Partial nitrification—operational parameters and microorganisms involved

Nitrite is a common intermediate in at least three different oxidative or reductive biochemical pathways that occur in nature (nitrification, denitrification and dissimilatory or assimilatory nitrate reduction). Nitrite accumulation or partial nitrification has been reported in literature for decades. In engineered systems, partial nitrification is of interest as it offers cost savings in aeration as well as in the form of lesser need for addition of organic carbon as compared to the conventional denitrification. A broad range of operating parameters and factors has been reviewed in this paper which are essential for achieving partial nitrification. Of these, pH, dissolved oxygen (DO), temperature, free ammonia (FA) and nitrous acid concentrations, inhibitory compounds are important factors in achieving partial nitrification.Two groups of bacteria, namely ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) are involved in nitrification. Chemolitho-autotrophic AOB are responsible for the rate-limiting step of nitrification in a wide variety of environments, making them important in the global cycling of nitrogen. Characterization and identification of the bacterial populations in an engineered system which have been considered to be a “black box”, has been made possible by using non-cultivation based techniques such as fluorescent in situ hybridization technique (FISH), polymerase chain reaction (PCR), denaturing gradient gel electrophoresis (DGGE), Sequencing and other techniques involving quantitative chemical analyses of specific biomarkers including quinones. Accordingly, this paper also attempts to give examples of how various molecular techniques can be used for characterizing various microorganisms involved in biological nitrogen removal.