1. National Academy of Science, Nitrates: An Environmental Assessment, Panel on Nitrates of the Coordinating Committee for Scientific and Technical Assessment of Environmental Pollutants, Washington, DC (1978).
2. P. Norgaard, K. Helmo, and E. Sorensen, Renseproces til kvcestoffjernelse styret af NADH, Vand og Jord., 3, 125–129 (1996).
3. C. W. Randall, J. L. Barnard, and H. D. Stensel (eds.), Principals of Biological Nutrient Removal, Design and Retrofit of Wastewater Treatment Plants for Biological Nutrient Removal, pp. 25–84, Technical Publishing Company. Inc., Lancaster, PA (1992).
4. US Environmental Protection Agency, Process Design Manual for Nitrogen Control, Office of Technology Transfer, Washington, DC (1975).
5. M. Wagner, G. Rath, H. P. Koops, J. Flood, and R. Amann, In situ analysis of nitrifying bacteria in sewage treatment plants, Water Science and Technology, 34, 237–244 (1996).