Comparative phosphorus removals using modified activated sludge processes

Abstract

The operation of three continuous flow units as modified activated sludge models using mean cell residence time as a principal operational parameter has led to the following conclusions:

1. Lower mean cell residence times result in higher phosphorus removal efficiencies in biological reactors. 2. Higher mean solids residence times result in higher phosphorus removal efficiencies in strictly chemical reactors. 3. Calcium-phosphate precipitation can occur in continuous flow reactors in a normal activated sludge pH range (7.5-8.5) given sufficient Ca++ concentrations. 4. Calcium-phosphate precipitation can occur in the activated sludge process without hindering COO removal efficiency. 5. The phosphorus sludge content only exceeded the one to two percent range in the biochemical and chemical units, where phosphorus precipitation was the predominate phosphorus removal mechanism. 6. The anaerobiosis and acid stripping procedure, as used in this investigation, is not effective in enhancing either a biological or chemical unit's ability to remove phosphorus.