Interaction between denitrification and phosphorus removal in a nutrient removing SBR system

Batch experiments were performed to investigate simultaneous denitrification and phosphorus removal by denitrifying phosphorus accumulating organisms (DNPAO). The results show that while using the same amount of carbon source, DNPAO are able to uptake phosphorus by using nitrate as 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 concentration. As expected, nitrate hindered the release of phosphorus in the anaerobic stage due to denitrifiers competing with PAO for their carbon source. The DNPAO however, remained competitive in a nitrate-enriched system in the anaerobic phase.