Meeting the phosphorus consent with biological nutrient removal under UK winter conditions

Abstract

AbstractIt is estimated that up to 342 wastewater treatment plants (Wwtps) in England and Wales will require a phosphorus (P) consent by 2010. Although biological P removal is considered to be the most sustainable option for P removal, it has always been problematic for plants that remove both nitrogen and P due to the inadequate concentration of organic material during wet periods. Two biological nutrient removal (BNR) configurations, the Johannesburg (JHB) process and a combined JHB and five‐stage Bardenpho process, were evaluated over a period of 2 years to assess the impact of sewage strength on bio‐P removal. The JHB achieved an average effluent total phosphorus (TP) of 2.4 mg/L and the combined JHB and five‐stage process averaged 1.4 mg/L effluent TP. The major problems affecting the performance of both configurations were: dissolved oxygen (DO) in the recycled mixed liquor, nitrate in the return activated sludge (RAS) and low influent biological oxygen demand (BOD) concentrations. Acetate dosing proved successful as a source of volatile fatty acids (VFAs) in the anaerobic zone during periods of low‐strength sewage. An acetate dosing strategy based on the influent flow rate to the plant was found to be a simple and effective technique that ensured that a consent of <1 mg TP/L could be met.