Enhancement Technique Of Biological Nitrogen Removal Of A Sewagetreatment Plant In Tianjin

Enhancement technique of biological nitrogen removal of a sewage treatment plant in Tianjin was studied,and design and operation parameters were provided for it`s reconstruction and expansion project.A sewage plant in Tianjin is a sewage treatment plant for iron and steel industry wastewater.At a cumulative frequency of 90 %,the influent ammonia concentration was 102 mg/L,the TN was 127 mg/L,and the COD was 103 mg/L.its B/C was 0.1 and C/N was 0.8.The pilot test showed that the removal of total nitrogen and COD by the Bardenpho process is insufficient.The influent is high concentration of ammonia and low concentration of bio-refractory COD wastewater,and its quality fluctuates greatly and biodegradability is poor.It is showed that the biological treatment process had poor,unstable nitrogen removal effect and large carbon source consumption.Batch test were conducted to study the conditions and rate of complete nitrification in actual wastewater,and the optimum carbon nitrogen ratio of denitrification.It was showed that when the influent ammonia concentration was 100 mg/L,MLSS was 2800~3000 mg/L,HRT was 5h,the effluent ammonia concentration can be lower than 1 mg/L.When HRT of denitrification was 4 h,C/N was 7,the effluent TN concentration was less than 10 mg/L.When MLSS was 1500~1600 mg/L,MLVSS was 612~685 mg/L,a nitrite accumulation which rate was 42.8 % occurred in the reactor.When DO was 0.4~2.0 mg/L,A nitrite accumulation which rate was 32.9 %~47.6 % occurred in the reactor.Treating simulated wastewater by moving biofilm bed two stage A/O reactor showed that when the influent ammonia concentration was 50.2~55.3 mg/L,TN concentration was 50.2~55.8 mg/L,COD concentration was 12~105 mg/L,C/N was 7,the HRT of the reactor was 4.9 h in anterior hypoxia pond,6.1 h in the anterior aerobic pond,3.4 h in posterior anoxic pond and 0.4 h in posterior aerobic pond,the effluent ammonia was below 1 mg/L,and the TN concentration was 1.1~8.9 mg/L.Compared with two stage A/O reactor,the ammonia load increased by 69.9 %,and the TN load increased by 49.6 %,and the efficiency of denitrification was obviously improved.Treating actual wastewater by moving biofilm bed two stage A/O reactor showed that when the influent ammonia concentration was 84.9~90.6 mg/L,TN concentration was 86.1~95.0 mg/L,HRT was 16.6 h,the optimum carbon and nitrogen ratio was 6.Under the operation conditions,the effluent ammonia concentration was 1.0~1.6mg/L,and the ammonia removal rate was 97.1~98.9%,the effluent TN concentration was 9.6~13.9 mg/L,and the TN removal rate was 83.8 %~89.5 %.It was found that a nitrite accumulation of 42 %~78 % occurred in the reactor when MLSS was reduced.