The US Environmental Protection Agency (EPA) adopted numeric nutrient criteria (NNC) for total nitrogen (TN) and total phosphorus (TP) in inland lakes and flowing waters for the State of Florida in November 2010. Fifteen months was given for cities, businesses, utilities, and other stakeholders to develop strategies for implementing and meeting these criteria. In addition, EPA is working to develop similar criteria for coastal and estuarine waters and canals by 2012, affecting nearly all wastewater utilities in the State of Florida. This leaves many utilities with unanswered questions, including questions about available treatment technologies that can reliably meet the low nitrogen and phosphorus concentrations mandated by the NNC.
This paper will present a summary of potential alternatives available to Florida utilities to help meet the new NNC including an assessment of their potential and current stage of development for full-scale use, selected case studies, potential capital and operating costs, and strategies for choosing and implementing an appropriate technology
The best performance for nutrient removal across the State has historically been accepted as Advanced Wastewater Treatment (AWT) limits. These limits are 5 mg/L carbonaceous five-day biochemical oxygen demand (cBOD5), 5 mg/L total suspended solids (TSS), 3 mg/L TN, and 1 mg/L TP. Typically, biological nutrient removal (BNR) facilities with tertiary filters are able to meet the AWT standards consistently and reliably. EPA’s adopted NNC limits are significantly lower than these levels, at 0.67 to 1.87 mg/L for TN and 0.06 to 0.49 mg/L for TP for flowing waters. Should the EPA NNC survive expected legal challenges, some wastewater utilities may need to implement technologies capable of meeting these new standards.
In other areas of the country, technologies are in use that can meet the NNC limits for TP. These include tertiary coagulation, clarification, and filtration; tertiary membrane filters; membrane bioreactors (MBRs); reactive filtration; and wetlands. Removal of residual TN may be even more difficult, however technologies exist that may be able to meet the new NNC. Technologies with the potential to meet very low TN criteria, potentially at lower cost than the traditional gold standard of reverse osmosis (MF/RO), include separate stage biological treatment, granular activated carbon (GAC), advanced oxidation processes with biological treatment and membrane filtration, and land based systems including soil-aquifer treatment and wetlands.
Stone, E. and Reardon, R. Technologies to Meet Numeric Nutrient Criteria. Florida Water Resources Journal, Vol. 63, No. 9, pp. 8-15, 2011.