Abstract
In this study, we aimed to develop an effective biological nitrogen removal method by applying a membrane bioreactor (MBR). Two different processes, A and B, were investigated using a pilot-scale plant with a capacity of 52 m3·d-1·Both processes are based on three-stage nitrification-denitrification with a post-denitrification process. In process A, membrane separation was carried out after the post-denitrification tank treatment, whereas in process B, mixed liquid was circulated directly from the post-denitrification tank to the first and third anoxic tanks. Raw wastewater was supplied to both processes. The T-N concentration of raw wastewater was 35 mg·l-1 on average. It was confirmed that a T-N concentration of less than 3 mg·l-1 could be achieved in process A with hydraulic retention time (HRT) of 11 hrs. It was also confirmed that a T-N concentration of less than 5 mg·l-1 could be achieved in process B with HRT of 10 hrs. In process B, effective phosphorus removal by enhanced biological phosphorus removal (EBPR) was observed, because the post-denitrification tank caused material in the first anoxic tank to become anaerobic. It was suggested that ORP control in the use of the denitrification tank is essential to ensure satisfactory denitrification in process A. The excess sludge production per inflow SS was 0.64 kg·kg-SS-1 with SRT of 20 days. It was confirmed that the proposed biological nitrogen removal processes could achieve a high level of nitrogen removal and reduce excess sludge production, while occupying only half the area of the existing multistage nitrification-denitrification process.
