Effects Of Sludge Rheology On Microbes And Bio-gas Production In Anaerobic Digestion Process

With the introduction of"carbon neutral"policy,sludge anaerobic digestion technology has received widespread attention as a"negative carbon emission"sludge treatment and disposal technology.However,the shortcoming that the biogas produced by the sludge anaerobic digestion process may be lower than its operating and construction costs has been criticized.Since the homogenization and gas extraction inside the anaerobic digestion reactor depend on the consistency and structural characteristics of the sludge,the rheology of the sludge seriously affects the function and efficiency of the anaerobic degradation of microorganisms.Therefore,it is necessary to explore the rheological properties of the sludge,helping improve the gas production efficiency of anaerobic digestion.In this experiment,five different rheological sludges with the same organic content were prepared by adding inert sludge inside the reactor,and the changes in sludge gas production,dehydration,rheological properties and microbial community during anaerobic digestion were studied.(1)It have determined that when the dosage of polymethyl methacrylate(PMMA)is 30 g/kg substrate(ie SM-2 group),the sludge will be at its peak when the stirring speed is 180rpm and the viscosity reaches 0.036Pa·s.The best gas production is225.24 m L/g VS.After anaerobic digestion,the sludge viscosity change and the sludge particle size change showed a positive correlation.The SM-2 group had the best sludge dewatering performance after anaerobic digestion,which was 16.7%higher than the blank(CK)group.Fitting the cumulative gas production of the sludge reactor in this test by the Gompertz model found that the SM-2 group reached the maximum methane production potential and the maximum methane production rate,which were3.72%and 27.34%higher than those of the CK group,respectively,indicating appropriate sludge rheological effects Reactor gas production performance.It is suggested that the shape and speed of the agitator can be changed to make the sludge rheology in the reactor in a proper state in the actual project,so as to improve the homogenization of the internal materials of the reactor,and increase the gas production and dehydration performance.(2)The fitting degree of the H-B model for the flow curves of the five groups of reactors during the anaerobic digestion process is all above 0.97.In the process of anaerobic digestion,the yield stress showed a logarithmic decrease.The thixotropy increased during the 3rd d of anaerobic digestion and disappeared on the 5th d.As the anaerobic digestion of sludge progressed,the fluidity of the sludge gradually increased.After anaerobic digestion,the yield stress and dehydration performance of the five groups of test sludges showed a good linear relationship.The goodness of fit is above 0.95.In the anaerobic digestion process,the sludge consistency coefficient and the gas production showed a good linear relationship,and the goodness of fit was above 0.96,indicating that the sludge consistency coefficient can be used as an indicator of the gas production in the anaerobic digestion process,and the sludge yields Stress can be used as an indicator to characterize the performance of sludge dewatering.(3)Diversity analysis of sludge microorganisms(bacteria,archaea)shows that too high or too low shear rates inside the reactor are not conducive to the abundance of microbial populations,and higher and lower shear forces are conducive to strengthening the reactor Diversity of internal archaea;lower shear rate inside the reactor is conducive to enhancing the abundance and diversity of bacterial populations,and bacteria are more suitable to grow at a lower shear rate;OUT clustering tree based on 5 groups of test samples Graph analysis shows that the archaea and bacteria in the SM-3 and SM-4 groups are similar;the archaea and bacteria in the CK,SM-1and SM-2 groups are similar.The dominant archaea of the 5 groups of experiments is Methanothrix;typical acetic acid trophic methanogens.Firmicutes,Bacteroidetes,Chloroflexi,and Proteobacteria are the main dominant bacteria inside the reactor.The dominant bacteria that appeared in the five experiments were Firmicutes.Firmicutes can produce cellulase,protease and other extracellular enzymes,which play an important role in the hydrolysis and acidification of sludge.The five groups of experimental bacteria have a large difference in the proportion of different bacterial phyla at the phylum level,indicating that the bacteria are more sensitive to changes in the internal shear stress of the reactor,and higher or lower shear rates will cause the bacterial population abundance in the reactor.Predicting the function of the archaea flora through the FAPROTAX database shows that the function of the five groups of test archaea is mainly methanogenesis,and the function of bacteria is mainly the fermentation function,indicating that the change of the sludge flow does not destroy the methanogenesis and fermentation functions of the microorganisms inside the reactor.(4)Pearson correlation analysis results show that there is a strong correlation between sludge yield stress and dewatering performance(R~2=0.988,P<0.01),and sludge can be used as a characteristic index to characterize sludge dewatering performance.;Sludge yield stress and archaea Shannon index(R~2=-0.819,P<0.05),sludge flow index and archaea Ace index(R~2=0.788,P<0.05)showed a good correlation;sludge yield stress It shows a good correlation with the bacterial Simpson index(R~2=0.701,P<0.05).It shows that the rheological properties of sludge have the potential to be an indicator for characterizing,regulating and monitoring microbial characteristics in anaerobic digestion reactors.Principal component analysis method is used to analyze the main factors of sludge dewatering performance and total sludge production.The results show that sludge’s yield stress and consistency coefficient are the main factors of sludge dewatering performance and total sludge gas production.The sludge flow index is limiting factors for dehydration performance and total gas production.In actual engineering,it is possible to consider changing the shape,operating speed and frequency of the stirring blade to change the rheological characteristics of the sludge,thereby improving the anaerobic digestion of the sludge,the dewatering performance and the community distribution of microorganisms in the reactor.