Denitrification: Processes, regulation and ecological significance

In order to fulfill the increasingly stringent discharge standards, new technologies and operational strategies have been elaborated for the removal of nitrogen from wastewater. Denitrification is considered as the second stage of conventional nitrogen removal from wastewater. The detection of new organisms is making the nitrogen cycle increasingly complicated, to the point that traditional descriptions of nitrification (ammonia is oxidized to nitrate via nitrite) as the first stage, denitrification (conversion of nitrate and nitrite to nitrogen gas) as the second stage, and nitrogen fixation are rather simplistic and insufficient for explanation of nitrogen pathways in real life. Nitrate or nitrite may be denitrified, reduced to the form of ammonia (either assimilatory or dissimilatory) or converted to organic nitrogen along with increase the nitrous oxide (N2O) and nitrogen gas (N2). True understanding of denitrification requires an extensive knowledge of biological nitrogen cycle to design the most efficient denitrification process. The development of biological nitrogen removal processes in different countries is based on the regulations of their municipalities. The impact of regulations on biological nitrogen removal processes has also been studied. This chapter reviews the various types of denitrification processes, and discusses the ecological significance and the regulation limitations.