Effect of Sludge Retention Time on Nitrite Accumulation in Real-time Control Biological Nitrogen Removal Sequencing Batch Reactor

Abstract

In this study, four sequencing batch reactors (SBR), with the sludge retention time (SRT) of 5, 10, 20 and 40 d, were used to treat domestic wastewater, and the effect of SRT on nitrite accumulation in the biological nitrogen removal SBR was investigated. The real-time control strategy based on online parameters, such as pH, dissolved oxygen (DO) and oxidation reduction potential (ORP), was used to regulate the nitrite accumulation in SBR. The model-based simulation and experimental results showed that with the increase of SRT, longer time was needed to achieve high level of nitritation. In addition, the nitrite accumulation rate (NAR) was higher when the SRT was relatively shorter during a 112-day operation. When the SRT was 5 d, the system was unstable with the mixed liquor suspended solids (MLSS) decreased day after day. When the SRT was 40 d, the nitrification process was significantly inhibited. SRT of 10 to 20 d was more suitable in this study. The real-time control strategy combined with SRT control in SBR is an effective method for biological nitrogen removal via nitrite from wastewater.