Carbon And Nitrogen Coupled Microbial Electrosynthesis Based On Electrically Driven Ion Migration

Microbial Electrosynthesis（MES）is a new technology at the inters-ection of biotechnology and electrochemistry,which can realize the pro-duction of chemicals by reducing CO₂while recycling wastewater.After more than 10 years of development,MES still faces the problems of low product value and single structure and function,etc.MES is mainly based on short-chain organic compounds（C1 and C2）,such as acetate.Due to the high water solubility of acetate and other short-chain organic compounds,it improved product separation and extraction costs for MES.Therefore,further conversion and utilization of short-chain organic compounds（such as acetate）through processes of carbon chain elongation and yeast culture to produce medium-chain fatty acids（MCFAs）and microbial proteins（MPs）is an important way to improve the competitiveness of MES.In addition,most of the currently reported MES reactors are dominated by a relatively single H-type structure and function,and further enrichment of MES functions can be expected to advance the application of this technology.It is worth noting that the synthesis of high value products such as MCFAs and MPs requires organic acids and/or inorganic nitrogen as precursors,and these charged precursors can be separated and recovered under the action of electric field in the MES reactor.Therefore,in this study,an MES coupled carbon achieve the generation of MCFAs.The MES coupled nutrient recovery system based on biocathode and chemical cathode was investigated,and the feasibility of MP production was examined by,in order to enhance the product value of MES and enrich its functions.Firstly,this study achieved efficient production of MCFAs in a three-chamber MES was achieved by integrating acetate generation,extraction and carbon chain elongation.A three-chamber MES reactor was constructed with a maximum acetate concentration of 4.5±0.2 g/L in the cathode chamber and recovery to 3.5±0.2 g/L acetate in the extraction stage of acetate production,maintaining a total FE_acetateof79.2%±2.3%.Secondly,the in situ/ex situ carbon chain elongation performance was compared,where the highest hexanoic acid concentration in in situ carbon chain elongation was 11.9±0.6 g/L with a selectivity of 78.7%±1.5%.The highest concentration of hexanoic acid in allotropic carbon chain elongation was 8.1±0.1 g/L,and the selectivity was 56.4%±0.5%.The simultaneous production of MCFAs by microorganisms from CO₂and ethanol was verified by isotope tracing technique and the enriched microbial community under different conditions was analyzed,Clostridium＿sensu＿stricto＿12 and BRH-c20a were found to be the major functional bacterial genus.This study provides an important reference for the efficient production of MCFAs by MES.Secondly,to enrich the functions of MES and realize the resourceful recovery of nitrogen and phosphorus from wastewater,a system of MES coupled with nutrient recovery based on biological cathode was constructed in this study.A four-chamber MES reactor was built to form a stable biofilm at the cathode.The highest acetate concentration was0.45±0.09 g/L in the cathode chamber and 0.08±0.05 g/L in the recovery chamber,and the acetate production started to stagnate after day3,probably due to the blockage of proton supply by the ion exchange membrane.Higher nitrogen and phosphorus removal(NH₄⁺-N 95.3%±5.4%,NO₃^--N 93.9%±5.8%,PO₄^3-97.1%±6.6%)and higher phosphate recovery（90.3%±5.9%）were obtained,but lower nitrogen recovery（NH₄⁺-N 44.7%±8.9%,NO₃^--N 41.8%±7.7%）,indicating that MES could achieve resource recovery of nitrogen and phosphorus from wastewater while reducing CO₂to produce organic matter.Finally,a three-chamber electrocatalytic reduction of CO₂coupled with nutrient recovery system was constructed using a chemical cathode instead of a biological cathode to address the problems of poor acid production and nitrogen recovery in the above-mentioned system of MES coupled with nutrient recovery from a biological cathode.The Cu-Sn catalytic cathode was prepared by electrochemical deposition to achieve stable catalytic reduction of CO₂to formate within 5 h at a constant current of 20 m A,with a maximum FE_formateof 68.4%±1.3%.During the operation phase,the highest formate concentration of 1.14±0.04g/L was obtained from the catalytic reduction of CO₂in the cathode chamber by keeping the cathode at a constant-2.0 V vs Ag/Ag Cl level for8 h.Meanwhile,high recoveries of nitrogen and phosphorus were obtained(NH₄⁺-N 90.5%±2.5%,NO₃^--N 81.1%±3.3%,PO₄^3-75.6%±1.2%).Unlike acetate,formate can not be used directly for metabolic growth of Saccharomyces cerevisiae.Therefore,this paper proposes an idea for MP production by MES coupled nutrient recovery:the formate produced in the coupling device is converted to acetate using acetate producing bacteria prior to Saccharomyces cerevisiae cultivation.In summary,this study addresses the problems of low product value and single structure function of MES,and combines MES with carbon chain elongation technology to produce MCFAs;realizes the resource recovery of nitrogen and phosphorus from wastewater by MES while reducing CO₂to produce organic matter;and uses the short-chain organic acid generated by CO₂reduction to produce yeast MP.This paper provides a research on electro-driven microbial carbon and nitrogen conversion and utilization thinking and insight.