Short Chain/Medium Chain Carboxylic Acid Was Produced From Food Waste

With the continuous consumption of fossil energy and the rapid growth of carbon emissions,today's society is increasingly urgent to turn to low-carbon energy system.With the continuous improvement of people's living standards,the per capital waste output is also increasing year by year,as well food waste accounts for more than 50%of urban domestic waste.In recent years,the production of medium chain carboxylic acids(MCCAs)from waste biomass via chain growth(CE)reaction has attracted the attention of researchers.The longer hydrophobic chain structure of MCCAs makes it easier to separate and extract MCCAs from fermentation broth compared with short chain carboxylic acids(sccas).Moreover,the O / C of MCCAs is low and the energy density is high.Compared with hydrogen and methane,it is more suitable to be used as fuel.The technology of making MCCAs from waste biomass is still in its infancy.How to improve the utilization efficiency of waste biomass remains to be explored.In this study,lactic acid and acetic acid were used as the electron donor and electron acceptor of CE reaction,and the optimal concentration of lactic acid and the molar ratio of lactic acid to acetic acid were explored.On this basis,the anaerobic SBR was developed to produce MCCAs,and the pure substance was used as the influent to start the reactor.Finally,the fermentation liquid of mixed fermentation of food waste and excess sludge was used as the fermentation liquid.The feasibility of producing MCCAs by substrate was discussed.The purpose is to provide a new idea for the treatment and resource utilization of kitchen waste.In this study,a series of sequential batch experiments were set up to analyze the effects of lactate concentration and the molar ratio of lactate to acetic acid on the yield of MCCAs.The results showed that the highest concentration of caproic acid was2.96g/l when the concentration of lactic acid was 15 g / L and the ratio of lactic acid to acetic acid was 5:1,and the selectivity of MCCAs was 50.70%.The results showed that the yield and selectivity of MCCAs in the experimental group with added acetic acid were higher than those in the experimental group without added acetic acid,and the increase of caproic acid concentration was faster.It was speculated that the added acetic acid could promote CE reaction.At the same time,the concentration of acetic acid in the experimental group with lactic acid as a single substrate increased obviously,and there was the accumulation of acetic acid.The concentration of acetic acid in the experimental group with acetic acid added first decreased and then increased,and the concentration in the later period was also significantly higher thanthat of the added concentration.Therefore,it was speculated that the oxidation of lactic acid to acetic acid occurred in the reaction.Acetic acid and lactic acid were used as substrates to produce MC through CE reaction In the process of CAS,acetic acid acts as both the substrate at the initial stage of the reaction and the intermediate product in the process of the reaction,so it is speculated that lactic acid can be used as a single substrate for CE reaction.In this study,MCCAs of anaerobic SBR production was studied.The optimal parameters of the sequencing batch experiment were used as the starting conditions,four pure material water inflow stages were set,the acetic acid input was gradually reduced to lactic acid as a single water inflow substrate,and finally the feasibility of food waste residual sludge co fermentation broth as the water inflow was explored.The results showed that the decrease of acetic acid did not have a significant negative effect on caproic acid.The growth rate of caproic acid concentration slowed down in the fourth stage when lactate was used as a single substrate,reaching the maximum concentration of caproic acid of 4.13g/l.During the reaction,lactate showed a more significant downward trend,indicating that the utilization efficiency of lactate was gradually improved.It was speculated that a proper reduction of HRT might lead to a higher MCCAs In the last stage,when the influent was changed into the co-fermentation liquid of kitchen waste and excess sludge,the maximum concentration of caproic acid was 3.21g/l,and the concentration of sccas and heptanic acid,the intermediate products,also showed an increasing trend,which could provide sufficient conditions for the continuous CE reaction.It was confirmed that the anaerobic SBR reactor could be used to produce MCCA after the start-up of the co-fermentation liquid of food waste and excess sludge The feasibility of as provides a new idea for the effective treatment and resource utilization of food waste.