Phosphate removal mechanism in an airlift-loop reactor under limited filamentous bulking conditions

Abstract

This study presents detailed evaluations of nutrients removal efficiencies, micro-organism community structure, and phosphate removal mechanism in a specific airlift-loop reactor (ALR) under limited filamentous bulking (LFB) state. The removal efficiencies of chemical oxygen demand (COD), total phosphate (TP), total nitrogen (TN), and ammonium () were approximately 90, 93, 86, and 93%, respectively. The result of polymerase chain reaction–denaturing gradient gel electrophoresis analysis suggested that Rhodocyclaceae and Thiothrix sp. were the main polyphosphate-accumulating micro-organisms (PAOs) and filaments, respectively, under LFB state. Batch tests indicated that PAOs included 38% denitrifying PAOs (DPAOs). Under anaerobic condition, when COD was below 24.1 mg O2/L, PAOs would stop phosphate (P) release; when COD was below 21.3 mg O2/L in anoxic condition or below 60.8 mg O2/L in aerobic condition, PAOs began to recover the storage pool of polyphosphate. In the ALR, P-uptake occurred in the aeration zone while P-release happened at the bottom of the riser. Hence, high and stable P removal efficiency was observed.