Research On Regulation Of Volatile Fatty Acid Accumulation By Syntrophic Propionate-oxidizing Consortium During Anaerobic Digestion Process

The Volatile fatty acids?VFAs?,such as acetate,propionate and butyrate,are important intermediate metabolite during anaerobic digestion process.VFAs often accumulates under an excessively high organic loading rate or complexity of raw materials,which may cause a rapid and instability acidification as well as inhibit the growth of microbes and anaerobic digesters.Moreover,the anaerobic conversion of propionate and butyrate to acetate,CO₂ and H₂ is highly endergonic and does not occur naturally.Thus,the degradation of VFAs is regarded as the rate-limiting step in anaerobic digestion.Studies showed that VFAs could be degraded by the syntrophic cooperation of syntrophaceae andmethanogens.In this paper,we constructed a syntrophic propionate-oxidizing consortium on the basis of the effects of oxidative degradation of VFAs.Through the study of physiological and biochemical parameters of the consortium,we improved and confirmed optimization of the operating parameters of propionate anaerobic oxidation,and established a rapid removal process of propionate accumulation.The syntrophic propionate-oxidizing consortium were used to regulate and controlthe acidifying anaerobic digestion system,so as to guaranteed system stability,meanwhile the microbial community structure in the anaerobic digestion system before and after regulation were analyzed.All of these provided theoretical and technical basis for the application of anaerobic digestion system.?1?The stable syntrophic propionate-oxidizing consortium which could degrade propionate efficiently was obtained by Hungate anaerobic technology and continuous domestication,using pharmaceutical wastewater as inoculum,and propionate as sole carbon source.Syntrophic propionate-oxidizing consortium could degrade 3000 mg/L propionate completely in 24-26 d,and the methane content was not less than 58%.Results of clone library showed that the main bacteriumbacterium were Pelotomaculum,while Methanosarcina and Methanospirillum were the main archaea.?2?The growth of syntrophic propionate-oxidizing consortium was promoted,the lag phase of propionate anaerobic oxidation and methanogenic metabolism were shortened,the yield of methan was improved by adding organic nitrogen sources?YE and BBL?to medium.The addition of BBL had a higher methane production,and the addition of YE and BBL had a significantly higher methane production rate than other groups.The result of high-throughput sequencing showed that Pelotomaculum of Firmicutes,Methanosaeta and Methanoculleus dominated in the syntrophic propionate-oxidizing consortium,which function in propionate oxidization and methanogenesis,respectively.In addition,There was no obvious effect on the microbial community structure of Archaea in the system,but could influence the abundance and variety of bacteria after adding organic nitrogen sources to medium during the batch cultivations.?3?Syntrophic metabolismcould be promoted by adding solid type carriers.Thereinto,solid type carrie glass sand addition had the highest conversion efficiency of propionate.3000 mg/L propionate could be degraded completely in 19 d,and the methane content was not less than 64%.Active carbon felt addition resulted in improvement of anaerobic digestion start efficiency and it contributed to a better conversion of butyrate to methane.Eventually,we chose glass sand as solid type carrie,BCTY as culture medium toestablish a rapid removal process of propionate accumulation,in which condition the rate of methane production and propionic acid degradation were the fastest.?4?Based on the syntrophic propionate-oxidizing consortium,acidulated anaerobic digestion system was recovered.The result showed that at the beginning,substrate in CSTR_control and CSTR_treatment was fermented by Clostridiales etc and produced a large amount of H₂ and short-chain VFAs,especially acetate and butyrate,the pH value decreased rapidly around 5,which inhibited methanogenic metabolism,inducing anomalies in the system.The reactors CSTR_recover and acidified CSTR_treatment were connected by Separator,through gradual attenuation and circulation function,the removal of accumulated VFAs in CSTR_treatment was promoted effectively,methanogenic metabolism was restored normal after 18 d.In the process of recoverment,members of Acinetobacter were capable of degrading acetate and butyrate principally.With the gradual circulation function of digestion liquid between CSTR_recover and CSTR_treatment,the dominant species and their abundance of two reactors were converging.