Influence of water characteristics on partial nitrification in a sequencing batch reactor

Due to the potential benefits on energy/cost savings from partial nitrification, this study carried a series of laboratory tests to study the combined influence from water temperature, organic carbon and dissolved oxygen (DO) on partial nitrification. The purpose of this study was to obtain a general direction to operate activated sludge systems for partial nitrification under changing environment conditions and wastewater strengths. The time profiles of the mixed liquor NO₂-N and NO₃-N during a 11 h aeration phase were monitored in a 6 L bench scale sequencing batch reactor (SBR) under varying water temperatures (20°C to 30°C), organic carbon abundances (initial mixed liquor COD/N ratio ranged 2.8 to 14), and DO levels (0.4 to 4.0 mg L^-1). Results showed that organic carbon abundance should be firstly lowered to below a certain threshold level (14 in this study) in order to allow nitrification to occur. Then, water temperature should be kept at relatively higher levels (at least 30°C) and DO should be controlled at relatively lower levels (depending on aeration duration). However, the adverse effect on partial nitrification from low water temperatures can be compensated by a low DO, while the favoring effect on partial nitrification from high water temperatures can be reversed by a high DO and/or excess aeration. Although it was not the focus of this study, simultaneous nitrification and denitrificaiton (SND) was also indicated viable when organic carbon abundance was kept at relatively higher levels but still below the inhibitory level for nitrification. Successive study is recommended to further quantify the interactions between these influential factors on partial nitrification and to improve and better understand the reliability and sensitivity of activated sludge systems in achieving partial nitrification under normally always changing reaction conditions. The overall conclusion is that partial nitrificationis under normally always changing reaction conditions.