Research On Phosphorus And Nitrogen Removal By Modified A～2/O Process With Low-carbon And Low-energy Consumption

Many problems exist in the traditional AAO process that can remove phosphorus and nitrogen simultaneously by biological method, for instance: firstly, PAO and denitrifying bacteria rival for limited carbon source, which results in that high removal for phosphorus and nitrogen simultaneously hardly is realized in the process; secondly, to obtain a high removal effect for nitrogen, it needs a high internal return sludge ratio, which leads to high operation cost. As for the above mentioned problems, we bring forward to modified A²/O process, which uses the distribulary technology of carbon source from the anaerobic phase and pre-anoxic denitrifying technology of recycled sludge to enhance the nutriment removal and reduce the run expense.This research studied the optimum technical condition of modified A²/O process, and we tested its running results on the optimum technical condition by lab-scale equipment. It demonstrates that, firstly Surpass Ratio (SR) is one of the most important factors of modified A²/O process, and improper SR will lead to high nitrogen concentration in the effluent, which may not be able to comply with the criteria, furthermore, SR is not invariable but varies with the influent condition; secondly when HRT of pre-anoxic phase is 0.6 hour, the system can get better effluent qualities than 0.35 hour, and when HRT is shorter, it tends to accumulate nitrite in the system, which means harder management; thirdly in the optimum technical condition, TP, NH₃-N, TN, COD concentration can reach less than 1.0, 1.0, 15, 50 mg/L respectively in the effluent, which is lower than strictest criteria.This research also validates the experiment result by material balance method. It demonstrates that nitrogen and phosphorus balance rates is 84.1% and 96.1% respectively, which provides a high reliability to us. At the same time, we can know that nitrogen is mainly removed by oxidation, approximately accounts for 48.6%, but phosphorus is removed mainly by discharging waste activated sludge, accounts for 95.2%. Furthermore, by calculating the phosphorus uptake rates of the anoxic and aerobic tanks, we know that the phenomenon of denitrifying phosphorus removal...