TECHNOLOGY UPDATE Wastewater-to-fertilizer process under investigation in major cities Both New York City and Washington, D.C., are contemplating purchases of a promising new treatment technology for removing nitrogen from wastewater. The ammonia recovery process extracts nitrogen-rich ammonia from sewage, livestock, and industrial waste streams, transforming it into commercial-grade fertilizer. Treatment plants that discharge into sensitive waters such as estuaries are under increasing pressure to limit their effluent's nitrogen content, said Bob Bastian, senior environmental scientist for EPA's Office of Wastewater Management. This is a problem that many facilities across the country now face because nitrogen, like phosphorus, is a nutrient that can cause hypoxia in water bodies, explained Charles Noss, deputy director of research for the Water Environment Research Foundation. New York City's nitrogen discharge limits are being tightened in hopes of ameliorating the Long Island Sound's summertime bouts with hypoxia, said Luis Carrio, chief of process planning for the city's Bureau of Wastewater Pollution Control, where the new technology was pilot-tested last year. Water managers for the Florida Keys, Nevada, and the Chesapeake Bay (which receives wastewater from the District of Columbia as well as a number of smaller cities and large chicken farms) also are considering imposing nitrogen limits Bastian said. The sewage sludge piped into wastewater treatment plants typically contains about 7% nitrogen (on a dry weight basis), according to the Pacific Northwest National Laboratory. Anaerobic sewage digestion converts 2040% of the nitrogen into ammonia. In the past, this ammonia was usually shunted back into the wastewater treatment process, according to Alex Fassbender, executive vice president © 1999 American Chemical Society
of engineering and technology for ThermoEnergy Environmental Corp. of Richland, Wash., the company marketing the new technology. Many areas limit ammonia discharges into streams on account of its aquatic toxicology, prompting some wastewater treatment plants to use a biological nitrification process, Bastian said. Because this converts the ammonia into nitrates which are restricted in drinking water, however, nitrification can trigger problems downstream in some rivers if a complementary biological denitrification process is not used he added The new ammonia recovery process can be used by itself or in conjunction with nitrification and/or denitrification Fassbender said EPA's Technology Verification program was planning to release a statement by last month attesting that the new process is capable of removing and recovering ammonia with efficiencies ranging from 75 to 99+%, according to Brian Rustia, project manager for the Civil Engineering ResearchFoundation, which performed the verification in conjunction with EPA. The ammonia removal occurs in the ammonia adsorption columns through which the digested liquid passes after being separated from the sludge This step alone plant's capacity by 20-50% by reducing the load on its nitrification and denitrification treatment sections Fassbender said The remaining steps in the ammonia recovery process ultimately produce ammonium sulfate fertilizer. To remove the ammonia from the adsorption columns, the process uses an ion-exchange method with a regeneration solution containing sulfuric acid and zinc sulfate that can be used repeatedly until its ammonia concentration reaches about 15,000 parts per million (ppm). After that point, the solution is heated
and cooled to form zinc ammonium sulfate hexahydrate crystals. When these double-salt crystals are roasted in a furnace, they produce gases and zinc sulfate. The zinc sulfate is collected for reuse in the regeneration process, and the water, ammonia, and sulfur trioxide gases are mixed with sulfuric acid to form ammonium sulfate, which undergoes a few more steps to produce the fertilizer. Although the concept of transforming treated sewage sludge into fertilizer is not new, the fertilizer produced by the new process stands out because it is dry, sterile, and odorless, and has a much more uniform chemical composition, Fassbender said. Although the ammonium sulfate can be sold, Carrio deemed the revenue it would generate for his plant to be minimal. The new ammonia recovery process costs $0.03-$0.06 per gallon of treated liquid, according to ThermoEnergy. Carrio calls this an "attractive" price because it is on a par with other newer technologies for enhancing the removal of nitrogen and ammonia from wastewater, including air and steam stripping, that he also is investigating. Although the pilot proved the new technology's effectiveness, Carrio said he remains concerned by its relatively short track record. ThermoEnergy is trying to remedy this concern by offering to put up the bond that cities require to protect taxpayers in the technology fails and their investment sours The technology also can be used to treat wastewater from large confined animal feedlots operated by the hog, chicken, and dairy industries, Fassbender said, noting that ammonia levels in chicken manure can reach 10,000 ppm. ThermoEnergy is discussing installing a system at a "major animal feedlot operator's facility," he said. The company also sees dozens of other applications for the new treatment, including petroleum refining, ammonia manufacture and aquaculture KELLYN S. BETTS
NOVEMBER 1, 1999 / ENVIRONMENTAL SCIENCE & TECHNOLOGY / NEWS » 4 4 3 A
