Study On Microbial Characteristics Of Excess Sludge Reduction In An Anoxic+oxic-settling-Anaerobic Activated Sludge Process

Anaerobic hydrolysis and acidification?endogenous respiration?uncoupling metabolism are the principal factors of sludge reduction in an A+OSA process.These factors of sludge reduction is always present in the whole process?influence each other in different process conditions,play a different role within the system together to achieve reduction of excess sludge.And these factors are closely related to microbial properties in the sludge reduction system.It can provide some scientifically theoretical supporting for revealing the mechanism of the excess sludge reduction by studying microbial activity and microbial community structure.We can find out the amount of excess sludge reduction and the influence to the biological treatment system operation because of sludge reduction within the system,by comparing the A+OSA process with sludge returning and A1/A2/O process without sludge returning.Studying microbial characteristics,microbial community structure and its variation,through monitoring the activity of dehydrogenase?alkaline phosphatase and catalase.(1)Microbial activity is declined in each reactor of A+OSA process because of long term recycle of excess sludge,it decline the elimination efficiency of CODCr.Comparing with A1/A2/O process,the removal rates of CODcr of every reactor is lower.The CODCr of final effluent in A+OSA process is more than 100mg/L beginning from seventeenth week.In the experimental conditions,total removal of CODcr is 84.9%,achieving better removal.The average CODCr of final effluent in A,/A2/O process is 69.22 mg/L,more stable.Total removal of CODCr is 89.01%.(2)It can improve the elimination efficiency of chroma in the A+OSA process by the recycle of excess sludge.The chroma of final effluent in A+OSA and A1/A2/O process are 50 times and 70 times.The anaerobic stage is the main section of color removal,the decolorization ratio were 59.51%and 56.11%in the A1 and A2 segments.(3)Under the condition of the same inoculation concentration(MLSS was 3.142g/L),MLSS of A1 and O segment have the similar variation tendency,MLSS of A2 segment drop down to a lower value early in the test,then hold steady after increasing slowly.At the end of this test,MLSS of A1?A2?O segment are 2.141g/L?1.502g/L?1.038g/L.The sludge yield deviations of these two systems is 0.3g/d,it has a good effect of excess sludge reduction in the A+OSA process.(4)The variation tendency of the activity of dehydrogenase?alkaline phosphatase and catalase of each segment in the A+OSA process is similar,increase at first and then decreased.The activity of dehydrogenase?alkaline phosphatase and catalase in the O segment are all the highest,the activity of dehydrogenase?alkaline phosphatase in the A2 segment are all the lowest.It shows that microbial activity will be obviously reduced because of long term recycle of excess sludge,and it will affect operation of the system.(5)During the test,the observed sludge yield coefficient in O and O' segment are 0.41 g/g and 0.49g/g,the observed sludge yield coefficient reduce gradually in the A+OSA process because of long term recycle of excess sludge.The variation tendency of the observed sludge yield coefficient and enzyme activity are in substantial agreement.(6)phylogenetic analysis revealed that the bacteria in the initial sludge samples fell into 38 kinds of bacteria and 5major groups,Gammaproteobacteria was the main community;the bacteria in the A1 samples fell into 36 kinds of bacteria and 7 major groups,Alphaproteobacteria and Gammaproteobacteria were the main community;the bacteria in the A2 samples fell into 25 kinds of bacteria and 7 major groups,Gammaproteobacteria was the main community;the bacteria in the O samples fell into 32 kinds of bacteria and 9 major groups,Gammaproteobacteria was the main community.(7)When the system is running to the thirteenth week,the microorganism sort of A1?A2?O segment decrease to 36?25?32.The percent of Some of these bacteria is very low,even lower than 1%.The main community is close to the Alphaproteobacteria?Betaproteobacteria?Flavobacteriia?Gammaproteobacteria.At this moment,the main community has begun to emerge in the each reactor.