Interaction between Denitrification and Phosphorus Removal in a Sequencing Batch Reactor Phosphorus Removal System

Batch experiments were performed to investigate simultaneous denitrification and phosphorus removal by denitrifying phosphorus accumulating organisms (DNPAO). The results showed that while using the same amount of carbon source, DNPAOs are able to uptake phosphorus by using nitrate as an electron acceptor. It was observed that higher nitrate concentration required a longer anoxic period for denitrifying phosphate uptake. In addition, the effect of the presence of nitrate in substrate was studied. Phosphorus release occurred as long as substrate was present in the anaerobic phase regardless of nitrate concentrations. It also was noticed that nitrate hindered the release of phosphorus in the anaerobic stage because of denitrifiers competing with phosphorus accumulating organisms for their carbon source. The DNPAOs, however, remained competitive in a system with nitrate in the anaerobic phase.