August 10, 2017 Arun Kumar (arunku@civil.iitd.ac.in)

1

Wk2

by Dr. Arun Kumar (arunku@civil.iitd.ac.in)

Wk2:Water Pollution

Objective: To introduce water pollutants (chemical, biological) and nutrients which might cause problems

August 10, 2017 Arun Kumar (arunku@civil.iitd.ac.in)

2

Water Treatment Plant Schematic

Objective: To introduce water treatment plant schematic and need for different unit processes

Step 1. List water quality characteristics which need to be removed

• Parameters:

– Ions (arsenate; chromate ions;nitrate)

– Organic compounds (pesticides, etc.)

– Pathogens (viruses, if we have human fecal pollution)

– Solids (depends if there is a fracturing in subsurface)

– Gases(methane, etc.)

August 10, 2017 3

Step 2. Identify unit(s) which can remove at least one type of contamination

• Ions (removal by: adsorption; coagulation-

flocculation; chemical precipitation; bio-adsorption;

membrane process)

• Organic compounds (degradation/removal by:

oxidation; adsorption; biodegradation; reduction-

oxidation; irradiation; membrane process)

August 10, 2017 4

Step 2 contd.

• Pathogens (killed by : adsorption; coagulation-

flocculation; chemical precipitation; disinfection;

boiling; irradiation; membrane process)

August 10, 2017 5

Step 2 contd.

• Solids (removal by : settling; filtration; membrane

process)

• Gases (removal by) : aeration; adsorption;

solubilization)

August 10, 2017 6

Example 1: Groundwater �produce drinking water)

August 10, 2017 7

August 10, 2017 8

Treatment schematic (GW� Potable drinking

water)

• Raw Ground water � aeration chamber �

Softening unit � Filtration with chlorination

�Disinfection � Storage

• See sequence of units used

• Chemical is required to be added

• Water is treated

• Chemical sludge is produced

August 10, 2017 9

Units used for (GW� Potable drinking water)

• Aeration chamber (to remove gases; using air)

• Softening unit (to remove cations; using softener and/or cation exchangers)

August 10, 2017 10

Treatment schematic (GW� Potable drinking

water)

• Filtration with chlorination (to remove solids; to kill microbial growth on filter unit surface)

• Disinfection (to kill microorganisms before water is supplied for public consumption)

• Storage

August 10, 2017 11

Example 2: Yamuna River Water �produce drinking water)

• Think for 5 minutes for two steps.

• Step 1: water quality characteristics determination

• Step 2: selection of units, their order

August 10, 2017 12

Example 2: Yamuna River Water �produce drinking water)

August 10, 2017 13

Example 2 schematic contd.

August 10, 2017 14

Pathogenic Microorganisms

1. Microorganisms

Pathogenic Microorganisms

1. Microorganisms

Q: Can you list sources which might give you exposure of pathogenic microorganisms?

Sizes of Microorganisms and Other

Particles (size influences removal through

filtration method)

1. Microorganisms

Inorganic Pollutants

• Heavy Metals

• Arsenic

• Nitrates

• chromium

• Asbestos

• Other?

2. Inorganics

Effect =f(valency type,

concentration)

For example: toxic effects of

arsenate(AsIV)) and

arsenite (As(III)) might be

different.

Q: Can you list sources which might give you exposure of these inorganic pollutants?

• Petroleum constituents:

– benzene and substituted benzenes

– prevalent in gasoline, diesel fuel, heating oil

– most easily transported, slow degradation, toxic

CH2CH3CH3 CH3

CH3

Benzene Toluene Ethylbenzene m-Xylene

Volatile Organic Compounds (VOCs)

3. Organics

• Oxygentated gasoline additives

– added to gasoline to improve air quality

– very soluble, resistant to degradation, toxic

– attempt to solve one problem caused another

(spills)

CH3 C

CH3

CH3

O CH3

Methyl tertiary butyl ether (MTBE)

Volatile Organic Compounds (VOCs)

3. Organics

• Chlorinated solvents

– C1 and C2 aliphatics

– widely used in degreasing, dry cleaning, extraction

– somewhat soluble, volatile, difficult to degrade

C

Cl

Cl

Cl

Cl C

Cl

Cl

Cl

H C C

Cl

Cl

Cl

H

H

H

C C

H

H

Cl

H

carbon tetrachloride chloroform 1,1,1-trichloroethane vinyl chloride

Volatile Organic Compounds (VOCs)

3. Organics

Pesticides (hydrophobic organic

compounds)• Organochlorine Insecticides: were commonly used

in the past (e.g. DDT and chlordane).

• Organophosphate Pesticides: most are

insecticides, some are very poisonous (they were

used in World War II as nerve agents)

• Carbamate Pesticides: affect the nervous system

• Pyrethroid Pesticides: were developed as a

synthetic version of the naturally occurring pesticide

pyrethrin, which is found in chrysanthemums

3. Organics

naphthalene anthracene phenanathrene

pyrene benzo[a]pyrene

Polycyclic Aromatic Hydrocarbons (PAHs)

Polycyclic aromatic hydrocarbons (PAHs) are a group of over 100 different chemicals that are formed during the incomplete burning of coal, oil and gas, garbage, or other organic substances.

They are potent carcinogens, hydrophobic organiccompounds and they tend to associate with particles.

3. Organics

• Polychlorinated biphenyls are mixtures of individual chlorinated compounds (known as congeners).

• PCBs are either oily liquids or solids that are colorless to light yellow.

• PCBs have been used as coolants and lubricants in transformers, capacitors, and other electrical equipment.

• The manufacture of PCBs was stopped in the U.S. in 1977.

• They are hydrophobic and they bio-accumulate in the food chain.

Polychlorinated biphenyls (PCBs)

Biphenyl

Cl

Cl

Cl

2,3',4-trichlorobiphenyl

3. Organics

Other Organic Pollutants

• Fertilizers

• Surfactants

• Explosives, propellants

• Chlorination By-Products (e.g. trihalomethanes)

• Antibiotics

• Pharmaceuticals

• Personal care products

• Cyanobacterial toxins

• nanomaterials

3. Organics

Microcystin-LR(hepatotoxin)

Excess Nutrients

• Nitrogen and phosphorus are nutrients required by all living organisms. They are considered pollutants when they are in excess.

• Excessive nutrients often lead to large growths of algae which in turn become oxygen-demanding material whey they die and settle.

4. Excess Nutrients

Excess Nutrients

106 CO2 + 16 NO3- + HPO4

2- + 122 H2O →

C106H263O110N16P + 138 O2

Algae + O2 => CO2 + H2O + NH3

algae

Nitrogen and phosphorus are typically the limiting factors

Phosphorus

• Phosphorus is typically the limiting nutrient in lakes, and algae growth is linked to phosphorus inputs.

• P Sources

– fertilizers

– detergents

– wastewater

• P can exist in a variety of chemical forms

Excess Nutrients

Nitrogen

• Nitrogen is often the limiting nutrient in ocean waters and some streams

• Nitrogen can exist in numerous forms, but nitrate (NO3

-), nitrite (NO2-), ammonia

(NH3) are most commonly measured

• Sources are primarily from fertilizers and acid deposition

Excess Nutrients

Factors Controlling Eutrophication

• Stoichiometry of photosysnthesis (C,N,P, O & H)

106 CO2 + 16 NO3- + HPO4

2- + 122 H2O → C106H263O110N16P + 138 O2

• Liebig’s law of the minimum – growth will be limited by the availability of the nutrient that is least available relative to the need

• Most fresh water systems are phosphorus limited

2.7311

1416=

×

×=

P

N It takes ~ 7 times more N than P to produce a given mass of algae

• Dissolved solids, or salts, may be present as any number of ions

– cations: Na+, K+, Mg2+, Ca2+

– anions: Cl-, SO42-, HCO3

-

• Typically measures as total dissolved solids (TDS)

• Water classification

– freshwater <1500 mg/L TDS

– brackish water 1500 – 5000 mg/L

– saline water >5000 mg/L

– sea water 30-34 g/L

Salts

Salts

• Sources

– industrial discharges

– deicing

– evaporative losses

– minerals

– sea water intrusion

• Effects

– natural fresh water population threatened

– limits use for drinking

– crop damage/soil poisoning (cannot use for

irrigation)

Salts

Salts

Suspended Solids• Organic and inorganic particles in water are

termed suspended solids

• May be distinguished from colloids, particles that do not settle readily

Suspended Solids

• Problems

– sedimentation

– may exert oxygen demand

– primary transport mechanism for many metals, organics and pathogens

– aesthetic

– complicates drinking water treatment

• Sources

– storm water

– wastes

– erosion

• When organic substances are broken down in water, oxygen is consumed

organic C + O2 → CO2

• For example:

CH3COOH + 2O2 => 2CO2 + 2H2O

C6H15O6N + 6O2 => 6 CO2 + 6 H2O + NH3

Oxygen-Demanding Wastes

Oxygen Demanding Wastes

Oxygen-Demanding Wastes

• High oxygen levels necessary for healthy stream ecology.

• For example:

– trout require 5-8 mg/L dissolved oxygen (DO)

– carp require 3 mg/L DO

Oxygen Demanding Wastes

Oxygen Demanding Wastes-

measurement/estimation• Estimated stoichiometrically by theoretical oxygen

demand (ThOD)

• Measured by oxygen demand potential

– biochemical oxygen demand (BOD)

– Nitrogenous oxygen demand (NBOD)

– chemical oxygen demand (COD)

August 10, 2017 Arun Kumar (arunku@civil.iitd.ac.in)

37

by Dr. Arun Kumar (arunku@civil.iitd.ac.in)

Parameter Measurements

Objective: To introduce parameters to indicate pollution and methods to measure them

Parameters• Suspended solids

• Pathogens

• Inorganic ions

• Organic compounds

• Excess nutrients

• Oxygen demanding wasters– Estimated stoichiometrically by theoretical oxygen demand

(ThOD)

– biochemical oxygen demand (BOD)

– Nitrogenous oxygen demand (NBOD)

– chemical oxygen demand (COD)

Solids• Used in controlling biological process; drinking water

quality, etc.

• Gravimetric analysis is based on the determination of

constituents or categories of materials by measurement

of their weight.

• Three analytic operations:filtration, evaporation, and

combustion.– Filtration is used to separate suspended or particulate (non-filterable)

fraction from dissolved or soluble (filterable) fractions.

– Evaporation separates water from material dissolved or suspended in it.

– Combustion differentiates between organic and inorganic matter.

Organic matter will be destroyed completely by burning at 550oC for 30

min.

•

August 10, 2017 39

Ref: AWWA, WEF, APHA, 1998, Standard Methods for the Examination of Water

and Wastewater (2540 D. Total Suspended Solids Dried at 103-105oC; 2540 E.

Fixed and Volatile Solids Ignited at 550oC)

Total Suspended SolidsProcedure:

• Filter samples (50 ml); Oven dry at 103oC for 30 min ; At this stage all water will be evaporated and only suspended solids will be retained on filter.

• Total suspended solids

mg total suspended solids =1000*(A-B)/(sample volume in mL) (1)

Weight crucibles (mass=C) and then weight crucible and filter (total

mass=E); Initial filter weight=B; Weigh filters now (mass =A g).

August 10, 2017 40

Volatile and Fixed Suspended Solids

• Put crucibles with filter paper in muffle furnace and Ignite at 550oC for 15 min. At this stage all volatile components of solids will be volatilized and only fixed inert solid materials will be left in crucible. Weigh crucible after proper cooling (mass=D g).

• Volatile suspended solids (F) :

mg volatile suspended solids/L =1000*(E-D)/(sample volume in mL) (2)

• Fixed suspended solids (G) :

mg volatile suspended solids/L =1000*(D-C)/(sample volume in mL)

•

•

August 10, 2017 41