This Water Environment Research Foundation study considered the relationship between varying nutrient-removal levels at wastewater treatment plants, greenhouse gas emissions, receiving water quality (measured by potential algal production), and costs. The effluent nutrient concentrations required by some U.S. permits are very low, approaching the technology-best-achievable performance. This study evaluated five different treatment levels at a nominal 40 ML/d (10 mgd) flow. Greenhouse gas emissions and costs increase gradually up to the technologies' best-achievable performance, after which they increase exponentially. The gradual increase is attributed to additional biological treatment facilities, increased energy and chemical use, and additional tertiary nitrogen and phosphorus removal processes. Within the limited focus of this study, the evaluation shows that a point of diminishing return is reached as nutrient-removal objectives approach the technology-best-achievable performance, where greenhouse gas emissions and cost of treatment increases rapidly while the potential for algal growth reduce marginally.

No abstract

The WERF Nutrient Challenge has developed a series of projects to provide information regarding evolving numeric nutrient criteria, how reliable existing technologies perform to meet treatment objectives, the sustainability impacts of nutrient removal at meeting various treatment levels, and other factors. This paper provides a national perspective on the approaches taken by states and other agencies to set in-stream nutrient criteria and the approach to set discharge limits for treatment plants. The approaches range from implementing EPA's ecoregion criteria to TMDL based load allocations. In some cases an adaptive management approach is used. While these approaches vary nation wide, their implications is often to move to very low nutrient concentrations.A study of 22 full scale wastewater treatment plants forms the basis for assessing the reliability and variability of nutrient removal plants achieving stringent limits. The results using technology performance statistics show that the averaging period for meeting discharge limits plays a key role in the ability of a plant to meet permit. The performance statistics also indicate the ideal performance that can be expected. Combining this information with nutrient speciation studies, the best achievable performance for nutrient removal can be identified for a specific technology.Additional facilities and resources are needed to meet increasingly stringent nutrient discharge requirements. The sustainability impacts of the additional treatment is presented in terms of the greenhouse gas (GHG) emissions from operation of the facilities, as required for discharge limits ranging from secondary treatment to limits below conventional treatment capability (requiring reverse osmosis). The evaluation of benefits associated with reduced algal growth potential and increasing GHG emissions, shows that the cost benefit ratio change significantly when the nutrient limits are reduced below < 3 mg N /L total nitrogen and < 0.1 mg P/L total phosphorus. Alternative nutrient management and control strategies could be considered for these lower limits.

No abstract

No abstract