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

Abstract

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 has been 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 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. When seasonal and annual limits are equally protective of the environment as monthly limits, both the regulated and regulatory communities would be better served by reducing the frequency of reporting violations for events that have no environmental consequence.

Introduction of New Process Technology into the Wastewater Treatment Sector

“…Because of pending changes to require low effluent requirements across broad regions of the US, our nation will likely go from hundreds to thousands of nutrient removal plants in a relatively short span of time. Yet it has been shown that there is significant risk of violations for existing technologies for the range of effluent limits being proposed (Parker et al, 2009). Nitrogen removal technologies in particular need reevaluation, as many were developed in the seventies and eighties (e.g.…”

“…Yet processes that use external carbon either for the entire job of nitrogen removal or to supplement wastewater carbon appear to do marginally better when seeking very low nitrogen limits (e.g. see Parker et al, 2009). However, not even the best performing processes can meet some of the proposed limits, leading design professionals to indicate that they will need to be followed by highly costly tertiary processes, such as microfiltration and reverse osmosis.…”

“…This allows potential technology adopters access to information that would otherwise not be available and to independent judgments about the technology, separate from those available from process advocates or marketing materials. An example of third party evaluations is the WEF/WERF cooperative study of nutrient removal plants which for the first time has allowed an objective assessment and technology ranking for alternative nutrient removal methods, using statistical methods for performance assessment (Parker et al, 2009).…”