Study On Treatment Of Low C/N Municipal Wastewater Denitrification In SBR With High-concentration Actdiviated Sludge

In this study,in order to reduce the difficulty and cost of high-efficiency nitrogen removal from low C/N municipal wastewater and improve the reuse value of effluent,a pre-denitrification SBR loaded with high-concentration activated sludge was used to simultaneously remove COD from the influent and residual nitrate in the pre-denitrification stage(A stage),thereby reducing the need of aeration in the aerobic stage(O stage),and the first-weak-then-strong pattern of aeration was adopted to weaken the role of aerobic heterotrophic bacteria while intensify the coupling of nitrification and denitrification in the O stage,thereby achieving high-efficiency nitrogen removal without external carbon source addition and pH control.Such a study would provide technical reference for high-efficiency nitrogen removal from municipal wastewater for safe reuse in water-shortage northern China.Through preferential cultivation of nitrifying bacteria and subsequent strengthening the coupling of nitrifying and denitrifying bacteria,common activated sludge became high-concentrated with fast settling rate and good nitrogen removal ability in the pre-denitrification SBR after 60 days of cultivation.Then,the pre-denitrification SBR loaded with the cultivated high-concentration activated sludge was used for processing municipal wastewater with C/N=4,with emphasis on the influences of aeration pattern in the O stage,the water exchange rate and the influent load on nitrogen removal from municipal water.The results showed that with constant weak aeration in the O stage,good coupling between nitrifying and denitrifying bacteria favored high nitrogen removal efficiency(73%),despite that the volume load was small;with constant strong aeration,nitrifying and denitrifying bacteria was little coupled,and the overall nitrogen removal efficiency was low(55%)with the effluent nitrate concentration exceeding the allowed discharge standard.Two-stage(first-weak-then-strong)aeration in the O stage weakened the adverse effects of heterotrophic aerobic bacteria on nitrifying and denitrifying bacteria to favor well coupled nitrification and denitrification for high-efficiency nitrogen removal through.At water exchange rates of 40%and 45%,well coupled nitrification and denitrification in the O-stage resulted in high efficiencies of nitrogen removal(72.4%and 70.2%,respectively),with the ammonia nitrogen concentration in effluent met the A level national discharge standard for urban sewage.When the water exchange rate was 30%,the coupling of nitrification and denitrification in the O stage was weakened but the role of denitrification in the role of pre-denitrification stage was enhanced,and overall,high-efficiency nitrogen removal(71.2%)was still achieved and the volume load was highest(0.41 kg COD/(m3·d)),with the effluent meeting the A level national discharge standard of municipal wastewater.Under the condition of 45%water exchange rate,occasional increase of the influent load by 25%resulted in the concentration of ammonia nitrogen in effluent exceeding the national discharge standard.However,the effluent ammonia concentration met the standard in the third cycle after influent load turned to be normal.This study showed that the pre-denitrification SBR with high concentration activated sludge could withstand considerable fluctuations in the influent load and was suitable for high-efficiency nitrogen removal and COD removal from low C/N municipal wastewater.