The potential of heterotrophic bacteria to nitrify in a

The oxidation of inorganic nitrogenous compounds by chemoautotrophic bacteria such as Nitrosomonas and Nitrobacter spp. is believed to contribute and be responsible for the majority of global nitrification. Although the function of the autotrophic nitrifier in natural ecosystems is well known, little is known about the function, if any, of heterotrophic nitrifiers. In biological nutrient removal (BNR) activated sludge treatment it has always been accepted that nitrification is performed by autotrophs and denitrification by heterotrophs. However, some environmental studies have found heterotrophic nitrification rates to be only one or two orders of magnitude lower than those of the autotrophs. Taking this into account and the heterotrophic dominance in activated sludge, heterotrophs may notably be contributing to nitrification in BNR systems. Therefore, there is a need for insight into the potential involvement of heterotrophic bacteria in nitrification occurring in BNR systems in order to further optimize and economize this process. This study aimed at assessing potential nitrification by heterotrophic bacteria present in the Darvill BNR process situated just outside Pietermaritzburg in Kwazulu Natal. Heterotrophic bacteria were isolated, using nitrificatio