Research On The Experiment And Model Of Low C/N Municipal Wastewater Pollutant Removal

Mudan River is the second largest tributary of the Songhua River. It is726km longwith the basin area of31,000square kilometers. It is one of the major rivers in China. Inrecent years, with the development of area along the river, the pollution of Mudan Riveris getting worse. To protect the water quality and safety of Mudan River, subsidized bynational12th five-year plan, the test based on A-A2/O process, adding a return sludgesystem which is from secondary clarifier to head end of aerobic pond as well as fillerinto aerobic pond begins. Against the problem of poor treatment under the condition oflow C/N of wastewater from Mudan River. The test researched the treatment effect oflow C/N sewage by the process and established the pollutant removal model.The test studied the factors of test process. The results showed that, in thecondition of controlling anaerobic DO <0.2mg/L, anoxic DO0.2mg/L~0.5mg/L,aerobic DO2.5mg/L~3.5mg/L, the inlet ratio of1:9, MLSS of3000~4000mg/L, SRT ofabout15d, when the sludge recycle ratio of pre-anoxic was15%, sludge reflux ratio ofaerobic was30%, internal recycle ratio was300%, the technical and economic effect ofsystem was the best. At this point, COD effluent concentration was40.88mg/L andremoval rate was81.83%; Ammonia effluent concentration was1.56mg/L and removalrate was95.83%; TN effluent concentration was8.18mg/L and removal rate was87.47%; TP effluent concentration was0.15mg/L and removal rate was96.49%.The test examined the influences of different influent C/N on treatment effects oftest process. The results showed that, when the influent C/N were2.5,3.0,3.5,4.0, theeffluent COD, ammonia nitrogen, TN, TP satisfied national standard A; But wheninfluent C/N was2.0, TN could not satisfy national standard A. Degradation of organicsand nitrification were less affected by influent C/N. When the influent C/N was lessthan3.0, the effect of nitrogen removal was significantly affected, the effect ofphosphorus removal was severely affected. When the influent C/N was between3.0to4.0, the efficiency of nitrogen and phosphorus removal under five conditions was closer.Against the problem of excessive nitrogen under the condition of influent C/N of2.0,the test changed the influent water mode. The best step feed ratio was0.3, and at thispoint, effluent COD, ammonia nitrogen, TN, TP satisfied national standard A.The filler comparison were carried out, according to speed of microorganism growing on the five kinds of filler biofilm under the low C/N water condition, andbiomass on unit filler, the combined filler was determined to be the trial filler, whichwas added to the first compartments of aerobic tank. The results showed that addingfiller enhanced aerobic nitrification and simultaneous nitrification and denitrificationeffect, but at the same time phosphorus removal efficiency was reduced. At40%,60%,80%three kinds of dosing ratio, the effluent COD, ammonia nitrogen, TN, TP satisfiednational standard A. When dosing ratio was60%, COD, ammonia nitrogen and TNremoval rate were highest, the optimal dosing filler ratio was ultimately determined tobe60%.Experimental study the effect of adjusting SRT on nitrogen and phosphorusremoval process after dosing filler, the results indicate that dosing filler effectivelyeasing the contradiction of SRT between denitrification and phosphorus removal, byincreasing the amount of sludge could be greatly improved the efficiency of phosphorusremoval based on decreasing the removal efficiency reasonably. When the SRT was14d,12d,10d,8d,6d, the effluent ammonia nitrogen, TN, TP satisfied national standard A.When the SRT is6d, TP is close to the limits of standard requirements, so as to ensurethe system stable water quality standards, SRT should be a minimum of8d.The organic matter degradation model in anaerobic tank, denitrifying phosphorusremoval model in anoxic tank, nitrification model in aerobic tank were researched, theconcentration steady-state formula of effluent COD from anaerobic tank, effluentphosphorus concentration from anoxic tank and effluent ammonia from aerobic tankwere established. The maximum deviation rate between predicted and experimentalmeasured values of effluent COD from anaerobic tank was15.96%and the minimumdeviation rate was2.36%; The maximum deviation rate between predicted andexperimental measured values of effluent phosphorus concentration from anoxic tankwas12.79%and the minimum deviation rate was6.5%; The maximum deviation ratebetween predicted and experimental measured values of effluent ammonia from aerobictank was6.16%and the minimum deviation rate was3.47%.