Optimisation of ozone treatment for colour and COD removal of acid dye effluent using central. composite design experiment

Central composite design experiment is used to study the effect of ozone treatment for acid dye effluents and to optimise the variables such as salt concentration, pH and time, which influence the efficiency of colour and COD removal of dye effluents. Acid Red 88 dye is used for this study and the salt additive sodium sulphate is varied between 5 and 15 g/l, pH is between 3 and 11 and the treatment time is varied between 30 and 360 s. It is observed from the results that the treatment time plays a major role in decolouration and COD removal of the dye effluent. The increasing decolouration efficiency is obtained with increasing treatment time. At neutral pH, the efficiency of ozone is low in terms of decolouration when compared with that at acidic and alkaline pH. Lower salt concentration gives faster decolouration of the effluent while increasing the salt concentration interferes with the decolouration efficiency. Maximum COD removal of 64% is obtained at lower salt concentration in about 195 s at alkaline pH. (C) 2004 Elsevier Ltd. All rights reserved.