| The purpose of this study was to explore the feasibility of high-efficient butanol fermentation from food waste as substrate and lactic acid as co-substrate under anaerobic conditions using Clostridium saccharoperbutylacetonicum N1-4.In other words,the lactic acid pre-fermentation method was used to inhibit the bacteria and preserve the carbon of food waste,and the co-fermentation of food waste and lactic acid was used to produce butanol efficiently.On the other hand,the conversion of lactic acid into butanol adds significant value of the ABE fermentation and more attractive from a performance perspective.The results showed that strain N1-4 could directly use food waste to produce butanol.Under the condition of solid/liquid ratio 1:1,the concentration of butanol was 12.1 g/L,the highest rate of butanol production was 0.705 g/L/h,and the carbon conversion rate was 0.402 C-mol/C-mol.As the ratio of solid to liquid was 1:2,the production rate of butanol by direct fermentation was 2.05 times higher than that by enzymatic hydrolysis saccharification,because the direct fermentation avoids the substrate inhibition caused by enzymatic saccharification of food waste.In this study,Lactobacillus plantarum was used for the pre-fermentation of lactic acid,and the strain showed good antibacterial effect.Moreover,the feasibility of the co-fermentation of starch and lactic acid by strain N1-4 to produce butanol was investigated.As the initial lactic acid concentration was 15.0 g/L and the starch concentration was 50.0 g/L,the butanol yield was 15.2 g/L.As the initial concentration of lactic acid was greater than 15 g/L,the fermentation was inhibited.In addition,lactic acid cannot be used as the sole carbon source but can only be used as a co-carbon source for the production of butanol.In the batch fermentation of lactic acid pre-fermentation combined with ABE(Acetone-Butanol-Ethanol)fermentation(LAF-ABE),14.8 g/L butanol was obtained,and the highest butanol production rate was 1.02 g/L/h.In order to explore the antimicrobial and carbon fixation mechanism of lactic acid pre-fermentation,the effects of enhanced lactic acid pre-fermentation and natural lactic acid pre-fermentation on subsequent butanol fermentation were compared and analyzed using food waste as substrate.After 72 h storage,there was almost no difference in term of concentration of lactic acid between the two fermentation methods.The lactic acid concentration in the enhanced group was 9.20 g/L,and that in the natural group was 9.60 g/L.The highest lactic acid concentration was 0.47 g/L/h in the enhanced group and only 0.29 g/L/h in the natural group.Besides,high-throughput sequencing analysis showed that the enhanced lactic acid pre-fermentation had obvious bacteriostatic effect on the spoilage bacteria in the food waste,and the bacteriostatic effect of carbon fixation was significantly better than that of the natural group.During the study,it was found that enhanced(LAF-ABE),under the non-open system(with sterilization)can be successfully carried out,and produce butanol of concentration 8.70 g/L.In particular,the enhanced group was more beneficial to the subsequent butanol production than the natural group.In other words,the proportion of butanol in the total solvent was increased in the enhanced group.It was found that the lactic acid bacteria in the enhanced lactic acid pre-fermentation group and the natural group had obvious inhibitory effect on the strain N1-4.The relative abundance was only 10%,and conventional batch fermentation could not under the open system(without sterilization).However,LAF-ABE fermentation of food waste under open system was successfully carried out by using high cell density fermentation mode.As results,the concentration of butanol was 12.9 g/L,the fermentation time was shortened by 12 h,and the concentration of butanol was increased by 32%.In this study,the system of enhanced lactic acid pre-fermentation combined with ABE fermentation(LAF-ABE)was established,which provided a new way for the production of butanol to improve the cheap raw materials,and for the recycling of food waste. |
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