Excessive nitrogen levels caused by inadequate wastewater treatment are harming water resources all over the United States. Hypoxia is a well-documented problem in the Gulf of Mexico and Long Island Sound, as are the nitrogen-related declines of shellfish and aquatic plant life in the Chesapeake Bay, Florida coastal waters, southern New England, and Cape Cod. Additionally, water supply aquifers which exceed the public health standard of 10 ppm of nitrate-N are becoming more common and causing public health officials to force remedial actions. As a result, many states require nitrogen removal in environmentally sensitive watersheds, for water supply and environmental protection. The limits of nitrogen removal technology for centralized wastewater treatment is 3 ppm TN effluent concentrations. Decentralized wastewater systems need to address nitrogen removal to avoid the potentially expensive and disruptive sewering requirements. Carbon feed systems needed for good nitrogen removal have historically been operator intensive and too complex for small flow systems (say less than 10,000 gpd) and especially for the individual septic systems, which serve approximately 40 % of the US population. The passive Nitrex~TM Filter system has been developed and tested in a number of independent EPA and State sponsored programs and demonstrates the technology is capable of producing an effluent with TN values of 3 –4 ppm when wastewater temperatures are above 40 and 48 ℉. Technology modifications can be made for lower temperatures. The results of the LaPine, Oregon and Polson, MT evaluation projects are presented along with a discussion of system performance and cost competitiveness.
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