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

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-nitrogen/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 (yH), from 18 to 30 d, and room temperature, from 218C to 308C, was investigated. The modification of yH 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.

Under the pseudo-steady-state experimental conditions, the treatment performance of the A1/A2/O system was almost unaffected by the variation of the yH, room temperature and influent pollutant levels since more than 90% COD and approximately 100% phenol removals were steadily achieved. However, a longer yH level would lead to the redistribution of overall COD removal at different stages in the A1/A2/O system, and the decrease in overall ammoniacalnitrogen removal, ammoniacal-nitrogen at A1 and A2/O stages by 8, 3, and 10%, respectively. In the A1/A2/O system, biomass assimilation played a significant role in ammoniacal-nitrogen removal. The increase in room temperature led to A1 A2/O NH3–N removal (%) n=3 n=3 n=4 A1/A2/O n=3 n=3 n=3 n=5 Temperature (°C) Fig. 3. Effect of room temperature on ammoniacal-nitrogen removal at different stages.