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ABSTRACT:In this paper, natural (chitosan and starch) and novel pre-hydrolysed coagulants (PACl, PAFC, PFS and PFC) were performed with coagulant aid for colour removal from a biologically treated textile wastewater including multiple dyes (indigo and reactive). According to the experimental results, optimum coagulant dosages which provide the best colour removal for PACl, PAFCl, PFS (%10) and PFCl (%10), were determined as 80 mg/L, 10 mg/L, 3 mg/L and 40 mg/L, respectively, at pH 4 and pH 6,98 (natural pH of studied wastewater, pHnww). Maximum colour removal was determined as 97% for PAFCl, minimum removal was 23% for PFCl at pH 4, while it was calculated as 75% and 52% at pHnww. COD removal was observed as 45% at pH 4 and 55% at pHnww for maximum colour removal. Sludge production rate was measured as 71 kg/d while this rate was found as 60 kg/d at pHnww. On the other hand colour removal efficiencies were determined in the range of 55-88% at pHnww and pH 3 for chitosan while it was calculated as 52% for starch at pHnww and pH 9. According to the results, PAFCl and chitosan were found as the best coagulants for colour removal of investigated textile wastewater. According to the economic analysis results, the best colour effiency were found as 97% with PAFCl and the second best colour removal were found as 88% with Chitosan. Due to lower sludge production than PAFCl and lower chemical costs; Chitosan can be considered as a reasonable alternative for this wastewater.

a b s t r ac tThe aim of this study was to investigate the reuse possibility with nanofiltration (NF) membranes of biologically treated textile wastewater (COD: 350 mg/L, color: 108.9 m -1 and conductivity: 2,843 µS/cm) of a local textile factory (denim washing and dyeing) in Tekirdag, Turkey. For this aim, the flux and permeate quality was evaluated within the context of COD, color and conductivity with different NF membranes (NP010 and NP030) under various pressures (4, 6, 8 and 10 bar). On the other hand mass transfer coefficients were calculated with Nernst-Planck equation based on experimental results. When compared with literature, NF permeate water was found to be alternative to freshwater in textile wet processing. According to the Nernst-Planck equation, the B s (mass transfer coefficient) and R s (removal coefficient) values are obtained. R s and B s values were determined as follows: 0.982 and 0.994 for COD, 0.995 and 0.959 for color, 0.295 and 0.3403 for conductivity and 6.79 and 3.38 for COD, 4.90 and 0.54 for color, 27.39 and 15.87 for conductivity, respectively. According to B s and R s , NP030 membrane was determined as the most convenient membrane for aerobically pre-treated wastewater.