Sodium Ethoxide Pretreatment And Lactic Acid Fermentation From Sugarcane Bagasse

Biomass energy is a potential low-carbon renewable energy,the development and utilization of which has become a research focus around the world.The conversion of biomass to lactic acid needs three steps:pretreatment,enzymatic hydrolysis and microbial fermentation.In this study,sugarcane bagasse（SCB）was used as raw material and was pretreated with sodium ethoxide in lactic acid production for the first time.Then two fermentation methods including separate hydrolysis and fermentation（SHF）and simultaneous saccharification and fermentation（SSF）were carried out under optimum fermentation conditions to produce lactic acid.Furthermore,alum was used for the first time to detoxify the pretreated SCB hydrolysate and the concentrations of it were optimized.The turbidity and inhibitors of the hydrolysate were analyzed to disscuss the mechanism of alum detoxification effects initially.The SCB was pretreated with different concentrations of sodium ethoxide and 2%pretreatment group was the best taking the total enzymatic efficiency as standard.The total enzymatic efficiency could reach 83.81%,and the content of cellulose and xylan were 54.61%and 28.67%respectively,which increased obviously compared with raw materials.The lactic acid fermentation conditions of Bacillus coagulans were optimized using single factor experiments and orthogonal experiments.Using glucose as substrate,the optimal fermentation conditions were using the initial glucose of 15 g/L,1.6%yeast extract as nitrogen source and the initial B.coagulans OD₆₀₀ at 0.4.Under these conditions,the yield of lactic acid0.96 g/g.Using the 2%sodium ethoxide pretreated SCB as substrate,the highest concentration of lactic acid was 10.93 g/L with a yield of 0.59 g/g and an average production rate of 0.91 g/L/h in SHF.Under the same fermentation conditions,the highest concentration of lactic acid was only5.89 g/L with a yield of 0.32 g/g and an average production rate of 0.16 g/L/h in SSF.Different concentrations of alum were added into pretreated SCB hydrolysate to test the detoxification effect of alum,taking the reducing sugar concentration in hydrolysis at 72 h as standard.The hydrolyzates pretreated by 0.5%sodium ethoxide showed little inhibitory effect on the enzymatic hydrolysis process,while the inhibitory effect on enzymatic hydrolysis increased obviously with an increase concentration of sodium ethoxide in pretreatment.When concentration of sodium ethoxide in pretreatment was 2%and the concentration of alum was 1%,the detoxification effect of alum was the best.The content of glucose and xylose were 37.31 g/L and 18.88 g/L,which were increased by 71.13%and 75.86%respectively compared with hydrolyzates without alum.There were obvious apparent changes in the pretreated hydrolyzate and the turbidity of it decreased from 212.67 to 38.14 after adding alum.The removal rates of vanillin,furfural,coumaric acid and syringic acid in the hydrolyzate adding 1%alum were57.69%,4.35%,18.05%and 100%respectively.