44901511 Industrial Waste Water Treatment

Industrial WastewaterTreatment

This page intentionally left blankThis page intentionally left blank

Imperial College PressICP

NG Wun JernNational University of Singapore

Industrial WastewaterTreatment

British Library Cataloguing-in-Publication DataA catalogue record for this book is available from the British Library.

Published by

Imperial College Press57 Shelton StreetCovent GardenLondon WC2H 9HE

Distributed by

World Scientific Publishing Co. Pte. Ltd.5 Toh Tuck Link, Singapore 596224USA office: 27 Warren Street, Suite 401-402, Hackensack, NJ 07601UK office: 57 Shelton Street, Covent Garden, London WC2H 9HE

Printed in Singapore.

For photocopying of material in this volume, please pay a copying fee through the CopyrightClearance Center, Inc., 222 Rosewood Drive, Danvers, MA 01923, USA. In this case permission tophotocopy is not required from the publisher.

ISBN 1-86094-580-5ISBN 1-86094-664-X (pbk)

Editor: Tjan Kwang Wei

Typeset by Stallion PressEmail; [email protected]

All rights reserved. This book, or parts thereof, may not be reproduced in any form or by any means,electronic or mechanical, including photocopying, recording or any information storage and retrievalsystem now known or to be invented, without written permission from the Publisher.

Copyright 2006 by Imperial College PressINDUSTRIAL WASTEWATER TREATMENT

KwangWei - Industrial Wastewater.pmd 11/27/2006, 1:13 PM1

FAApril 3, 2006 16:43 SPI-B354: Industrial Wastewater Treatment (Ed: Kwang Wei) fm

PREFACE

Students and engineers new to industrial wastewater treatment have often posedquestions regarding the subject which may be answered from experience gainedduring multiple eld trips. Organizing such site visits can however, be a dif-cult task because of time-management issues as well as the difculties in gainingaccess to the various factories. This book was written to address some of thesequestions and to substitute a few of the site visits. It is a discussion of the materialthat goes into industrial wastewater treatment plants, the reasons for their selectionand, where appropriate, how things may go wrong. Many photographs have beenincluded so that the reader can get a better feel of the subject matter discussed.

Typically, students and engineers who wish to pursue a career in wastewaterengineering begin from the study of domestic sewage and the design of sewagetreatment plants. Their studies would thenmost likely extend to municipal sewage,which is a combination of domestic, commercial, raw and pretreated industrialwastewaters. Following which, some of these students may be briey introducedto industrial wastewater treatment but their exposure to the subject would unlikelybe of the same level as that of domestic sewage. Indeed, much of the expertise inthe subject is gained through work experience. Many engineers, at least early intheir careers, attempt to use the sewage treatment plant template or a modicationof it for an industrial wastewater treatment plant.

How different is industrial wastewater treatment from sewage treatment? Isthere a need to highlight the differences?Would these differences be large enoughto result in differences in conceptualization, design and operation of industrialwastewater treatment plants? What are the potential pitfalls engineers should beaware of? There are obviously lessons to be learnt in sewage treatment which arerelevant to industrial wastewater treatment. There is then the issue regarding theamount that can be transferred and the considerations that need to be taken intoaccount to ensure an appropriate design is generated and the plant successfullymanaged.

v


vi Preface

Industrial wastewaters can be very different from sewage in terms of theirdischarge patterns and compositions. Notwithstanding this, many industrialwastewater treatment plants, for example and like sewage treatment plants, usebiological processes as key unit processes in the treatment train. Given thevariations in wastewater characteristics, ensuring these biological processes andupstream/downstream unit processes are appropriately designed presents a greatchallenge. The problems intensify when information on the wastewaters and theirtreatment is lacking. Textbooks frequently emphasize on the theories and equa-tions used in designing unit processes. However, industrial wastewaters are sovaried that it is difcult for the aspiring engineer to imagine why a certain pro-cess is selected over another, or why a particular variant is even selected at all.Additionally, there is a scarcity of books on Asian wastewaters and treatmentfacilities, which seems to be incongruous to the growing demand for Asia-focusedbooks because of Asias rapid economic development.

This book is intended to introduce the practice of industrial wastewater treat-ment to senior undergraduate and postgraduate environmental engineering stu-dents. Practitioners of the eld may also nd it useful as a quick overview of thesubject. The book focuses on systems that incorporate a biological treatment pro-cess within the treatment train, with the material of the book largely drawn fromthe authors practice and research experiences. It does not delve into the details oftheory or the mathematics of design, but instead discusses the issues concerningindustrial wastewater treatment in an accessible manner. Some prior knowledge ofthe theory behind the unit processes discussed and the manner in which they aresupposed to work is assumed. A description of a typical sewage treatment plant isprovided to afford readers a point of familiarity and basis for comparison so thatthe differences can bemore apparent. The book approaches the develpment of suit-able treatment strategies by rst identifying and addressing important wastewatercharacteristics. In the latter part of the book, a number of specic wastewaters areidentied to serve as case studies so that individual treatment strategies and plantconcepts can be move clearly illustrated.

Ng Wun JernApril 2005


CONTENTS

Preface v

Chapter 1 Introduction 1

Discussion on the impact of industrial wastewater discharges on the environmentwith a focus on Asia.

Chapter 2 Nature of Industrial Wastewaters 12

Discussion on a number of the key industrial wastewater characteristics whichmay impact on plant design and successful plant operation. Tables showing thecharacteristics of wastewaters arising from a variety of industries are included.A portion of this information is on wastewaters not usually found outside of trop-ical or sub-tropical regions. It is intended this chapter becomes a reference forprofessionals seeking information on wastewaters.

Chapter 3 The Sewage Treatment Plant Example 28

Brief description of the possible treatment trains in a sewage treatment plant based on the continuous-ow bioreactor and cyclic bioreactor. This is intendedto provide a framework for comparison so that readers can more readily appreci-ate the differences and similarities between sewage treatment plants (STPs) andindustrial wastewater treatment plants (IWTPs).

Chapter 4 The Industrial Wastewater TreatmentPlant Preliminary Unit Processes 42

Discussion on the preliminary treatment required to prepare industrial wastew-aters for secondary treatment. This chapter includes discussions on removal ofsuspended solids, O&G, inhibitory substances, pH adjustment, nutrients supple-mentation, and equalization.

vii


viii Contents

Chapter 5 The Industrial Wastewater TreatmentPlant Biological 61

Discussion on the biological processes used for secondary treatment of industrialwastewaters to remove organics and nutrients (where necessary). Aside from dis-cussion on aerobic processes such as the conventional activated sludge and thecyclic SBR, space is also devoted to anaerobic processes used as the rst stage ofa biological treatment train to reduce organic strength prior to aerobic treatment.The difculties faced by biological processes in industrial wastewater treatmentare highlighted.

Chapter 6 The Industrial Wastewater TreatmentPlant Sludge Management 99

The preliminary and secondary treatment stages generate sludges. These may beorganic, inorganic, or a combination of the two. This chapter discusses sludgemanagement approaches commonly adopted at IWTPs.

Chapters 4, 5 and 6 draw on experiences with actual wastewaters to illustratepoints made in the discussions. These three chapters and Chapters 710 are pro-vided with numerous photographs of plants, equipment, and site conditions so thatthe reader can develop a feel for the issues inherent in industrial wastewatertreatment.

Chapter 7 Chemicals and PharmaceuticalsManufacturing Wastewater 106

The pharmaceutical wastewater example provides a framework for discussion onthe importance of segregation and blending, and the impact of inhibition.

Chapter 8 Piggery Wastewater 112

The piggery wastewater example provides a framework for discussion on thenecessity to note the differences in wastewaters which may arise because of dif-ferences in industry practices (between Asia and Europe in this instance) and theapproach taken to deal with high concentrations of SS in a highly biodegradablewastewater.

Chapter 9 Slaughterhouse Wastewater 125

The slaughterhouse wastewater example provides a framework for discussion onthe importance of pretreatment to reduce a nitrogenous oxygen demand so that


Contents ix

total oxygen demand may be reduced. Failing this the strong nitrication mayrequire alkalinity supplementation with attendant implications in terms of treat-ment chemicals and construction materials needed.

Chapter 10 Palm Oil Mill and Renery Wastewater 134

The palm oil mill wastewater example provides a framework for discussion on theuse of anaerobic processes to treat wastewaters and not as is usually encounteredin STPs to treat sludges.

References 145

Index 147

This page intentionally left blankThis page intentionally left blank

FAApril 3, 2006 16:43 SPI-B354: Industrial Wastewater Treatment (Ed: Kwang Wei) ch01

CHAPTER 1

INTRODUCTION

1.1. The Backdrop

In many parts of the world, economic, social and political problems have arisenfollowing rapid industrial development and urbanization, resulting in adverseeffects on the quality of life. Urbanization in general initially places pressureon and overstrains public amenities. However, long-term and wider issues wouldeventually also be encountered as industrialization and urbanization exert pressureon the larger resource base that supports the community. This larger resource baseincludes forestry, freshwater and marine resources, as well as space suitable forfurther development. The difculties associated with environmental degradationoften originate from industrial development. They are amplied by rapid urban-ization that is responsible for the growth of many major cities. In Asia, urbaniza-tion is exacerbated by large ruralurban migrations. These migrations emerge inresponse to perceived opportunities for a better livelihood in industrialized, eco-nomically booming urban areas. Rapid industrialization and its concentration inor near urban centers have placed very high pressures on the carrying capacityof the environment at specic locations. At these locations waterbodies such asrivers, lakes, and coastal waters have typically been severely affected.

Freshwater is a vital natural resource that will continue to be renewable aslong as it is well managed. Preventing pollution from domestic, industrial, andagro-industrial activities is important to ensure the sustainability of the localesdevelopment. Undoubtedly the water pollution control efforts which have beenunderway in many countries have already achieved some success. Nevertheless theproblems that are confronted grow in complexity and intensity. It is estimated that785 million people in Asian developing countries have no access to sustainablesafe water (Sawhney, 2003). The pollution of freshwater bodies with the conse-quent deterioration in water quality can only worsen the situation. Such pollutionhas been brought about by the discharge of inadequately treated sewage and indus-trial wastewaters. This book focuses on the latter. Perhaps not unexpectedly, as thedemand for more water is met, the volumes of wastewater can also be expected

1


2 Industrial Wastewater Treatment

to increase. Coastal waters are also under pressure as they receive efuents dis-charged directly into them or indirectly from rivers. While most communities inAsia do not use coastal waters as a source of potable water (via desalination),there is already a movement towards this direction, as in the case of Singapore.Even though coastal waters are not yet a major source of potable water, they are,nevertheless, very important since they support sheries and tourism industries.The ecosystems in many of Asias coastal waters are fragile; damage to theseecosystems as a result of pollution can adversely affect shery industries. Thelatter, in many instances, depend on mangrove forests as spawning grounds formarine life which are subsequently harvested.

Industrial wastewaters (including agro-industrialwastewaters) are efuents thatresult from human activities which are associated with raw-material processingand manufacturing. These wastewater streams arise from washing, cooking, cool-ing, heating, extraction, reaction by-products, separation, conveyance, and qualitycontrol resulting in product rejection. Water pollution occurs when potential pol-lutants in these streams reach certain amounts causing undesired alterations to areceiving waterbody. While industrial wastewaters from such processing or man-ufacturing sites may include some domestic sewage, the latter is not the majorcomponent. Domestic sewage may be present because of washrooms and hos-tels provided for workers at the processing or manufacturing facility. Examples ofindustrial wastewaters include those arising from chemical, pharmaceutical, elec-trochemical, electronics, petrochemical, and food processing industries. Examplesof agro-industrial wastewaters include those arising from industrial-scale animalhusbandry, slaughterhouses, sheries, and seed oil processing. Agro-industrialwastewaters can be very strong in terms of pollutant concentrations and hence cancontribute signicantly to the overall pollution load imposed on the environment.It is perhaps ironic that the very resources which promoted industrial develop-ment and urbanization in the rst place can subsequently come under threat fromsuch development and urbanization because of over and inappropriate exploita-tion. Appropriate management of such development and resources is a matter ofpriority. The South Johore coast was such a case (ASEAN/US CRMP, 1991). Thiswas then, economically, one of the fastest growing areas in Malaysia and poten-tial damage to the environment of such development, if not properly managed,was recognized.

The impact of industrial wastewater discharges on the environment and humanpopulation can be tragic at times. Some 50 years ago, the Minamata diseasewhich spread among residents in the Yatsushiro Sea and the Agano River basinareas in Japan was attributed to methyl mercury in industrial wastewater (Matsuo,1999). However, tragedies as dramatic as the Minamata episode have not occurredfrequently. Nevertheless, instances of pollution with potentially adverse impacts


Introduction 3

in the longer term have continued to occur. In the interim before the realization ofthese longer term impacts, a decline in the quality of life arising from the deteriora-tion in water quality which various populations must access may become increas-ingly discernable. Examples of these, their recognition, and the efforts made toremedy the situations in the 1980s include the protection of Malaysian coastalwaters from renery wastewater (Yassin, 1987), the Tansui River in Taiwan wherepesticides and heavy metals were discovered in the sludge (Liu & Kuo, 1988), theNam Pong River in Thailand which was polluted by the pulp and paper industry(Jindarojana, 1988), and the Buriganga River in Bangladesh which had been pol-luted by, among other industries, tanneries (Ahmed & Mohammed, 1988). Simi-lar reports in the 1990s include the Kelani River in Sri Lanka (Bhuvendralingamet al., 1998), the Laguna de Bay in the Philippines (Barril et al., 1999), andthe Koayu River which had occurrences of Cryptosporidum oocysts and Giar-dia cysts after receiving inadequately treated piggery wastewater (Hashimoto &Hirata, 1999). Such reports are still frequent in the 2000s and caused concerns inVietnam (Nguyen, 2003) and Korea (Kim et al., 2003). The fact that water pollu-tion due to discharges of inadequately treated industrial wastewater has occurredover decades in Asia obviously means solutions have not been found for all suchoccurrences. Towards the end of 2004, the Huai River in China was reportedto have been so seriously polluted by paper-making, tanning and chemical fer-tilizer factories, farmers in Shenqiu County had fallen very ill after using theriver water (The Strait Times, 2004). There has, however, been progress and anexample is the successful ten year river pollution clean-up program in Singapore(Chiang, 1988).

Agro-industrial wastewaters, as a sub-class of industrial wastewaters, can haveconsiderable impact on the environment because they can be very strong in termsof pollutant strength and often the scale of the industry generating the wastewaterin a country is large. Citing ASEAN countries in Asia as examples, agro-industrialwastewaters had and in some instances still contribute very signicantly to pollu-tion loads. For example in 1981 the Malaysian palm oi and rubber industries con-tributed 63% (1460 td1) and 7% (208 td1) of the BOD (Biochemical OxygenDemand) load generated per day respectively. This is compared with 715 td1of BOD from domestic sewage (Ong et al., 1987). In the Philippines, pulp andpaper mills generated 90 td1 of BOD load (Villavicencio, 1987). Agro-industrialsites are therefore often the largest easily identiable point sources of pollutantloads. While there are exceptions, individual industrial wastewater sources asso-ciated with manufacturing in Asia are, in contrast, more often small to mediumsized compared to the former. The classications of a small and medium-sizedmanufacturing facility have been dened in terms of the numbers of employeesemployed at such sites 10 49 persons and 50 199 persons respectively.



Notwithstanding their small to medium sizes, the collective contribution fromsuch enterprises to pollution is not necessarily negligible.

It should also be noted that while industrial wastewater sources may be smallto medium-size, they are generally located in urban centers where building con-gestion is already a problem. To aggravate the situation, such factory operationsmay have no long-range project planning and are also unable to exploit advantagesassociated with economies of scale. A number of such operations may also try tomaximize prots by reducing overheads and unnecessary expenditure associ-ated with pollution control requirements the result of an absence of an appro-priate corporate culture and hence a weaker social conscience in terms of carefor the environment. On a positive note, however, economic development over thelast few decades has enabled necessary managerial, nancial, and technologicalcapabilities to address problems of pollution and environmental degradation overthe broad spectrum of factory sizes. There is also a growing realization that thecost (in terms of the human and economic costs) of cleaning up after the act isfrequently more than preventing the pollution in the rst place.

1.2. What is Industrial Wastewater?

To begin the discussion on industrial wastewater, it may be useful to compareindustrial wastewater with domestic sewage since designers of wastewater treat-ment facilities often begin their careers and almost certainly their education inenvironmental engineering by looking at sewage and sewage treatment plants. Thelatter can then provide a familiar framework which the reader can use to compareindustrial wastewater and its treatment.

Domestic sewage is wastewater discharged from sanitary conveniences in res-idential, ofce, commercial, factories and various institutional properties. It is acomplex mixture containing primarily water (approximately 99%) together withorganic and inorganic constituents. These constituents or contaminants comprisedsuspended, colloidal and dissolved materials. Domestic sewage, since it containshuman wastes, also contains large numbers of micro-organisms and some of thesecan be pathogenic. Waterborne bacterial diseases that can be present in sewageinclude cholera, typhoid and tuberculosis. Viral diseases can include infectioushepatitis. Inorganic constituents include chlorides and sulphates, various forms ofnitrogen and phosphorous, as well as carbonates and bicarbonates. Proteins andcarbohydrates constitute about 90% of the organic matter in domestic sewage.These arise from the excreta, urine, food wastes, and wastewater from bathing,washing, and laundering, and because of the latter, soaps, detergents, and othercleaning products can be found as well. Domestic sewage has a ow pattern which


Introduction 5

typically shows two peaks in the morning before the start of working hoursand in the evening after the population has returned from work. Typically thesehydraulic peaks would also become more distinct as the sewage ows consid-ered come from smaller populations and consequently smaller sewer networks.Variations in sewage characteristics across a given community tend to be rela-tively small although variation across communities can be more readily detected.Notwithstanding these variations, the composition of domestic sewage is such thatit lends itself well to biological treatment in terms of the availability of and bal-ance between carbonaceous components and nutrients. The biodegradability ofsewage can be estimated by considering its Chemical Oxygen Demand (COD)and the corresponding BOD5 (5 day BOD), and is indicated by its COD:BOD5and BOD5:N:P ratios. This would typically be about 1.5:1 and 25:4:1 respectively.The nitrogen, N, would typically be in the form of organic nitrogen and ammonia-nitrogen (Amm-N). Nitrates (NO3-N) would not be expected to be present as con-ditions in the sewers would be such that nitrate formation is unlikely while nitratedegradation because of anoxic reactions is likely. The phosphorous (P) would bea combination of organic and phosphate (PO4) forms. The pH of sewage wouldbe within the range of 69 and this is generally considered suitable for biologi-cal processes. Examples of values of BOD5, TSS (Total Suspended Solids), andTKN (Total Kjeldhal Nitrogen) which have been used for purposes of plant designare 250, 300 and 40mg L1 respectively. As indicated earlier in this paragraph,sewage characteristics can vary across communities and a raw sewage BOD5 of500mg L1 has been encountered.

Industrial (including agro-industrial) wastewaters have very varied composi-tions depending on the type of industry and materials processed. Some of thesewastewaters can be organically very strong, easily biodegradable, largely inor-ganic, or potentially inhibitory. This means TSS, BOD5 and COD values may bein the tens of thousands mg L1.

Because of these very high organic concentrations, industrial wastewaters mayalso be severely nutrients decient. Unlike sewage, pH values well beyond therange of 69 are also frequently encountered. Such wastewaters may also be asso-ciated with high concentrations of dissolvedmetal salts. The ow pattern of indus-trial wastewater streams can be very different from that of domestic sewage sincethe former would be inuenced by the nature of the operations within a factoryrather than the usual activities encountered in the domestic setting. A signicantfactor inuencing the ow pattern would be the shift nature of work at factories.These shifts may be 8 h or 12 h shifts and there can be up to three shifts per day.These shifts may mean that there can be more than the two peaks in ow seen insewage and there may be no ow for parts of the day. Factories may operate ve to



seven days per week. A consequence of this can be the possibility of zero ow ondays when a factory is not operating. In contrast to the narrower band of variationin the characteristics of domestic sewage within a community, industrial wastew-aters can have very different characteristics even for wastewaters from a singletype of industry but from different locations. The cause of these differences hasmuch to do with the operating procedures adopted at each site and the raw materi-als used therein. To further complicate matters, wastewater characteristics withina factory can also vary with time because it may practice campaign manufactur-ing, or it may practice slug discharges on top of its usual discharges. Apart fromthese events which occur on a regular basis, there would be spillages and dump-ing which may occur within the factory infrequently but can have very adverseimpacts on the performance of the wastewater treatment plant. Consequently itwould be prudent to assess an industrial wastewater, as well as its pretreatmentand treatment requirements very carefully and not immediately assume that itswastewater characteristics and treatment requirements are similar to a previouslyencountered example. It would also be prudent to acquire some understanding ofthe nature of the factorys operations. A more detailed discussion of the character-istics of industrial wastewaters is made in Chapter 2.

On some occasions industrial wastewaters are discharged into a sewerage sys-tem serving commercial and residential premises. Such a combination of wastew-ater streams is known as municipal wastewater and the quality of such a mixtureof wastewaters can vary depending on the proportion of industrial wastewaters init and the type of industries contributing the industrial wastewater streams. Usu-ally the domestic and commercial components in municipal wastewater can beexpected to provide some buffering in terms of the characteristics of the combinedow. This is then expected to enable the combined wastewater to be treated eas-ily compared to the treatment of the industrial wastewater on its own. However,even where the option of discharging into a sewerage system is available, somedegree of pretreatment is frequently required at the factory before such dischargeis permitted. Such pretreatment may include pH adjustment to 69 and BOD5reduction to 400mg L1 as being currently practiced in Singapore (Pakiam et al.,1980). This is to protect the receiving sewers from corrosion and also protect theperformance of the receiving treatment plant from an organic substrate overload.

1.3. Why is it Necessary to Treat Industrial Wastewater?

All major terrestrial biota, ecosystems, and humans depend on freshwater (i.e.water with less than 100mg L1 salts) for their survival. The earths water isprimarily saline in nature (about 97%). Of the remaining (3%) water, 87% of it


Introduction 7

is locked in the polar caps and glaciers. This would mean only 0.4% of all wateron earth is accessible freshwater. The latter is, however, a continually renewableresource although natural supplies are limited by the amounts that move throughthe natural water cycle. Unfortunately precipitation patterns, and hence distribu-tion of freshwater resources, around the globe is far from even. Where precipi-tation does fall heavily, there are often difculties with storage because of spaceconstraints. Furthermore the available freshwater has to be shared between naturalbiota and human demands. The latter, aside from direct human consumption,includes water for agricultural, urban, and industrial needs. Freshwater shortagesincrease the risk of conict, public health problems, reduction in food produc-tion, inhibition of industrial production expansion, and these problems threatenthe environment.

Freshwater shortages are, however, not only due to uneven distribution offreshwater resources and demand for freshwater but also, increasingly, due tothe declining water quality in freshwater sources already in use. This decliningwater quality is primarily due to pollution. It should not be forgotten that in thewider context of resources associated with water, the marine environment is alsoincluded in the picture. While the latter was, in the past, primarily associated withthe sheries resource, it can also include tourism and the feed for desalination inthe current context. Untreated industrial wastewaters would add pollutants intowaterbodies freshwater and saline. These receiving waterbodies, freshwaterand marine, can include ponds, lakes, rivers, coastal waters, and the sea. It wouldbe useful to bear in mind that pollutants introduced into a river or some otherfreshwater waterbody do eventually end up in the sea, the ultimate receptacle forwaterborne pollutants if these are permitted to nd their way through the environ-ment unimpeded. An example of riverine pollution are the rivers owing throughurban and industrial areas such as Hanoi and Ho Chi Minh City in Vietnam pick-ing up pollutants such as heavy metals and organochlorine pesticides and herbi-cides. These pollutants reach the sea eventually and therein threaten the sheries(Nguyen et al., 1995). On Hainan Island (Southern China), for example, industriessuch as sugar reneries, paper mills, shipyards, and fertilizer plants accounted forabout half the total wastewater generated and reaching the sea. This had resulted inincidences of the red tide in Houshui Bay and an area northwest of the island (Du,1995). Obviously then, inadequately treated industrial wastewaters dischargedinto rivers would not only affect the freshwater in these areas but also the receiv-ing coastal and sea waters. Eventually coastal resources such as the mangroveand reef ecosystems, and thereafter sheries would be affected. The discharge ofinadequately treated industrial wastewaters can therefore have far-reaching con-sequences. In the last decade, the emergence of industrial pollution has been



identied as a trend in the coastal areas of Southern China, Vietnam, Kampuchea,and Thailand.

The effects pollutants have on the water environment can be summarized in thefollowing broad categories:

(a) Physical effects These include impact on clarity of the water and inter-ference to oxygen dissolution in it. Water clarity is affected by turbiditywhich may be caused by inorganic (Fixed Suspended Solids or FSS) and/ororganic particulates suspended in the water (Volatile Suspended Solids orVSS). The latter may undergo biodegradation and thereby also have oxida-tion effects. Turbidity reduces light penetration and this reduces photosynthe-sis while the attendant loss in clarity, among other things, would adverselyaffect the food gathering capacity of aquatic animals because these may notbe able to see their prey. Very ne particulates may also clog the gill sur-faces of shes and thereby affecting respiration and eventually killing them.Settleable particulates may accumulate on plant foliage and bed of the water-body forming sludge layers which would eventually smother benthic organ-isms. As the sludge layers accumulate, they may eventually become sludgebanks and if the material in these is organic then its decomposition would giverise to malodours. In contrast to the settleable material, particulates lighterthan water eventually oat to the surface and form a scum layer. The lat-ter also interferes with the passage of light and oxygen dissolution. Becauseof the former, these scum layers affect photosynthesis. Discharge limits onwastewater or treated wastewater discharges typically have a value for TSSsuch as 30mg L1 or 50mg L1. Many industrial wastewaters contain oiland grease (O&G). While some of the latter may be organic in nature, thereare many which are mineral oils. Notwithstanding their organic or mineralnature, both types cause interference at the air-water interface and inhibit thetransfer of oxygen. Apart from their interference to the transfer of oxygenfrom atmosphere to water, the O&G (particularly the mineral oils) may alsobe inhibitory. Unlike domestic sewage, industrial discharges can have temper-atures substantially above ambient temperatures. These raise the temperaturesof the receiving water and reduce the solubility of oxygen. Apart from this,rapid changes in temperature may result in thermal shock and this may belethal to the more sensitive species. Heat, however, does not always have anegative impact on organisms as it may positively affect growth rates althoughthere are limits here too since the condition may favor certain species withinthe population more than others and over time biodiversity may be negativelyaffected;


Introduction 9

(b) Oxidation and residual dissolved oxygen As suggested in the precedingparagraph, waterbodies have the capacity to oxygenate themselves throughdissolution of oxygen from the atmosphere and photosynthetic activity byaquatic plants. Of the latter, algae often plays an important role. However,there is a nite capacity to this re-oxygenation and if oxygen depletion, as aresult of biological or chemical processes induced by the presence of organicor inorganic substances which exert an oxygen demand (i.e. as indicated bythe BOD or COD), exceeded this capacity then the dissolved oxygen (DO)levels would decline. The latter may eventually decline to such an extentthat septic conditions occur. A manifestation of such conditions would be thepresence of malodours released by facultative and anaerobic organisms. Anexample of this is the reduction of substances with combined oxygen suchas sulphates by facultative bacteria and resulting in the release of hydrogensulphide. The depletion of free oxygen would affect the survival of aerobicorganisms. DO levels do not, however, need to drop to zero before adverseimpacts are felt. A decline to 34mg L1, which still means the water con-tains substantial quantities of oxygen, may already adversely affect higherorganisms like some species of sh. If inhibitory substances are also present,then the DO level at which adverse effects may be felt can be even higherthan before. The case of elevated water temperatures due to warm dischargesis somewhat different. The elevated temperatures can affect metabolic ratespositively (possibly twofold for each 10C rise in temperature) but elevatedtemperatures also reduce the solubility of oxygen in water. This would meanincreasing demand for oxygen while its availability declines. Because of theimpact of DO levels on aquatic life, much importance has been placed ondetermining the BOD value of a discharge. Typical BOD5 limits set are val-ues such as 20 and 50mgL1;

(c) Inhibition or toxicity and persistence These effects may be caused byorganic or inorganic substances and can be acute or chronic. Examples ofthese include the pesticides and heavy metals mentioned in the preceding sec-tion. Many industrial wastewaters do contain such potentially inhibitory ortoxic substances. The presence of such substances in an ecosystem may biasa population towards members of the community which are more tolerant tothe substances while eliminating those which are less tolerant and resultingin a loss of biodiversity. For similar reasons, an awareness of the impactsuch substances have on biological systems is not only relevant in terms ofprotection of the environment but is of no less importance in terms of theirimpact on the biological systems used to treat industrial wastewaters. Evensuccessful treatment of such a wastewater may not necessarily mean that the



potability of water in a receiving waterbody would not be affected. For exam-ple small quantities of residual phenol in water can react with chlorine dur-ing the potable water treatment process giving rise to chlorophenols whichcan cause objectionable tastes and odors in the treated water. Apart from theorganic pollutants which are potentially inhibitory or toxic, there are thosewhich are resistant to biological degradation. Such persistent compounds canbe bioaccumulated in organisms resulting in concentrations in tissues beingsignicantly higher than concentrations in the environment and thereby mak-ing these organisms unsuitable as prey/food for organisms (including Man)higher up the food chain. While some organic compounds may be persistent,metals are practically non-degradable in the environment;

(d) Eutrophication The discharge of nitrogenous and phosphorous compoundsinto receiving waterbodies may alter their fertility. Enhanced fertility can leadto excessive plant growth. The latter may include algal growth. The subse-quent impact of such growth on a waterbody can include increased turbidity,oxygen depletion, and toxicity issues. Algal growth in unpolluted waterbod-ies is usually limited because the water is nutrient limiting. While nutrientswould include marco-nutrients like nitrogen, phosphorous, and carbon, andmicro-nutrients like cobalt, manganese, calcium, potassium, magnesium, cop-per, and iron which are required only in very small quantities, the focus in con-cerns over eutrophication would be on phosphorous and nitrogen as quantitiesof the other nutrients in the natural environment are often inherently adequate.In freshwaters the limiting nutrient is usually phosphorous while in estuarineand marine waters it would be nitrogen. Treatment of industrial wastewater(or domestic sewage for that matter) can then target the removal of eitherphosphorous or nitrogen, depending on the receiving waterbody, to ensurethat the nutrient limiting condition is maintained. Given the litoral nature ofmany nations in Asia, removal of nitrogen would likely be necessary if thewastewater contained excessive quantities. When the nutrient limiting condi-tion is no longer present in the waterbody, and when other conditions such asambient temperature are appropriate, excessive algal growth or algal blooms(e.g. the red tide) may occur. Apart from aesthetic issues, such algal bloomsmay affect the productivity of the sheries in the locale. It should be noted thatnot all industrial wastewaters contain excessive quantities of nutrients, macroand micro. This deciency, if there is, results in process instability and/or theproliferation of inappropriate microbial species during biological treatment ofthe wastewaters. Bulking sludge is a manifestation of such an occurrence. Toaddress this deciency, nutrients supplementation is required. The quantitiesused should be carefully regulated so that an excessive nutrients condition is


Introduction 11

not inadvertently created and these excess nutrients subsequently dischargedwith the treated efuent. In terms of BOD:N:P, the optimal ratio for biotreat-ment is often taken as 100:5:1 while the minimum acceptable condition can be150:5:1;

(e) Pathogenic effects Pathogens are disease-causing organisms and an infec-tion occurs when these organisms gain entry into a host (e.g. man or ananimal) and multiply therein. These pathogens include bacteria, viruses, pro-tozoa, and helminthes. While domestic and medical related wastewaters maytypically be linked to such micro-organisms (and especially the bacteria andviruses), industrial wastewaters are not typically associated with this categoryof effects. The exception to this is wastewaters associated with the sectors inthe agro-industry dealing with animals. The concern here would be the pres-ence of such organisms in the wastewater which is discharged into a receivingwaterbody and diseases, if any, are then transmitted through the water. Whilemany of these organisms can be satisfactorily addressed with adequate disin-fection of the treated efuent and raw potable water supplies during the watertreatment process, there are those which cannot be dealt with so easily. Twoexamples of such organisms, Cryptosporidum and Giardia, were identiedin Sec. 1.1. These belong to the protozoa family. The difculty is that theinfected host does not necessarily shed the organism but is likely also to shedits eggs or oocysts. The latter can unfortunately be resistant to the usual disin-fection processes. An outbreak of cryptosporidiosis, a gastrointestinal disease,would result in the hosts suffering from diarrhea, abdominal pain, nausea, andvomiting.

With the above effects in view, industrial wastewater treatment would typicallybe required to address at least the following parameters:

(a) Suspended solids (SS);(b) Temperature;(c) Oil and grease (O&G);(d) Organic content in terms of biochemical oxygen demand (BOD) or chemical

oxygen demand (COD);(e) pH;(f) Specic metals and/or specic organic compounds;(g) Nitrogen and/or phosphorus;(h) Indicator micro-organisms (e.g. E. Coli) or specic micro-organisms.


CHAPTER 2

NATURE OF INDUSTRIAL WASTEWATERS

In the previous chapter a large variety of industrial wastewaters was mentioned.There are those with constituents which are primarily inorganic and thus wouldnot be suitable for biological treatment. The focus of this book is on those withquantities of organics requiring removal and where biological treatment is a viabletreatment option. It is very important for the designer and operator of a wastewa-ter treatment plant to have as much knowledge of the wastewaters characteristicsas possible. This is to ensure a suitable plant design is developed and the subse-quently constructed plant is appropriately operated.

Industrial wastewater characteristics which would require considerationinclude the following:

(i) biodegradability;(ii) strength;(ii) volumes;(iv) variations and;(v) special characteristics which may lead to operational difculties.

An appreciation of the industrial processes used at a site is also often usefulfor understanding the reasons why particular attributes are either present or absentand why the variations occur. In time the designer may be able to anticipate someof the potential difculties a plant may experience by observing operations at anindustrial site.

2.1. Biodegradability

For an industrial wastewater to be successfully treated by biological means itshould have quantities of organics requiring removal and these (and any otherconstituents present in the wastewater) should not inhibit the biological process.The quantity of organics in a wastewater is indicated by the wastewaters BOD5and COD (dichromate) values. Since the BOD is the oxygen demand exerted by

12


Nature of Industrial Wastewaters 13

micro-organisms to degrade organicswhile the COD is that required to chemicallyoxidize organics without considering the latters biodegradability (i.e. approxi-mately equivalent to the total organics present), the difference between the CODand BOD values would provide an indication of the quantity (in a relative sensebut not in absolute terms) of non-biologically degradable organics. Similarly thenthe COD:BOD5 ratio can provide an indication of how amenable a wastewater isto biological treatment. Since the dichromate COD value would always be largerthan the BOD5 value in an industrial wastewater, the COD:BOD5 ratio shouldalways be greater than 1.

It has, however, been noted that wastewaters with COD:BOD5 ratios of 3 orlower can usually be successfully treated with biological processes. COD:BOD5ratios of 3 or lower are encountered in many of the agricultural and agro-industrialwastewaters. Table 2.1.1 provides information on six poultry slaughterhousewastewaters. All six cases practice blood recovery although they may not havedone so to the same extent. All have also practiced recovery of feathers and againin varying degrees. The COD:BOD5 ratios of ve of the examples which rangedfrom 1.3:1 to 2.5:1 suggested that such wastewaters are easily biodegradable andthis has been noted to be so at the treatment plants. Case-5 had much higherCOD:BOD5 ratios and this was because this source was not only wastewater froma slaughterhouse like the rest but also wastewater from a facility processing andcooking the resulting meat.

Table 2.1.1. Slaughterhouse (poultry) wastewater characteristics.

Parameters/Cases Case-1 Case-2 Case-3 Case-4 Case-5 Case-6

Qavg , m3 h1 24 9 40 66 18 16Qpk , m3 h1 45 15 70 85 20 COD, mgL1 2970 2700 20004000 5200 20002500 2300BOD5, mgL1 1480 1100 15003000 2500 500750 1200

COD:BOD 2.0:1 2.5:1 1.3:1 2.1:1 3.3:14.0:1 1.9:1TSS, mgL1 950 800 1000 1800 1000 1000VSS, mgL1 320 300 400O&G, mgL1 80 100 200 1100 150250 150

pH 6.07.5 6.08.0 6.57.5 6.08.0 6.08.5 6.07.5Amm-N, mgL1 50 40 120 10190 6070TKN, mgL1 200 170 200 310 15300 200250

Temp, C 2630 2634 2634 2634 2635

Note: Where two values have been provided these represent the minimum and maximum compos-ite daily average values noted for a particular parameter over a monitoring period. Single values arethe average values of composite daily samples. A means information for that parameter is notavailable.



Table 2.1.2. Tobacco processing wastewatercharacteristics.

Parameters Values

Qavg , m3 d1 150No. of shifts, d1 1 8 h shiftCOD, mgL1 450011800BOD5, mgL1 7604200SS, mgL1 140600

O&G, mgL1 1040pH 4.05.5

Agro-industrialwastewaters need not always have such low COD:BOD5 ratios.For example tobacco processing wastewater (Table 2.1.2) can have a COD:BOD5ratio of about 6:1. This is a strongly colored (brown coloration arising from thetobacco leaves) wastewater which can be difcult to treat to meet COD dischargelimits because residual organics following biological treatment are resistant tofurther biological treatment.

Examples of more extreme COD:BOD5 ratios may be found in some chemi-cal wastewaters such those arising from dyestuff manufacturing. An example hada wastewater COD of 4400mgL1 but a BOD5 of only 55mgL1. The result-ing COD:BOD5 ratio was therefore 80:1 which meant biological treatment wouldunlikely to be successful in removing sufcient quantities of the organics so as tomeet the discharge limits (i.e. high efuent COD).

It is important to realize a low COD:BOD5 ratio suggests biological treatmentmay be successful but does not necessarily mean biological treatment will be suc-cessful. A wastewater would have other properties which may be no less importantto the success (or failure) of biological treatment. A number of these propertiesare explored in the following sections.

2.2. Strength

Industrial wastewaters often have organic strengths which are very much higherthan those encountered in sewage. Agro-industrial wastewaters are among thosewhich may have very high organic strengths. Chapter 10 explores such a strongwastewater, palm oil mill efuent (POME). Table 2.2.1 provides additional exam-ples drawn from tapioca starch, sugar milling and coconut cream extractionindustries.

Such wastewaters may benet from anaerobic pretreatment ahead of theaerobic treatment stage so that organic strength can be reduced and hence reducing



Table 2.2.1. Characteristics of tapioca starch extraction, sugar milling andcoconut cream extraction wastewaters.

Parameters/Industry Starch extraction Sugar milling Coconut cream

Qavg , m3 d1 3.6 over 8 h 120 over 20 h 112 over 24 hBOD5, mgL1 2700 25000 8900COD, mgL1 41000 50000 12900

pH 67 45TSS, mgL1 23000 2900Zn, mgL1 25

O&G, mgL1 15 1560S1, mgL1 0.2

Cr(total), mgL1 0.2 B, mgL1 2

Phenol, mgL1 2 Temp, C 2528

TDS, mgL1 100 000

the aeration and the consequential energy requirements. Typically the biologicalprocesses address the dissolved and colloidal organic components in a wastewatersince the particulate component can be easily addressed using physico-removalmethods. For example the coconut cream extraction wastewater could have ben-eted from this approach and certainly the starch extraction wastewater with23000mgL1 SS can be treated with a ne screen initially and the 41000mgL1COD would then have been very substantially reduced.

However, there are strong wastewaters with SS which may not respond in asimilar manner. Table 2.2.2 provides details on distillery wastewater. The widerange in wastewater organic strengths reect the varying degrees of dilutionbrought about by the merging of various wastewater streams at a distillery. Dis-tilleries can have two major wastewater streams the fermentation and washstreams. The fermentation stream is usually very strong and would have character-istics somewhat similar to Distillery Case-2 except that the SS which would havebeen substantially higher. It would have been ineffective to attempt to remove thisSS with screens since the material can penetrate even ne screens and can easilyblind such screens because of its stickiness.

2.3. Volumes

It can be a common misconception that industrial wastewater treatment plantshandle volumes which are smaller than sewage ows. While this may be so



Table 2.2.2. Distillery wastewater characteristics.


Wastewater ow, 42 over 60 over 1000 over 60 over 1225 over 221 overm3 d1 8 h 8 h 24 h 8 h 20 h 24 h

BOD5, mgL1 4000 59000120000 3200 4100 1000 15000COD, mgL1 6000 100000150000 5350 9600 3000 18000TSS, mgL1 3500 10002000 900 180 4030

pH 35 3.54.0 47 6.27.2 69Amm-N, mgL1 1200 1.5 TKN, mgL1 TP, mgL1 TDS, mgL1 9000 4800 Temp, C 95 35 105Feedstock kaoliang molasses rice rice mixed grains

when compared with sewage ows received by sewage treatment plants servingmetropolitan areas, not all sewage treatment plants serve large communities andnot all industrial wastewater ows are small. The range of industrial wastewatervolumes to be treated can be very large, not only from one industry to the nextbut also from factory to factory within an industry. Table 2.2.1 shows an exam-ple with only 3.6m3 d1 (starch extraction wastewater) but there are industrialwastewaters, such as those from paper mills (Table 2.3.1) and breweries (Table2.3.2), with very large volumes. Paper mills are probably among the largest interms of volumetric loads. For example, Paper Industry Case-1 is equivalent tosewage ows arising from 160000 equivalent population in terms of hydraulicload and 1.7 million equivalent population in terms of BOD load if it had been asewage ow.

Breweries, although not generatingwastewater ows as large as the papermills,are typically also associated with the larger ows. A major contributor to this largeow of wastewater is the bottling line in the brewery. This is because glass bottlesused are returnable and the returned bottles are washed before they can be used tobottle beer again.

The soft drinks industry (Table 2.3.3) has features similar to the breweries inthat the bottling lines (where present) also contribute substantially to the waste-water ow. These bottling lines also depend largely on reusable glass bottles whichhave to be washed before being used again. The bottle washing process (andthe dumping of rejected products) can be a cause for the differences in organicstrength at the various bottling plants. Apart from the organic components in thewastewater, these washing lines also give rise to debris such as broken glass, bits



Table 2.3.1. Paper industry wastewater characteristics.

Parameters/Cases Case-1 Case-2 Case-3 Case-4

Qavg , m3 d1 27240 over 24 h 11000 over 24 h 11000 over 24 h 4 over 8 hQmax , m3 d1 36320 over 24 h 15000 over 24 h 13800 over 24 h BOD5, mgL1 2540 1950 1550 850COD, mgL1 5080 3500 2770 6660TSS, mgL1 1600 500 200 490

pH 59 79 79 8.1O&G, mgL1 20 10 40TN, mgL1 TP, mgL1 TDS, mgL1 1000 800 Temp, C 5080 4555 4060

Phenol, mgL1 13Cu, mgL1 8Mn, mgL1 2 Pb, mgL1 4Fe, mgL1 5 5 Product recycled paper newsprint recycled paper cartons

Table 2.3.2. Brewery wastewater characteristics.

Parameters/Cases Case-1 Case-2 Case-3

Qavg , m3 d1 2500 over 24 h 800 over 24 h 700 over 24 hQmax , m3 d1 4320 over 24 h 1600 over 24 h BOD5, mgL1 8001600 6001500 1650COD, mgL1 12502550 17003600 2800TKN, mgL1 2535 PO-P4, mgL1 2030 TSS, mgL1 150500 270 400

pH 412 6.57.5Temp, C 1840 35

of paper labels, and drinking straws. The inclusion of screens to protect down-stream mechanical equipment is therefore an important requirement.

Although six soft drinks cases have been provided as examples, it should benoted that they are not bottling the same product (but all bottle carbonated drinks).The differences in product formulation have also contributed to the differencesin wastewater characteristics. A signicant impact at a bottling plant would bethe number of products produced on a campaign manufacturing basis using the



Table 2.3.3. Soft drinks wastewater characteristics.


Qavg , m3 d1 1680 over 2500 over 400 over 720 over 1675 over 800 over24 h 20 h 8 h 20 h 24 h 16 h

BOD5, mgL1 600 1500 15002000 1000 800 800COD, mgL1 1440 3000 25003000 2240 1410TSS, mgL1 45 100300 150 510 460TN, mgL1 3 TP, mgL1

O&G, mgL1 80 1015 5060 30 1020 1025pH 5.510.5 311 25 8.79.4 8.59.1

Detergent, mgL1 35 Fe, mgL1 16 Temp, C 35 35 35 35 35 35

same bottling lines. This would require shutting down and cleaning the productblending tanks and bottling lines at the conclusion of a particular manufacturingepisode resulting in the discharge of stronger wastewater than that experienced ata single product (per bottling line if not per factory) manufacturing premises.

To allow rst estimations to be made of wastewater volumes which need tobe addressed (especially for situations where a factory has not entered produc-tion yet), unit wastewater generation rates shown in Table 2.3.4 can be helpful.It should, however, be noted there are wide variations within any group and thiscan be due to the different specic products made and processes used within ageneric group (e.g. sh processing can include freezing, frying as in sh ngers,and boiling as in shrimp processing). Even when factories are manufacturing thesame products and using the same processes, differing housekeeping practicescan result in very different unit wastewater generation rates. As such the guresprovided should only be used as crude guides and with extreme caution. Pollu-tant loads, such as BOD and COD loads, may be developed using the gures inTable 2.3.4 with data shown in the other tables in this chapter.

2.4. Variations

The study of wastewater characteristics provided in the preceding tables wouldalready show that the wastewaters generated by different factories vary evenwithin the same industry group. This is so for every parameter indicated andparticularly so in the case of the volumes of wastewater discharged. In part thevariation would have been the result of different quantities of materials processed



Table 2.3.4. Wastewater generation rates for various industries.

Industry Unit wastewater generation rate Additional information

Soft drinks 32.4m3 1000 bottles1 Returnable glass bottlesFish processing 515m3 1000 kg1 product Includes frozen and cooked

products

Fruit & vegetables 0.92.0m3 1000 kg1 Includes fruits such asprocessing processed material pineapples

Canned milk 2.8m3 1000 kg1 product Sweetened condensed milkPasteurized milk 1.8m3 1000 L1 product Usually packed in paper

cartons

Yoghurt 5m3 1000 kg1 product Industrial kitchen 9.612.8m3 1000 meals1 Includes ight kitchens

Poultry slaughterhouse 8.920.6m3 1000 birds1 Very largely chickensPapermills 1230m3 1000 kg1 product Large component of

recycled paper

Winery 2.3m3 1000 kg1 product Grain basedIndustrial alcohol 0.1m3 1000 kg1 product Molasses basedSugar milling 1.53.0m3 1000 kg1 cane Sugar cane

Pig slaughterhouse 0.6m3 animal1 Serving nearby communityPig farm 2045m3 1000 spp1 d1 Washed and not scrapped

pens

Palm oil milling 23m3 1000 kg1 oil extracted Palm oil rening 0.2m3 1000 kg1 oil rened Physical reningPalm oil rening 1.2m3 1000 kg1 oil rened Chemical rening

at different locations but even in terms of unit quantity of materials processedthere are still variations and this is due to differences in housekeeping practicestherein.

Perhaps of greater importance to the designer and operator of a particular plantwould be the variations which occur at a given site. For example the precedingtables have shown a Qavg with a discharge period following, e.g., 42m3 d1 over8 h. If the discharge period is less than 24 h per day, then it must follow the wastew-ater is not discharged continuously throughout the day. An 8 h discharge periodwould have meant the wastewater treatment plant receives no wastewater for 16 hper day unless the holding capacity has been provided so that the wastewater owcan be redistributed over 24 h to ensure continuous ow conditions are met at thetreatment plant. It is important to bear in mind that wastewater is typically only



produced when a factory is in operation and wastewater ow data provided interms of m3 d1 can be misleading.

Table 2.1.1 shows another wastewater ow phenomenon that there are peri-ods of low and high ows during a days operation and peak ow Qpk , canbe very substantially higher than the average ow, Qavg . While Qpk conditionsmay not last long, such short period high ows or surges can easily upset theunit treatment processes. Surges can be caused by batch discharges (or dumping)which is particularly common at the end of a shift/working day or at the end of amanufacturing campaign.

Although the data presented in Table 2.4.1 may not immediately suggest batchdischarges, especially the noodle case which had 30m3 d1 over a 24 h period,in both cases, because of the nature of the manufacturing processes used, the dis-charges had to a very large extent occurred as batch discharges at the end of eachshift. This meant that the noodle case had three batch discharges while the vermi-celli case had one. A batch discharge with the consequent surge would representan extreme ow variation situation.

Even in the absence of batch discharges, ows can show wide uctuations overa days operation at a factory. This can be due to initiation of certain processeswhich generate larger volumes of wastewater and subsequently the ending of suchprocesses as activity moves to the next phase of processing. Industrial kitchens(Table 2.4.2) can behave in this manner as activity shifts from preparation of rawmaterials to cooking and nally packing/serving. Peak ows in such cases maylast for a few hours in the working day and sometimes may even be over in lessthan an hour.

Table 2.4.1. Noodles/Vermicelli manufacturing waste-water characteristics.

Parameter/Cases Noodle Vermicelli

Qavg , m3 d1 30 over 24 h 35 over 8 hBOD5, mgL1 410 1050COD, mgL1 1000 2000

pH 410 78TN, mgL1 TP, mgL1 TSS, mgL1 200TDS, mgL1 1000O&G, mgL1 300800 20

Temp, C 2530 2630



Table 2.4.2. Industrial kitchen wastewater characteristics.

Parameters/Cases Case-1 Case-2 Case-3 Case-4 Case-5

Qpk , m3 h1 13 21 36 5 525Qavg , m3 d1 128 over 16 h 40 over 6 h 520 over 24 h 10 over 8 h 3645 over 24 hBOD5, mgL1 600800 600 300690 600 500COD, mgL1 1400 7701550 1000TSS, mgL1 200600 400 220580 500 500O&G, mgL1 100400 50190 20 350

pH 6.58.5 6.28.9 Food product airline canteen fastfood bakery airline

Table 2.4.3. Seasonal wastewater variations at a vegetable processing plant.

Parameters/Periods Period-1 Period-2 Period-3

Qavg , m3 d1 550 over 24 h 350 over 24 h 400 over 24 hBOD5, mgL1 8501800 170340 480820TSS, mgL1 270350 80170 200890TN, mgL1 90170 220 50190TP, mgL1 1020 12 2030Raw material peas beans potatoes

While the preceding discussion had focused on the short term variations, a fac-tory can exhibit longer term or seasonal variations and these may be tied to manu-facturing campaigns as discussed earlier. Table 2.4.3 shows an example which hasthree campaigns in a year and each dealt with a different product. In this instance,the change in raw material handled arose out of the different seasonal harvestsencountered. The impact of such seasonal harvests on the wastewater treatmentplant is substantial as it would not only have to deal with a high ow period whichis 1.6 times higher than the low ow period but also daily BOD loads which canbe 8 times higher.

The example provided in Table 2.4.3 shows seasonal changes in the raw mate-rial handled and consequently changes in the wastewater ow and other charac-teristics. There can also be seasonal variations which are caused not by campaignmanufacturing or changes in the material harvested but by the necessity to processmore of the same raw material as the latters production or harvest peaks. Seafoodprocessingwastewater Case-1 and Case-2 (Table 2.4.4) are examples of such agro-industrial activity. These processing plants are located at ports, receive the catchdaily and freeze it. In Case-2 the high season ow is three times higher than the



Table 2.4.4. Seafood processing wastewater.

Parameters/Cases Case-1 Case-2 Case-3 Case-4

High season Qavg , m3 d1 200 1200 135 580Low season Qavg , m3 d1 150 400 135 580

BOD5, mgL1 750 3000 400 4900COD, mgL1 1440 4200 2000 TSS, mgL1 350 1500 1000 1130

pH 6 6.67.1 68 TDS, mgL1 10000 TN, mgL1 25 90 405TP, mgL1 5 95

O&G, mgL1 50 Temp, C 1825 1440

Raw materials sh sh, shrimp tuna sh, shrimp, tunaProcess activity freezing freezing canning canning

low season ow. Case-3 and -4 differ because these are downstream processorswhich cook the seafood and the latter is then canned.

Some seasonal variations may not necessarily be due to peaks in harvest butmay be due to peaks in demand. Food related industries can be affected by this,particularly during the period leading to the festive season. In Asia these are themonths of October to January. For example, poultry slaughterhouse Case-3 inTable 2.1.1 has a wastewater ow of 550m3 d1 for 10 months of the year butover 2 months leading to the festive period its ow can increase to 1000m3 d1.Wastewater quality in such instances need not necessarily change but quantity canchange substantially.

2.5. Special Characteristics

Industrial wastewaters may have certain characteristics, the effect of which maynot be apparent from the sort of wastewater data usually provided. These may,however, have signicant adverse impact on the equipment or unit process perfor-mance, and aesthetics of a wastewater treatment plant. This section explores a fewof these characteristics.

For example, if the COD:BOD ratios of dairy productwastewaters (Table 2.5.1)are considered, the conclusion would be such wastewaters are likely to be easilytreated with biological systems. The treatment plant design may then focus onthe O&G and BOD strength. Most wastewater treatment plants for milk relatedwastewaters include O&G removal devices such as oil traps and DAFs. The



Table 2.5.1. Dairy product wastewater characteristics.


Qavg , m3 d1 750 over 120 over 800 over 120 over 50 over 100 over24 h 24 h 16 h 24 h 8 h 8 h

Qpk , m3 h1 75 40 70 BOD5, mgL1 1800 3400 480 3000 1230 940COD, mgL1 3600 4300 920 1970 1240TSS, mgL1 1000 2000 120 1500 440 360O&G, mgL1 150 1800 250 2500 115 40

pH 312 6.07.5 68 411 4.310.0 4.86.8TN, mgL1 310 85 260 60 10TP, mgL1 1 40 Temp, C 2640 2632 3040 Product milk based ice cream condensed ice cream & re-constituted fresh milk

snacks & milk yoghurt milkice cream

relatively high O&G content in these wastewaters may be due to the inclusionof vegetable oils in the products (to augment milk fats). Oil traps have been effec-tive at removal of the free O&G but can become sources of strong odor as wouldany part of the plant which is not regularly cleaned. The use of DAFs can helpalleviate this odor problem. Good housekeeping at the treatment plant is, nev-ertheless, always important. This is because the biological degradation of milkrelated substances under non-aerobic conditions results in odorous organic com-pounds. Notwithstanding the organic strength of the wastewater, the selection ofan anaerobic biological process for organic reduction prior to aerobic treatmentwould probably not be an appropriate strategy.

It is important to bear in mind the TSS parameter can be due to many differenttypes of particulate material. A concern which can possibly be associated withsome of these particulates is their abrasive properties. While the TSS associatedwith a dairy wastewater arising from cowsheds may well immediately suggestgrit and hence suggest wear on pumps and valves, this may be less obvious inthe case of the coffee and sauce industries identied in Table 2.5.2. In the caseof coffee (Table 2.5.2 Cases-1 to -3), coffee bean nes contributed substantiallyto the TSS. These nes have been found abrasive on mechanical equipment. InCases-4 and -5 (Table 2.5.2), the abrasive component in the TSS which damagedthe pumps turned out to be the chili seeds when chili was processed into sauces.

Foaming can be a particularly difcult condition to address at a biological treat-ment plants aeration vessels. While there are instances where foaming can bedue to the biological process responding to organic loading conditions or certain



Table 2.5.2. Coffee processing and sauce making wastewater characteristics.

Parameters/Cases Case-1 Case-2 Case-3 Case-4 Case-5

Qavg , m3 d1 140 over 24 h 400 over 24 h 76 over 16 h 300 over 24 h 50 over 8 hQpk , m3 h1 7 15 40 9

BOD5, mgL1 80009000 15002000 2660 5000 8001480COD, mgL1 1100012000 30004000 4800 10000 18002880TSS, mgL1 50005100 500600 1000 800 130170O&G, mgL1 100200 20170 TN, mgL1 15 TP, mgL1 2

pH 7.07.4 4.06.5 4.5 3.06.5Temp, C 4450 3642 3045 3042Product instant instant decanated chili & chili &

coffee coffee mix coffee sayo sauce tomatowith milk sauceand sugar

constituents in the wastewater, there are also instances when the wastewater hadcomponents within it which can cause foaming even without interaction with thebiological process. Detergents are a key component in this latter group. In indus-trial wastewaters, detergents can appear very frequently because they can be usedin cleaning operations at the manufacturing facility. The problem becomes tougherwhen a facility is manufacturing products which include detergents in their formu-lations. Examples of these are Case-1, -2, -5 and -6 in Table 2.5.3 which includeshampoos or soaps in their list of products. While Case-3 and -4 did not includedetergents related products in their list of products, foaming was also observedwhen these wastewaters were treated.

Aside from the foaming, this group of wastewaters can also be very variablein terms of the specic components they contain if these are tracked over time.This is a consequence of the relatively large numbers of chemicals they use andthe campaign nature of their manufacturing activities. For example Case-3 had aminimum of 180 entries on its list of chemicals brought into the factory at anypoint in time.

Upon careful examination of the characteristics of some industrial wastewaters(and especially specic compounds therein), it is possible to identify componentswhich may require special attention as these may adversely affect the biologicaltreatment process. For example the manufacture of monosodium glutamate, whichis used as a avor enhancer in food preparation, generates a wastewater streamwith high concentrations of BOD5 (2400032200mgL1) and a COD:BOD ratioof about 2.5. While this may suggest amenability to biological treatment, con-sideration has to be given to the wastewaters ammonia-N (32005000mgL1)



Table 2.5.3. Personal care and pharmaceutical products wastewater characteristics.

Parameters Case-1 Case-2 Case-3 Case-4 Case-5 Case-6Cases

Qavg , m3 d1 180 over 8 h 40 over 10 h 250 over 24 h 1000 over 24 h 130 over 8 h 100 over 16 hQpk , m3 h1 40

BOD5, 20003000 500800 1001020 4000 820012400 250400mgL1

COD, mgL1 65008500 20003400 1501820 8500 1340018500 600800TSS, mgL1 Negligible 3040 300 1500 600 100200O&G, mgL1 100150 400 500 40006300 2540

pH 46 6.07.3 67 3.57.5TN, mgL1 100125 1530 130 TP, mgL1 03 30 Sulphate, 100150 mgL1Sulphide, 20 mgL1Temp, C 3035 Product Cough Personal Pharma Pharma Soaps Personal

drops & care incl nutritionals care shampoo incl antibiobitics incl

shampoo & vitamins shampoo

and sulphate (2500040000mgL1) contents. A similar difculty can be encoun-tered when handling rubber serumwastewater which has lower but still substantialamounts of ammonia-N (210mgL1) and sulphate (4500mgL1). Aside fromthe preceding, metals may also be encountered. Zinc can be frequently encoun-tered in rubber related wastewaters. Rubber thread manufacturing generates largevolumes of wastewater with relatively high BOD5 values (4000mgL1) of whichacetic acid would be the main component. The latter is an easily biodegradablecomponent. This wastewater is, however, difcult to treat because of the presenceof zinc (250mgL1). An example from the food industry is aspartame which isused as an articial sweetener in the soft drinks industry. This component hasbeen noted to cause some difculty in terms of process stability during biologicaltreatment.

Food industry wastewaters can be difcult to treat because of the slug dis-charges of disinfectants whenever a plant shutdown and clean-up takes place.This can occur as frequently as at the end of each shift. Examples of disinfectantswhich may be encountered include paracetic acid, hydrogen peroxide, chlorineand sodium hypochlorite. The slug entry of such compounds into the biologicalprocess basin would likely destroy the microbial culture therein and this would ineffect have ended the plants ability to treat the wastewater.



Treating chemical industry wastewaters is frequently known to be difcult.While this may be due to the presence of specic components which are inhibitoryor resistant to biological degradation (as in the dyestuff wastewater discussed inSec. 2.1), the difculties experienced may also be due to the presence of largequantities of very easily degradable organics. For example the organic componentin a vinyl acetate wastewater is largely made up of acetic acid. The presence ofsuch an easily degradable component can lead to bulking sludge in the activatedsludge (or its equivalent) process. Bulking sludge in turn leads to poorer settledefuent quality, difculties in adequate sludge return (and hence eventual processfailure), and higher moisture content in the dewatered sludge.

2.6. The Manufacturing Process

Some knowledge of the manufacturing process can be helpful in understandingwastewater characteristics. For example a factory typically collects all its waste-water streams before channeling these collectively to the wastewater treatmentplant in a single pipe or drain. An understanding of the streams contributing to thecombined wastewater stream may help reduce the volume which requires treat-ment. Case-2 in Table 2.5.3 has a total wastewater ow of 40m3 d1 but 23m3 d1of this is an overow from the cooling processes and this latter stream wouldnot require treatment to meet the discharge limits. Removing this stream wouldreduce treatment of the wastewater ow to 17m3 d1, which is a very substantialreduction.

In other instances, knowledge of the manufacturing process sequence mayallow a particular stream to be intercepted for pretreatment before it is allowedto join the rest of the wastewater streams for further treatment. Table 2.2.1 high-lighted the characteristics of a coconut cream extraction wastewater. The coconutprocessing sequence is as follows: (1) receiving coconut fruits, (2) shelling,(3) raring, (4) washing the kernel, (5) grinding the kernel, (6) pressing the groundkernel for milk, (7) spray drying the milk, (8) homogenizing the resulting creamand, (9) packaging the coconut cream product. Wastewater streams arise fromstages (3), (4), (5), (7) and (9). This is a wastewater with considerable amounts ofTSS and much of this comes from equipment washing in stage (5) grinding. Ifthis stream of wastewater had been intercepted for screeming, then the size of thescreen could have been much smaller given the smaller hydraulic load.

In a condom manufacturing plant the sequence of manufacturing activities isas follows: (1) withdrawing latex from storage, (2) compounding, (3) pre-aging,(4) leaching, (5) rinsing, (6) acid cleaning, (7) rinsing, (8) cleaning, (9) latex dip-ping, (10) powdering, (11) vulcanization, (12) depowdering, (13) pinhole testing



and, (14) product packing. Continuous wastewater ows arises from stages (2),(5), (7) and (8) but knowing when the batch discharges from stages (3), (4) and(6) occur can help the designer and operator anticipate the surges in terms of tim-ing, volume, and strength.

Occasionally issues can only become apparent after observing factory opera-tions. To illustrate this, consider the appearance of mineral O&G in wastewaterfrom a soft drinks bottling plant. Mineral O&G obviously would not have been inthe drinks formulation and should not appear anywhere in the sequence of activ-ities leading from preparing the drinks to bottling. A day spent beside a bottlingline, however, showed the line operator oiling the bottle conveyor belt at regularintervals to ensure smooth movement. Excess oil dripped onto the oor and thiswas then washed, with other drippings and spills, into the drains leading to thewastewater treatment plant and hence the appearance of substantial quantities ofO&G at the treatment plant.


CHAPTER 3

THE SEWAGE TREATMENT PLANT EXAMPLE

3.1. The STP Treatment Train

Any wastewater treatment plant, with no exception of the sewage treatment plant,is a combination of separate unit processes arranged in a sequence such that eachwould support the performance of the downstream unit process or processes aswastewater with a particular range of characteristics progresses through the plant.This sequence of unit processes forms the treatment train. At the end of thistreatment train, the resulting efuent is expected to meet a specied quality. Theamount of treatment, and hence the complexity of the plant, is dependent on thetreated efuent quality objectives and the nature of the raw wastewater. Notwith-standing the size and engineering complexity of some of these treatment plants,the unit processes in these plants can be classied into ve groups:

(i) Preliminary treatment;(ii) Primary treatment;(iii) Secondary treatment;(iv) Tertiary treatment and;(v) Sludge treatment.Readers who are familiar with sewage treatment plants (STPs) would have

recognized the sequence of treatment stages described above. Sewage treatmentplants typically include Stages 1, 2, 3, and 5 although increasing numbers of plantscan now include Stage 4, tertiary treatment, as well.

To provide a frame of reference for the reader as he/she progresses throughthe remaining chapters, this chapter provides a brief description and discussionof the unit processes in STPs. Subsequent chapters would then draw the readersattention to the possible differences one may encounter in industrial wastewatertreatment plants (IWTPs), as compared to STPs, because of the differences incharacteristics between industrial wastewaters and sewage. The treatment train ofa STP without tertiary treatment can comprise of the inlet pump sump with itsracks or bar screens, grit removal, primary sedimentation, biological treatment

28


The Sewage Treatment Plant Example 29

process, secondary sedimentation and disinfection before discharge of the treatedefuent. In some STPs nowadays, the primary clariers may be replaced bymechanically cleaned ne screens. Sludge from the primary clarier and wasteactivated sludge from the secondary clarier would be thickened, stabilized (typ-ically by aerobic means in small plants and anaerobically in large plants), condi-tioned, dewatered, and the resulting sludge cake disposed off.

3.2. Preliminary Treatment

The front boundary limit of a STP is typically the inlet pump station. The incomingsewer discharge the sewage into a pump sump and the inlet pumps therein wouldlift the sewage up to the level of the headworks in the plant. The incoming sewerdraws its sewage from a sewer network designed to collect sewage from all theindividual sources located within its catchment. The inlet pump sumps of STPscan be deep with the deeper pump sumps associated with the larger plants. Thisis because the larger plants serve larger communities and this would have meantmore extensive sewer networks and hence larger distances covered. The depthof the pump sump is determined by the necessity for an appropriate hydraulicgradient to ensure, where feasible, gravity ow of sewage in the sewer towards theSTP. The reachable depth of the sloping sewer as it traveled from its catchment tothe STP would be at its greatest just when it reaches the inlet pump station. Onoccasions when distances are large and the sewer would have been too deep if itwere to run uninterrupted from catchment to STP, sewage pump stations may beinserted at intervals to lift the sewage and then to allow it to ow by gravity to thenext pump station before being lifted again.

Preliminary treatment takes place at the headworks. This stage can also includeow measurement, but does not change the quality of the sewage substantiallyin terms of the typically monitored efuent quality parameters (eg. BOD5). Itenhances the performance of downstream processes by removing materials whichmay interfere with mechanical, chemical, or biological processes. For examplethe racks and coarse screens used are intended to remove relatively large sizedsuspended material and such devices typically have screen apertures of 25mm orlarger. These devices may be manually cleaned as in basket screens or automat-ically cleaned as in mechanically raked bar screens. Material collected on suchscreens can include rags and plastic bags (Fig. 3.2.1) and these can damage down-stream mechanical equipment such as pumps by binding the impellers. The mate-rial collected on these racks and screens would be removed regularly to avoidodorous conditions from developing and to prevent blinding of the screens whentoo much material has collected on it.



Fig. 3.2.1. Example of screenings collected on a manually cleaned rack. Note the gross materialwhich includes pieces of paper and plastic wrapping. These can blind the screen unless regularlyremoved.

The mechanical equipment in contact with sewage may also suffer from exces-sive wear caused by the grit present in the latter. Grit is inert inorganic materialsuch as sand particles, eggshells, and metal fragments. Grit removal devices relyon differences in specific gravity between organic and inorganic solids to effectseparation. It is important the device does not remove the organic solids but toallow these to continue with the sewage flow to the next unit process. Grit removaldevices may look like rectangular channel-like structures or the more compact cir-cular chambers. The channel-like devices are frequently aerated along one side ofthe channel to assist the separation by creating a rolling motion in the water asit flows through while the circular devices would rely on centrifugal forces assewage is injected tangentially into the chamber.

Aside from grit, sewage may also contain quantities of oil and grease (O&G).The bulk of this O&G is associated with cooking in the homes and is thereforeorganic in nature. The mineral oil content can be expected to be low. ExcessiveO&G combined with particulates may blind downstream screens. The O&G maythen continue into the aeration basins and interfere with oxygen transfer in thebiological processes there. Excessive quantities of O&G entering these biological


The Sewage Treatment Plant Example 31

reactors may also result in mud-balling of the biomass where the latter agglom-erate into small ball-like structures.

Process performance may then deteriorate because of diminished contactbetween the microbial population and substrate. Where it is considered an issue,the O&G is removed with O&G traps. These are often bafed tanks with man-ual or mechanical skimmers for the removal of the free O&G which has oatedto the surface of the water during the time the water spends in the trap and isthen retained against the bafe. Like the screenings on the racks and screens, thetrapped O&G has also to be regularly removed to avoid formation of odorousconditions.

3.3. Primary Treatment

Primary treatment follows the preliminary treatment stage. The purpose of pri-mary treatment is to remove settleable suspended solids (SS) and typically about60% of these may be so removed with unaided gravity settling. While a smallportion of the colloidal and dissolved material may be removed with the SS, thisis incidental. Notwithstanding this, 3040% of the BOD5 in the raw sewagemay be removed with the SS. In gravity clariers, the relatively quiescent condi-tions therein would allow the settleable solids to settle to the bottom of the clari-er forming a sludge layer there. To achieve such settling conditions, the surfaceoverow rates chosen for design and operation of a clarier usually range from0.3 to 0.7mms1. In large clariers a scrapper located near the base of the clari-er moves the sludge into a hopper from where it would be pumped to the sludgetreatment stage. The settled sewage exits the clarier by overowing the outletweirs. Typically these weirs extend around the periphery of the clarier. This is toaccommodate the weir overow rate deemed appropriate for a particular design.Where there is such a necessity, the weir length may be extended by supportingthe launder on brackets some distance from the wall of the clarier. Large STPstypically operate either circular or rectangular clariers while the smaller ones canuse either circular or square clariers.

Primary (and secondary) clarication in STPs is typically unaided in terms ofcoagulant use. Where coagulants have been used, SS and BOD5 removals up to90% and 70% respectively have been achieved. While the application of coagu-lants on a large scale in sewage treatment is relatively rare in Asia, it has appearedwhere there is a requirement to remove phosphorous. The coagulant may then beinjected before primary clarication or into the biological aeration vessels.

While primary treatment is usually achievedwith gravity clariers, rotating andstatic ne screens have been used sometimes. Such screens typically have screen



openings of about 0.8mm to 2.3mm. Since ne screens are operated at hydraulicloading rates an order of magnitude higher than those applied on clariers, theyoccupy much less space for equipment installation. If the sewage contains sub-stantial quantities of O&G, then the screen would likely to be located after theO&G trap. This reduces the risk of the O&G combining with ne particulates andblinding the ne screen. Fine screens are not expected to remove as much of theSS and BOD5 as primary clariers would. Consequently a STP which has nescreens in place of primary clariers would need to have its secondary treatmentstage appropriately sized.

Primary clariers and screens can be major sources of malodors. Avoidingover-designs especially in clariers (resulting in overly long hydraulic retentiontimes and the consequent development of septic conditions) and good housekeep-ing would help reduce the incidence of such odors. The development of septicconditions in screens is less likely to occur since the passage of sewage throughthe screen does provide a degree of aeration.

3.4. Secondary Treatment

The role of the secondary treatment is to remove the colloidal and dissolved mate-rial remaining after the preliminary and primary treatment stages. In sewage treat-ment, the secondary stage typically includes a biological process. The latter, oftenan aerobic suspended growth process where the microbial population used to treatthe wastewater is suspended in the mixed liquor of the reactor, is housed in anaeration vessel or reactor which has been designed to be complete-mix, plug-ow, or a condition between these two extremes arbitrary ow (see Sec. 5.3for discussion on reacto

44901511 Industrial Waste Water Treatment

Documents

Transcript of 44901511 Industrial Waste Water Treatment