Study On Nitrogen And Phosphorus Removal Performance Of Modified A~2/O Process For Low-carbon Municipal Wastewater Treatment

A modified A²/O process were studied in this paper. Raw water according to acertain proportion get into anaerobic tank and anoxic tank separately, which candistribute carbon for denitrification and anaerobic phosphorus release reasonably. Theeffluent of anaerobic and anoxic both get into aerobic tank. Some carrier was added intoaerobic tank and anoxic tank, which can stabilize the effect of nitration anddenitrification and improve the performance of nitrogen removal.The effect of different influent distribution of anaerobic and anoxic being6:4,5:5and4:6to the modified A²/O process were studied. The result found that the removal ofCOD and NH₃-N were not impact by water allocation. TN removal increased with thedistribution ratio of anoxic tank increasing, but TP decreased due to the carbon sourcereduction for anaerobic phosphorus release，which lead to TP concentration increased ineffluent. Considering both nitrogen and phosphorus removal, the influent distribute ofanaerobic tank and anoxic tank ratio remain5:5are more appropriate.In the study of sludge and mixture return ratios, the influent distribution remained5:5, it found that the modified A²/O process performance good nitrogen and phosphorusremoval in the condition of sludge and mixture return ratios being50%and200%respectively. The average removal efficiency of COD, TN and TP reached to85%,70%and90%. The nitrification was stable, and the removal of NH₃-N was more than95%.The average values of COD, NH₃-N, TN and TP in effluent were29.7mg/L,0.1mg/L,11.8mg/L and0.4mg/L respectively. The effluent could meet to Grade A discharging standard ofpollutants for municipal wastewater treatment plant （WWTP）（GB18918-2002）.In the resarch of C/N ratios, the result indicated that TN removal rate was about60%and TP reduced to70%when C/N being4, just because of carbon lacking. themodified A²/O could perform well on nitrogen and phosphorus removal when C/N beingmore than5.5, but overtop was not benefit for TP removal. In order to better understand thecharacteristics of nitrogen and phosphorus removal, some batch tests were used to observethe function of sludge and biofilm. The result manifested that the sludge had goodfunction in nitrogen and phosphorus removal, and the biofilm played an important rolein nitrogen removal.Low temperature being adverse to microbial activity, which can affect nitrification and denitrification of the biological treatment systems. But the modified A²/O processgreatly reduced the adverse effects of low temperature by means of adding carrier andincreasing sludge return. The result shown that the influent temperature was about14℃and the average concentration of COD, NH₃-N, TN and TP were269.5mg/L,33.74mg/L,42.31mg/L and4.94mg/L, after modified A²/O process treatment, the average removalrate of COD, NH₃-N, TN and TP were85.10%,95.7%,70.37%and90.73%. Theeffluent average concentration were40.1mg/L,1.45mg/L,12.54mg/L and0.46mg/L,respectively, which can surely meet to Grade B discharging standard.