Effluent Treatment Process in Garment Manufacturing

Items	Raw Water (regulating	Biochemical treatment system		Physiochemical treatment system
	tank)	Effluen t	Removal rate	Effluent	Removal rate
pH	8-12	7-8		6-9
CODcr (mg/L)	1000-2000	100- 200	90	£100	50
BOD5 (mg/L	300-600	15-30	95	£30
Color (times)	100-600	60	80	£40	35

ETP FOR TEXTILE INDUSTRY

Categorization of Waste Generated in Textile Industry:

Textile waste is broadly classified into four categories, each having characteristics that demand different pollution prevention and treatment approaches.

1. Hard to Treat Wastes

   This category of waste includes those that are persistent, resist treatment, or interfere with the operation of waste treatment facilities. Non-biodegradable organic or inorganic materials are the chief sources of wastes, which contain color, metals, phenols, certain surfactants, toxic organic compounds, pesticides, and phosphates. The chief sources are:

   • Colour & metal à dyeing operation
   • Phosphates à preparatory processes and dyeing
   • Non-biodegradable organic materials à surfactants
   • Since these types of textile wastes are difficult to treat, the identification and elimination of their sources are the best possible ways to tackle the problem. Some of the methods of prevention are chemical or process substitution, process control, optimization recycle/reuse, and better work practices.

2. Hazardous or Toxic Wastes

   These wastes are a subgroup of hard-to-treat wastes. But, owing to their substantial impact on the environment, they are treated as a separate class. In textiles, hazardous or toxic wastes include metals, chlorinated solvents, non-biodegradable or volatile organic materials. Some of these materials often are used for non-process applications such as machine cleaning.

3. High Volume Wastes

   The large volume of wastes is sometimes a problem for the textile processing units. The most common large-volume wastes include:

   • The high volume of wastewater
   • Wash water from preparation and continuous dyeing processes and alkaline wastes from preparatory processes
   • Batch dye waste containing large amounts of salt, acid, or alkali
   • These wastes sometimes can be reduced by recycling or reuse as well as by process and equipment modification.

4. Dispersible Wastes

   The following operations in the textile industry generate highly dispersible waste:

   • The waste stream from continuous operation (e.g. preparatory, dyeing, printing, and finishing)
   • Print paste (printing screen, squeeze and drum cleaning) Lint (preparatory, dyeing and washing operations)
   • Foam from coating operations Solvents from machine cleaning
   • Still bottoms from solvent recovery (dry cleaning operation)
   • Batch dumps of unused processing (finishing mixes)

POLLUTION PROBLEMS IN THE TEXTILE INDUSTRY

Colour

• The presence of color in the wastewater is one of the main problems in textile
• Colors are easily visible to human eyes even at very low concentrations. Hence, color from textile wastes carries significant aesthetic
• Most of the dyes are stable and has no effect of light or oxidizing
• They are also not easily degradable by the conventional treatment
• Removal of dyes from the effluent is a major problem in most textile

Dissolved Solids:

• Dissolved solids contained in the industry effluents are also a critical paremeters
• The use of common salt and Glauber salt in processes directly increase the total dissolved solids (TDS) level in the effluent.
• TDS are difficult to be treated with conventional treatment systems
• Disposal of high TDS bearing effluents can lead to an increase in TDS of groundwater and surface water

Toxic Metals

Wastewater of textiles is not free from metal contents. There are mainly two sources of metals.

1. The metals may come as impurities with the chemicals used during processing such as caustic soda, sodium carbonate, and salts.
2. The source of metal could be dyestuffs like metalized mordant dyes. The metal complex dyes are mostly based on chromium

Others

Textile effluents are often contaminated with non-biodegradable organics termed refractory materials.
Detergents are a typical example of such materials. The presence of these chemicals results in high chemical oxygen demand (COD) value of the effluent.

Organic pollutants, which originate from organic compounds of dyestuffs, acids, sizing materials, enzymes, tallow, etc are also found in textile effluent, such impurities are reflected in the analysis of biochemical oxygen demand (BOD) and COD.

PRECONDITIONS AND MEANS FOR RESOLVING THE PROBLEM

For a long time, the toxicity of released wastewater was mainly determined by the detection of biological effects from pollution, high bulks of foam, or intensively colored rivers near textile plants. Today, the identification and classification of wastewater are in accordance with existing municipal regulations. General regulations define the most important substances that are critically controlled by consumers and propose a set of activities that should be applied in order to minimize the amount of released hazardous substances.

The characteristics of textile effluents vary and depend on the type of textile manufactured and the chemicals used. The textile wastewater effluent contains high amounts of agents causing damage to the environment and human health including suspended and dissolved solids, biological oxygen demand (BOD), chemical oxygen demand (COD), chemicals, contain trace metals like Cr, As, Cu, and Zn and Color.

The activities to treat hazardous wastes can range from legal prohibition to cost-saving recycling of chemicals. Depending on the type of product and treatment, these steps can show extreme variability. Effluents treatment plants are the most widely accepted approaches towards achieving environmental safety. But, unfortunately, no single treatment methodology is suitable or universally adaptable for any kind of effluent treatment. Therefore, the treatment of waste stream is done by various methods, which include physical, chemical, and biological treatment depending on pollution load. Our aim is to adopt technologies giving minimum or zero environmental pollution.

During the last 50-75 years, there have been ever-increasing efforts to somehow arrange manufacturing processes in such a way that they cause minimal damage to the environment. At the same time, these efforts are aimed at developing appropriate technologies for wastewater treatment and establishing an adequate relationship between regulators and industry. To decrease the quantity of generated wastewaters it is necessary applying of a systematic approach to reducing the generation of waste at the source. In other words, this approach prevents the creation of wastewaters in the first place, rather than treating it once it has been produced by end-of-pipe treatment methods.

 

This is a technique that should be applied to all inputs and outputs of a production process. Once waste minimization has been carried out in the factory, effluent will still be produced that will require some form of treatment prior to disposal to sewage, river, or sea. Reducing the quantities of generated wastewater is important because it contributes to reducing operating costs, the risk of liability, and the need to treat the effluents with end-of-pipe methods. It also helps to increase the efficiency of production processes, environmental protection and health, increasing awareness, and raising the morale of employees.

Treatment of Textile Effluents

Typically, textile effluent would involve the following steps

• Reactive dye concentrates can be treated in a conventional anaerobic digester
• Exposure to the biomass to achieve de‐colorization and tolerance of the microorganisms to concentrations of the dye
• Additional carbon source( eg. glucose) is necessary to maintain the microbial metabolic state
• The presence of Nitrate in the system inhibits de‐colorization
• Adsorption of the dye to the biomass also causes de‐colorization
• The degradation products of the dye after anaerobic digestion may be isolated and identified

Treatment of Wastewater

After every effort that can be made to reduce waste strength and volume, there still remains the problem of disposing the final remains of polluted waste into any water stream, thus the waste may be treated in various methods either singly or in combination and the best combination of methods differs from plant to plant.

Flow chart for ETP

Preliminary Treatment level

After the removal of gross solids, gritty materials, and excessive quantities of oil and grease, the next step is to remove the remaining suspended solids as much as possible. This step is aimed at reducing the strength of the wastewater and also facilitating secondary treatment.

Purpose: Physical separation of big sized impurities like cloth, plastics, wood logs, paper,

Common physical unit operations at the Preliminary level are:

Screening

• A screen with openings of uniform size is used to remove large solids such as plastics, cloth, etc. Generally, a maximum of 10mm is Coarse suspended matters such as rags, pieces of fabric, fibers, yarns, and lint are removed. Bar screens and mechanically cleaned fine screens remove most of the fibers. The suspended fibers have to be removed prior to secondary biological treatment; otherwise, they may affect the secondary treatment system. They are reported to clog trickling filters, seals, or carbon beads.
• Screening is the filtration process for the separation of coarse particles from  influent
• Stainless steel nets with varying pore sizes can be utilized
• Screens are cleaned regularly to avoid clogging

Sedimentation

• Physical water treatment process using gravity to remove suspended solids from The suspended matter in textile effluent can be removed efficiently and economically by sedimentation. This process is particularly useful for the treatment of wastes containing a high percentage of settable solids or when the waste is subjected to combined treatment with sewage.
• The sedimentation tanks are designed to enable smaller and lighter particles to settle under gravity. The most common equipment used includes horizontal flow sedimentation tanks and center-feed circular clarifiers. The settled sludge is removed from the sedimentation tanks by mechanical scrapping into hoppers and pumping it out subsequently.
• In this tank, sludge is settled down

• Effluent is discharged from the plant through a fish pond
• Sludge is passed to the sludge thickening unit

 

• Clarification: Used for separation of solids from fluids
• Equalization: Effluent streams are collected into a sump pit. Sometimes mixed effluents are stirred by rotating agitators or by blowing compressed air from below. The pit has a conical bottom for enhancing the settling of solid particles
• Equalization makes the wastewater homogeneous
• Retention time depends upon the capacity of the treatment plant. (Generally, 8-16 hours)

Primary Treatment Level

Purpose: Removal of floating and settleable materials such as suspended solids and organic

Methods:  Both physical and chemical methods are used in this treatment level.

Chemical unit processes

• Chemical unit processes are always used with physical operations and may also be used with biological treatment processes
• Chemical processes use the addition of chemicals to the wastewater to bring about changes in its quality.

Example:  pH control, coagulation, chemical precipitation, and oxidation

Neutralization: Normally, pH values of cotton finishing effluents are on the alkaline side. Hence, the pH value of equalized effluent should be adjusted. The use of dilute sulphuric acid and boiler flue gas rich in carbon dioxide is not uncommon. Since most of the secondary biological treatments are effective in the pH 5 to 9, the neutralization step is an important process to facilitate.

pH Control:

• To adjust the pH in the treatment process to make wastewater pH neutral
• For acidic wastes (low pH): NaOH, Na2CO3, CaCO3or Ca(OH)2
• For alkali wastes (high pH): H2SO4, HCl

Chemical coagulation and Flocculation

• Coagulation refers to collecting the minute solid particles dispersed in a liquid into a larger mass.
• Chemical coagulants like Al2(SO4)3 {also called alum} or Fe2(SO4)3 are added to wastewater to improve the attraction among fine particles so that they come together and form larger particles called flocks

• A chemical flocculent (usually a polyelectrolyte) enhances the flocculation process by bringing together particles to form larger flocs, which settle out more quickly
• Flocculation is aided by gentle mixing which causes the particles to collide

Chemical coagulation and Mechanical flocculation: Finely divided suspended solids and colloidal particles cannot be efficiently removed by simple sedimentation by gravity. In such cases, mechanical flocculation or chemical coagulation is employed.

In mechanical flocculation, the textile wastewater is passed through a tank under gentle stirring; the finely divided suspended solids coalesce into larger particles and settle out. Specialized equipment such as clariflocculator is also available, wherein a flocculation chamber is a part of a sedimentation tank.

In order to alter the physical state of colloidal and suspended particles and to facilitate their removal by sedimentation, chemical coagulants are used. It is a controlled process, which forms a floc (flocculent precipitate) and results in obtaining a clear effluent free from matter in suspension or in the colloidal state. The degree of clarification obtained also depends on the number of chemicals used. In this method, 80-90% of the total suspended matter, 40-70% of BOD, 5days, 30-60% of the COD, and 80-90% of the bacteria can be removed. However, in plain sedimentation, only 50-70% of the total suspended matter and 30-40% of the organic matter settles out.

The most commonly used chemicals for chemical coagulation are alum, ferric chloride, ferric sulfate, ferrous sulfate, and lime.

Secondary Treatment Level

Methods: Biological and chemical processes are involved in this level.

Biological unit process

• To remove, or reduce the concentration of organic and inorganic compounds.

• The biological treatment process can take many forms but all are based around microorganisms, mainly bacteria.

The main purpose of secondary treatment is to provide BOD removal beyond what is achievable by simple sedimentation. It also removes appreciable amounts of oil and phenol. In secondary treatment, the dissolved and colloidal organic compounds and colors present in wastewater are removed or reduced to stabilize the organic matter. This is achieved biologically using bacteria and other microorganisms. Textile processing effluents are amenable for biological treatments [3]. These processes may be aerobic or anaerobic. In aerobic processes, bacteria and other microorganisms consume organic matter as food. They bring about the following sequential changes:

• Coagulation and flocculation of colloidal matter
• Oxidation of dissolved organic matter to carbon dioxide
• Degradation of nitrogenous organic matter to ammonia, which is then converted into nitrite and eventually to

Anaerobic Processes

• The anaerobic treatment processes take place in the absence of air (oxygen).
• Utilizes microorganisms (anaerobes) that do not require air (molecular/free oxygen) to assimilate organic impurities.
• The final products are methane and biomass

Anaerobic treatment is mainly employed for the digestion of sludge. The efficiency of this process depends upon pH, temperature, waste loading, absence of oxygen, and toxic materials. Some of the commonly used biological treatment processes are described below:

Aerated lagoons: These are large holding tanks or ponds having a depth of 3-5 m and are lined with cement, polythene, or rubber. The effluents from primary treatment processes are collected in these tanks and are aerated with mechanical devices, such as floating aerators, for about 2 to 6 days. During this time, a healthy flocculent sludge is formed which brings about oxidation of the dissolved organic matter. BOD removal to the extent of 99% could be achieved with efficient operation. The major disadvantages are the large space requirements and the bacterial contamination of the lagoon effluent, which necessitates further biological purification.

• The function of aeration is oxidation by blowing air
• Aerobic bacteria are used to stabilize and remove organic material present in the waste.

SCHEMATIC DIAGRAM OF AERATION

 

Trickling filters

The trickling filters usually consist of circular or rectangular beds, 1 m to 3 m deep, made of well-graded media (such as broken stone, PVC, Coal, Synthetic resins, Gravel, or Clinkers) of size 40 mm to 150 mm, over which wastewater is sprinkled uniformly on the entire bed with the help of a slowly rotating distributor (such as rotary sprinkler) equipped with orifices or nozzles. Thus, the wastewater trickles through the media. The filter is arranged in such a fashion that air can enter at the bottom; counter-current to the effluent flow and a natural draft is produced. A gelatinous film, comprising of bacteria and aerobic micro-organisms known as Zooglea, is formed on the surface of the filter medium, which thrives on the nutrients supplied by the wastewater. The organic impurities in the wastewater are adsorbed on the gelatinous film during its passage and then are oxidized by the bacteria and the other micro-organisms present therein.

Activated sludge process

This is the most versatile biological oxidation method employed for the treatment of wastewater containing dissolved solids, colloids, and coarse solid organic matter. In this process, the wastewater is aerated in a reaction

tank in which some microbial floc is suspended. The aerobic bacterial flora brings about biological degradation of the waste into carbon dioxide and water molecules, while consuming some organic matter for synthesizing bacteria. The bacteria flora grows and remains suspended in the form of a floc, which is called Activated Sludge. The effluent from the reaction tank is separated from the sludge by settling and discharge.

A part of the sludge is recycled to the same tank to provide an effective microbial population for a fresh treatment cycle. The surplus sludge is digested in a sludge digester, along with the primary sludge obtained from primary sedimentation. Efficient aeration for 5 to 24 hours is required for industrial wastes. BOD removal to the extent of 90-95% can be achieved in this process.

 

Sludge thickening unit

• Here sludge is dried and
• A partial amount of sludge is returned back to the aeration tank from thickening unit through recycle tank called return sludge tank and disperse

SCHEMATIC DIAGRAM OF SLUDGE THICKENING UNIT

 

Oxidation ditch

This can be considered as a modification of the Conventional Activated Sludge process. Wastewater, after screening in allowed into the oxidation ditch. The mixed liquor containing the sludge solids is aerated in the channel with the help of a mechanical rotor. The usual hydraulic retention time is 12 to 24 hrs and for solids, it is 20-30 days. Most of the sludge formed is recycled for the subsequent treatment cycle. The surplus sludge can be dried without odor on sand drying beds.

Oxidation pond

An oxidation pond is a large shallow pond wherein stabilization of organic matter in the waste is brought about mostly by bacteria and to some extent by protozoa. The oxygen requirement for their metabolism is provided by algae present in the pond. The algae, in turn, utilize the CO2 released by the bacteria for their photosynthesis. Oxidation ponds are also called waste stabilization ponds.

Anaerobic digestion

Sludge is the watery residue from the primary sedimentation tank and humus tank (from secondary treatment). The constituents of the sludge undergo slow fermentation or digestion by anaerobic bacteria in a sludge digester, wherein the sludge is maintained at a temperature of 35oC at pH 7-8 for about 30 days. CH4, CO2, and some NH3 are liberated as the end products.

Tertiary / Advanced Treatment

Purpose: Final cleaning process that improves wastewater quality before it is reused, recycled, or discharged to the environment.

Mechanism: Removes remaining inorganic compounds, and substances, such as nitrogen and phosphorus. Bacteria, viruses, and parasites, which are harmful to public health, are also removed at this stage.

Methods:

• Alum: Used to help remove additional phosphorus particles and group the remaining solids together for easy removal in the
• Chlorine contact tank disinfects the tertiary treated wastewater by removing microorganisms in treated wastewater including bacteria, viruses and
• The remaining chlorine is removed by adding sodium bisulfate just before it’s

It is worthwhile to mention that textile waste contains significant quantities of non-biodegradable chemical polymers. Since the conventional treatment methods are inadequate, there is the need for an efficient tertiary treatment process.

Oxidation techniques

A variety of oxidizing agents can be used to decolorize wastes. Sodium hypochlorite decolourizes dye baths efficiently. Though it is a low-cost technique, it forms absorbable toxic organic halides (AOX) [4].

Ozone on decomposition generates oxygen and free radicals and the latter combines with coloring agents of effluent resulting in the destruction of colors [5]. Arslan et al. investigated the treatment of synthetic dyehouse effluent by ozonization, and hydrogen peroxide in combination with Ultraviolet light [6]. The main disadvantage of these techniques is it requires an effective sludge-producing pre-treatment.

 

Electrolytic precipitation & Foam fractionation

Electrolytic precipitation of concentrated dye wastes by a reduction in the cathode space of an electrolytic bath has been reported although extremely long contact times were required.

Foam fractionation is an experimental method based on the phenomena that surface-active solutes collect at gas-liquid interfaces. However, the chemical costs make this treatment method too expensive.

Membrane technologies

Reverse osmosis and electrodialysis are important examples of the membrane process.

The TDS from wastewater can be removed by reverse osmosis. Reverse osmosis is suitable for removing ions and larger species from dye bath effluents with high efficiency (up to > 90%), clogging of the membrane by dyes after long usage and high capital cost are the main drawbacks of this process.

The dyeing process requires the use of electrolytes along with the dyes. Neutral electrolyte like NaCl is required to have high exhaustion of the dye. For instance, in cotton dyeing, NaCl concentration in the dyeing bath is in the range of 25-30 g/l for deep tone and about 15 g/l for a light tone but can be as high as 50 g/l in exceptional cases. The exhaustion stage in reactive dyeing on cotton also requires a sufficient quantity of salt.

The reverse osmosis membrane process is suitable for removing high salt concentrations so that the treated effluent can be re-used again in the processing. The presence of electrolytes in the washing water causes an increase in the hydrolyzed dye affinity (for reactive dyeing on cotton) making it difficult to extract.

In electrodialysis, the dissolved salts (ionic in nature) can also be removed by impressing an electrical potential across the water, resulting in the migration of cations and anions to respective electrodes via anionic and cationic permeable membranes. To avoid membrane fouling it is essential that turbidity, suspended solids, colloids, and trace organics be removed prior to electrodialysis.

 

Electrochemical processes

They have lower temperature requirements than those of other equivalents non-electrochemical treatment and there is no need for additional chemicals. It also can prevent the production of unwanted side products. But, if suspended or colloidal solids were high concentration in the wastewater, they impede the electrochemical reaction. Therefore, those materials need to be sufficiently removed before electrochemical oxidation [9].

Ion exchange method

This is used for the removal of undesirable anions and cations from wastewater. It involves the passage of wastewater through the beds of ion exchange resins where some undesirable cations or anions of wastewater get exchanged for sodium or hydrogen ions of the resin. Most ion exchange resins now in use are synthetic polymeric materials containing ion groups such as sulphonyl, quaternary ammonium group, etc.

 

Photocatalytic degradation

An advanced method to decolorize a wide range of dyes depending upon their molecular structure. In this process, photoactive catalyst illuminates with UV light, generates highly reactive radical, which can decompose organic compounds.

Adsorption

It is the exchange of material at the interface between two immiscible phases in contact with one another. Adsorption appears to have considerable potential for the removal of color from industrial effluents.

Owen (1978) after surveying 13 textile industries has reported that adsorption using granular activated carbon has emerged as a practical and economical process for the removal of color from textile effluents.

Thermal evaporation

The use of sodium persulfate has a better oxidizing potential than NaOCl in the thermal evaporator. The process is eco-friendly since there is no sludge formation and no emission of toxic chlorine fumes during evaporation. The oxidative decolorization of reactive dye by persulphate due to the formation of free radicals has been reported in the literature.

Effluent Treatment Practices: Textile industry encompasses a range of unit operations, which use a wide variety of natural and synthetic fibers to produce fabrics.

ETP SYSTEM FOR DYEING INDUSTRIES

Textile dyeing industries need a huge quantity of water for textile dyeing, which they normally pump out repeatedly from the ground or natural water sources resulting in depletion of groundwater level.

In the dyeing process textile industries generate huge quantity of toxic effluent containing colours, sodium sulphate, sodium chloride, sodium hydroxide and traces of other salts. These are generated after dyeing and after washing of garments / fabrics. After dyeing the waste water produced is called Dye Bath water and after washing the waste water generated is called wash water. Dye Bath contains higher solids in the range 4-5% whereas wash water contains only 0.5-1% solids.

 

Based on the above-mentioned fact “SSP” has developed a technology that can process such harmful toxic effluent water and transform it into reusable water. Thus, the textile industries will have the advantage of using the same water in the dying process repeatedly, also the salt used for dyeing can be reused or sold in the market. The technology offered by SSP can overcome all problems pertaining to environmental pollution in respect to textile dying industries.

EFFLUENT GENERATION AND CHARACTERISTICS

Wet processing of textiles involves, in addition to extensive amounts of water and dyes, a number of inorganic and organic chemicals, detergents, soaps, and finishing chemicals to aid in the dyeing process to impart the desired properties to dyed textile products. Residual chemicals often remain in the effluent from these processes.

In addition, natural impurities such as waxes, proteins, and pigment, and other impurities used in processing such as spinning oils, sizing chemicals, and oil stains present in cotton textiles, are removed during resizing (Desizing is the process of removing the size material from warp yarns after a textile fabric is woven.), scouring(Scouring is the process of removing the impurities such as oil, fat, wax dust and dirt from the textile material to make it hydrophilic).and bleaching(Bleaching is the chemical treatment for removal of natural coloring matter from the fabric). operations. This results in an affluent of poor quality, which is high in BOD and COD load.

DISCHARGE QUALITY STANDARD FOR CLASSIFIED INDUSTRIES

There are various types of ETPs and their design will vary depending on the quantity and quality of the affluent, the amount of money available for construction, operation, and maintenance, and the amount of land available. There are three mechanisms for treatment which are: Physical, Chemical, and Biological. These mechanisms will often be used together in a single ETP.

There are generally four levels of treatment, as described below: 

• Preliminary: Removal of large solids such as rags, sticks, grit, and grease that may result in damage to equipment or operational problems (Physical);
• Primary: Removal of floating and settable materials, e. suspended solids and organic matter (Physical and Chemical);
• Secondary: Removal of biodegradable organic matter and suspended solids (Biological and Chemical);
• Tertiary: Removal of residual suspended solids / dissolved solids (Physical, Chemical, and Biological)

There are many ways of combining the operations and processes in an ETP: 

• A properly designed biological treatment plant, which typically includes screening, equalization, pH control, aeration, and settling, can efficiently satisfy BOD, pH, TSS, oil, and grease However the compounds in industrial effluent may be toxic to the microorganisms so pre-treatment may be necessary. Most dyes are complex chemicals and are difficult for microbes to degrade so there is usually very little color removal.
• Another option is a Physico-chemical treatment plant, which typically includes screening, equalization, pH control, chemical storage tanks, mixing unit, flocculation unit, settling unit, and sludge dewatering. This type of treatment will remove much of the color depending on the processes It can be difficult to reduce BOD and COD to meet effluent standards and it is not possible to remove TDS.
• Most often, Physico-chemical treatment will be combined with biological The typical components of such a plant are screening, equalization, and pH control, chemical storage, mixing, flocculation, primary settling, aeration, and secondary settling. The physicochemical treatment always comes before the biological treatment units. Using a combination of treatments will generally reduce pollutant levels to below the discharge standards. 4-8
• Another form of biological treatment is the reed bed, which can be used with a settling tank, or in combination with other treatment processes, It presents a natural method of treating effluent which is often lower in the capital, operation, and maintenance costs. Reed beds can contribute to a reduction in color, a decrease in COD, increased dissolved oxygen, and a reduction in heavy metals, but function best with some form of pre-treatment.

As discussed, there are many options for the design of an ETP. The type of plant and the various components of the plant will depend on the characteristics of the effluent. In evaluating an ETP design in an application for an ECC, it is necessary to determine whether the components of the ETP are sized correctly for the flow and to assess whether the effluent is likely to meet the requirements of the discharge standards.

CASE-STUDY – Performance Evaluation of Effluent Treatment Plant for Textile Industry in Kolhapur of Maharashtra

Introduction

The textile industry is one of the leading sectors in the Indian economy as it contributes nearly 14 percent to the total industrial production (business.mapsofindia.com). The untreated textile wastewater can cause rapid depletion of dissolved oxygen if it is directly discharged into the surface water sources due to its high BOD value. The effluents with high levels of BOD and COD values are highly toxic to biological life. The high alkalinity and traces of chromium which is employed in dyes adversely affect the aquatic life and also interfere with the biological treatment processes (Palamthodi et al., 2011).

The quality of such effluent can be analyzed by their physicochemical and biological analysis. Monitoring of the environmental parameters of the effluent would allow having, at any time, a precise idea on performance evaluation of ETP and if necessary, appropriate measures may be undertaken to prevent adverse impact on the environment. The obtained results were very much useful in the identification and rectification of operational and maintenance problems and they can be also utilized to establish methods for the improved textile industry and plant waste minimization strategies.

The present textile industry is having a weaving capacity of 10 million meters per annum. During the production process, effluent generated in the plant is drained to ETP. The samples were collected daily and analyzed for Physico-chemical and biological parameters except for BOD as it takes three days for analysis for the period of one month during the training period. On average, approximately 200 liters of water are required to produce l kg of textiles. The risk factors are primarily associated with the wet processes- scouring, desizing, mercerizing, bleaching, dyeing, and finishing. Desizing, scouring, and bleaching processes produce large quantities of wastewater (Yusuff et al., 2004). The large volumes of wastewater generated also contain a wide variety of chemicals used throughout processing. These can cause damage if not properly treated before being discharged into the environment (C Parvathi et al., 2009).

 

Table 1: Effluent Characteristics from Textile Industry