The effects of a phosphate detergent ban on a biological nutrient removal plant and anaerobic digester

Abstract

This study investigated the effects of the detergent phosphorus ban implemented on January 1, 1988 in Virginia, on the treatment streams of the York River Wastewater Treatment Plant, a biological nutrient removal (BNR) system. Evaluation of the available historical data indicated that the influent phosphorus load entering the plant in the post-ban period had decreased 27% compared to the pre-ban period. The influent phosphorus concentration had decreased 29% from the pre- to the post-ban period. No definitive conclusion could be reached concerning the effects of the influent phosphorus decrease on the treatment efficiency due to operational changes which occurred at the time of the ban implementation. The combination of operational changes and the phosphorus ban resulted in 54% and 59% decreases in the effluent phosphorus load and concentration, respectively.

Measurements and modelling of the anaerobic digester contents indicated that several minor changes had occurred in the digester which may be attributable to the phosphorus ban, but the equilibria of the digester regarding phosphorus compounds had not been dramatically altered. This was primarily due to improved operation of the clarifiers and sludge thickeners, which delivered Similar phosphorus loads to the digester in the pre- and post-ban periods.