ECOLOGICAL SELECTION OF PHOSPHORUS-ACCUMULATING BACTERIA IN SEQUENCING BATCH REACTOR ACTIVATED SLUDGE PROCESSES FOR SIMULTANEOUS REMOVAL OF PHOSPHORUS, NITROGEN AND ORGANIC SUBSTANCES

Abstract

Laboratory-scale sequencing batch reactor (SBR) activated sludge processes were operated to clarify the behavior of microorganisms responsible for phosphorus removal during operation of the SBR and to demonstrate the related performance for simultaneous removal of nitrogen, phosphorus and BOD under modified operational schedule of the conventional SBR process. The best performance for phosphorus removal was noted in operations where anoxic/anaerobic reactions were introduced into the fill period. Remarkable release of phosphate from the solid into water phase (supernatant of mixed liquor) during the fill was followed by the luxury uptake of phosphate under aeration. On the contrary, little phosphorus was removed in conventional operations in which aeration continued throughout a cycle. Change from the operation with anoxic/anaerobic reaction during the fill to that with aerobic reaction throughout a cycle immediately decreased the activity of phosphorus removal. Operation with anaerobic reaction, however, was not sufficient condition to remove phosphorus and, in addition, ecological selection and/or enrichment of the phosphorus accumulating bacteria were also necessary to remove phosphorus under operation with anaerobic condition.