WEF/WERF Cooperative Study of BNR Plants Approaching the Limit of Technology: I. What Can We Learn About the Technologies?

The Water Environment Federation (WEF) and the Water Environment Research Foundation (WERF) cooperated in a comprehensive study of nutrient removal plants designed and operated to meet the “Limit of Technology” (LOT) for nutrient removal. LOT is loosely defined as plants meeting 3 mg/L TN and 0.1 mg/L TP. This effort focuses on maximizing what can be learned from existing full scale plants. In the first year of the project, eleven exemplary plants were investigated. In general, there were technologies that can reliably meet these requirements, but the key issue is the “averaging” period. Only some of the technologies can meet the LOT limits on a maximum month basis without significant violations during a permit cycle; alternatively, annual rolling average permits embody much less risk of violations. In some environments, seasonal and annual limits can be equally protective to the environment as monthly permits, but periods with longer averaging permits will often serve both the regulated and regulatory communities better, reducing frequency of reporting violations for events that may have no environmental consequence.