Stable Operation Of Aerobic Granular Sludge Treating Municipal Wastewater

Wastewater treatment with aerobic granular sludge is becoming increasingly popular.Aerobic granular sludge(AGS)can be applied to improve the sewage treatment efficiency of the sewage treatment facilities.Aerobic granular sludge technology has a high cost performance and can achieve great improvement effects with small engineering investment.However,most of the domestic research on aerobic granular sludge is concentrated on theoretical research,and there is little research progress in practical engineering applications.This study was conducted to investigate the treatment efficiency of aerobic granular sludge system treating low-concentration actual domestic sewage under different aeration intensities,and analyse the diversity of microbic community structure.In addition,the effect of aeration intensity on the stability of AGS would be investigated based on the balance between AGS and flocculent activated sludge and the sludge properties of AGS.Thereas,research the microbical community structure and microbial species richness.Three sets of SBR with different sludge components RN1,RN2,and RN3 were set up.The control process in system RN1 was aerobic granular sludge with a mixed liquor suspended solid(MLSS)concentration of 5,000 mg/L,that of RN2 was a part of flocculent activated sludge with MLSS concentration of 2,500 mg/L and AGS with MLSS concentration of 2,500 mg/L.RN3 was started up with only flocculent activated sludge and was operated for 42 days.After 42 days of operation,the aeration intensity of RN1 and RN2 was reduced from the original 2L/min to 1L/min,and the two groups of systems were continuously operated for another 30 days.All three systems showed great removal efficiency on COD,but TP removal efficiency was not ideal.RN1 and RN2 showed greater removal efficiency on nitrogen(N)than system RN3.There was no nitrite(NO2--N)accumulation in RN1 and RN3 have not accumulated nitrous nitrogen.During the initial period of the test,RN2 had nitrite(NO2--N)accumulation.After the aeration intensity was changed,the second test began.At the beginning of the second test there was nitrite(NO2--N)accumulation found in RN2.Aeration intensity had great impact on removal efficiency of TN and NH4+-N,while it had little effect on removal efficiency of COD and TP.The reactors showed greater removal efficiency of nitrogen(N)when the aeration intensity was 1L/min.Experimental results indicated that AGS with a particle size between 0.2 mm and 0.6 mm has the strongest stability.In the initial days of the first test,flocculent activated sludge gradually appeared in the system RN1,and the particle size decreased.At the same time,the particle size of the system RN2 also decreased.However,after the aeration intensity was changed to 1L/min,the amount of EPS secreted by the microorganisms in both RN1 and RN2 decreased,and the average particle size of sludge in both systems increased,it seems that sludge granulation would have been proved.During the operation,when the aeration intensity was 1L/min,the alpha-diversity of the sludge community in the two sets of systems both decreased.During this period,the degree of sludge granulation also increased.Compared with system substrate,aeration intensity has little effect on the microbial community structure of the sludge in the system.Saprospiraceae,Fusibacter,and Microscillaceae are relatively highabundance functional bacteria in the aerobic granular sludge system treating actual municipal wastewater.