The textile and dyeing industry are responsible for releasing highly contaminated colored effluent leading to intense water pollution. This paper reports the results of an efficient electrochemical removal of color and reduction in toxicity of textile industry effluents. The electrochemical behavior is analyzed and assessed in terms of removal of color, decrease in absorbance, time taken to completely remove color from the dye solution, decrease in chemical oxidation demand, total dissolved solids and disappearance of any reduction peak in colorless solution, thereby indicating the absence of electro-chemically active break down product. This paper discusses about the novel solutions available for waste management in textiles. The paper also addresses the pollution control and effective effluent treatment available for textile industries.
Keywords: Economy, pollution, BOD, COD, residual dye, effluents, allergy, wastewater
Textile industry plays an important role in the economy of the country like India and it accounts for around one third of total export. Textile industry is one of the main source of pollution problem worldwide. Textile effluent is characterized by high BOD (from 700 to 2,000 mg/l) and COD loads, suspended solids, mineral oils and residual dye. 10-25% of textile dyes are lost during the dyeing process, and 2-20% is directly discharged as aqueous effluents in different environmental components. Traditionally produced fabric contains chemical residues, used during their manufacturing. These chemical residues may evaporate in air or may be absorbed through our skin thus causing allergy. According to a June 5, 2005 article in Business Week, the population allergic to chemicals will grow to 60% by the year 2020. The paper deals with the various operations involved in the textile industry and discusses about the water usage and wastewater characteristic of textile industry. It also gives a brief idea about the treatment technologies for treating waste water. The existing waste water treatment technology is often inadequate to control color of effluent and toxicity of wastewater to aquatic organisms. Hence very little decomposition of these organic molecules takes place by aerobic and anaerobic wastewater treatment processes and discharge level of COD cannot be achieved by these processes without some form of post treatment1,2. The electrochemical methods have found use in destruction of toxic and non- biodegradable organics by direct or indirect oxidation/ reduction3,4. Electrochemical methods are very promising as they involve the controlled degradation of the pollutants. They are moreover very effective towards the reduction of chromophoric groups of dyes and color removal, which is the main disturbing factor for water recycling in most of the industries.
The main challenge for the textile industry today is to modify production methods, so they are more ecologically friendly at a competitive price, by using safer dyes and chemicals and by reducing cost of effluent treatment/disposal. Recycling has become a necessary element, not because of the shortage of any item, but because of the need to control pollution. There are three ways to reduce pollution: (1) use of new, less polluting technologies; (2) effective treatment of effluent so that it conforms to specified discharge requirements; and (3) recycling waste several times over before discharge.
Water – the energy resource for textile operations
The water requirement for textile processing is large and varies from one mill to another and this depends on factors like: (a) source of water and its availability; (b) the quantity and quality of the fabrics produced; and types of processing and its sequence. The water usage for different purposes in a typical cotton textile mill and synthetic textile processing mill is given in Table 1. To produce one metre of finished cloth the water consumption is in the range of 12 to 65 litres. The longer the processing sequence, the greater will be quantity of water used. The processing of yarn also requires equally large volume of water. Bulk of the water consumed in the washing of the fabric at the end of each process5,6.
Waste water characteristics for textile industry
Composite textile wastewater is characterized mainly by measurements of biochemical oxygen demand (BOD), chemical oxygen demand (COD), suspended solids (SS) and dissolved solids (DS). Typical characteristics of textile industry wastewater are presented in Table 2. Results in Table 1 show a large extent of variation from plant-to-plant and sample-to sample. As presented in Table 3, COD values of composite wastewater are extremely high compare to other parameter. In most cases BOD/COD ratio of the composite textile wastewater is around 0.25 that implies that the wastewater contains large amount of non biodegradable organic matter.
Pollution crisis in textile industry
Textile printing and dyeing processes include pre-treatment, dyeing and printing, finishing. The main pollutants are organic matters which come from the pre-treatment process of pulp, cotton gum, cellulose, hemicellulose and alkali, as well as additives and dyes using in dyeing and printing processes. Pre-treatment wastewater accounts for about 45% of the total, and dyeing/printing process wastewater accounts for about 50%~55%, while finishing process produces little. The chroma is one pollutant of the wastewater which causes a lot of concerns. In the dyeing process, the average dyeing rate is more than 90%. It means that the residual dyeing rate in finishing wastewater is about 10%, which is the main reason of contamination as shown in Table 3.
Technologies for waste water treatment
The textile dyeing wastewater has a large amount of complex components with high concentrations of organic, high-color and greatly changing characteristics. Owing to their high BOD/COD, their coloration and their salt load, the wastewater resulting from dyeing cotton with reactive dyes are seriously polluted. As aquatic organisms need light in order to develop, any deficit in this respect caused by colored water leads to an imbalance of the ecosystem. Moreover, the water of rivers that are used for drinking water must not be colored, as otherwise the treatment costs will be increased. Obviously, when legal limits exist (not in all the countries) these should be taken as justification. Studies concerning the feasibility of treating dyeing wastewater are very important. Some selected treatment processes for dyes and color removal of industrial wastewater are applied over the time into different textile units.
Textile industry consumes large amount of water. It takes about 12 to 65 litres of water to produce one metre of finished cloth and about 500 gallons to produce enough fabric to cover one sofa. Half a billion people already live in regions prone to chronic drought and by 2025; this figure is likely to have increased five folds. Global consumption of fresh water is doubling every 20 years. Keeping all this in mind it becomes extremely important to conserve water.
TRETMENT) Influent---------ETP---------------Effluent (SLUDGE)
Textile effluent is characterized to possess high COD & BOD 10-20 % of dyes were lost during dyeing and 2-20 % waste being discharged as an aqueous effluent. It may be allergic to our skin. In 2020, it is found that around 60% of water gets polluted. Textile industry is one of the main source of pollution problem in worldwide. Water discharged from homes, businesses, and industry enters sanitary sewers. Water from rainwater on streets enters storm water sewers. Combined sewers carry both sanitary wastes and storm water. Water moves toward the wastewater plant primarily by gravity flow. Lift stations pump water from low lying areas over hills.
Parameters of the CETP
Oiling and greasing 15 and 20 days Frequency of painting Once a year structures
Screen chamber: Remove relatively large solids to avoid abrasion of mechanical equipments and clogging of hydraulic system.
Collection tank: The collection tank collects the effluent water from the screening chamber, stores and then pumps it to the equalization tank.
Equalization tank: The effluents do not have similar concentrations at all the time; the Ph will vary time to time. Effluents are stored from 8 to 12 hours in the equalization tank resulting in a homogenous mixing of effluents and helping in neutralization. It eliminates shock loading on the subsequent treatment system. Continuous mixing also eliminates settling of solids within the equalization tank.
Aeration tank: The water is passed like a thin film over the different arrangements like staircase shape.
Clarifier: The clarifier collects the biological sludge. The outlet water quality is checked to be within the accepted limit as delineated in the norms of the Bureau of Indian standards. Through pipelines, the treated water is disposed into the environment river water, barren land, etc.
Sludge thickener: The inlet water consists of 60% water + 40% solids. Due to centrifugal action, the solids and liquids are separated. The sludge thickener reduces the water content in the effluent to 40% water + 60% solids. The effluent is then reprocessed and the sludge collected at the bottom.
Treatment of textile effluents using natural coagulants
Textile industry plays a major role by creating job opportunity for numerous employees worldwide. But it also creates an impact due to generation of large amount of pollutants, the waste generated can be solid or liquid wastes that pose a major challenge to the environment. The wastes that are generated from the textile industry usually originate from pre training stages. During the last decade, more interest has been given on the use of natural coagulants in treating industrial waste water. Natural coagulants are in general, used as point of technology in less developed communities, since they are relatively cost effective compared to chemical coagulants. Textile industry is one of the oldest industry which is highly complex and is characterized by high BOD, COD, suspended solids, settleable solids, sulphite, chloride and chromium. Coagulation-flocculation is one of the most important physiochemical treatment steps employed in industrial waste water. Moringa oleifera, Azadirachta indica were used as locally available natural coagulants. The tests were carried out using textile waste water with conventional jar test apparatus. Among them neem and moringa oleifera the better results of TDS reduction is found to be 44.18% with Moringa oleifera.
Treatment of textile effluents using photo catalytic method
Dye house effluent sourcing ---Estimation of effluent characteristics (COD, BOD, TDS, TSS) -------Photo catalytic treatment using TiO2, at different Ph under sunlight----Testing of the parameters after treatment---- COD (IS PART 58) TDS (IS PART 16) BOD—(IS PART 44) TSS (IS PART 17)—Providing the alternate solution to the industry. The below figure represents the fish tank model for sunlight reaction. In this model aeration along with shaking is given for the reaction. This will enhance the reaction at a faster rate giving better results. As sunlight have UV spectrum, visible spectrum and infrared spectrum the reaction will be faster in sunlight.
The following conclusions are drawn from the experimental study conducted on treatment of textile effluents using natural coagulants: The optimum dosage of Moringa oleifera and Neem leaf powder solution as coagulant is found to be 6 ml, 8 ml and 20 ml (Neem +MO). The optimum pH in coagulation process for Moringa oleifera and Neem leaf powder at optimum dosage is found to be 10.6 and 10.57 for 6 ml dosage and 9.43 and 10.23 for 8 ml, respectively. Increasing dosage of Moringa oleifera lead to increase in parameters reduction. Among the three natural coagulants used in the study, maximum TDS reduction is found to be 44.18% with Moringa oleifera. Among the three natural coagulants used in the study, maximum BOD reduction is found to be 38.23% with Moringa oleifera. And turbidity is removed - 100NTU. As it is observed that Moringa Oleifera is consistent in turbidity reduction of almost above 23.00% for all COD concentrations. Hence it is concluded that Morimga oleifera has the potential to be utilized for textile effluent treatment.
Among the two natural coagulants used in the study, Moringa Oleifera has the COD reduction of 38.00% . Hence it is concluded that as compare to other two coagulants Moringa oleifera is the effective coagulant in treating textile effluent.
The following conclusions are drawn from the experimental study conducted on treatment of textile effluents using photo catalytic method: The highest degradation was found for RGOT catalyst under sunlight in alkaline pH with 94.44% and the effluent was degraded 92.54% for TiO2 catalyst under sunlight in alkaline pH. In the presence of TiO2 catalyst, under optimized conditions, the COD of the treated sample is reduced from 3200 mg/L to 20 mg/L in, the BOD of the treated sample is reduced from 1080 mg/L to 24 mg/L, the TDS of the treated sample is reduced from 23622 mg/L to 6 × 10-8 mg/L and the TSS is found to be reduced from 328 mg/L to 0 mg/L. In the presence of RGOT catalyst, under optimized conditions, the COD of the treated sample is reduced from 3200 mg/L to 60 mg/L in, the BOD of the treated sample is reduced from 1080 mg/L to 21 mg/L, the TDS of the treated sample is reduced from 23622 mg/L to 4 × 10-8 mg/L and the TSS is found to be reduced from 328.
- Ecofriendly processing of sulphur and vat dyes from Indian Journal of Fibre & Textile Research Vol.26.March-June 2001, pp.101-107.
- Electrochemical treatment of effluents from textile industries, journal of scientific & industrial research, Rajeev Jain, Nidhi Sharma and Meenakshi Bhargava, Vol.63, May2004, pp.405-409.
- Recent developments in dyeing techniques, Rahul Guglani, 2006.
- Redox mediated electrochemical method for vat dyeing in ferric-oxalate-gluconate system: process optimization studies, R. Senthil Kumar, K. Firoz Babu, M. Noel, M. Anbu Kulandainathan, J Appl Electrochem (2009).
G Devanand & Dr.M.Parthiban*
*Department of Textile Technology, K.S.Rangasamy College of Technology, Trichengode
**Department of Fashion Technology, PSG College of Technology, Coimbatore