TREATMENT OF EXHAUSTED REACTIVE DYEBATH EFFLUENT USING ANAEROBIC-DIGESTION - LABORATORY AND FULL-SCALE TRIALS

Reactive dyes are difficult to remove from textile waste water due to their solubility and they pass through conventional aerobic biological sewage treatment systems and enter the receiving water body. Investig ations into the use of anaerobic digestion to decolourise reactive azo dyes have been successful on a laboratory scale and the investigation was extended to full-scale trials. Exhausted reactive dyebath effluen t (3 kl/d) was discharged into a primary digester (1.34 Ml) on weekday s for a 151-d period. On average, 48 kl/d of sludge was fed to the exp erimental and control digesters. The overflow was monitored for colour , sodium and sulphide concentrations. A laboratory digester was also s et up to simulate the full-scale conditions but was operated at twice the exhausted dyebath loading recipe. No visual difference in colour w as noted between the overflow of the primary or laboratory digester an d the control digester, but elevated levels of sodium and sulphide wer e obtained due to the high concentration of sodium sulphate used in th e reactive dyeing process. The laboratory digester became unstable at sulphide concentrations of 400 mg/l. However, the sulphide concentrati ons in the primary digester never increased such that it threatened di gester stability.