Pollutants of Textile Wastewater and their effect on environment By Engr. Uttam Kumar Nath1, Dr. Md Mahbubul Haque2, 1
Managing D irector, Aquatech Engineering Services Ltd. 2 Professor, Department Of Textile Technology, Ahsanullah University Of Science and Technology. Abstract: In the recent years lot textile wet processing industries were established to cater the RMG sector of Bangladesh. Most of the installed factories are spinning, weaving, denims and knit dyeing plants. Apart from this there are lot of garment washing plants in the country. Some of these plants generate huge amount of wastewater, which find their way into the canals or Small Rivers. These wastewaters are highly polluted and cause various types of short term as well as long-term consequences and complicacies. Department of Environment (DOE), Government of Bangladesh has undertaken tough measures to fight the environmental pollution. As a result lot of factories have already installed Effluent Treatment Plants (ETP). Lot of ETP’s are in various stages of their commissioning /operation.. Setting up of ETP does not and will not always ensure a safe environment. It is a collective and social responsibility to monitor and ensure clean environment. In order to make it a collective issue it will be necessary to make awareness about the harmfulness of environmental pollution. Concerned individuals need to understand the harmfulness of textile process wastewaters. It is also important to have the idea about the characteristics of effluent generated by various types of textile wet processing industries. All polluting industries should not be categorized as equally harmful for the environment. Effluent generated from different industries has different level of harmfulness. There are many other industries and business establishments that contribute too much greater damage to the environment than some textile industries do. The DOE should also address these things. 1. INTRODUCTION: Wastewater discharged from a textile wet processing plant contains various types of impurities depending on the type of raw materials, dyes, chemicals, auxiliaries and process used. Some of these impurities are considered toxic while some are not. Off course the toxicity or harmfulness also depends on the amount present in a certain amount of processed or wastewater. Various countries have different standards for acceptable level of toxicity for various purposes. Different types of water application also require different level of acceptable toxicity. For example water is used for drinking purposes, irrigation in the fields, in various types of textile, chemical, food processing, leather processing and pharmaceutical industries, and also to maintain the aquatic life in the canals and rivers. In all these cases different level of purity in terms of toxicity and harmfulness are required. Table 1 shows the acceptable level of various pollutants of wastewater generated from textile wet processing industry (Source BUET). 2. METHODS AND ANALYSIS: The work reported here is based on the raw effluent test conducted in Bangladesh University of Engineering and technology (BUET). Before designing an effluent treatment plant (etp) it is necessary to know the characteristics of the effluent of the concerned factory. The tests were conducted either by the ETP suppliers or by the concerned industries. The tested results are accumulated and shown in table –2. Columns 3-10 of table 2 show the values of various toxic parameters found in textile effluent. Off course there are many other pollutants are found in textile wastewater but the toxicity level of these pollutants were found to be most harmful for the environment. For better clarity, the individual effluent parameters were compared with corresponding acceptable standard values. There are eight parameters, for each parameter a separate table was presented (please see tables 3-10). Therefore the data shown in tables 3 to 10 are related to tables 1 & 2. Table 1: Characteristics of wastewater to be discharged into the environment. (Recommended by the dept. of environment, Government Of Bangladesh) Sl. No. 1 2 3 4 5 6
Water quality parameters PH BOD COD TSS TDS Oil & Grease
Unit mg/L mg/L mg/L mg/L mg/L mg/L
Standard value for discharging into * Inland river On land for irrigation 6-9 6-9 <50.0 < 100 <200.0 < 400 <150.0 <200 <2100 < 2,100 < 10 < 10
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7 Colour Co-pt unit 0 8 Temperature C 3. RESUTS AND OBSERVATIONS
<150 <300C
<150 < 30 0C
The values of various pollutants shown in each row of 3rd to 10th row of table 2 referred to a particular sample of the effluent from referred textile establishment. As was mentioned the values of the polluting parameters vary to a considerable extent due to the change of raw materials, dyes, chemicals, auxiliaries and process. For example a factory sometime process 100% cotton and sometime process 50/50 cotton & polyester blend or even 100% polyester. The three different cases will require two different dyes and chemicals of varying quantity. For white goods no dyes are used at all, and in that case too the effluent characteristics will be different from that of dyeing effluent. For woven (sized) fabrics the effluent characteristics will be different from that of knit fabrics due desizing of woven fabric. The effluent characteristics will also change due to the change of colour and depth of colour (ie shade). Therefore ETP designers always design their plants on the basis of a range of pollutants characteristics, rather than particular tested results. Table 2: Characteristics of wastewater of textile wet processing plants. Name of the factory
1 Ahsan Composite Reedisha Knitex Ltd. Fakhruddinn Textile Mills Ltd Grameen knitwear Southeast Epyllion Knit Ltd. Aboni Textiles Ltd. Greenland garments ltd. Ha-Meem Denim Jamuna Denim Ltd Partex denims
Type of the factory /plant
BOD mg/L 3 300 300 450
Concentration of pollutants present in the wastewater COD TDS TSS Oil & Colour Temp 0 mg/L mg/L mg/L Grease Co-pt. C mg/L 4 5 6 7 8 9 437 2210 82 ND* ND ND 449 3380 3118 ND ND ND 1000 3500 100 ND Dark ND
2 Knit dyeing Knit dyeing Knit dyeing
10 9.39 9.01 9-11
Knit dyeing Knit dyeing Knit dyeing Knit dyeing Knit dyeing Denim Denim Denim
600 450 450 350 450 850 640 1300
1200 1000 1400 1050 1000 2150 1312 2456
10 11 9 11 6-9 9 11 ND
3500 3500 3500 4500 3633 5320
1000 100 200 200 100 350 305 900
10 --60 40 ND 20 --ND
Dark Dark 600 140 Dark <1000 1380 7620
ND ND 60 35 ND 35 --ND
PH
* ND- Not done 3.1 pH of the effluent Various standards suggests that Aquatic Life" should have pH values between 6.5 and 9.0. Very high (greater than 9.5) or very low (less than 4.5) pH values are unsuitable for most aquatic organisms. All submerged plants and animals, including algae, are constantly removing dissolved oxygen from the water and excreting carbon dioxide during normal respiration. The release of carbon dioxide has an acidifying effect. In addition to respiration, during daylight hours all plants, which include all algal forms, actively involve in photosynthesis. They absorb carbon dioxide from the water and use the sun’s energy to convert it to simple organic carbon compounds. As we have already said, carbon dioxide in solution is slightly acidic, so as the plants remove it, the water becomes more alkaline. The more sunshine and algae – the more alkaline the water will become. Young fish and immature stages of aquatic insects are extremely sensitive to pH levels out side (5 – 8) and may die beyond these pH values. High pH levels like (9-14) can harm fish by denaturing cellular membranes. Rapid changes in pH are stressful to fish and should be avoided. Changing the pH by more than .3 units per day is known to stress fish. Each species of fish has its own very narrow range of pH preference and levels outside of this range will cause health problems. For example, koi prefer a range between 7 and 8.5, while some tropical fish prefer water that is slightly acidic. High acidity or alkalinity can cause direct physical damage to skin, gills and eyes. Prolonged exposure to sub-lethal pH levels can cause stress, increase mucus production and encourage epithelial hyperplasia (thickening of the skin or gill epithelia) with sometimes-fatal consequences. Table 3 shows the pH of six factories. The table shows that in some cases the pH is outside the limit and off course for certain type of treatment the pH may rise to as high as 14. Therefore it will be necessary to adjust the pH before releasing them in the environment.
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Table 3: Comparison of pH with Bangladesh standard. Name of the factory
Type of the factory /plant
1 Ahsan Composite Southeast Ha-Meem Denim Jamuna denim
2 Knit dyeing Knit dyeing Denim Denim
pH
Standard value for discharging into Inland river On land for irrigation
3 9.39 11 9 11
4 6-9 6-9 6-9 6-9
6 6-9 6-9 6-9 6-9
3.2 Biochemical Oxygen demand (BOD): The strength of the wastewater is often determined by measuring the amount of oxygen consumed by microorganism like bacteria in biodegrading the organic matter. The measurement is known as the Biochemical Oxygen Demand (BOD). Microorganisms such as bacteria are responsible for decomposing organic waste. When organic matter such as dead plants, leaves, grass clippings, cellulose components, manure, sewage, organic waste like dyes, fats and oils, or even food waste is present in a body of water, the bacteria will begin the process of breaking down this waste. When this happens, the bacteria rob the available dissolved oxygen necessary to survive by the other aquatic organisms like fishes and aquatic insects. If there is a large quantity of organic waste in the water supply, a large number of bacteria present in the water body will be working to decompose the waste. When the bacteria consume organic waste they will require oxygen. Under this circumstance there will be an additional demand for dissolved oxygen (DO). This additional demand for DO is regarded as BOD. As the waste is consumed gradually or dispersed through the water, BOD levels will begin to decline. Table 4: Comparison of (BOD) with Bangladesh standard. Name of the factory 1 Ahsan Composite Reedisha Knitex Ltd. Ha-Meem Denim Partex denims
Type of the factory /plant 2 Knit dyeing Knit dyeing Denim Denim
BOD mg/L 3 300 300 850 1300
Standard value for discharging into Inland river (mg/L) On land for irrigation (mg/L) 4 6 <50.0 <100 <50.0 <100 <50.0 <100 <50.0 <100
The presence of Nitrogen and phosphates in a body of water can also contribute to high BOD levels. Nitrates and phosphates are plant nutrients and can cause plant life and algae to grow quickly. When plants grow quickly, they also die quickly. This contributes to the organic waste in the water, which is then decomposed by bacteria. This also results in a high BOD level. The temperature of the water can also contribute to high BOD levels. For example, warmer water usually will have a higher BOD level than colder water. As water temperature increases, the rate of photosynthesis by algae and other plant life in the water also increases. When this happens, plants grow faster and also die faster. When the plants die, they fall to the bottom where they are decomposed by bacteria. The bacteria require oxygen for this process so the BOD becomes high in that location. Therefore, increased water temperatures will speed up bacterial decomposition and result in higher BOD levels. Table –4 shows the level of BOD found in various types of textile wet processing plants. The results suggest that denims plants generate highest amount of BOD followed by knit dyeing plants. The higher BOD of denim plant is probably due to the use of starch-based sizes in the dye-sizing bath. BOD and DO (Dissolved oxygen) The amounts of oxygen present in a certain amount of water in dissolved state are known as Dissolved Oxygen or simply DO. DO is normally expressed as mg/l, water may contain DO ranging from 0 to 18 mg/l but in most cases of normal waters, DO lies between 7-9 mg/l. Aquatic lives require certain level of DO to survive in the water and the DO level required to survive in the water varies from one species to another. Even if we talk about fish, some fish require more DO to survive than some other fishes. For a particular body of water, BOD is inversely related to DO i.e higher the BOD, lower the DO and vice versa.
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3.2 Chemical Oxygen Demand (COD): Like BOD, COD is also a harmful pollutant of wastewater. It is based on the fact that nearly all-organic compounds can be fully oxidized to carbon dioxide with a strong oxidizing agent under acidic conditions. When some wastewater is discharged into a water body, the organic compounds of the textile dyes and auxiliaries may be oxidized by means of the dissolved oxygen present in the water as a result the level of DO falls. As a result there will be demand for oxygen, which is termed as Chemical Oxygen Demand (COD). Table 5: Comparison of COD with Bangladesh standard. Name of the factory 1 Ahsan Composite Reedisha Knitex Ltd. Ha-Meem Denim Partex denims
Type of the factory /plant 2 Knit dyeing Knit dyeing Denim Denim
COD Mg/L 3 437 449 2150 2456
Standard value for discharging into Inland river (mg/L) On land for irrigation (mg/L) 4 6 <200.0 < 400 <200.0 < 400 <200.0 < 400 <200.0 < 400
COD is also a means of measuring the ability of wastewater to sustain aquatic life, essential for the preservation of the environment. It also enables proper assessment of effluent treatment plant performance. Aquatic organisms and animals require dissolved oxygen to flourish. The Chemical Oxygen Demand (COD) test gives an indication of the impact of discharge waters on aquatic life by measuring the oxygen depleting nature of the discharge water. The process of measuring COD causes the conversion of all organic matter into carbon dioxide. For this reason, one limitation of COD is that it cannot differentiate between biologically active and those which biologically inactive. One major advantage of COD over BOD is that COD can be measured in just three hours where as BOD measurement takes at least five days. The value of COD is always higher than BOD, this is because BOD accounts for only biodegradable organic compounds while COD accounts for all organic compounds e.g. biodegradable as well as non biodegradable but chemically oxidisable. Table-5 shows that the COD of several factories, the results show that the COD of denim plant is very high and that of knit dyeing is somewhat moderate for irrigation land while high for inland rivers. Therefore it will be necessary to treat these wastewaters before discharging them in to the environment. 3.3 Total suspended Solids (TSS):
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TSS is mainly organic in nature, is visible and can be removed from the wastewater by physical/ mechanical means e.g. screening and sedimentation. TSS is measured by filtering a certain quantity of effluent and then drying the filtrate at certain temperature e.g. 1050C followed by weighing. TSS is expressed as parts per million or in milligram/litre. The pore size of the filter paper is very important in estimating the TSS, the nominal pore size 1.58 micro metre. In comparison to other pollutants the effect of TSS is nominal. When TSS is high the sunlight is prevented from reaching to some aquatic plants that may need them for photosynthesis. It can be seen in Table 6, that in most cases the TSS is much higher than the acceptable level of standard and it will necessary to reduce them.
Table 6: Comparison of TSS with Bangladesh standard. Name of the factory 1 Ahsan Composite Reedisha Knitex Ltd. Ha-Meem Denim Partex denims
Type of the factory /plant 2 Knit dyeing Knit dyeing Denim Denim
TSS
Mg/l 3 82 3118 350 900
3.4 Total Dissolved Solids (TDS):
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Standard value for discharging into Inland river (mg/l) On land for irrigation (mg/l) 4 6 <150 <200 <150 <200 <150 <200 <150 <200
TDS -is the sum total of all of the dissolved things in a given body of water. It's everything in the water that's not actually water. It includes hardness, alkalinity, cyanuric acid, potassium, chlorides and sodium , bromides, sulfates, silicates, and all manner of organic compounds. Some of these ions have little or no short-term effects, but toxic ions (lead arsenic, cadmium, nitrate and others) may also be dissolved in the water. Every time we add anything to the water, we are increasing its TDS. TDS is referred to as the total amount of mobile charged ions, including minerals, salts or metals dissolved in a given volume of water. Textile effluent inherits TDS from dyes, chemicals and auxiliaries that are used in processing. Table 7: Comparison of TDS with Bangladesh standard. Name of the factory 1 Ahsan Composite Reedisha Knitex Ltd. Ha-Meem Denim Partex denims
Type of the factory /plant 2 Knit dyeing Knit dyeing Denim Denim
TDS Mg/L 3 2210 3380 5320
Standard value for discharging into Inland river (mg/L) On land for irrigation (mg/L) 4 6 <2100 <2100 <2100 <2100 <2100 <2100 <2100 <2100
TDS may be the most misunderstood factor in the whole field of chemical processing. In most cases it is misunderstood because no one knows exactly what effect it is going to have on any particular body of water. TDS is directly related to the purity of water and the quality of water purification systems and affects everything that consumes, lives in, or uses water, whether organic or inorganic, whether for better or for worse. Table 7 shows that the level of TDS in textile effluent is very high and treatment will be required to reduce them. At low levels, TDS does not present a problem. In fact, a certain amount of TDS is necessary for water balance and Hardness and Total Alkalinity are both part of TDS. For textile processing the acceptable value of TDS is around 1 mg/l. The standards for bath and swimming pool are between 1,000 and 2,000 ppm, with a maximum of 3,000 ppm. For irrigation the acceptable values of TDS are around 1500 ppm. Use of fertilizers increases TDS of the environment. High TDS can cause eye and skin irritation, even though the pH is right and there are no chloramines in the water. High TDS can permit an algae bloom, even with 2-3 ppm chlorine residual. If we drink water of high TDS some of this will stay in the body, causing stiffness in the joints, hardening of the arteries, kidney stones, gallstones and blockages of arteries, microscopic capillaries and other passages in which liquids flow through our entire body. 3.5 Dyes and the Environment: The loss of dyes to effluent can be estimated to be 10% for deep shades, 2% for medium shades and minimal for light shades. Dyes are present in the effluent at concentrations of 10 mg/l to 50 mg/l with 1 mg/l being visible to the naked eye. Dyes are complex organic compounds, which are refractory in aerobic treatment systems. Some contain metals such as Cr, Cu and Zn. In the aquatic environment, dyes can undergo bio concentration, ionization, abiotic oxidation, abiotic and microbial reduction and precipitation. The ionic dyes such as acid, direct, basic and metal complex dyes will not volatilize whereas, in principle, solvent, disperse, vat and sulphur dyes have the potential to be volatile. Sorption should also play a major role as dyeing is a sorption process. Hydrolytic reactions are not important because if the dyes survive the biological treatment processes, it is unlikely to degrade rapidly in the environment. Photochemical reactions may be important, as dyes are good absorbers of solar energy. Aquatic plants will not be able to produce food by the process of photosynthesis. As a result their life will be endangered. Table 8 shows that the colour pollution by denim is very worse. Experience shows that the effluent of knit dyeing will also pose considerable effect on the environment. Therefore it will be necessary to reduce colour up to an acceptable level. Table 8: Comparison of Color point with Bangladesh standard. Name of the factory 1 Grameen knitwear Southeast
Type of the factory /plant 2 Knit dyeing Knit dyeing
Colour
Co.pt 3 Dark Dark
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Standard value for discharging into Inland river (Co.pt) On land for irrigation (Co.pt) 4 6 <150 <150 <150 <150
Ha-Meem Denim Partex denims
Denim Denim
1000 7620
<150 <150
<150 <150
3.6 Effect of temperature on Environment: Temperature of water is a very important factor for aquatic life. It controls the rate of metabolic and reproductive activities, and determines which aquatic species can survive. Different aquatic species require different quantity of DO to survive in the water. Temperature inversely affects the rate of transfer of gaseous oxygen into dissolved oxygen. On the other hand at higher temperature the metabolic rate of aquatic plants and animals increases producing an increase in oxygen demand. The aspect of temperature is also discussed in section 3.1. International regulations related to water temperature and aquatic life classifies water, as "Class 1 Cold Water Aquatic Life" should never have temperatures exceeding 20°C, while waters classified, as "Class 2 Warm Water Aquatic Life" should never have temperatures exceeding 30°C. These regulations also state that temperature for these classes shall maintain a normal pattern of day to day and seasonal fluctuations with no abrupt changes and shall have no increases in temperature of a magnitude, rate, and duration deemed harmful to the resident aquatic life. Generally, a maximum 3° C increase over a minimum of a 4-hr period, lasting 12 hrs maximum, is deemed acceptable. Temperature preferences among aquatic species vary widely, but all species tolerate slow, seasonal changes better than rapid changes. Respiration of organisms is temperature-related; respiration rates can increase by 10% or more per 1° C temperature rise. Therefore, increased temperature of textile wastewater not only reduces oxygen availability, but also increases oxygen demand, which can add to physiological stress of organisms. Increased temperature influence the activity of bacteria and toxic chemicals secreted by the bacteria in water. The BUET test results are not always provide catual temperature of the effluents as factories are far away from Dhaka and take hours to travel to BUET. The onsite test shows that effluent temperature is around 50-600C which is quite harmful for aquatic species. 3.7 Oil and greases The term oil and grease, as commonly used, includes the fat, oils, waxes, and other related constituents found in wastewater. Oils and fats are mainly due to the sizing process and also as oils and grease comes in contact with the fabric during processing. Apart from this small amount oils is found in the cellulose fibres. These oils and fats are removed during scouring process and finally pass with the wastewater. If the wastewater contains oils and fat, it form a layer at the top surface of the wastewater. As a result the oxygen cannot come in contact with the water and becomes difficult to increase DO level. Oil & grease discharged into the environment typically has deleterious effects. Oily wastes discharge may have objectionable odors, cause undesirable appearance, burn on the surface of receiving water creating potential safety hazards and consume dissolved oxygen necessary to forms of life in water. Bioassay data indicate that oil is toxic to fish. In greater quantities, it limits oxygen transfer, hindering biological activity. Oils and grease affect respiration of fish by adhering to the gills, it adhere to and destroy algae and plankton. Feeding and reproduction of water life (plant, insect, and fish) is affected by oils and fat. Aesthetics is affected by sheens of oils. Table 7 shows that the level of oil and grease in textile wastewater is above the standard and needs to be reduced. It is not clear about the denim data as additional fats/oils are added during the sizing of denim process so that the oil and grease of denim plant effluent should be very high and must be higher than that of knit dyeing plants. Table 7: Comparison of oil and grease with Bangladesh standard. Name of the factory 1 Grameen knitwear Epyllion Knit Ltd. Ha-Meem Denim Partex denims ND- Not done
Type of the factory /plant 2 Knit dyeing Knit dyeing Denim Denim
Oil and grease(mg/l) 3 10 60 20 ND
4. CONCLUSION/SUGGESTIONS
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Standard value for discharging into Inland river On land for irrigation 4 6 < 10 < 10 < 10 < 10 < 10 < 10 < 10 < 10
a) b)
c) d) e)
f) g) h) i) j)
If all the factories do not install appropriate ETP and do not run them properly then there will be an unequal price competition among fabric producers where the honest etp owners will always lose the battle. Entrepreneurs can be encouraged to set up industries far away from the crowded greater Dhaka. This will at least reduce the pollution burden on the Dhaka dwellers to some extent. Setting up of industries near big rivers or coastal areas could be a much better option because effluents can be directly released into the very large river or sea. Use of synthetic sizes rather than starch based sizes will reduce the high toxicity of the effluent generated from denim plants. The starch-based sizes contribute to highest amount of BOD. Government should reduce or exempt the tariffs and taxes on the synthetic sizes, so that synthetic sizes can replace cheap starch based sizes that contribute to very high BOD. Attempt should be made to explore the idea of developing woven sector. The material to liquor ratio of woven dyeing is very low in comparison to knit dyeing. Less effluent means less raw water will be required, this in turn will reduce the amount of gas/electrical energy required to pump and heat water. The profit margin of woven garments is also very high. Reconstitution of processed effluent should be examined for every stage of processing like scouring, bleaching, mercerization, dyeing and finishing baths. This will reduce the quantity of ultimate effluent. Decisive and efficient use of dyes, chemical and auxiliaries will reduce the quantity and toxicity of the effluent to a great extent. Selection dyes, chemicals and auxiliaries that generate lower pollutants will reduce ultimate pollution load. Like many developed countries, Government can offer free water and wastewater test facilities. Though some people may take advantage of this facility but for greater interest of the country this type of initiative will help in understanding, administering and researching the over all-environmental pollution scenario. Environment is violated not only by the textile processing plants but also by many other factories/establishments like slaughtering houses, sweet manufacturers, bakeries, poultry farms etc. Their pollution load should be examined and should also be brought under strict scrutiny. Universities should offer degree courses on environmental education; apart from this we need research based education to study our environment and change in environment. Research is also necessary to study and upgrade the existing treatment procedures in order to reduce operating cost and also to combat future violation of the environment. At present some courses on environmental education are included in Civil, Chemical and Textile Engineering but this is not sufficient to deal our environmental problem.
REFERENCES [1] Metcalf & Eddy, “Wastewater Engineering” Tata McGraw –HilPublishing Co. (Pvt) Ltd., 2003. [2] B. C Punmia and et.al, “Waste Water Engineering” Laxmi Publications (Pvt) Ltd., 2001 [3] S. N Kaul and et.al, “Utilization of Waste Water in Agriculture & Aquaculture” Pawan Kumar, Scientific Publishers Ltd., 2002. [4] Soli J Areceivala, “Waste water Treatment for Pollution Control” Tata McGraw –Hill Publishing Co. (Pvt) Ltd., 2004. [5] Mark J. Hammer and et.al, “Water & Waste water Technology” Hall of India Private Ltd., 2003. [6] N. F. Gray, “Water Technology” An Introduction for Environmental Scientist and Engineers, Elsevier Butterworth – Heinemann, 2005. [7] Lenore S. Clesceri, “Standard Methods for Examination of Water & Wastewater” American Public Health Association, 1998. [8] Numerous related web sites and web pages were visited. Acknowledgement: The author is indebted to few textile factories for using their effluent test results.
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