Unlocking the Mystery of Biological Phosphorus Removal Upsets and Inhibited Nitrification at a 30 mgd BNR Facility

The objective of this paper is to summarize the methodology used to investigate nitrification and biological phosphorus removal (BPR) challenges at a 30 mgd facility with a 3-stage Virginia Initiative Plant (VIP®) process. With regard to nitrification challenges, an analysis of historical data and process model calibration verified an inhibited nitrifier growth rate. On-site testing demonstrated that the nitrite oxidizing bacteria may be more susceptible than ammonia oxidizing bacteria to the inhibitor and/or low temperatures. As a result, further study of the inhibitory issues and nitrifier growth is underway. With regard to phosphorus removal, it was determined that most of the problems stem from a high phosphorus load to the biological nutrient removal system, which frequently exceeds the assimilative capacity of the phosphorus accumulating organisms. Low pH values and unfavorable (low) BOD to TP ratios are also potential contributors to variable BPR performance.