A Parametric Model for Biological Excess Phosphorus Removal

Abstract

Biological excess phosphorus removal in nitrification-denitrification single sludge activated sludge processes is shown to be stimulated by having a concentration of rapidly biodegradable COD (Sbsa) ≧25 mg/ℓ in the anaerobic reactor; the magnitude of the P removal is determined by a P removal propensity factor (Pf) defined by the product of (Sbsa−25) and the fractional mass of sludge in the anaerobic reactor. Sbsa is rapidly depleted by nitrate entering the anaerobic reactor; in the Phoredox process treating municipal waste flows if the TKN/COD ratio of the influent is greater than about 0,08 mgN/mgCOD the process, if designed to ensure efficient nitrification, is unlikely to remove all the nitrate and nitrate is recycled to the anaerobic reactor whereupon P removal declines. A new process is proposed that protects the anaerobic reactor from the nitrate in the effluent; tests indicate that this process can give excess P removal for TKN/COD ratios up to 0,14 mgN/mgCOD.