Co-culture of microalgae and enriched nitrifying bacteria for energy-efficient nitrification

The aim of this study was to investigate the possibility of using microalgae as an oxygen supplier for nitrification. In order to measure oxygen demands of nitrification, the activated sludge were cultured in a selective medium for 150 days, and enriched nitrifying biomass was successfully obtained. The enriched nitrifiers were used to estimate oxygen demands for nitrification and used for co-culturing with microalgae. Oxygen transfer rates (OTR) were also measured for various mixing conditions to determine if mixing without forced aeration could satisfy oxygen demands of nitrification. For all mixing conditions, OTR were lower than the oxygen uptake rates (OUR) of nitrifiers. As a result, nitrification without forced aeration was incomplete due to oxygen deficiency. Meanwhile, oxygen production rates (OPR) of 6 microalgae species were measured, and it was demonstrated that C. vulgaris, S quadricauda, D. communism and C. emersonii could supply sufficient oxygen for nitrification at all mixing modes. Based on these results, 4 species of microalgae with sufficient oxygen supplying capabilities were selected for co-culturing with enriched nitrifiers, and full nitrification was accomplished without forced aeration. Finally, the electric energy of co-culture was estimated and showed that energy consumption by co-culture was lower than that of aerated nitrifiers.