The biological removal of phosphorus in a sequencing batch reactor

Abstract

Biological phosphorus removal was first proposed in 1955 by Greenburgh et al.1 The authors suggested that activated sludge could take up phosphorus at a concentration beyond that required for normal growth. The progress made since that time is summarized in the publications from two conferences in 1982; the International Association on Water Pollution Research (IAWPR) Post Conference on Phosphorus Removal in Biological Treatment Processes, Pretoria, South Africa,2 and a U. S. Environmental Protection Agency (EPA) Workshop on Biological Phosphorus Removal in Municipal Wastewater Treatment, Annapolis, Md.3 The report on the Annapolis workshop discusses the probable economic advantages of in corporating biological rather than chemical phosphorus removal at treatment facilities. A major conclusion of the report was that biological phosphorus removal is a viable alternative to chemical treatment and should be considered in either retrofit or new plant designs. Proprietary biological phosphorus removal systems are cur rently marketed by several manufacturers. The A/O process is patented and marketed by Air Products and Chemicals, Inc. The system has a short hydraulic retention time. A sludge with approximately 6% phosphorus is wasted from the system.4,5 The Bardenpho system, licensed to the EIMCO Process Equip ment Company in the U. S., has a long hydraulic retention time. Sludge production results in a phosphorus-rich sludge containing 4 to 6% phosphorus.6 The PhoStrip system is marketed by Biospherics Incorporated. Phosphorus removal occurs by lime precipitation of phosphorus that is elutriated from a sludge side stream.7 The University of Cape Town (UCT) process is used with wastewaters containing a low ratio of total chemical oxygen demand to Kjeldahl nitrogen (COD/ TKN)8 with an additional recycle stream for eliminating nitrate from the anaerobic zone. Other systems have been brought to the attention of the authors including a periodic system marketed in Denmark9 but the four mentioned above constitute the major configurations either in operation or being discussed at this time.