Biological phosphorus removal at an experimental full-scale plant in France

Abstract

In France, all phosphorus removal treatment has been based on precipitation by means of chemical reagents. With a view to reducing costs, a series of laboratory experiments was initiated and subsequently followed up by full-scale studies in early 1984 at the Saint-Mars-la-Jaille treatment plant. This is the first biological P-removal plant to be put on line in France.The plant operates at low loading levels with extended aeration. Nitrification–denitrification is achieved in controlled aerobic and nonaerobic zones through a multi-mini-step process in a plug–flow reactor. Complete nitrate removal results in a release of phosphorus during the anaerobic phase and, hence in a high level of phosphorus accumulation in the aerobic sludge.Phosphorus removal was optimized by replacing the thickener with a new flotation thickener to minimize P-release in the anaerobic sludge blanket. The phosphorus removal levels obtained varied from 35% at the outset of the study to 89% upon stabilization. This paper outlines the basic technical alterations made to ensure efficient phosphorus removal with this type of sewage plant as well as the analytical procedures used, and identifies the polyphosphates accumulated in activated sludge, on the basis of 31-phosphorus nuclear magnetic resonance (31P nmr).Results concerning phosphorus removal at low temperatures are also provided. Key words: activated sludge, wastewater treatment, biological phosphate removal, anaerobic conditions, restricted oxygen, nuclear magnetic resonance, flotation, temperature.