Study On Production Of Medium Chain Carboxylic Acids By Batch/EGSB Process Based On Lactic Acid And Acetic Acid

Waste biomass can be recycled through biochemical processes such as anaerobic fermentation and composting,but these biochemical or thermochemical products have low value.There is an urgent need to develop and expand alternative technologies for green and efficient recycling of high-value products from waste biomass.The use of waste biomass to recover medium-chain carboxylic acids(MCCAs)is one of the research hotspots of high value and significance,but many factors that restrict production have not been determined and resolved.In this study,lactic acid was used as the electron donor to explore the performance of MCCAs under different control conditions and analyze the microbial community structure to clarify the limiting factors and solutions for the lactic acid-based MCCAs production.Provide a basis for technological process control,parameter optimization and yield improvement.In this study,we set up experiments under different pH conditions to determine the optimal pH for acid production when lactic acid and acetic acid are the substrates;we set up reactors with different pH control methods to explore whether pH control is necessary during the reaction process.So as to explore whether it is possible to reduce the dosage of acid-base substances during operation by not controlling the pH value.The research results showed that the reaction conditions of pH=5 were more suitable,and the average concentration of caproic acid under this condition was the highest,reaching 362.34 mg/L.During the chain elongation reaction,pH adjustment was necessary.The average concentrations of SCCAs and MCCAs in the reactor with pH adjustment(5.681 g/L and487.92 mg/L)were significantly higher than those in the reactor without pH adjustment2.717 g/L and 326.39 mg/L),which may become one of the main cost in anaerobic fermentation of actual waste biomass to produce MCCAs.It is possible to find other substances that are lower in cost and can maintain the pH of the reactor to replace the addition of acid and alkali substances to reduce operating costs and make the resource recovery process more valuable.In a continuous flow reactor,the production of MCCAs was achieved by optimizing operating parameters.Studies have shown that the chain growth reaction of continuous flow reactors will have a longer lag period,but the MCCAs production was much higher than that of sequential batch reactors.When the ULV was controlled at 1.150 m/h and the pH was in the range of 4.9-5.1,the substrate utilization rate was the highest,the highest concentration of caproic acid could reach 4.43 g COD/L;HRT=24h was more suitable for chain growth reaction than 36 h.After HRT dropped to 24 hours,the butyric acid concentration increased from 98.58 mg/L to 3601.55 mg/L,35 times increased,and the caproic acid concentration increased to 1766.18 mg/L.In a continuous flow reactor,appropriately shortening the HRT was a more suitable parameter condition change for the chain extension reaction.Microbial diversity analysis showed that in the long-term production of MCCAs with lactic acid as a single electron donor,Firmicutes bacteria became the most important phylum,Caproiciproducens,Pseudoramibacter,norank＿f＿＿Eubacteriaceae,and Oscillibacter were the dominant microorganisms.genus.