Research On The Electrochemical Synthesis Of Butyric Acid By CO₂ Microorganisms Based On Hollow Fiber Aeration Membranes

Microbial electrosynthesis system(MES)is a technology that can synthesize energy substances or chemicals while reducing CO₂.However,the supply mode of CO₂often affects the types of products and synthesis efficiency of the MES system.Aiming at the above research background,this research designed a new type of biocathode made of a combination of carbon felt and hollow fiber aeration membrane to promote the direct transfer of CO₂ to microorganisms in MES.First,according to the different positions of the hollow fiber aeration membranes,two reactors of CO₂ internal mass transfer(IMT)and external mass transfer(EMT)were constructed,and analyze its electrochemical performance,the pH of the cathode and the production of products,etc.Preliminary evaluation of the overall performance of the reactor under different CO₂ supply modes.The results show that when the biofilm grows and matures,the anode organic matter removal rate of IMT and EMT was as high as 90.0±2.0%and 83.0±2.0%.IMT has a high current density while obtaining high organic matter removal rate.At the same time,the cathode in IMT compared with EMT,a lower pH was obtained,and the inorganic carbon concentration was stable at350.0±20.0 mg/L,while the inorganic carbon in EMT accumulates as the reaction progresses,up to 1553.8 mg/L.Analyzing the products of the MES system,it was found that IMT and EMT accumulated acetic acid:549.3 mg/L,831.2 mg/L,butyric acid:615.4 mg/L,450.2 mg/L,methane:8.6ml,5.7ml,no other organic matter was detected,indicating that CO₂ supply inside the electrode can effectively improve the performance of the reactor.Subsequently,two sets of experiments of constant pH(7.0±0.10)and non-constant pH were set up to explore the influence of pH on the performance and products of the cathode of the MES system.The study found that the stabilization time of the MES system under non-constant pH conditions was twice that under constant pH conditions.MES system product results show that when the pH of the cathode is neutral,total enrichment of IMT and EMT within 15 days:acetic acid:1359.8 mg/L,1063.3 mg/L,butyric acid:79.02 mg/L,53.93 mg/L;methane:9.8ml,9.2ml,without adjusting the pH of the cathode,IMT and EMT accumulate acetic acid:698.2 mg/L,543.18 mg/L;butyric acid:606.59 mg/L,297.42 mg/L,of which the highest yield of IMT butyric acid can reach 107.2 mg/L/d,no other organic acids were detected during the whole experiment.In addition,the MES system can effectively increase the production of butyric acid pH value(pH=6.6).The results show that the non-constant pH is more conducive to the enrichment of more high value-added products in the MES system.Finally,the analysis of the microbial community of the MES system showed that87.1%of Clostridia were enriched in the IMT biocathode,while the entire microbial population of EMT was dominated by mixed microorganisms,with only 14.5%of Clostridia.The results showed that although mixed bacterial inoculation was used,the use of CO₂ to supply in the electrode can obtain a more efficient single bacteria,and the way of CO₂ supply will directly affect the microbial population structure.It is inferredthat the supply of CO₂ in the electrode can maintain the weak acid environment inside the carbon and promote the increase in a large number of acid-producing bacteria,while the internal pH of the carbon supplied by conventional CO₂ is mainly alkaline,thus forming a more complex biomembrane structure.At the same time,the analysis of the electron transfer pathway found that the direct supply of CO₂ can effectively promote the direct transfer process of electrons,improve the electron utilization rate,the performance of the MES electrochemical system and the yield of butyric acid.