| 80% of the existing wastewater treatment plants adopt activated sludge system. A2/O process which is the most simple simultaneous nutrient removal process is widely used in wastewater treatment plants. But there are some challenges troubled with A2/O process, such as carbon competition between phosphorus-accumulating organisms and denitrifier, effect of nitrate on phosphorus removal, sludge retention time conflict between autotrophic bacteria and heterotrophic bacteria. A modified A2/O process was presented in this thesis, and its modified configuration included (1) an anoxic selector at the head of A2/O process. (2) step-feed in anoxic selector and anaerobic tank. (3) stage aeration tank in aerobic zone. The thesis focused on characteristics and control of modified A2/O process treating South China wastewater tipical of low strength. The main conclusions are drawn as follows.(1) Anoxic selector could remove 35% of nitrate and 30% of nitrite in return sludge when 10% of influent entering selector. The removal of nitrate was more stable than nitrite. Denitrification mainly completed in selector and anoxic tank other than anaerobic tank, so selector improved conditions for phosphorus release in anaerobic tank.(2) MLSS should be determined according to F/M=0.10-0.12, and excess MLSS was not suitable for treating low strength wastewater. Excess sludge discharge could improve removal of COD, NH3-N, TP and SS. Without excess sludge discharge, effluent SS fluctuated badly and denitrification was also affected. If influent TN was very low, selection of mixed liquid recycle ratio should based on co-consideration of run cost and phosphorus removal. Because low mixed liquid recycle ratio could result in more nitrate in return sludge disturbing phosphorus release.(3) Characteristics of stage aeration tank were as follows.The mixed condition of single tank (L=1.58B) of stage aeration tank was closer to plug flow. Its configuration was simpler compared to channel aeration tank.The degradation of COD and NH3-N in stage aeration tank was afford to first order reaction. Simulation of stage aeration tank should base on multi-stage mode other than considering stage aeration tank as a whole.MLSS in stage aeration tank is uneven. This was attributed to excess sludge discharge amount and different mixed condition in each tank.If the mixed condition in single tank was CSTR, after adopting staging strategy, reaction rates could be improved and volume of biomass tank could be reduced. And the volume could be minimun when volume of each was the same. It is convenient to modify conventional aeration tank to stage aeration tank, and this modification could get higher removal rate.(4) When influent was fluctuated with weak alkaline(pH8.0-8.5), it did not have a negative effect on system performance, phosphorus and NH3-N removal maintained, TN removal improved. When influent phosphorus was very low, phosphorus removal improved 15.9%, but time for completed nitrification was extended.(5) Excess aeration resulted in deterioration of phosphorus removal and improved TN removal. SS in surface effluent was increased and also SVI of sludge. NH3-N removal rate was improved due to high DO concentration, so aeration time should be shortened in order to maintain less DO owing to mixed liquid recycle from anerobic tank to anoxic tank.(6) ASM stoichiometric coefficients and kinetic parameters of AnQing wastewater treatment plant were as follows.Water quality parameters:ratio of Ss, Xs, SI, XI to COD was respecially 4.8%,10.5%, 21.5%,62.7%.Ratio of NH3-N, NOX-N, SND, XND to TN was respecially 71%,11%,7%, 11%.Sludge parameters:YH, bH,μH was respecially 0.71 g(COD)/g(COD),0.40 d-1,2.0 g(Xs)/g(XH).d...
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