Wastewater Management Studies In Textile Processing

Abstract

The textile processing industry has the importance of its own, being one of the basic needs of society. Textile processing industries are water, chemical, and energy intensive industries concerned with the dyeing, printing and finishing of textiles using various dyes, dye auxiliaries, chemicals etc. These industries generate high quantity and highly polluting wastewaters having the non-exhausting auxiliary chemicals. Mixing of this wastewater with other textile processing wastewaters makes the wastewater treatment very difficult and costly, and compliance with the applicable effluent standards almost impossible. Further, this mixing reduces the recycle and reuse potential of the treated effluents. Segregation and handling of the dye bath dump separate from the other wastewaters has been considered as an appropriate solution to the problem in this study. The objective of this research was to suggest the strategies for the wastewater management and to develop the treatment technology for textile processing industries. This was achieved through an extensive literature review and reconnaissance visits to textile processing industries. The study was conducted to perform the critical analysis of water and wastewater management practices of the industrial unit, and understanding the merits and limitations of the management practices currently in practice. A few selected streams of water and wastewater (depending on the need for the characterization) were sampled and analysed. An integrated and multimedia approach, wherein due importance is given to the USEPA's hierarchy of waste management was followed for the conceptualization and development of the water and wastewater management model. The process modifications to conserve water, energy and chemicals and to minimize wastewater generation were outlined respectively with each type of the fabric, fiber and yarn processed in the respective processing industries. The environmental inputs/outputs (process water requirements, chemical consumption, water consumption, steam consumption, wastewater generation etc.) was listed accordingly in this research. In-plant measures and strategies have been identified to have the potential to conserve water and minimize wastewater generation. This study presents and compared the actual scheme and the modifying scheme of the textile (Cotton, polyester and acrylic: - fabric, fiber and yarn) processing steps and evaluates the reduction in the water, steam, chemicals consumption and wastewater generation. The reduction in process water and the steam requirement for Industry-I was estimated to 73.6 % and 23.1 % respectively. The reduction in wastewater generation was 71.6 %. The reduction in process water and the steam requirement for Industry-II was estimated to 31.1 % and 3.05 % respectively. The reduction in wastewater generation was 31.5 %. In the second part of study pre-treatment technologies was evaluated and developed for selected critical wastewater streams (sulphate rich wastewater, chloride rich wastewater and softener application wastewater). The coagulation and flocculation process was tried using factorial experimental design as per CCD and it was concluded that alum (500 mg/L) was the better option for achieving the color and turbidity removal efficiency of 89.6 % and 95.7 % respectively when pH was adjusted in between 5.5 to 6.0. In the electrolytic treatment of sulfate-rich textile dyebath wastewater using RSM, four electrode combinations viz. Fe–Fe, Fe (Anode)–Al (Cathode), Al–Al, and SS–SS was tried. Iron electrodes were found superior to the aluminium electrodes. Best results of 74% COD removal and 95% colour removal were observed with iron electrodes at 12 volts for 15 minutes duration. Power consumption was 168 KWh/m3. The chloride rich textile dyebath wastewater was treated efficiently with iron electrodes. At 12 V and 15 min. treatment time, the maximum removal efficiency of 98.8 % for color was observed with sludge generation rate of 22.7 g/L at the current density of 2598.98 A/m2 with power consumption of 196 KWh/m3. ANOVA model was significant with Fe-Fe electrodes and optimized process conditions are 1 V and 8.2 min. to achieve 96.6 % color removal efficiency with only 0.46 g/L of sludge generated and TOC removal efficiency of 69.5 %. The membrane processes (MF, UF and NF) was used to treat textile cotton dyebath wastewater rich in sulphate. The dyebath wastewater with high values of chemical oxygen demand (1573.5 mg/L) and total dissolved solids (~21 gpl) was first segregated from the dyeing processing as dyebath and treated separately using pressure driven membranes in the batch process. The chemical oxygen demand and color removal efficiencies were 97.6% and 98.9% respectively after Nano-filtration (NF) treatment. The 80% of the dissolved solutes were recovered in retentate feed of NF, which can be used in the reconstitution of dyebath. The effectiveness of the microfiltration and ultrafiltration membrane separation techniques in treating softener wastewater was also tried in this study. The Turbidity and Total suspended solids removal efficiencies were 77.8 % and 87.5 % in cotton softener application wastewater and 90.9 % and 80 % in polyester softener application wastewater respectively with MF and UF membrane processes. The outcome of this research can provide the comprehensive information regarding wastewater management and development of treatment technology in the textile processing industry.