Biological phosphorus removal at Stratford upon Avon, UK: the effect of influent wastewater characteristics on effluent phosphate

Abstract

Severn Trent as part of their wastewater development strategy have built a full scale biological nutrient removal plant at Stratford-upon-Avon, where Mainstream and Sidestream Phostrip® processes are studied. The plant, designed to treat 5000 m3/d, was commissioned in November 1993 and whilst the Phostrip® plant has consistently achieved the target level of 1 mg/l P, the UCT plant is able to achieve this standard only with the addition of fermenter liquor containing sufficient concentrations of Short Chain Fatty Acids (SCFA). Enforced decommissioning of the sludge fermenter provided an interesting period of study when both the anaerobic phosphorus release and aerobic phosphorus uptake deteriorated as the concentration of combined phosphate in the polyP biomass fell steadily to a level of less than 3% phosphorus. Effluent performance was restored following subsequent recommissioning of the sludge fermenter and the authors conclude that the Stratford sewage, despite having a BOD:P ratio greater than 20 and considered a strong sewage, still required the addition of SCFA for consistent phosphorus removal. The authors conclude that SCFA addition to mainstream Enhanced Biological Phosphorus Removal Plants (EBPR) is required to maintain the poly P sludge in satisfactory condition to both release and uptake phosphorus and meet the UWWTD standard of 1 mg/l P.