth description of the behaviour of each of these lagoons can be

accessed from Wastewater Engineering 4th edition chapter 8 table 8-29.

In the textile industry, the effluent from the primary treatment methods are collected in these

earthen basins and treated for 2-6 days. The mechanical aerators ensure the oxidation of the

organics. Up to 99% of the BOD present in the wastewater can be removed via this process.

Aerobic lagoon with solid recycle essentially is the same as extended aeration activated-

sludge process but in an earthen basin.

Source: http://wpcontent.answers.com/wikipedia/commons/1/1d/Surface-Aerated_Basin.png

FIGURE29 The process of design of lagoon basically consider these factors

a. BOD removal

b. Effluent characteristics

c. Temperature effects

d. Oxygen requirement

e. Energy requirements for mixing

f. Solid separation

In depth information of the aforementioned can also be found in Wastewater engineering 4th

edition.

4.5.2.2 Trickling filtration

Trickling filters typically have a rectangular or circular bed, with 1 to 3 meter depth, that is

filled of a well-graded media such as Gravels, Clinkers, Synthetic resins, Coal, PVC or

broken stone of sizes between 40 and 150 mm (Babu, 2008 and Das, 2005). The textile

62

wastewater is sprayed uniformly over the solid medium from a slowly rotating distributor

equipped by nozzles or orifices (such as rotary sprinkler). As the wastewater seeps through

the entire bed the growth of microorganisms (Larvae, worms or helminthes, algae, fungi,

bacteria and protozoa) accelerates. The organic compounds inside the wastewater are

consumed as the main nutrients for microorganisms and in the mean time oxygen is flowed in

a counter-current direction to that of wastewater flow to provide an aerated condition at the

outer side of the filter. All these together produce a gelatinous layer of aerobic

microorganisms and bacteria called “Zooglea” on the medium surface. By increasing the

amounts of nutrients and oxygen supplied, the thickness of the film increases and more

organics, nitrates, sulphates, carbon dioxide and other stable by-products are produced. Then

these materials coagulate at the feed side of the filter and subsequently removed from that

region. The following relationship simply shows the trickling procedure;

Organisms + Organics → Solid Wastes + CO + More Organisms

When the slime layer becomes extremely thick it blocks the wastewater flow through the solid

medium; therefore, it is cleaned up in the final settling tank. In some cases the filtered effluent

is circulated back to the main stream, once or twice, in order to enhance the overall efficiency

of the filtration process.

Trickling filtration is a cost effective method that requires low energy supply, forms small

portions of sludge and is suitable for treating biodegradable matters inside the effluents

(Ahmed, 2006). Moreover this technique has shown great results in removing ammonia from

the wastewater. The hybrid systems of trickling filtration and chemical methods have shown

advantageous features in wastewater treatment.

63

FIGURE30 COMPACT CHEMICALLY ENHANCED-TRICKLING FILTER SYSTEM (AHMED, 2006)

4.5.2.3 Activated sludge

Biological treatments are all basically natural self purifying processes which are enforced by

some artificial bio compounds injected into the system (Ramesh Babu, 2007). Gaining the

original quality of the present aquatic environment is the ideal objective of these types of

treatments.

Activated sludge process is one of the most flexible biological oxidation techniques mainly

used for removing coarse solid organic compounds, colloids and dissolved solids from the

textile wastewater (Das, 2005). The elimination rate of oxidizable material processed in this

method is up to 90% (Babu B. V., 2008). In this process the effluent is aerated by some

aerobic microbial flocs that is suspended in a reaction tank. Subsequently the waste is

biodegraded to water and carbon dioxide molecules. The fast growing suspended microbial

floc is called Activated Sludge. The effluent and the activated sludge are separated from each

other by settling their mixture in the reaction tank. A portion of the sludge is reused and

injected to the tank to enhance the microbial reaction. The remaining sludge, in addition to

what is achieved from the primary sedimentation is digested in a sludge digester.

The main problem is that most of the dyes and chemicals used in the textile industry are not

highly biodegradable and using the activated sludge individually will not effectively reduce

the contamination of the wastewater. Therefore, this method is generally applied in

combination with other techniques or by adding adsorbents such as activated carbon or

bentonite clay to remove the toxic-organic matters and non-biodegradable components from

the textile effluent (Ramesh Babu, 2007). Subsequent oxidative chemical treatments or

reaction with organic flocculants are options can be applied in frequently after the biological

treatment.

Biological aerated filtration (BAF) is a biological treatment that has been developed recently

and takes advantage of aeration of a stationary organism as a medium.

64

FIGURE31 ACTIVATED SLUDGE (BABU B.V., 2008)

4.5.2.4 Oxidation ditch

A similar method of pre-treatment used in the textile industry in oxidative ditch method.

Oxidation ditch is an aerobic process similar to the activated sludge process. However, an

oxidation ditch is ring-shaped and is equipped with mechanical aeration devices. It could be

classified under biological treatment method and particularly suitable for treating BOD,

Alkalinity, TSS polluted wastewater.

http://www.gec.jp/JSIM_DATA/WATER/WATER_2/img/Fig_231-1.jpg

FIGURE32

4.5.2.5 Anaerobic digestion

65

In this step the sludge, which has been formed in the primary sedimentation process, and the

waste obtained from the humus tank are both digested and fermented slowly in reaction with

anaerobic bacteria in a sludge digester (Das, 2005). The sludge is maintained for 30 days in

this tank at pH of 7-8 and temperature of 35 ˚C. CO2, CH4 and small portions of NH3 are the

main final products of this process.

The textile sludge can be effectively treated by anaerobic digestion process (Asia et al., 2006).

Considerable reductions in nitrates, phosphates, COD, BOD and suspended solids have been

observed via processing the textile wastewater in this system. Gaining bio-fertilizer and

biogas as the final products makes this method more advantageous. Moreover, this method

has a relatively low operation costs in comparison with other secondary treatments.

There are many bacteria that are capable of decolourizing azo dyes under anaerobic

conditions (Georgiou, 2006). In the first stage the highly electrophilic azo bonds are broken

via bacterial reactions, the azo dye is decolorized and the aromatic amines are formed.

Basically the uncharged azo dyes in anoxic sediment environments tend to reduced to their

corresponding amine; Amines which are extremely carcinogenic, toxic and mutagenic.

Despite easy reduction of azo dyes under laboratory conditions, the complete molecular

mineralisation of these dyes is hard.

The main disadvantage of the conventional anaerobic biological techniques is the long

hydraulic residence time of sludge in the tank. This weakness leads to provide high volume

reactors due to long generation time of anaerobic bacteria (Georgiou, 2003). Therefore some

systems and methods are coupled to this method that prevent biomass from accumulation and

subsequently reduce the hydraulic residence time.

4.5.2.6 Oxidation techniques

Oxidation treatment methods are applicable to textile wastewater for the removal of colours,

66

BOD, COD etc. However, conventional oxidation techniques have been found quite

inefficient in the removal of colours which are mainly produced from insoluble dyes and

complex organic structure at low concentration. Therefore, advanced oxidation processes

have been applied to the treatment of wastewater in the textile industry. These processes

generate hydroxyl free radical by different techniques such as combination of ozone (O3)

Hydroxyl peroxide (H2O2) and Ultra-violet light The goal is to furnish hydroxyl ions to

destroy colours, complex organic pollutants and compounds which cannot be destroy by

conventional oxidation methods. A list of possible route of producing hydroxyl radicals are

shown in table 3. The Generation of hydroxyl radicals is quickened by combining O3, H2O2,

TiO2, UV radiation, electron-beam irradiation and ultrasound. The most promising are

O3/H2O2, O3/UV and H2O2/UV which hold efficient routes to oxidize textile wastewater.

TABLE 6

Source: Al-kdas A. et al. (2005)Treatment of textile wastewater by Advanced Oxidation Processes

4.5.2.7 Electrolytic precipitation

The use of electrolytic precipitation in the treatment of textile wastewater involves the

application of electric current to the wastewater in a cell. Electro-precipitation corresponds to

the use of an electrochemical reactor with membrane. This facilitates the removal of heavy

metals from the wastewater which are usually from dyestuffs. In the cell, the polluted

wastewater is maintained at the cathode side. When the system is started up the pH in anodic

part decreases by oxidation reaction of water to oxygen gas. On the other hand, in cathodic

part, hydrogen is released by reduction reaction of water. The pH in this part is slowly

increased until it reaches the precipitation pH of metal contained in the solution leading to the

removal of heavy metal from wastewater.

67

Source: http://www.chemistryexplained.com/images/chfa_02_img0277.jpg

FIGURE33

4.5.2.8 Membrane Process

Membrane separation, as an in-plant process, is a feasible method due to high water costs and

the importance of water profligate re-usage( Ramesh Babu, 2007). Membranes offer a great

way of reducing dyeing auxiliaries and hydrolysed dyes. Moreover, they play an essential role

in the decolouration of the effluent and descending BOD and COD levels of waste water.

Reverse osmosis, Nanofiltration, Ultrafiltration and Microfiltration are the main membrane

methods which are used in the textile industry. Qualitative characteristics of the final product

define the specific membrane method that should be used.

4.5.2.8.1 Reverse Osmosis

Reverse osmosis membranes typically have a retention rate of 90% or higher for ionic

compounds and enable superior permeate quality (Ghayeni et al., 1998). Reverse osmosis

facilitates the removal of chemical auxiliaries, hydrolyzed reactive dyes and mineral salts.

The waste from the dyeing sector can be decolourized via a single pass reverse osmosis. The

concentration of dissolved salt is highly important in this method and if it is increased the

osmotic pressure role becomes more significant.

4.5.2.8.2 Nanofiltration

Nanofiltration membranes retain dyeing auxiliaries, hydrolyzede reactive dyes, large

monovalent ions, devalentions and low molecular weight organic compounds (Ramesh Babu,

2007). The combination of a preceding adsorption process joined to a nanofiltration system

can be used effectively for treatment of coloured effluents. By decreasing the concentration

68

polarization of the waste in the adsorption process the quality of the final product, after

passing through the nanofilter, becomes much higher.

4.5.2.8.3 Ultra filtration

Ultra filtration is a good method for eliminating macromolecules and particles but it is a weak

technique in terms of removing polluting components such as dyes (only between 32% and

75%) (Ramesh Babu, 2007). The water treated by ultra filtration is rarely re-used as feed

water in the textile industry and especially not in those sensitive processes such as dyeing.

Ultra filtration can be used for enhancing a biological reactor performance or as a pre-

treatment, carried out before the reverse osmosis section.

4.5.2.8.4 Microfiltration

Microfiltration can be applied effectively for treating effluents containing pigment dyes and

the waste of the subsequent rinsing baths (Ghayeni et al., 1998). This method can be

considered as a suitable pre-treatment for micro and nanofiltration.

4.5.2.9 Electrochemical method

Inorganic salts and elevated levels of toxic colorants, present in textile effluent, are considered

as the main threads for the ecosystem (Sundaram, Kupferle), (Esteva, Silva, 2004)

Electrochemical oxidation technique, which has been developed in the 90’s, is a relatively

effective method in decolourization of the wastewater. No sludge formation, low or no

consumption of chemicals in this method and removal of some specific pollutants such as

polyaromatic organic compounds like anthraquinones all together make this method much

more advantageous to other traditional physical or chemical treatments. This method is

considered as an advanced oxidation technique. In both, Direct and Indirect Electrochemical

methods, the chemical structure of dyes and chemicals and the residence time of processing

the wastewater are amongst the main influential factors on the treatment efficiency

(Sanroman, et al., 2004).

The effects of some factors, such as the effluent conductivity, PH, addition of

polyelectrolytes, and Power requirement on the efficiency of electrochemical method have

been investigated (Lin & Peng, 1993). Based on these studies most the effluents obtained

from the finishing mill and dyeing sectors have the conductivities within the acceptable range

for electrochemical procedure and therefore no extra conductivity adjustment is required. The

69

common PH of 5 to 10, mainly exists in the textile wastewater, also doesn’t show any

negative influence on the process efficiency. The addition of 40 mg/l of polyaluminium

chloride (PAC) and providing power density of about 92.5 amp/m2 can result in higher

efficiency and a greater COD removal. Therefore, it can be concluded that Electrochemical

technique is an effective method for treating textile wastewater. However the main problem of

this method is the cost of electricity.

The Indirect electrochemical oxidation has been observed as an efficient technique to

complete colour and COD removal. In indirect Electrochemical method NaCl molecules,

present in textile wastewater, are used in order to form active chlorine based oxidants to

decolorize highly coloured azo-compounds at the anode (Sundaram, Kupferle).

4.5.2.9.1 Ion-Exchange

The main objective of this process is to clean the wastewater from the undesirable cations and

anions present in waste (Das, 2005). In this sector textile effluent is passed through the beds

which have already enriched by ion-exchange resins. These resins are responsible for

absorbing anions and cations inside the waste and exchange them by hydrogen and sodium

ions separated from the resins structures. The main Ion exchange resins in use today are those

synthetic polymeric materials which contain ionic groups of quaternary ammonium,

sulphonyl groups and etc. Ion-exchange treatment can be used for lowering COD, Reducing

the concentration of metallic ions such as Fe, reducing Alkalinity, conductivity, total hardness

SS and TSS of the textile effluent (Lin, Chen, 1996).

4.5.2.9.2 Photo catalytic

Photo catalytic treatment has been applied to textile wastewater polluted with colours,

dyestuffs and complex compounds. This is an advanced method to decolourize a broad range

of dyes and colour compounds comprising complex structures. In this process, photoactive

catalyst illuminates with UV light, generates highly reactive radical, which facilitates the

decomposition of pollutants. Titanium dioxide and Zinc oxide are particularly utilised as

70

photo catalysts. The work of Attia A.J. et al (2007) practically investigated the use of TiO2

and ZnO in the textile industry wastewater. Treatment followed screening and pre-treatment

to removed TSS and other solids. After which TiO2 and ZnO suspended in the polluted textile

wastewater are placed in a photoreaction cell.

.

(A) gas container, (B) gas flow meter, (C) circulating water thermostat (D) magnetic stirrer (E) quartz cell, (G)

lenses, (H) low pressure mercury lamp, (I) power supply unit. (Attita, et al., 2007)

FIGURE34 SCHEMATIC DIAGRAM OF THE EXPERIMENTAL APPARATUS FOR PHOTOCATALYTIC REACTION

4.5.3.0 Adsorption

The use of adsorption treatment method for textile wastewater entails usually the use of

granular activated carbon for the exchange of pollutants between the two immiscible phases.

Owen’s work (1978) shows that adsorption is an economical and feasible route for

eliminating colour from textile wastewater. Also, recent studies have investigated the use of

powdered activated carbon in the removal of cationic and anionic dyestuffs such as methylene

blue, basic yellow etc from textile wastewater under different experimental conditions

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degree of concentrations. The results of the wastewater samples presented in this case study

were collected over a period of two months while sampling and analysis were done to obtain a

daily average. The daily averages were subsequently subjected to statistically analysis and a

general average presented.

FIGURE37 SCHEMATIC DIAGRAM OF THE TEXTILE FINISHING MILL SHOWING DIFFERENT SECTIONS

Source: Savin and Butnaru /Environmental Engineering and Management Journal 7 (2008)

(1. Burning Sector; 2. CH Station; 3. Bleaching Station; 4. Mercerization Section; 5. Thermo fixing

Section, 6. Chemicals Warehouse, 7. Dyestuff Warehouse; 8. Dyeing Sector; 9. Dyeing Gauge; 10. Printing

Sector; 11. Printing Warehouse; 12. Dressing Sector, 13. Wastewater Treatment Plant)

TABLE 7

73

Source: Savin and Butnaru /Environmental Engineering and Management Journal 7 (2008)

The tables above show the concentrations of ten pollutants from different sections of the mill.

Fixed residue and COD predominately have the highest values. Tables 7, 8, 9, 10, 11 and 12

shows that fixed residues and COD had values of 3840.4 and 2629.3 mg/L, 6590.9 and 2688.5

mg/L, 3877.2 and 2788.2mg/L, 2016 and 1907.8mg/L, 2178.3 and 3606.3mg/L, 358.6 and

74

1097mg/L respectively. This clearly shows that fixed residue was the most obtained pollutant

from most of the section of the textile mills.

4.7 EXAMPLE 2- TEXTILE WASTEWATER TREATMENT PLANT Amaravathi Common Effluent Treatment Plant is an example of a real treatment plant that is

studied in this part in order to give a better idea about the more popular methods applied in

treating textile effluent (Das, 2005). Amaravathi plant has located in Karur, the north-central

of Tamil Nadu in India. The effluents of 43 different textile processing units are collected via

pipelines and all transferred to this plant. The following table provides useful information

about numbers and dimensions of the components exist in this plant.

TABLE 8 Components Numbers Dimensions (meter)

Screen Chamber 1 4×1×3.5

Receiving Sump 1 8×5.25

Equalization Tank 1 31×20×3

Flash Mixer 1 1.7×1.7×1.7

Clarriflocculator 1 12×3.3

Aeration Tank 2

2

23×16×3

22×16×3

Clarifier 2 13×4

Sludge well 1 6×3

Sludge Thickener 1 7×3.3

Centrifuge 1 7×4

Generator Room 1 7×3

Office/Lab 1 12×6.2 floors

Transformer Yard 1 14×7.5

Sludge Drying Beds 12 4.9×4.9

In this plant, equalization and neutralization sectors serve as the main preliminary treatments.

The next steps are sedimentation, floatation, screening and physical flocculation that are

considered as primary treatment methods. In the third step the waste is passed to the

secondary treatment section which constitutes of biological oxidation systems and facilitated

chemical/physical separation methods. The main objective of this unit is removing organic

compounds from the waste. In the final part the effluent is transferred to the tertiary treatment

unit which is very important in the means of polishing the waste treatment.

75

4.7.1 Plant operation The collected waste from all those 43 textile factories is treated by passing through the

following stages:

1. Screen chamber

Large solids are removed by objective screens provided in this chamber to avoid clogging of

hydraulic system and abrasion of mechanical equipments

2. Collection tank

Effluents collected from the screening chamber are stored for a while in the collection tank

and then transferred to the equalization tank.

3. Equalization tank

Wastewater is stored for 8 to 12 hours in this tank for a homogeneous mixing. Therefore the

concentration of the effluent becomes constant that subsequently results in more constant pH

in all parts of the waste stream. The effluent gets neutralized in this system and the shock

loading on the next treatment unit is reduced. The settling of solids is also eliminated by

continuous mixing of the wastewater in the equalization tank.

4. Flash mixer

In this part the following coagulants are added to the effluent;

Coagulant Concentration (ppm) Effects

Lime 800-1000 Raise the pH 8-9

Ferrous Sulphate 200-300 Remove colour

Poly electrolyte 0.2 Settle the suspended solids

In the Flash mixer the above mentioned flocculates are added to the homogenized waste

stream via rapid mixing. This process results in micro flocs production.

5. Clarriflocculator

In this part the wastewater is stirred continuously. The overflowed water is passed to the

aeration tank to settle down the solid wastes, collect them separately and finally dry them.

Flocculation part is responsible for mixing the wastewater slowly, producing maro flocs

76

settling particles in the clarifier zone. Settled solids such as primary sludge are transferred to

the sludge dyeing beds.

6. Aeration tank

A thin film of wastewater is passed over the staircase arrangement. In this part the direct

Aeration of the waste leads to great reduction in BOD which has calculated to be up to 90%.

7. Clarifier

This part receives the biological sludge. Subsequently the treated wastewater is accepted by

Bureau of Indian standard is disposed to rivers via pipelines.

8. Sludge thickener

The input wastewater constitute of 60% water and 40% solids. The centrifugal system

provided in this part reduces the water content of the mixture and changes the constitution to

40% of water and 60% of solids. By repeating this process the solids are slowly separated

from water.

9. Drying beds

In this section the sludge obtained from primary and secondary units are subjected to solar

evaporation to be dried. The magnitude amounts of died sludge after treatment is collected

and packed in polyethylene bags and covered in water proof sheets. This bulk of sludge

should be disposed in an offsite location stated by the State Pollution Control of Tamil Nadu,

India.

TABLE 9 Hazardous waste Hazardous

waste

Quantity

generated

per day

State of waste Type of Hazard Mode of storage and

disposal

sludge

2.5 mT

solid

Chemical

sludge

Packed in polyethylene bags

covered with water proof

sheets

TABLE 10 Effluent Quality Management (average for a month) Quality parameters Inlet water Outlet water

77

pH 6-10 6.5-8.5

Biological Oxygen demand 100-150 mg/l 20-30 mg/l

Chemical Oxygen Demand 300-400 mg/l 140-250 mg/l

Total Dissolved solids 2500-3000 mg/l 1800-2100 mg/l

Suspended Solids 70-200 mg/l 50-90 mg/l

Chlorides 1000-1500 mg/l 700-1000 mg/l

Sulphites 1-2 mg/l Nil

TABLE 11 Regulatory Standards to which effluent needs to be treated Quality parameters Tolerance limits

pH 5.5-9

Biological Oxygen demand 30 mg/l

Chemical Oxygen Demand 250 mg/l

Total Dissolved solids 2100 mg/l

Suspended Solids 100 mg/l

Chlorides 1000 mg/l

Sulphites Nil

The following figure provides a schematic diagram of the Amaravathi Common Effluent Treatment Plant.

78

FIGURE38 AMARAVATHI COMMON EFFLUENT TREATMENT PLANT

CASE STUDY 2:

79

5 INTRODUCTION

One of the most difficult pollutions to control are those not discharged at point source but

those which enters surface water through water that runs over urban or agricultural land or

mineral rich areas (Gray,2005). Essentially, these pollutants do not originate from a single

point (Diffused) and among which are pollutants from oil and other hydrocarbons. Against

this background, the focus of this section is to understudy discharges from a typical oil

storage facility in Nigeria with the view to identifying the source, input measuring parameters

and standards, treatment technologies, monitoring, management techniques and legislations.

The ideas are to overview current practices and recommend ways of improving the system in

other to reduce and/or manage liquid effluent to acceptable standards as stipulated by

legislation. The oil storage depot uses substantial volume of water in their operations which

are discharged as surface water coupled with oil from leakages and handling. To a large

degree, wastewater discharge is hazardous to human health, damage aquatic live and alter the

environment. On the whole, liquid effluent are treated to assert physical and chemical quality

to ensure that degradation standards are not exceeded before it is discharged to the

environment or recycled (Mark J. H, 2001).

80

5.1 EFFLUENT SOURCE

The characteristic of an industrial effluent is to a large extent dependent on the diverse

activities going in the environment. However not peculiar with diffuse source, there are

several environmental problems associated with liquid effluent which can be defined by the

toxicity, groundwater contamination (sediment), nuisance in the form of surface water,

change in taste of portable water supplies and contamination of urban streams (Gray, 2005).

The hot spot of discharge in an oil storage facility are namely;

• Discharge from car maintenance

• Floating , production, storage and offloading (FPSO) vessels

• Waste oil disposal

• Spill from handling

• Road run-off and industrial run-off

• Domestic sanitary wastewater from toilets, sinks, showers and laundries. The volume

and concentration of which dependent on time, facility occupancy and operational

conditions (Nigerian Manual of Petroleum Laws, 1969).

•

Substantial amount of discharge also arises from the storage tanks containing oil and process

water which is allowed in other balance the vessel as well as provide a platform for removal

of any external impurities that may be associated with the oil. This is majorly associated with

routine clean up exercise where the process water contaminated with oil and other impurities

in the storage tanks are flushed. Other significant causes of wastewater include equipment

failure, leakages, malfunctioning oil separators, spills arising from overfilling of tanks and

leakages from loading. These contaminants are usually picked by process water and rainwater

of which may be routed to sea or river and a subsequent impact on the aquatic environment if

unmanaged. Minor leakages within the facility are usually contained using dust or

bioremediation techniques which encourage the growth of micro organism by degrading the

oil molecules (Harrison, 1995). In a case of major spill, the oil is scooped or skimmed for

recovery. However, the remaining part is flushed with pressurised water and further collected

via sewer manhole or storm drain and channelled to the settling tank through an interceptor in

form of a bar screen to remove large materials such as sticks, plastic material, rock bits and

81

paper. The essence is to capture materials capable of damaging equipment for treatment and

properly disposed while other material that floats is skimmed from the surface of the

separation tank. the combination of process water and sewage is known as clarified water

which is treated to eliminate or reduce the waste content to acceptable levels before it finally

discharged as effluent (Obot et al., 2007)

FIGURE39 OIL STORAGE TANK

5.3 EFFLUENT PARAMETERS The nature of pollutants determines potential control options in the sense that there can be

variable elemental pollutants from difference sources. The composition of pollutants in

wastewater discharge in an oil depot includes; acids, alkalis (pH), oil (free and dissolved),

sulphides, ammonia/nitrates, cyanides, heavy metals, heat, other organic materials,

nutrients, settle-able solids, colour, toxic compounds, taste and odour producers (Stephan T.

O, 2008).

Table 12 depicts the composition of effluent, characteristics and exposure limits in an oil

82

storage facility in line with the Federal Environmental Protection Agency (FEPA) and the

Department of Petroleum Resources (DPR). Basically, these parameters relates to the oil

storage facility for a maximum period of 24hours. It is worthy of that contaminant analysis of

oil and wastewater is quite associated with business interest and as such, it is not readily given

out as it is regulated by various laws and standards with compliance being a major issue.

TABLE 12 Liquid effluent Parameter Effluent Characteristics Exposure Limits, Maximum/day

BOD, mg/l 10

COD, mg/l 40

Total Dissolved Solids (TDS), mg/l <2000

Total Suspended Solids (TSS), mg/l 30

Total Hydrocarbon Content (THC) mg/l 10

Turbidity 10

PH 6.6-8.5

Temperature, oC 30

Sulphide as H2S (mg/1) 0.2

Ammonia (NH4+), mg/l 0.2

Lead 0.05

Phenols (Total), mgl 0.5

Cyanide, mg/l as CN 0.05

Chromium Cr+6,mg/l 0.03

Total Chromium mg/I 0.3

Pb+2, mg/I 0.05

Total Iron (Fe), mg/I 1

Cu+2, mg/1 1.5

Zn+2,mg/1 1

Hg 0.1

Odour Not detected

Source: Nigerian Manual of Petroleum Laws, 1969

Empirically, the total levels of contamination are assessed by the following parameters;

• Total suspended solids, finely divided solid matter suspended in water

• Total dissolved salts

• Total inorganic salts dissolved in water

• Chemical oxygen demand (COD), amount of oxygen consumed in chemical oxidation

83

• Biological oxygen demand (BOD) index representing content of biodegradable

substances in the water

• Total organic carbon determination of all organic carbon present and total nitrogen

determination of all nitrogen

5.4 EFFLUENT TREATMENT

Wastewater can be eliminate d or reduced to the barest minimum at source. This however cuts

down on the amount of liquid effluent to be treatment before it is discharged into the river

environment. Treatment procedures methods includes; pre-treatment, primary, secondary and

tertiary treatment. The schematics of treatment procedures is as shown in Fig #

5.4.1 PRE TREATMENT

Liquid effluent Pre treatment involves stripping of sour water being collected and screened

and then it is sent for further treatment. At this stage oil and wastewater undergoes two pre

treatment processes namely; neutralization and emulsion breaking before it is sent to the

primary treatment facility (DPR, 2008)

Neutralisation: this is the basic reaction between acid and alkali used to adjust the PH of

wastewater before it is discharged. It a necessary step towards ensuring proper condition

before oxidation – reduction reaction which is used for precipitation of heavy metal as

hydroxide and more so, for clarification and better adsorption.

Emulsion breaking: the breaking up of emulsions is a necessary step used to separate oil and

water by batch process. The spend emulsions are collected in a tank equipped with agitators

and skimmers with the tank content at fixed position for 2-8hrs to allow for time to rise to the

surface before it is removed. The tank is further agitated and emulsion breaking chemicals

like coagulants, flocculants and wetting agent are added. Further more, free oil is separated by

gravity separators or liquid-liquid cyclones and thereafter, the PH is adjusted before the

wastewater is clarified using flotation (DPR, 2008), (Stefan T. O, 2008).

84

5.4.2 PRIMARY TREATMENT

This is the first major stage of treatment following pre treatment and involves;

• Screening: to remove large objects like stones or sticks using gravity separators which

are capable of blocking the inlet tank.

• Grit chamber: slows down flow to allow for grit fall out

• Clarifiers: the effluent is passed through gravity separators or corrugated plate

interceptors with sufficient residence time to allow free oil to rise to the surface and

skimmed off as shown in Fig 39.

FIGURE40 PROCESS DIAGRAM OF TREATMENT METHODS SOURCE: STEFAN T. O, 2008

5.4.3 SECONDARY TREATMENT

The dissolved and colloidal organic matter is oxidized by micro organism followed by air

flotation or filtration to remove fine oil droplets from water (Gray, 2005). The basic idea

being that oil droplets are carried to the surface by small gas bubbles resulting from the

introduction of air to the system. Further more, the bubbles attach themselves to oil globules

or suspended particles and floated to the surface. Chemicals such as coagulants, acid and or

alkalis are added to promote more removal and on the other hand, oil is filtered from the

aqueous stream through a sand or anthracite medium. It then backwashed to prevent high

pressure drop and to remove oil collected (Stefan T. O, 2008).

5.4.4 TERTIARY TREATMENT

Further treatment ensures the removal of the remaining BOD, suspended particles, bacteria,

specific toxic compounds or nutrients through biological treatment (Gray, 2005). This

involves the use of micro organism to break down organic material with aeration and agitation

85

and then, allow solid to settle out. Most commonly used is activated sludge which is

continually re circulated back to the aeration tank to maintain residual dissolved oxygen in

other to increase the rate of decomposition and biological growth. The wastewater and the

bacteria-containing activated sludge are held in contact at substantial residence time to

stabilize the incoming organic material and more so, to achieve the desired effluent quality.

The mixture is then directed to the settling tank where the bacteria are separated from the

water and the waste is discharged while the bacteria are recycled (Stefan T. O, 2008).

5.5 LEGISLATION

The department of Petroleum Resources (DPR) and Federal Environmental Protection

Agency (FEPA) are two regulatory bodies respectively established in 1970 and 1988 under

the law of the Federal Republic of Nigeria (Nigeria Manual of Petroleum Laws, 1969). The

latter is charged with the overall responsibility of protecting and developing the general

environment and DPR basically is concerned with monitoring and enforcing standards and

guidelines as it relates to the oil and gas industry. The general standard and regulation for oil

and gas operations are a combination of laws for environmental pollution and governed by

principal legislation of Petroleum Act 1969, the Mineral Oils (Safety) Regulation of 1963, the

Petroleum Regulations 1967; the Oil in Navigable Waters Decree Regulations 1968 ; the Oil

Pipeline Ordinance of 1956 as amended by the Oil Pipeline Act 1965 and; the Petroleum

Refining Regulations 1974 which prohibits the direct discharge of oily wastewater from

general industrial oil handling facilities onshore or offshore unto land, public drain, sewer and

water bodies (fresh, brackish, tidal or non-tidal, swamp, coastal or offshore waters) used for

domestic consumption, or as may affect micro-fauna activities (Federal Govt. of Nigeria,

1990,FEPA, 1971)

The pollution control measures as specified in the guidelines and standards of these

respective regulations in Nigeria, takes into consideration the treatment necessary to satisfy

the set limitations for quality of the oily waste water from oil production, storage and

offloading operations, prior to disposal, with special attention to;

• Effluent limitations

• Water quality for industrial water uses at point of in-take

• Industry emission limitations

• Noise exposure limitations

• Management of solid and hazardous wastes

86

• Pollution abatement techniques

CHALLENGES AND WAYS OF IMPROVING THE SYSTEM

The forgoing case points to a few challenges bordering around point of collection of oily

wastewater and the treatment procedure before discharge to the environment. The scenario is

a bit peculiar as compliance to standard procedure is hardly followed. Furthermore,

substantial amount of leaked oil is lost, reason being the absence of good channel of passage

for onward transfer to separation tank, spill on sand and consequent impact on plant and

animal. Against this stand point, the following recommendation is made;

• In view of good containment of spill and leakages, the holding environment for oil

storage facility should be floored and with gutters created for proper drainage and

collection and recovery

• Strict compliance to standards and regulation is crucial considering the huge negative

impact of non compliance

• Persistent training and update of the best available techniques as applicable to other

international communities

5.6 TREATMENT TECHNOLOGIES

Petroleum and related products handling facilities is known to be one of the highest industrial

sectors that generate the largest volume of liquid effluent. However, in offshore operations the

effect of effluent discharged may be diluted using chemicals like (surfactants, foaming agents,

demulsifiers, emulsion breaker and coagulating agents) which is subsequently dissipated by

currents further reducing/minimising the hazards and effects to the environment. Meanwhile,

liquid effluents to be discharged on land or into brackish waters may undergo a well

programmed treatment procedure using technologies as may be approved by DPR, following

the guidelines and standards procedures for contaminant concentrations, quantity of oily in

wastewater, loading rates into the environment and the condition of the accepting water body.

Producers of the oily wastewater however are responsible for managing their discharges as

best available technology is advised to take advantage of the following (FGN, 1988);

• gas flotation devices,

• parallel or tilted plate coalescers,

• loose or fibrous media filtration,

• gravity separation and,

• Chemicals addition to assist oil-water separation.

87

The following technologies are applicable in Nigeria based on the recommendation of DPR;

Air flotation devices: This is of the oldest method for the removal of solids, oil and grease

from wastewater, where gravity settlement may inappropriate. It is the production of air

bubbles, which enhances the natural tendency of some materials to float by carrying

wastewater contaminants to the surface of the tank for removal by mechanical skimming or

removed by suction. The process is defined by the method(s) by which air is supplied, which

could be vacuum flotation, induced air floatation or dissolve air floatation. The dissolve air

floatation device (DAF) is the most common system used in industrial sectors. As can be seen

in figure 1 below, the waste stream is first pressurized with air in a closed tank.

After passing through a pressure-reduction valve, the wastewater enters the flotation tank

where, due to the sudden reduction in pressure, minute air bubbles in the order of 50- 100

microns in diameter are formed which adhere to the particles and are carried to the surface

(Environment Agency,1990).

Source: FAO of the United Nations, 1996

FIGURE41 FIG. 1 DISSOLVED AIR FLOTATION SYSTEM

Centrifugal separators: This technique is often used to thicken sludge where concentrations

greater than 5% are required. The denser water phase is moved to the outer region by means

of the centrifugal forces obtained by inducing a rotating fluid flow. The lighter oily materials

collect near the vortex core and are subsequently removed. This requires the oil collecting

mechanism to be designed to remove a small column of oil at the centre line to be effective in

oil-in-water emulsions. Example of this separator is hydro cyclones as depicted in the figure

below (Environment Agency 1990; Ital Traco SRL).

88

Source: NETAFIM, 2009

FIGURE42 FIG. 2 HYDRO-CYCLONE SEPARATOR

Emulsion separators: This are systems that can be used for enhancing oil droplet jointure

such as granular media filter and coalescing media. In this technique, separation of the water

and oil is simply due the specific gravity difference of the two liquids. However, a separator

cannot easily separate water and oil that exists as an emulsion, in other words, the water and

oil must be as free liquids in the separator, as exemplified in the granular media pressure filter

(Sjöblom, 2001; ITAL TRACO SRL).

Gravity separators: This technique is simply based on the specific gravity difference

between the oil and wastewater. The easiest way to separate one liquid in another is just to let

it sit in place. In most cases it will sooner or later coalesce, settle out and form two distinct

layers with the help of gravity. An example of this technology is the API oil-water separator,

which is a rectangular system designed to contain and separate large volume of oil and

suspended solids from wastewater effluents of oil refinery, petrochemical plants, chemical

plants and in other industrial sources. Figure 1 below, depicts a typical API oil-water

separator. As earlier seen, the API separator works under gravitational effect, designed by

Stokes law, which defines oil droplets on the basis of size and density. The separator is

designed based on the specific gravity difference between the oil and the wastewater. The API

separator allows the oil settle at the top, with the wastewater in the middle, between the oil

and the solids that settles at the bottom. The oil is usually skimmed off, and reprocessed,

while the water layer is sent onward for further treatment for removal of any residual oil, and

biological treatment to remove the undesirable dissolved chemical compounds.(API,1990)

89

Source: American Petroleum Institute, February 1990

FIGURE43 API OIL-WATER SEPARATOR

Use of Biotechnology : This system involves the use of biologically micro-organisms for the

degrading and treatment of the dissolved oil and other chemically stabilized emulsions that

can pose severe problems to the environment, if discharged. The petroleum refineries and

most major oil treatment facilities, implore this method too, with the system being more

effective, if high dilution and pre-treatment is achievable, due to the fact that too much oil in

the wastewater, could result to more problem for the biological system as it is absorbed by the

microorganism quicker than can be metabolized.

The figure below shows a typical schematic of a biological plant. Biologically treated

effluents usually contain less than 15 ppm of oil. (ITAL TRACO SRL)

90

Source: ITALTRACO SRL

FIGURE44 A TYPICAL BIOLOGICAL TREATMENT PLANT

5.7 LIQUID EFFLUENT MONITORING

Regulatory bodies of different countries, have various set guidelines for monitoring of

effluents from all industrial and domestic sectors, with the basic objective of having a zero

percent effluent. In order to carry out effect monitoring of liquid effluent in oil handling

facilities, there is need for frequent sampling in the life of the plants operation, especially

during start up conditions, so as to establish a record of consistencies in view to lay down

legislative parameters limit, and this can be achieved with the analysis of the sample collected

and result determined in a given lab, as shown below. Liquid effluents should be monitored

daily or periodically for all the parameters listed, as well as heavy metals too, when the need

arises. The tabulation below is a typical guideline on effluent monitoring in the petroleum

refining sector.

91

Source: http://www.indiamart.com/mettexlaboratories/laboratory-testing-services.html

FIGURE45 WASTE WATER ANALYSIS LABORATORY

Monitoring data should be analyzed and reviewed at regular intervals and compared with the

operating standards so that any necessary corrective actions can be taken. Records of

monitoring results should be kept in an acceptable format. The results should be reported to

the responsible authorities and relevant parties, as required.

TABLE 13 MONITORING REQUIREMENTS FOR PETROLEUM REFINING PROCESSES EFFLUENT DISCHARGE

DISCHARGE

TYPE

MONITORING REQUIREMENTS

PARAMETER/EFFLUENT

CHARACTERISTIC

MONITORING

FREQUENCY

COMMENTS

1.Treated

process/oily

waste waters

Volume/Discharge Rate

pH

Temperature

Electrical Conductivity Salinity as

(Cl-)

Total Hydrocarbon Contents

Total organic Carbon TOC)

BTEX & PAH's

Total Suspended Solids (TSS)

Total Dissolved Solids(TDS)

Daily

“

“

“

“

“

Once per week

“

“

92

Chemical Oxygen Demand (COD)

Biochemical Oxygen Demand

(BODS)

Dissolved oxygen

Phenols

Cyanide (Total)

Sulphide (as H2S)

Ammonia (as NH4+)

Total Phosphorous(as PO4-)

Total Nitrogen (as NO3-)

Surfactants

Sulphate as(S04-)

Mercaptans

Heavy Metals e.g. Ni, Cr+6, Cd,

Hg, Pb, Cu, Zn, V, Fe+3,C03-

H C03

Naphthalene

Acetanaphthalene

Anthracene

Benz(a) anthracene

Phenanthrene Fluorenthene

3,4 Benzofluorenthene

Fluorene

Vinyl Chloride

2,4-Dimenthyl Phenol

2, Methyl Phenol

4, Methyl Phenol

1-Chloro-m-cresol

Pryene

Chrysene

Components of all

Catalysts

“

“

“

“

“

“

“

“

“

“

“

“

“

“

“

“

“

“

“

“

As requested

“

“

“

“

“

“

“

2 Surface Drainage

& Storm water

Volume

pH

Conductivity

Salinity

Total Hydrocarbon Contents

Turbidity

Daily

Once per week

“

“

“

“

93

3 Oil/Product Tank

Sludges; Oily

Sludges

Quantity/Weight

pH

Total Hydrocarbon

Content

Heavy Metals e .g. Ni, Cr+6,

Cd, Hg, Pb, Cu, Zn, V. Fe+3,

and Ti, LSA/NORM

During Tank

Cleanout/desludging

And other activities

4 Sanitary Wastes

Water

Discharge Rate,

Residual Chlorine

Total Coliform Bacteria

BOD5

Dissolved Oxygen

Total Suspended

Solid

Daily During discharge

Source: Environmental Guidelines and Standards For The Petroleum Industry In Nigeria

(EGASPIN)

94

LEGISLATIONS

95

6 LEGISLATIONS ON TEXTILE INDUSTRY CASE STUDY:

The Indian textile industries are bound under the ISO: 14001 Environmental Management

System. The textile industries in India have proved to be under these limitations. The case

study deals about an industry in the southern part of India which is quite successful in having

its limits as per the ISO standards. The Indian legislations are amended by keeping the

following key points in view:

• Conserving natural resources by effective management of energy, water and

other important resources.

• Reduced COD and BOD of waste water.

• Reduced environmental impacts of recycling, reuse, etc.

• Motivation in people or employees of the industry on protecting environment.

Indian textile market is a well recognised all over the world and is one of the biggest

manufacturing countries in the world. The garments are exported to most parts of the world.

As the demands grow, the country’s production annually is also growing; this in turn makes

the Governing legislations to amend the regulations on industrial outlets.

TABLE 14 The list of the exports from India to different countries: Country Million USD

USA 1988

UK 588

Canada 179

France 532

Germany 508

Italy 216

Spain 149

UAE 43.6

Australia 5.0

South Africa 4.8

Source: Indian National Textile Workers Federation

The private organisation studied in the case study has good adaptation of newer trends to

96

avoid contradicting with the legislation put up the Government of India. According to

V.Jaganathan, the secretary of the Indian National Textile Workers Federation the textile

industries in India have been spending more than 20% of their overall process money on

waste water treatment.

The various acts amended in India so far are as follows:

• Silk textiles undertaking act, 1972

• Textiles undertaking act, 1983

• Jute companies act,1985

• The handloom act 1985

• Textiles undertakings act 1995

These are some of the acts which had mentioned about the waste water standards and there

were a few timely changes in the limitations and standards.

7 LEGISLATIONS

It was in the early 20th century when certain parts of the world made a taught to put

limitations and regulations and fix a boundary for the industries using water bodies for their

waste outlet.

During 1900 the US government made a few legislations keeping the water qualities in mind,

the main objectives were:

• Removal of Suspended solids and floatable material in the waste water.

• Treatment of bio-degradable composition in the waste water.

• Elimination of pathogenic organisms.

However a report in the early 1950s mentioned that the industries are not following the

legislative limitations to a very good extent. This enforced the implementation of strict acts

and boundaries on the industries. This led to the amendment of Federal Water Pollution

Control Act in 1972, which was also known as the Clean Water Act. This was one of the

major moves by the US environmental agencies, which had some drastic changes on the

waste treatment techniques. Due to this amendment the industries had to implement newer

trends for waste water treatment to see to that they are not violating the rules put under the

Clean Water Act.

The main objective of the Clean Water Act was to maintain the chemical, physical and

biological integrity of the Nations waters. This was also known to be the most major Act

97

passed by the US government as this is a basis to the new technologies and the current ones as

well.

According to Section 304(d) of The Public Law 92-500, the US Environmental Protection

Agency published its definition of secondary treatment in 1973. But major revisions were

made regarding treatment of sewer wastes and regarding the standards allowed after treatment

in 1985.

Then soon after in the year 1987, the Water Quality Act was amended. This was known to be

a major revision to the Clean Water Act.

The main objectives of the Water Quality Act were to:

• Strengthening of federal water quality regulations.

• Amending the CWA’s formal sludge control program.

• Providing funding for state and EPA studies for defining the sources of

pollutants.

• Priorities and permit requirements for storm water.

• Construction grants and financing publicly owned treatment works.

This has been the present act under use and is been amended in terms of standard levels of

pollutants allowed after treatment.

The EU prospective on textile industries:

Water pollution legislations started to amend from the 1970s in the European unions. They

basically have three major considerations or can be put down as three main pillars of the

legislations on textile waste water treatment.

• “Directives on waste water treatment and on nitrates from agricultural process,

1991” (The Nitrates Directive 91/676/EEC)

• “Flagship of EU Water Policy and Legislation, 2000” (Water Framework

Directive)

The directive was mainly to maintain the water qualities in the water resources like the rivers

and seas which were polluted very severely due to the industrial let-outs and the toxic

elements present in the industrial wastes.

The standards mentioned by the above directives are:

Biological Oxygen Demand – 25 mg/l

Chemical Oxygen Demand – 125 mg/l

Total Nitrogen – 15 mg/l

98

Total Phosphorus – 2 mg/l

There are a several ambitious environmental objectives and deadlines set by the Urban Waste

Water Treatment Directive till date. The European Commission has amended the legislation

as to implement these deadlines one by one in a step by step procedure. The previous reports

concluded as follows:

• The actions on maintaining the water quality in the rivers:

• Reduction of BOD levels by 20 to 30 %

• Reduction of total phosphorus by 30 to 35 %

• Total nitrogen levels to be cut down to 40%

• The actions on maintaining the water quality in the seas: Improved water

qualities in Baltic Sea and Mediterranean Sea.

• Member states like Austria, Denmark and Germany have shown improvements

in water qualities compared to previous years by using step by step

implementation.

• In the future more advanced treatment technologies have to be implemented

for maintaining the water qualities.

There are several other countries which deal with treatment standards in different ways

according to their present situations. Some of the under developing countries have no strict

rules. Having strict limitations and restrictions will definitely affect the development of the

industry in turn affects the development of the country. Therefore these limitations may vary

for some developing countries like the Asian countries, etc.

Some of the standards mentioned recently by one of the developed countries in been

mentioned in the table which follows the data. It is clear that these standards are not as low as

they are in some developed countries.

One of the major countries dealing with the textiles is Bangladesh, a small country in Asian

Sub-Continent. Below are the few standards mentioned by the Government of Bangladesh.

TABLE 15

99

Source: The Environmental Conservation Rules 1997.

8 REFERENCES

Lenntech Screening. [Online] http://www.lenntech.com/screening.htm [Accessed 17.03.09]

Epco. Designers of systems and equipment for the treatment of sewage and other biological

100

wastewater, Aeration. [Online] Queensland, Australia Available from:

http://www.epco.com.au/EQUIPMENT/aeration/aeration.htm [Accessed 17.03.09]

Epco, Australia. Designers of systems and equipment for the treatment of sewage and other

biological wastewater. [Online]. Queensland, Australia. Available from:

http://www.epco.com.au/equipment/clarifiers/clarifiers.htm [Accessed 17.03.09]

Activated sludge treatment Available from:

http://www.college.ucla.edu/webproject/micro7/studentprojects7/Rader/asludge2.htm

[Accessed 20.03.09]

Waste water treatment. Available from : http://www.wef.org/NR/rdonlyres/59E69C35-0E6F-

4593-A4B8-D420AA9C4819/0/WastewaterTreatment912.pdf [Accessed 17.03.09]

Water quality and health. Wastewater Chlorination: An enduring public health practice.

[Online].Available from: http://www.waterandhealth.org/wastewater/chlorination.php3

[Accessed 17.03.09]

Chlorination [Online] Available from:

http://water.me.vccs.edu/courses/ENV149/chlorinationb.htm [Accessed 17.03.09]

BiOzone Cooperation. Ozone waste water treatment. [Online]. Available from:

http://www.biozone.com/ozone_waste_water.html [Accessed 17.03.09]

Gray N. F, 2005, Water Technology; An Introduction for Environmental Science and

Engineers, pp.143-150, 2nd ed. Elsevier.

Harrison i. A., 1995, Microbiological Profile of Crude Oil in Storage Tanks. Department of

Botany, Delta State University, Abraka, Nigeria

Mark J. H, 2001, Water and Wastewater Technology, pp.313-316, 4th ed. Prentice Hall

Obot et al, 2007 Effluent And Solid Waste Analysis In A Petrochemical Company-A Case

Study of Eleme Petrochemical Company Ltd, Port Harcourt, Nigeria

Stefan T. O., 2008 Environmental Technology in the Oil Industry 2nd ed. Oxoid Ltd,

Hampshire, UK

Oil-In-Water Separation, (n d) [Internet] Available from: http://www.etna-

usa.com/zertech.pdf, (Accessed February 27 2008)

Nigerian Manual of Petroleum Laws, 1969

The Environment Agency, 1990 Effluent Treatment Techniques, The Stationary Office,

London ISBN 0113101279

Food and Agriculture Organization of The United Nations, 1996 Wastewater treatment in the

fishery industry [internet] Available from:

http://www.fao.org/docrep/003/V9922E/V9922E00.HTM (Accessed March 11, 2009)

NETAFIM (n d) Hydrocyclone Separators Technical Information [Internet] Available from:

101

http://www.netafim-usa-mining.com/Mining/p-hydrocyclone-tech.php [Accessed March 11,

2009]

Johan Sjöblom, 2001 Encyclopedic Handbook of Emulsion Technology MARCEL DEKKER,

INC. New York. SBN: 0-8247-0454-1

American Petroleum Institute, 1990 Management of Water Discharges: Design and

Operations of Oil-Water Separators, 1st ed. API.

FGN (1988): Federal Environmental Protection Agency Deem No. 58, 1988. Federal

Government of Nigeria.

Federal Govt. of Nigeria (FGN, 1990) “The Laws of the Federation of Nigeria”. Revised

Edition printed by Grosvenor Press (Portsmouth) Limited

Maine Department of Environmental Protection, 2004 Waste Discharge Program Guidance

[Internet] Available from: www.maine.gov/dep/rwm/spcc/pdf/depdischargeprog.pdf

(Accessed March 10, 2009)

Oil and Gas and Related Marine Guidance, 2002 Environmental Guidelines and Standards for

Petroleum Industry in Nigeria (EGASPIN), Department Of Petroleum Resources, Nigeria.

Water Environment Federation: A Wastewater Treatment Diagram [Internet] Available from:

http://www.wef.org/apps/gowithflow/theflow.htm (Accessed February 21, 2009)

Ramesh Babu B., et al., 2007, Textile Technology, Cotton Textile Processing: Waste Generation and Effluent Treatment, The Journal of Cotton Science (11) p: 141-153 [online], Available at: http://www.cotton.org/journal/2007-11/3/upload/jcs11-141.pdf Vandevivere P. C., et al., 1998, Treatment and Reuse of Wastewater from the Textile Wet-Processing Industry: Review of Emerging Technologies, Chem.Technol. Biotechnol. (72) p: 289-302 [online], available at: http://www3.interscience.wiley.com/cgi-bin/fulltext/10007841/PDFSTART Hans Huber AG., 2005, Mechanical Wastewater Screening, [online] Available at: http://www.huber.co.uk/upload/C344d0175X1199c31a8d5X2890/1209556386431/ro_ue_e.pdf Das s. S., 2005, Textile effluent treatment- A solution to environment pollution, India [online], Available at: http://www.fibre2fashion.com/industry-article/textile-industry-articles/textile-effluent-treatment/textile-effluent-treatment1.asp [Accessed 16 Feb 2009] Eswaramoorthi S., 2009, Performance Optimization of Wastewater Treatment Plants, ECP consulting [online], Available at: http://www.scribd.com/doc/10209693/Performance-

102

Optimization-of-Waste-Water-Treatment-Plants Ahmed S.A.R., 2006, Fast-Track Evalution of a Compact Chemically Enhanced-Trickling Filter System, Brazilian Journal of Chemical Engineering 24(02), p:171-184 [online], Available at: http://www.scielo.br/pdf/bjce/v24n2/02.pdf Babu B. V., 2008, Effluent Treatment: Basics & A Case Study, Birla Institute of Technology and Science (BITS) [online], Available at: http://discovery.bits-pilani.ac.in/~bvbabu/BVBabu_Water_Digest_Jan_2008.pdf Yusuff R. O., Sonibare J. A., 2004, Characterisation of Textile Industries’ Effluents in Kaduna, Nigeria and Pollution Implications, Global Nest: the Int. J. 6 (3), pp 212-221 [online] Available at: http://www.gnest.org/Journal/Vol6_No3/Yusuff_212-221.pdf Asia I. O., et al., 2006, Treatment of textile sludge using anaerobic technology, African Journal of Biotechnology 5(18), pp 1678-1683, Nigeria [online], Available at: http://www.fibre2fashion.com/industry-article/9/826/treatment-of-textile-sludge-using-anaerobic-technology1.asp Georgiou D., Aivasidis A., 2006, Decoloration of textile wastewater by means of a fluidized-bed loop reactor and immobilized anaerobic bacteria, Journal of Hazardous Materials pp 372-377 [online] Available at: http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TGF-4J2TSV8-4&_user=128590&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000010619&_version=1&_urlVersion=0&_userid=128590&md5=525723d679e918acf32c1e7122bbb5e0 Georgiou D., et al., 2003, Decolorization of Azo-Reactive dyes and Cotton-Textile Wastewater Using Anaerobic Digestion and Acetate-Consuming Bacteria, 8th International Conference on Environmental Science and Technology, Lemnos Island, Greece [online], Available at: http://www.gnest.org/cest8/8cest_papers/abstracts_pdf_names/p73_Georgiou.pdf Ghayeni S.B.S., et al., 1998, Water reclamation from municipal wastewater using combined microfiltration-reverse osmosis (ME-RO): Preliminary performance data and microbiological aspects of system operation, Desalination 116(1), pp 65-80 [online] Available at: http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TFX-3VM1T86-7&_user=128590&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000010619&_version=1&_urlVersion=0&_userid=128590&md5=e4713a6038590704d35d7f17bec4dbcf Chakraborty, S., M. K. Purkait, et al. 2003, "Nanofiltration of textile plant effluent for color removal and reduction in COD." Separation and Purification Technology 31(2), pp

103

141-151 [online] Esteves M.F., Silva J.D., 2004, ElectroChemical Degradation of Reactive Blue 19 Dye In Textile Wastewater, Guimaras, Portugal [online] Available at: https://repositorium.sdum.uminho.pt/bitstream/1822/2032/1/Elect.pdf Lin S.H., Peng C.F., 1994, Treatment of Textile Wastewater by Electrochemical Method,Wat.Res. 28(2), pp 277-282, UK [online] Sanroman M.A., et al., 2004, Electrochemical decolourisation of structurally different, Chemosphere 57, pp 233-239, Spain [online], Available at: http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V74-4D1DBY3-4&_user=128590&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000010619&_version=1&_urlVersion=0&_userid=128590&md5=f2cd94c8290d5466c8380096f7066a84 Sundaram V, Kupferle M.J., 234g Indirect Electrochemical Treatment of Textile Wastewater: Influence of Design and Parameters on colour removal [online], Available at: http://www.nt.ntnu.no/users/skoge/prost/proceedings/aiche-2005/non-topical/Non%20topical/papers/234g.pdf Lin S.H., Chen M.L., 1996, Purification of textile wastewater effluents by a combined Fenton Process and Ion-exchange, Desalination 109, pp 121-130, Taiwan [online], available at: http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TFX-3S9RDWY-2&_user=128590&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000010619&_version=1&_urlVersion=0&_userid=128590&md5=cb36d17fc85138dafaa03557c81192ea Das S., 2005, Textile Effluent Treatment: A Case Study in Home Textile Zone, India [online], available at: http://www.fibre2fashion.com/industry-article/3/215/textile-effluent-treatment-a-case-study-in-home-textile-zone1.asp Attai Abbas J., Salih H. Kadhim and Falah H. Hussein (2007): Photo-catalytic Degradation of Textile Dyeing Wastewater Using Titanium Dioxide and Zinc Oxide Chemistry Dept, College of Science, Babylon University, Iraq: Adel al-kdasi, Azni Idris, Katayon Saed Chuah Teong Guan (2005): Treatment of textile wastewater by advanced Oxidation processes – a review Al-kdas A. et al. (2005)Treatment of textile wastewater by Advanced Oxidation Processes Ghoreishi S.M. and Haghighi R. (2003), Chemical Catalytic Reaction and Biological Oxidation for

104

Treatment of non-Biodegradable Textile Effluent, Chemical Engineering Journal, 95, 163–169 Nemerow, N.L. (1978) Industrial Water Pollution: Origins, Characteristics and Treatment. Addison-Wesley, Reading, Massachusetts, pp 738. Lacasse K., Baumann W., (2006), Textile Chemicals. Environmental Data and Facts, Springer. Owen, G.R., (1978) Journal of Society of Dyers and Colourists, 94, 243-251. Savin and Butnaru (2008); Environmental Engineering and Management Journal 6, 859-864 Venceslau M.C., Tom S. and Simon J.J. (1994), Characterization of textile wastewaters-a review, Environmental Technology, 15, 917-929. Wastewater Engineering: Treatment and Reuse 4th Edition.