Study on the phosphorus and nitrogen removal by parallel of anaerobic/anoxic+oxic process controlled by multi-point cycle

Considering the competition of carbon source and sludge age contradictions of sludge age among the various functional bacteria in traditional A²/O process, parallel of anaerobic/anoxic+oxic process controlled by multi-point cycle was introduced. The relevant relationships between return sludge ratio of anaerobic/oxic and release/absorption of phosphorus and its impact on the treatment effect were analyzed, the influence of internal recycle ratio on nitrogen removal was also studied. Moreover, the distribution of the nutrients between anaerobic and anoxic with its impact on the treatment effect was researched, then the optimum parameters of the process was finally found. After calculating the solid retention time under the best conditions of process, physiological characteristics of various functional bacteria were investigated by PCR-DGGE and 16SrRNA sequence. The results showed that the optimum parameters of the process as following, the anaerobic sludge recycle ratio was 15%, aerobic sludge recycle ratio was 30%, nitrification liquid recycle ratio was 300%, anaerobic/anoxic influent ratio was 1:1. With the optimum parameters, the removal rates of COD and ammonia were 92.27% and 97.54%, the removal rates of TN and TP were 87.52% and 96.66%. Nitrogen and phosphorus removal was better than the A²/O process. The parallel of anaerobic/anoxic+oxic process controlled by multi-point cycle could solve the problems of the competition of carbon source and contradictions of sludge age among the various functional bacteria efficiently.