Production Of Medium Chain Fatty Acids From Ethanol-type Fermentation Wastewater By Chain Elongation

Environmental pollution and resource shortage are major problems facing mankind.Waste biomass is “treasure” rather than “waste” for containing enormous recyclable resources and energy,which can not only avoid improper disposal but also promote sustainable energy supply.More research is currently focused on development of new waste biomass utilization methods—production of medium chain fatty acids(MCFA),which has higher energy density and lower solubility that can be used as precursors of biodiesel or chemicals.Recently,chain elongation(CE)of reverse ?-oxidation pathway has provided different production route for MCFA.Fermentative biohydrogen technology has high yield,simple equipment and easy operation,but low conversion efficiency and secondary pollution are urgent technical bottlenecks.Using hydrogen fermentation broth as substrate,and discussed the feasibility of using it to produce MCFA,the research results obtained mainly include the following aspects.First of all,the feasibility of CE using biohydrogen wastewater to produce MCFA was studied.While keeping the ratio of electron donor(ethanol)and acceptor(acetic acid)fixed,two groups of high and low substrate concentration were set to explore effect of substrate concentration on MCFA production and composition.After inoculation of domesticated mixed bacterial,caproate was produced in both experiments.When the substrate concentration was low,the main products were propionic acid and butyric acid,and when the substrate concentration was high,the main products were butyric acid and caproic acid.The caproic acid concentration was 161.34±8.13 and 1550.89±25.42 mg COD/L respectively,and the selectivity of caproate was 10.29±0.52% and 16.92±1.00% respectively.Conclusions could be drawn after taking p H,headspace gas and EPS composition into consideration that higher MCFA concentration,selectivity and electron transfer efficiency were obtained in high concentration group.In order to promote MCFA production and selectivity,carbon nanotubes were introduced into CE system initially with addition concentrations of 0mg/L,500mg/L,1000mg/L and 1500mg/L to investigate effect of carbon nano materials on MCFA composition and concentration.In low substrate concentration group,results showed that MCFA concentration was lower when added carbon nanotubes.When adding 1500 mg/L carbon nanotubes,hexanoic acid,heptanoic acid and octanoic acid were detected in fermentation broth,which showed that the variety and richness of MCFA was improved.In high substrate concentration group,caproic acid concentration and selectivity reached the highest at 500mg/L carbon nanotubes,871.03±49.62mg/L and 21.07±1.20% respectively while MCFA concentration was 1935.44±110.26 mg COD/L,which was 24.80% higher than the control group.1500 mg/L carbon nanotubes also led to more kinds of MCFA produced.