Butanol Fermentation From Corn Stover And Detoxification Strategies

Lignocellulose is a highly abundant non-food biomass materials.Biofuels production from Lignocellulose biomass has attracted great attentions worldwide.However,high costs of lignocellulose biomass pretreatment and environmental pollution seriously limit its application.To solve the above problems,we established efficient detoxification strategies,and optimized acid and alkali pretreatment process for butanol fermentation.The main contents are as follows:（1）The toxin（e.g.aldehydes and phenolic）produced by the pretreatment of lignocellulose biomass has been a serious inhibitory effect on biobutanol fermentation.To reduce the toxicity of furfural residue（FR）hydrolysate,butanol production from FRs by C.saccharobutylicum DSM 13864 was investigated.Detoxification effect of active carbon is better than resin 711.Detoxification effect of activated carbon combined with resin 711 is superior to using resin or activated carbon alone.Mixed sterilization of FR hydrolysate and CSL is better than separated sterilization,because dissolved proteins in CSL can adsorb some toxins during sterilization procedure.Simultaneous sterilization and detoxification（SDS）of activated carbon or/and resin 711,furfural residue hydrolysate,CSL and mineral salt resulted the highest butanol titer of 8.48 g?L^-1 and ABE of 12.61 g?L^-1.（2）To improve the concentration of value-added by-product xylose produced by acid corn stover（CS）pretreatment,the acid pretreatment method was optimized.Sulphuric acid was used in the pretreatment of CS to obtain xylose.Pretreated CS is hydrolyzed to produce glucose for butanol fermentation.To achieve higher xylose and reduced wastewater,the pretreatment conditions were optimized:180℃,15 min,1:7 solid-liquid ratio(w?w^-1),0.6%(w?w^-1,1st batch)/0.93%(w?w^-1,2nd or 3rd batch)H₂SO₄ addition,in which pretreatment solution was recycled for 3 times.Under above conditions,pretreatment solution containing56.3 g?L^-1 xylose and 4.5 g?L^-1 glucose of was obtained.Pretreated CS residue was further hydrolyzed to result 35.7-39.9 g?L^-1 glucose.The condensed and non-detoxified CS hydrolysate was subjected to simultaneous detoxification and sterilization using 1%(w?w^-1)activated carbon,and then applied in butanol fermentation.The highest butanol titer of 9.47g?L^-1 was obtained in 72 h.（3）To reduce waste water from alkali-pretreated solution of corn stover.Detoxification process of pretreatment solution was developed.The lignin in the alkaline pretreatment solution was precipitated and removed by adding sulfuric acid,then the lignin-removed pretreatment solution was detoxified with activated carbon and reused in hydrolysis and fermentation.The optimum pH for precipitating alkali-soluble lignin was 3.8.Alkali pretreatment solution detoxified with different amount of activated carbon had no obvious effect on corn stover hydrolysis,whereas the addition of activated carbon exhibited a significant influence on butanol fermentation.When 1.5%activated carbon was added,the highest butanol concentration of 10.2 g?L^-1 was reached at 72 h.（4）Simultaneous saccharification and fermentation（SSF）process was applied for biobutanol production by Clostridium saccharobutylicum DSM 13864 from corn stover（CS）.The key influential factors in SSF process,including corn steep liquor concentration,dry biomass and enzyme loading,SSF temperature,inoculation size and pre-hydrolysis time were optimized.In 5 L bioreactor with SSF process,butanol titer and productivity of 12.3 g?L^-1 and0.257 g?L^-1?h^-1 were achieved at 48 h,which were 20.6%and 21.2%higher than those in separate hydrolysis and fermentation（SHF）respectively.The butanol yield reached 0.175g?g^-1 pretreated CS in SSF,representing 50.9%increase than that in SHF(0.116 g?g^-1pretreated CS).（5）To simplify the operation process and reduce energy consumption,the detoxification process were optimized.The effect of activated carbon on detoxification(by monitoring OD₄₂₀ and OD₂₈₀)before and after pretreatment（sterilization）was investigated.It was found that addition of activated carbon before sterilization had better effect than that after pretreatment（sterilization）（90℃,1 h）.Lignin was more easily leached by NaOH from acid pretreated corn stover.The higher temperature,the more lignin leached.The changes of OD₄₂₀and OD₂₈₀ were compared before and after the mixing of acid and alkali pretreatment solution,and the result suggests that part of toxins were adsorbed during the process of lignin precipitation.The recovery and utilization of pretreatment solution were studied.SSF of alkali pretreated corn stover,acid pretreated corn stover,and acid&alkali pretreatment solution and mixed detoxification were carried out.The concentration of butanol in 48 h reached 8.5 g?L^-1,5.8 g?L^-1 and 8.8 g?L^-1,respectively.