Effects of MCRT on Enhanced Biological Phosphorus Removal

Abstract

This paper presents the results of full scale experimental investigations into the fate of phosphorus in the Hyperion Treatment Plant, City of Los Angeles, CA, USA. For almost three decades, the activated sludge process, operated at standard rate has exhibited enhanced biological phosphate removal accompanied by initial anaerobic phosphate release and subsequent aerobic phosphate uptake. In 1989 when high rate treatment was initiated the enhanced phosphate removal and accompanying initial anaerobic phosphate release decreased and finally was eliminated. Phosphorus in the secondary effluent increased from 0.4 to 3.1 mg/l as the MCRT decreased from 3.1 to 1.5 days. Of added interest was the accompanying decrease in struvite (MgNH4PO4.6H2O(s)) build-up in the sludge dewatering processes downstream of the anaerobic digesters.