Effects of hydraulic loading and room temperature on performance of anaerobic/anoxic/aerobic system for ammonia-ridden and phenol-rich coking effluents Original Research Article

A lab-scale anaerobic/anoxic/aerobic (A1/A2/O) system with three cycles was developed to purify high-strength coking effluent, 8, 000–15, 000 mg chemical oxygen demand (COD)/L, characterized by high levels of toxic organics and ammonia, 1200–1700 mg phenol/L and 700–1800 mg ammoniacal-nitroge/L. Besides the partial return of settled sludge to the anaerobic column, partial final effluent was also circulated to anaerobic unit to dilute and detoxify the feed as well as to the anoxic unit. During the pseudo-steady-state operation, more than 90% COD and 100% phenol removals were stably achieved while approximately 60% ammoniacal-nitrogen was removed. The performance of different stages in the A1/A2/O system in terms of Hydraulic Retention Time (θH), from 18 to 30 d, and room temperature, from 21°C to 30°C, was investigated. The modification of θH did not have a substantial effect on the overall COD and phenol removal for the A1/A2/O system, but considerably influenced the distribution of COD removal between A1 stage and A2/O stages, and ammonium removal for A2/O stages and A1/A2/O system. Elevated room temperature increased overall ammonium removal and ammonium removal at A2/O stages, whereas the effect of temperature on ammonium removal at A1 stage was relatively weak.