Color removal from cotton textile industry wastewater in an activated sludge system with various additives

The low biodegradability of many dyes and textile chemicals indicates that biological treatment is not always successful in the treatment of cotton textile wastewater, in terms of color removal. In this study, a specific organic flocculant (Marwichem DEC), powdered activated carbon (PAC), bentonite, activated clay and commercial synthetic inorganic clay (Macrosorb) were directly added into the activated sludge laboratory pilot plant model. Before dosage, the optimum sludge retention time and hydraulic retention time were determined as 30 days and 1.6 days, respectively. The Monod kinetic constants were determined as Y = 0.76 kg MLSS/kg COD, K-d = 0.026 1/day, K-s = 113.3 mg/L, k = 0.42 1/day and mu(max) = 0.32 kg MLSS/kg COD day. Under these conditions the average COD removal was 94% and color removal was 36%. The addition of these materials did not change COD removal significantly. The most effective materials were found to be DEC and PAC for color removal. While the color removal efficiency for 120 mg/L DEC addition was 78%, it was 65% for 100 mg/L, 77% for 200 mg/L and 86% for 400 mg/L PAC addition. The advantage of DEC compared to PAC was the lower sludge production. Statistical analyses using multiple linear regression indicate that there is no relationship between the effluent color with the influent color and total suspended solids (TSS) for DEC and PAC addition. On the other hand, when only bentonite, activated clay and Macrosorb were added, the effluent color was primarily dependent on the influent color and the TSS concentration had little effect. When the data is examined by using Kruskal-Wallis H and Mann-Whitney U tests and it was found that there was a significant difference between the color data groups. (C) 2002 Elsevier Science Ltd. All rights reserved.