Effect of Nitrate and Nitrite on Anaerobic Phosphorus Consumption by Phosphate-Accumulating Microorganisms in a Laboratory Bioreactor

Ability of the aerobic PAO community enriched with Ca. Accumulibacter to use nitrate and nitrite as electron acceptors was investigated. Despite the presence of the genes related to denitrification, it was shown that replacement of oxygen by nitrate resulted in a loss of the PAO phenotype. This could be explained by the inability of Ca. Accumulibacter, which predominated in the bioreactor, to carry out the first stage of denitrification. Using nitrite in an acute experiment resulted in a noticeable cycling of phosphate concentrations in the bioreactor. Phosphate consumption during the anoxic period, however, was considerably less than under conditions of the aerobic cycle. It was concluded that Ca. Accumulibacter could use nitrite as an alternative elector acceptor, albeit with significantly lower phosphorus removal efficiency compared to this process in the presence of oxygen.