Indigo dyeing wastewater reclamation by membrane-based filtration and coagulation processes

In the present study. the possibility to reuse the indigo dyeing rinsing wastewater originating from a denim textile mill was investigated. Coagulation and filtration processes were selected as the pretreatment alternatives and applied to dyeing wastewater samples. Both physicochemical pretreatment alternatives and nanofiltration technique were optimized to produce an effluent satisfying the reuse criteria for the textile industry. The results showed that coagulation is not all effective and efficient pretreatment due to high dose of coagulant requirement. Microfiltration (MF) through 0.45 mu m pore-sized membrane provided 64%) removal in color and 29%. removal in COD leading to a color value of 2493 Pt-Co and COD of 892 mg/L in the permeate. Furthermore, ultrafiltration (UF) applied after MF revealed additional 62% color and 4% COD removals leading to a color value of 960 Pt-Co and COD of '856 mg/L. Hence, the sequential application of MF and UF and only MF as pretreatment alternatives were found to be promising prior to the application of nanofiltration (NF). NF experiments conducted using pretreated wastewater via only MF provided 99% color and 97% COD removals leading to a color of 15 Pt-Co and a COD of 20 mg/L and hence sequential application of MF and NF was found to be the optimum treatment scheme for the reuse of the dyeing wastewater of the Studied textile mill and reuse criteria was satisfied

Current status of filtration theory

Sludge dewatering is a difficult process in water and wastewater treatment, as commonly achieved through filtration practice. The purpose of sludge dewatering is to remove as much of the liquid portion of the sludge so that its transport and disposal becomes possible and feasible. The extent of the performance of the filtration operation is highly influenced by the characteristics of the sludge; such as its solids concentration, bound water content, organic content, cellulose content, pH, electrical charge of particles and other sludge specific parameters. To assess the filterability and dewaterability of sludges, parameters like specific cake resistance, capillary suction time and Buchner funnel filtration time are used. The most commonly used parameter is the average specific cake resistance evaluated by the parabolic filtration equation which was developed by Ruth in 1933 employing a heuristic analogy with Ohm's Law. However, it is noted that the average specific cake resistance is not a correct parameter to characterize the filtration characteristics of many types of sludges. Because operational parameters such as, filtration area, pore size of the filter medium, applied vacuum pressure and mode of filtration operation are reported to affect the average specific cake resistance. Besides the conventional filtration theory, in literature three major theories are proposed to define filtration. However, all these three approaches are not practically applicable to characterize the filterability and dewaterability of sludges. This study is a brief review of the current status of the filtration theory

Treatment of a denim producing textile industry wastewater using pilot-scale membrane bioreactor

The objective of this study was to investigate the performance of a pilot-scale membrane bioreactor (MBR) system for the treatment of a highly concentrated mixed wastewater from wet processes (dyeing, finishing, and sizing) of a denim producing textile industry. The MBR system, containing a Submerged hollow fiber membrane module in the aeration tank, was operated aerobically for about 3 months on-site at a continuous flow mode. The system was operated at two different operation stages: (1) 110 Sludge wastage with a typical permeate flux of 20 L/m(2)h and (2) a solids retention time of 25 days with the same flux. During the whole operation period, despite the high dissolved solids content in the influent, very high treatment efficiencies were achieved. The performance of the MBR system was not adversely affected by the variations in the influent characteristics, food/microorganism ratio, organic loading rate, and specific substrate utilization rate. The average values of some effluent quality parameters found In the entire operation period were color, 53 Pt Cc; turbidity, 0.31 NTU; TSS, 0.6 mg/L; BOD5, 15 mg/L; COD, 37 mg/L; NH3-N 1.0 mg/L; NO3-N, 9.6 and TN, 10.5 mg/L. Reduction in permeate flux due to membrane fouling was observed only once during all operation and such fouling was removed by applying chemical backwashing and chemical cleaning procedures. The results indicated that complex and highly polluted denim textile wastewaters could be treated very effectively by MBR systems. Color values from as high as 8100 Pt Co levels were significantly reduced to about 50 Pt Co levels, indicating that MBR effluent could be reused in the production processes