Effluent Treatment Process in Garment Manufacturing
Importance, merits, de-merits, techniques, technologies used in Textile Effluent Treatment Plants (ETP)
The textile industry is one of the leading sectors in the economy as it contributes to total industrial production. 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. 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 will be very much useful in the identification and rectification of operational and maintenance problems and they can be also utilized to establish methods for improvement.
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
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
|Sizing||Starch, waxes, carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), wetting agents.||High in BOD, COD|
|Desizing||Starch, CMC, PVA, fats, waxes, pectins||High in BOD, COD, SS,
dissolved solids (DS)
|Bleaching||Sodium hypochlorite, Cl2, NaOH, H2O2, acids, surfactants, NaSiO3, sodium phosphate, short cotton
|High alkalinity, high SS|
|Mercerizing||Sodium hydroxide, cotton wax||High pH, low BOD, high DS|
|Dyeing||Dyestuffs urea, reducing agents, oxidizing agents, acetic acid,
detergents, wetting agents.
|Strongly colored, high BOD, DS, low SS, heavy metals|
|Printing||Pastes, urea, starches, gums, oils, binders, acids, Thickeners, cross-linkers, reducing agents, alkali||Highly colored, high BOD, oily appearance, SS slightly alkaline, low BOD|
The flowsheet of ETP is shown in fig no. 2. The flowsheet to achieve the standard required as per the consent letter of Maharashtra Pollution Control Board comprises of the following units: 1] Screen Chamber 2] Equalization tank 3] Flash mixer 4] Flocculation Tank 5] Tube Settler-I 6] Fluidized Aerobic Bio-Reactor (FAB-I) 7] FAB-II 8] Tube Settler- II 9] Chlorine Contact Tank 10] Sludge Thickener 11] Centrifuge.
The wastewater generated from the plant is collectively passed through the screen chamber to remove the floating matter present in the wastewater. The quality and quantity of the wastewater are maintained in the equalization tank where an air blower is provided for the supply of oxygen. The wastewater then comes to the flash mixer in which lime and ferrous sulfate are the coagulants added to the wastewater with a detention time of 30 seconds. The floc gets formed due to the slow mixing and resultant settling of floc in the first tube settler reduces total suspended solids and BOD load on the secondary treatment.
The water is then allowed in the FAB-I where micro-organisms are attached to the media while media is suspended in the wastewater. The growth occurred in the media. The oxidation of organic matter is done with the help of micro-organisms. The sludge formed due to the biological processes gets settled in tube settler II. The wastewater treated by secondary treatment is then allowed in a chlorine contact tank to kill pathogens using the hypochlorite as a disinfectant. The treated wastewater is then sent to the common effluent treatment plant for further treatment. The sludge settled in the tube settlers is then sent to the sludge thickener then it is concentrated in a centrifuge using polyelectrolyte dosing. The concentrated sludge is sent to the hazardous waste disposal site at Rajangoan, Pune.
Results and Discussion
Table 1 shows the major processes involved in textile manufacturing and the nature of wastewater generated. For evaluating the performance of ETP, the accurate idea of the composition of effluents is very important. This is so because industrial effluents contain various pollutants that may alter the quality of the receiving water and the environment at large (Ogunlaja et al., 2009). The results of daily analysis of pH, COD, BOD and TDS, etc are represented in Table 2.
Table 2: Daily analysis of inlet and outlet parameters
|Date||Treated quantity||Inlet parameters||Outlet parameters|
The color of the effluent was brownish-black. In- complete use and the washing operations give the textile wastewater a considerable amount of dyes (Palamthodi et al., 2011). It has been documented that residual color is usually due to insoluble dyes which have low biodegradability as reactive blue 21, direct blue 80, and vat violet with COD/BOD ratios of 59.0, 17.7, and 10.8 respectively (Adel Al-Kdasi et al., 2004).
Coagulation and flocculation help to remove the color of the effluent (Wong, 2007). The Ph of the raw effluent is very high as the incoming wastewater is highly alkaline in nature. The bleaching agents used in the process are reasons for high alkaline wastewater.
The pH correction is done with the help of HCL and brings down to neutral which is favorable pH for biological treatment. TDS are composed mainly of carbonates, bicarbonates, chlorides, phosphates and nitrates, calcium, magnesium, potassium and manganese, organic matter salts, and other particles. No appreciable change was observed in the values of dissolved solids in the treated effluent. TDS detected could be attributed to the high color from the various dyestuffs being used in the textile mills (Mohabansi et al., 2011).
FAB consists of a tank filled with specially developed media. These media are made of special materials of suitable density that can be fluidized using an aeration device through diffusers. A bio-film develops on the media, which move along The COD and BOD of raw effluent varied from 1104 to 1475 mg/l and 242 to 358 mg/l respectively. The effluent in the reactor. The movement within the reactor is generated by providing aeration with the help of higher values of COD and BOD in raw effluent of diffusers placed at the bottom of the reactor.
This is attributed to the presence of chemical substances and breakdown of raw material used for the preparation of fiber respectively. The COD and BOD of treated effluents were reduced significantly to a greater extent due to the biological treatment process for which the effluent is passed through FAB I and The thin film on the media enables the bacteria to act upon the bio-degradable matter in the effluent and reduce BOD/COD content in presence of oxygen from the air used for fluidization (sanllersystems.com).
Most of the studied parameters are well within the Safety officer, Raymond Zambaiti Ltd, Kolhapur permissible limit prescribed by MPCB because the industry has installed an adequate treatment system to treat the raw effluent. The treated effluent is applicable for the land application so it is used for green belt development in the industrial premises and 30% for his guidance, suggestions, and encouragement. of the total effluent treated is reused for this purpose. The disposal of excess treated effluent to a common effluent treatment plant is the best and effective and environmentally acceptable option for better downstream conditions.