ETP

Effluent treatment plant

Introduction

Textile is a major source of income and of great importance for Bangladesh’s economy. At the same time textile processing has major environmental impact. A large proportion of the environmental issues are related to the use and discharge of water. Textile manufacturing is among the major industrial water users. To produce one kg of textile fabrication about 200 liters of water is used.

A lot of chemicals are added to the process for cleaning and dyeing purposes. Obviously the wastewater effluent from this unit contains considerable amounts of hazardous pollutants, and where heavy metals are very common. In Bangladesh most of the effluent from the textile industry is discharged untreated into rivers. Today 20% of available river water in Bangladesh is polluted by textile waste water Water treatment is a very important step to change these conditions and to achieve a sustainable situation. Bangladesh’s government has an awareness of this and limits for water effluent quality exist. Unfortunately, this regulation is not closely supervised and a lot of places do not follow the regulation.

Properties of effluent before processing.

1. Impart color to water bodies even if present in small quantity2. Not harmful but undesirable for aesthetic reason3. Reduces light penetration and photosynthesis4. Carcinogenic or mutagenic5. Azo dyes are more toxic as they affect microbes thereby affecting

biological degradation treatment.6. Dyes increases BOD of effluent thereby affecting aquatic life.7. Salts of chromium and aluminum & iron as mordents in dyes8. Toxic to fish & microbial organisms9. The discharge of heavy metals into aquatic ecosystems10. Increase in alkalinity of water11. The turbidity and color along with oil and scum create an unsightly

appearance. The mineral materials, mostly sodium salts increase salinity of the water.

Effluent’s Character

Wastewater discharged from a textile wet processing plant contains various

types of impurities depending on the type of 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 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 is required. This is

mainly intended for wastewater generated in the various textile wet processing

industries. Therefore, the present discussion will mainly be concentrated on

wastewater generated in various types’ textile-processing industries. Table 1

shows the acceptable level of various parameters of wastewater generated from

textile wet processing industry. This is Bangladesh Standard. The level of

toxicity was considered for water intended to be discharged into river or canals.

The wastewater generated in a textile wet processing industry can be recycled

back for consumption in the plant or even can be used for drinking purposes

but this is expensive enough. So wastewater is generally discharged into the

river or canals.

Table 2.1: Characteristics of wastewater to be discharged into the environment. (Stipulated by the

Dept. of Environment, Government of Bangladesh)

Parameter Limit

PH 6-9

BOD < 50 PPM or mg/L

COD < 200 PPM or mg/L

TSS <100 PPM or mg/L

TDS < 2,500 PPM or mg/L

OIL & GREASE < 10 PPM or mg/L

COLOUR CLEAN

TEMPERATURE < 30 0C

The typical characteristic of wastewater generated in a textile wet possessing

plant is given in table 2.2. Parameters have been referenced about a range rather

than a particular value of the parameters. This is because the characteristics of

textile wastewater for a factory are not always same which may be due to the

variation of raw materials, dyes, chemicals 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, 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. The values shown in table 2 are not actual

tested values of a particular industry rather they are average of various

anticipated wet processing pollution characteristics. The values are assumed on

the basis of experience about the contaminants present in a textile wet

processing industry.

Table 2: Characteristics of wastewater of a typical textile wet processing

industry.

Parameter Limit

PH 8 –14

BOD 400 - 600 ppm

COD 800 - 1,200 ppm

TSS 200 - 500 ppm

TDS 3,000 - 6,000 ppm

OIL & GREASE 30 – 60 ppm

COLOUR Dark Mixed

TEMPERATURE up to 60 0 C

As was mentioned textile wastewater may contain various types of

contaminants but in most cases the toxicity of the above eight parameters are

considered important before discharging them into the environment. The

parameters are now discussed below

Table:3 the characteristics of composite effluents estimated by ATIRA

Characteristics Estimated rangepH value 6.7-9.5Total alkalinity, mg/l 500-796TDS, mg/l 2180-3600Suspended solids, mg/l 80-720BOD, 20 , 5 days mg/l 60-540

COD, mg/l 592-800Chlorides (as cl) mg/l 488-1399Sulphates (as so4) mg/l 47-500Calcium (as Ca)mg/l 8-76Magnesium (as M) mg/l 7-53Sodium (as Na) mg/l 610-2175

Table: 4 the characteristics of effluents from different sectors of textiles industry

Characteristics Cotton Synthetic Wool scouring (dyeing)

pH 8-12 7-9 3-10(5-10)BOD 150-750 150-200 5000-8000(500-600)COD 200-2400 400-650 100000-200000(1700-

2400)Alkalinity 180-7300 550-630 80-100(240-300)Phenol 0.03-1 - -Oils and grease 4.5-30 - 2000-2500(400-500)SS 35-1750 50-150 5000-6000(500-700)TDS 2100-7100 1060-1080 100000-130000(800-

1000)

Table: 5 pollution load of sizing agent

Agents COD(mg O2/g) BOD(mg O2/g)Starch 900-1000 500-600CNC 800-1000 50-90PVA 1700 30-80polyacrylates 350-1650 50Glactomanans (Guar gum)

1000-1150 400

PET dispersions 1600-1700 50Protein-based 1200 700-800

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 water supply, the bacteria will begin the process of breaking down this waste. When this happens, bacteria in aerobic process, robbing other aquatic organisms of the oxygen they need to live, consume much of the available dissolved oxygen.If there is a large quantity of organic waste in the water supply, there will also be a

lot of bacteria present working to decompose this waste. In this case, the demand for oxygen will be high (due to all the bacteria) so the BOD level will be high. As the waste is consumed or dispersed through the water, BOD levels will begin to decline. 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 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 is high at this location. Therefore, increased water temperatures will speed up bacterial decomposition and result in higher BOD levels. When BOD levels are high, dissolved oxygen (DO) levels decrease because the bacteria are consuming the oxygen that is available in the water. Since less dissolved oxygen is available in the water, fish and other aquatic organisms may not survive. Textile Denim plant wastewater possesses a very high BOD like 800 – 2500 mg/l. It is necessary to reduce this BOD value up to a level less than 30 mg/l before discharging them into the environment like canals or rivers. If a water body of high BOD is discharged into the sea or very large river then off course the concentration of BOD decreases due to dilution and has little or no harmful effect on the aquatic life or environment. Therefore if it is possible to discharge a highly toxic effluent in sea or large river no treatment is necessary. Though it was not mentioned, the dissolved oxygen (DO) is a highly significant parameter to define the BOD or COD of a wastewater. The amount of oxygen present in a certain amount of water in dissolved state is known as DO. It 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. In case of wastewater the microorganisms require oxygen to consume the organic wastes. As a result the DO of water decreases tremendously and becomes a threat to the life of aquatic species. Textile effluents possess very low DO, which is unsuitable for discharging to the environment. During treatment of wastewater air is blown through the effluent

when oxygen is dissolved in the effluent as a result DO level raises and as they DO increases the BOD/COD decreases.

Chemical Oxygen Demand (COD): This is 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 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.COD is based on the fact that nearly all-organic compounds can be fully oxidized to carbon dioxide with a strong oxidizing agent under acidic condition. COD is another common measure of water-borne organic substances — 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 no biodegradable but chemically oxidisable.

Total suspended Solids (TSS): TSS is mainly organic in nature, are 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/liter. The pore size of the filter paper is very important in estimating the TSS, the nominal pore size 1.58 micro metre.

Total Dissolved Solids (TDS): TDS are the solids that are actually in solution, similar for example to mix sugar into hot coffee. Dissolved solids generally pass through the system unaffected. TDS is the sum total of all of the dissolved things in a given body of water. It is everything in the water that's not actually water. It includes hardness, alkalinity, cyanuric acid, chlorides, bromides, sulfates, silicates, and all manner of organic compounds. Every time we add anything to the water, we are increasing its TDS. This includes not only sanitizing and pH adjusting chemicals, but also conditioner, algaecides, and tile and surface cleaners. TDS also includes airborne pollutants and bather waste as

well as dissolved minerals in the fill water. TDS is referred to as the total amount of mobile charged ions, including minerals, salts or metals dissolved in a given volume of water, and are expressed in units of mg per unit volume of water (ppm).

List of some of the waste materials generated at each level of cotton textile processing:

Process Air emissions Wastewater Residual wastesFiberpreparation

Little or no air emissions generated

Little or no wastewater generated

Fiber waste; packaging waste; hard waste.

Yarn spinning Little or no air emissions generated

Little or no wastewater generated

Packaging waste; sized yarn; fiberwaste; cleaning and processing waste

Slashing/sizing Volatile organic compounds

BOD; COD; metals; cleaningwaste, size

Fiber lint; yarn waste; packagingwaste; unused starch-based sizes

Weaving Little or no air emissionsgenerated

Little or no wastewatergenerated

Packaging waste; yarn and fabricscraps; off-spec fabric; used oil.

Knitting Little or no air emissionsgenerated


Packaging waste; yarn and fabricscraps; off-spec fabric.

Tufting Little or no air emissionsgenerated


Packaging waste; yarn and fabricScraps; off-spec fabric.

Desizing Volatile organic compoundsfrom glycol ethers

BOD from water-soluble sizes;synthetic size; lubricants;biocides; anti-staticcompounds

Packaging waste; fiber lint; yarn waste;cleaning materials, such as wipes, ragsand filters; cleaning and maintenance

Wastes containing solvents.

Scouring Volatile organic compoundsfrom glycol ethers andscouring solvents

Disinfectants and insecticideresidues; NaOH; detergents;fats; oils; pectin; wax; knittinglubricants; spin finishes; spentsolvents

Little or no residual waste generated.

Bleaching Little or no air emissionsgenerated

Hydrogen peroxide, sodiumsilicate or organic stabilizer;high pH


Singeing Small amounts of exhaustgasses from the burners.



Mercerizing Little or no air emissions generated.

High pH; NaOH. Little or no residual waste generated.

Heat setting Volatilization of spin finish agents applied during synthetic fiber manufacture.

Little or no wastewater generated.


Dyeing Volatile organic compounds

Metals; salt; surfactants;toxics; organic processingassistance; cationic materials;color; BOD; sulfide; acidity/alkalinity; spent solvents.


Printing Solvents, acetic acid fromdyeing and curing ovenemissions;

Suspended solids; urea;solvents; color; metals; heat;BOD; foam

Little or no residual waste generated

combustiongasses; particulate matter.

Finishing Volatile organic compounds;contaminants in purchasedchemicals; formaldehydevapor; combustion gasses;particulate matter.

BOD; COD; suspended solids toxics; spent solvents.

Fabric scraps and trimmings; packaging waste.

ProductFabrication

Little or no air emissionsgenerated


Fabric scraps.

TYPES:

There are basically three types of effluent treatment methods. They are,

1. The physico-chemical method.2. The biological method.3. The combine method.

ALLIANCE KNIT COMPOSITE Ltd.

Location: Alliance Knit Composite Ltd. is situated at Saver Industrial area. Alliance Knit Composite Ltd. has newly joined for textile service among the world. This is fully export oriented knit composite Textile industry. This manufacturing industry is well organized with maintaining all the compliance and environmental issue. They established a physic-chemical Effluent Treatment Plant with latest technology. They treated 30 meter cube of effluent per hour. Their wet processing unit is of 5 ton/day capacity. For the better quality they use a high liquor ratio than the suggestion of dyeing machine manufacturer. So they have to treat more effluent than the theoretical demand. Effluent character of “Alliance Knit Composite Ltd.” is discussed;

Process flow chart of ETP

Blower

Hydro extractor

Sludge tank2

Lime

Aeration tank

Equalization tank

Filter

Primary clarifier

Secondary clarifier

FeSo4

Acid

Effluent In

Polymer

Sludge 2

Reaction Tank

Water Discharge

Control room

Mainly they use following chemicals for wet processing

1. Detergent (non-ionic).2. Anti creasing agent.3. Hydrogen per oxide.4. stabilizer5. Caustic soda.6. Soda ash.7. Common salt8. Glaubers’ salt9. Washing off agent.10.Acetic Acid.11.Softener.12.Anti foaming agent13.Optical brightener.14.Strong alkaline soap

Without these they use a lot of chemicals those vary due to order requirement. They use two types of dyes; reactive dyes & disperse dyes. Dyes and chemicals are soluble in water or in colloidal state. Some of suspended solid like wastages are also flow with raw effluent. They are mainly cotton fibers’ flocks or the yarn. The raw color of effluent is brown/ blue / black. All the liquors are coming through same drain of wet processing unit. So washing liquor, dye liquor, soaping liquor, scouring liquor, acid liquor all are getting mixture from the very beginning. The temperature, pH, BOD & COD of raw effluent liquor is given in the following table. In Bangladesh basically these four criteria are controlled for textile effluent.

Basic characteristics of raw effluent

SlNO

CHEMICAL CHARACTERISTICS

PARAMETERS UNIT AMOUNT

1. pH 11.82. Suspended solids mg/L 378.83. Biological Oxygen

Demand(BOD)mg/L 416

4. Chemical Oxygen Demand(COD)

mg/L 850

PHYSICAL CHARECTERISTICS

5. Color Brown to black6. Odour Not distinct7. Temperature 65

Picture of raw effluent

According to Alliance knit Composite ltd. Physico-chemical method is illustrated below:

Screening:

The effluent from the dyeing and finishing is first drained into the screening chamber. This chamber performs few physical filtrations. There is a series of netted filters positioned serially. For removing solid particles including suspended solids, yarn, fibers flocks, thickeners, etc, this process is important. After passing through these filters the effluent is free from solid bodies.

This chamber has a capability to keep the flowing effluent for two minutes as it has a volume of 2 cubic meters. The very first netted filter is made of M.S.Bar rod which is then followed by the second filter made of the same material having a hole of 4 square centimeter and the last but not the list is a filter made of stainless still having five holes per square centimeter.

Picture: The screening chamber

Cross-sectional view of sceen

Collection/Equalization Tank:

Here collection tank is nothing but the proper mixing of effluents of different types. It’s a rectangular tank of 20 m diameter and 2.5 meter surface water depth. So the volume effluent carrying is 800.75 cubic meter. Effluent is treated here for 10 hour 40 minutes. Here effluent without suspended solid and oil is mixed with air by means blower. Air is filtered first and then blows air at 1260 m3 per hour. 585 diffusers are used to supply air to the effluent for treatment. Here dissolved oxygen of water is increased by the air. The dissolved oxygen’s quantity is increasing to meet the Chemical oxygen demand by the effluent. 3

blowers are used to blow air for 16 hours continuously. And each blower is keeping working off for 8 hours. So 2 blowers of 50 kw/ hr are blowing air to the collection tank. After mixing properly effluent is allowed to pump to reaction tank.

Reaction tank:Effluent from the collection tank is directly passes to reaction tank for treating with chemicals used in physico-chemical process. In reaction tank the main chemistry of physico-chemical method for effluent treating is involved. It bears maximum maintenance cost for the treatment. This is a highlighted demerit for this method.

Picture: reaction tank (left) & X-section of reaction tank

Primary clarifier:

Equalization tank

Primary clarifier is used to sediment sludge and discharge clear water without color. As we discussed above that coagulation and flocculation removed all polis used to sediment sludge and discharge clear water without color. As we discussed above that coagulation and flocculation removed the toxic elements from here the crystal clear water is formed but it is alkaline. Here 2 chambers are used as primary clarifier. Each chamber is allowed to keep 105.625 cubic meter of effluent. And effluent’s treatment duration is about 2 hour 49 minutes.

Picture: X-section of primary clarifier and the surface primary clarifier.

This chambers bottom is sloped down around 45 degree to sediment sludge easily. Effluents from reaction tanks are directly pass to this tank. Here sludge sediment at bottom and the clear effluent pass out by means of over flow. Later a significant amount of sludge is pumped out to the sludge tank. Here the delivery effluent is alkaline and a fewer hot than the atmospheric temperature. The over flowed effluent is directly pass to the aeration chamber.

Aeration tank:

In aeration tank basically aeration is occurred by means atmospheric air. Air from atmosphere is firstly filtered then blower sucks them and flows air to the aeration tank through 860 diffusers. There are three blowers are used to perform their function. Every blower is running for 16 hours in the set of two. And every blower pauses blowing for 8 hours every day. Usually two blowers are running all the time to blow 1500 cubic meter of fresh air per hour. 860 diffusers are uniformly distributed around the 470 sq meter area.

Picture: blowers for aeration. Picture: aeration system to tank

Diffusers are kept at bottom of the tank floor. Blower takes air from atmosphere and then it passes though pipe to the diffusers. Then diffusers supply air as well as oxygen to the effluent. These blowers possesses the 25% cost of the plan. Blowers are highly stronger than the normal. These blowers are micro chipped program with the reader JUMO GMBH (it is a dissolve oxygen reader). When the dissolved oxygen comes up to 7.6 mg/L then the inverter of blowers’ motor worked to reduce rpm of blower.These are the description of plan for aeration tank. Now the question how does the function of air? This aeration does nothing but increase the quantity of dissolve oxygen. 4700cubic meter effluent is treated here for 47 hours, it’s a huge time. During this time oxidative chemicals are liked to fill up their oxygen demand from the water. That’s why increasing amount of dissolved oxygen is required to meet the demand. Without this the aquatic life in this tank ie, bacteria demands oxygen which is also filled up by this dissolved oxygen.

These are all about air, at aeration tank. During aeration bacteria is also involved to degrade effluents. Next chemical reactions will describe better.

.Secondary clarifier:

Picture: Secondary

clarifier

In aeration chamber acid is given to neutralize the solution with stirring. Though manufacturer suggests using a scrapper but the authority does not as they don’t need to use it. Without stirring relatively a few hot effluents is become cool naturally. Aeration tank has an open area around 490.625 sq. meter and its volume for effluent capacity is 2060.625 cubic meter. Effluent is treated here for 23 hour which is a huge time. So temperature is naturally fall down easily.The inlet pH of the effluent is 11.8. to neutralize its alkalinity around 7 liters of 33% concentrated hydrochloric acid per cubic meter is used. After neutralization its pH comes down to 7.16. If any sludge remains in the effluent they are allowed to sediment again in the secondary clarifier. From aeration tank neutralized effluent is entered to the secondary clarifier. 212 cubic meters this is kept here for 2 hour 52 minutes. Its time is sufficient enough to sediment sludge. The ground of secondary sludge is sloped down around 15 degree. Here treated effluent is also passing by means of over flowing. From here treated effluent is directly discharged to the cannel. Sludge from here is also passes to sludge tank by means of pumping arrangement.

Filtration: In filters, such as Pressure Sand Filter (PSF), the filtered waste water has to be regularly checked for quality (such as total suspended solids, trace elements, and residual chlorine) so that backwashing can be affected at the right time. Since regular sampling and analysis may not be possible in a large treatment facility, backwashing is automated with regular time intervals when the filtration flow is expected to decrease to a certain level. The chosen time interval for backwash operation is normally fixed arbitrarily based on the experience and expertise of the plant operator. Choosing an arbitrary backwash

interval may not be a perfect decision. It is possible that the planned time interval for backwash operation may either be longer or, shorter than it is actually necessary in most of the cases – as the feed quality and the condition of the treatment unit changes continuously. If frequent backwash is carried out, it may increase the downtime and reduce overall treatment capacity. Since backwash operation is normally conducted with water recovered from the reverse osmosis system down the line, frequent backwash can also result in overall decrease in the output of reusable water. Instead, if the backwash is delayed, it may reduce the operating capacity and filter efficiency. Thus, it is vital to optimize the filters for better performance to increase operating efficiency and reduce the maintenance cost.

Picture of filter

Outlet water:

Outlet water is colorless and odourless. Before draining the ETP water pH should be controlled in at range of 6-9.

Picture of outlet water

Sludge tank:In sludge tank there is a sand filtration system in which 2 feet of sand layer is kept and above that sand sludge is deposited. At the ground of tank there is a pipe arrangement with filtration which allows effluent without sludge passing to the collection tank. This is again treated.

Picture: Sludge tank

Hydro extractor:

Hydro extractor is a water removal machine. In effluent treatment plant hydro extractor is used to remove water from sludge thickener and finally to form sludge cake. There are many processes those are used to make cake from sludge but in Alliance Knit Composite Ltd. hydro extractor is used. Hydro extractor is easy to work. In sludge thickener tank, sludge pumps and put on the hydro extractor machine and switch on the machine. Here extra water is remove from the sludge and form cake.

Picture: Hydro extractorSludge:

The settable solids separated from the liquid during sedimentation (clarification). The sludge is very toxic in nature and needs to be deal with very carefully. Under no circumstances it should be mix with the environment again.

Picture of sludge cake

Results of Effluent Treatment (physico-chemical)

SLNO.

Effluent Quality parameters

Concentrationpresent in raw effluent

mg/L

Concentration present in treated effluent

mg/L

Bangladesh Quality Standard at Discharge

Inland surface water

mg/L

Public Swear at secondary treatment plant (WASA)mg/L

Irrigated land

mg/L

1 pH 11.8 7.16 6-9 6-9 N/A

2Biological Oxygen Demand (BOD)

450 45 50 250 100

3 Chemical Oxygen Demand (COD) 750 180 200 400 400

4 Time 50 hours

Costing: Costing is a secret thing that did not provide me of authority of Alliance Knit Composite Ltd. They have provided me approximately cost of ETP that is tk10000 for 720 m3. So per m3 cost is approximately tk1.39.

Advantages of Physico-chemical method:

1. This process posses a very low fixed cost which is around 80, 00,000 tk.2. Discharge effluent is colorless.3. Effluent is 100% pollutant free. 4. Non-biodegradable chemicals can treat here.5. Its maintenance does not demand highly skill professionals.6. It is applicable from all kinds of textile industries.7. It is very simple in technology.8. Dyer does not need to select chemicals with respect to its effluent treatment.9. It occupies minimal spaces around 15 kathas.

10. It possesses less treatment duration rather than biological treatment method which is around 50hours.

Disadvantages of physico-chemical method:

1. Treatment cost is very high around 12.92 tk per cubic meter. Cost will be equivalent with its fixed cost within 396 days (14 months) from its installation. Economically it brings loss.

2. This method is not that much modernized.3. It is chemical based for this reason treatment efficiency is highly

depended on its chemicals strength.

Conclusion: At present wet processing industry in Bangladesh are under pressure to install ETP. For financial and space constraints, it is difficult to meet the deadline of installation. From our findings, we like to state that it may not be necessary to use all methods to meet the permissible limit of the parameters set by the Department of Environment. One suitable method may be good enough to fulfill the requirements.

1. Screen Chamber2. Receiving Sump3. Equalizing Tank4. Flash mixer5. Clarriflocculator6. Aeration Tank7. Clarifier8. Sludge Well9. Sludge Thickener10. Centrifuge11. Generator Room12. Office Lab13. Transformer14. Sludge Drying Beds

P : Pump