Performance of a high-rate/high-shear activated sludge bioreactor treating biodegradable wastewater

A high-rate activated sludge (HRAS) bioreactor with high shear venturi aeration was operated in the laboratory at various organic loading rates to evaluate chemical oxygen demand (COD) removal efficiency and sludge production. Organic loading rates two orders of magnitude higher than conventional activated sludge loading were investigated in the modified HRAS reactor for a period of 41 weeks. Filtered COD removal efficiency varied from 81 to 92% for organic loading rates of 3 to 85 kg COD m(-3) d(-1). Observed sludge yield was determined to be 0.10-0.25 g TSS produced g(-1) COD removed, under hydraulic and solids retention times (SRTs) approaching less than two hours and two days, respectively. Observed sludge yield actually declined as loading increased and SRT decreased. It was concluded that high-shear forces created in the reactor due to intense aeration at high volumetric organic loading rates increased substrate utilization rate, improved filtered COD removal efficiency, and kept sludge yields relatively low (despite the very low operating SRTs).