Treatment of Recalcitrant Caprolactam Wastewater Using Electrooxidation and Ozonation

Advanced oxidation processes (AOPs) for the degradation of recalcitrant wastewater are of interest due to field application potential. We attempted the treatment of caprolactam (CL) wastewater which is highly acidic (pH 3.1) with low biodegradability index, using AOPs viz. electrochemical oxidation (EO) and ozonation. EO experiments under recirculation batch mode (20mLmin(-1)) in a three-dimensional carbon bed reactor confirmed 18% chemical oxygen demand (COD) reduction. The first order rate constant for the EO of CL wastewater was estimated as 1.38 +/- 0.15 +/- 10(-2) min(-1). The apparent Faradic efficiency and specific energy consumption were found to be 9.4% and 2.75kWhkg(-1) COD, respectively. Similarly, 27% COD and 26% total organic carbon were removed during 4-h ozonation. Various organic compounds present in the raw and ozone treated effluent have been identified using GC-MS; while many degraded partially, CL persisted even in 10-h reacted samples. Both EO and ozonation methods are insufficient for the degradation of highly non-biodegradable complex wastewater.