Study On Response Characteristics Of Microbial Community Of AnaEG Reactor In Industrial Application

Modified starch is one of the staple foods of human beings.Its mass production also produces a huge amount of starch processing wastewater(SPW)from its production.SPW is a kind of wastewater produced in wet screening,washing and dewatering process during the production of modified starch by changing the characteristics of natural starch by physical,chemical or enzymatic methods.Fuel ethanol,as a renewable clean energy,has been widely produced all over the world in recent years.Therefore,the pollution of ethanol processing wastewater(EPW)is also the focus of attention.EPW is a gelatinization,distillation and condensation wastewater produced in the production of fuel ethanol from corn,wheat and potatoes.AnaEG reactor is a new type of EGSB reactor which has no effluent circulation and realizes on a large amount of gas generated by the granular sludge itself and the uniform water distribution system to realize the full expansion of granular sludge.The reactor has the advantages of energy saving,high efficiency,environmental protection and convenience.As another typical representative of the third generation anaerobic reactor,IC reactor has also been widely used in industrial wastewater treatment in recent year.In this study,the spatiotemporal distribution of microbial community structure in an AnaEG reactor of engineering scale and the response characteristics of bacteria in different operating conditions were analyzed,and the differences of anaerobic granular sludge(AGS)and microbial distribution in SPW and EPW treated by AnaEG and IC reactor were compared.First,the 362-day monitor of the AnaEG reactor for treating modified starch processing wastewater(SPW)showed that,the removal rates of COD,TOC and VFA of SPW could always be maitained above 90% even when the influent quality fluctuated tempestuousely.The gradient degradation of pollutants was not found in the vertical direction of the reactor.The microbial community structure in AnaEG reactor was relatively stable within 15-week of continuous operation and also did not appear spatial distribution.The dominant bacteria,including Chloroflexi(16.40%),Proteobacteria(14.01%),Firmicutes(8.76%),Bacteroidetes(7.85%),Cloacimonetes(3.21%),Ignavibacteriae(1.80%),Synergistetes(1.11%),Thermotogae(0.98%)and Euryarchaeota(3.18%),constituted the main part of the total microbial community,which characterized the microbial community of the boreactor.The spatiotemporal distribution of microbial community was highly consistent with the wastewater treatment efficiency.Second,the AnaEG reactor could be restarted efficiently in a short period of time(1 week)after 4-week suspension,but the physicochemical indices,morphological characteristics and microbial community structure of AGS changed greatly after restart.When the reactor restarted to a stable state,the average biomass in AGS decreased from 58 mg/L to 38 mg/L,and the particle size of AGS increased from 850 to 950 um.The microbial community structure in the restart stage of AnaEG reactor shifted significantly from that in continuous operation stage,the change of microbial community structure was amplified when the reactor reached stable state again,and the Shannon index of AGS decreased from 6.5 to 6.1,but the species richness of the reactor was still higher than that reported in similar studies.The high microbial diversity and complementarity of functional bacteria made some unidentified low abundant species reproduce rapidly to compensate the function of some original dominant bacteria,thus ensuring the functional stability of the reactor.Bacteriooidetes,Firmicutes and Proteobacateria were sensitive to environmental changes,and their relative abundance fluctuated at different stages.However,other dominant members,including Chloroflexi,Cloacimonetes,Synergistetes and Euryarchaeota,were more tolerant to environmental fluctuations.In addition,the comparative analysis of the microbial community structure distribution of AnaEG and IC reactor which were used to treat SPW and EPW respectively showed that,the AGS formed in AnaEG reactor(900 μm)was significantly smaller than that in IC reactor(1200 μm).The surface of AGS treated with SPW was composed of filamentous and cocci bacteria,and the profile of AGS treated with EPW was mainly composed of filamentous and bacilli bacteria.Type of reactor was the main reason for the difference of species diversity,and the speicies diversity in AnaEG was significantly higher than that in IC reactor.The Shannon index of AnaEG was 6.2,while that of IC reactor was 5.7.The distribution of microbial community structure was mainly affected by the type of substrate,and the type of reactor also was one of the reasons.Although the dominant bacterial group formed in the two wastewater were different,some hydrolytic and acidogenic bacteria members,such as Proteobacteria,Chloroflexi and Bacteroidetes were the main dominant microorganisms in both wastewater.There was no obvious spatial distribution of microbial community in the AnaEG reactor,but its composition at the upper and bottom of the IC reactor was obviously different.Reason of this difference may be related to the complexity of the organic matter in wastewater and the characteristics of reactor design.Methanosaeta and Methanobacterium were the main methanogens in the sludge treated with EPW,while only Methanosaeta was the main methanogens in SPW sludge.In addition,the proportion of unidentified microorganisms detected in the AnaEG reactor was about 75%,while that in the IC reactor is 45%.There may be a large number of potential functional bacteria in the unidentified microorganisms of the AnaEG reactor.In conclusion,through the comprehensive analysis of the characteristics and microbial community structure of AGS formed in AnaEG reactor under different engineering aconditions,we found that AnaEG reactor is an efficient reactor which can produce smaller granular sludge,and has higher species diversity and homogeneous internal ecosystem.It can form a higher proportion of potential functional microorganisms.Therefore,the AnaEG reactor not only has broad prospects for future industrial applications,but also provides good materials for the research of functional genes and Germplasm Resources in industrial wastewater.