Reactive textile dye colour removal in a sequencing batch reactor

dTwo sequencing batch reactors (SBRs) with sequenced anaerobic/aerobic phas es were used to study biological colour removal from a simulated cotton tex tile effluent containing an azo reactive dye. One of the reactors was daily fed with Remazol Brilliant Violet 5R dye and the other was used as control . When operating with a sludge retention time (SRT) of 15 days the total CO D removal was around 80%, with 30% being removed anaerobically. After 40-50 days of acclimatization the colour removal efficiency reached a maximum, s table value of 90% from a feed dye concentration of 90 mg/l, almost all bei ng removed during the anaerobic phase. This colour removal was attributed t o microbial degradation rather than adsorption and colour removal capacity was not lost even after a seven-day absence of dye in the fed substrate. Th e dye-fed reactor experienced a reduction in the ORP values attained during the non-aerated phase, after acclimatization, an effect not observed in th e dye-free control. Under denitrifying conditions it was observed that the decolouration levels achieved in the anaerobic phase decreased from 90% to 70% after only two cycles with a feed containing 45-60 mg NO3/l. Reduction of the SRT value from 15 to 10 days reduced the biomass concentration from 2.0 to 1.2 g VSS/l and lowered colour removal levels from 90% to 30-50%. Wh en the SRT value was increased back to 15 days the colour removal capacity of the system was completely recovered, suggesting that with a SRT of 10 da ys the adequate microbial population could not be installed in the reactors .