Control Technique Of Anaerobic Ethanol Fermentation Using Biomass Generated Syngas

Ethanol produntion from syngas anaerobic fermentation appears to be a potential and promising technology.Currently,syngas fermentation is being developed as one option towards the production of bio-ethanol from biomass.To investigate the effects of different basic factors on anaerobic syngas fermentation and obtain an efficient experimental scheme increasing the ethanol fermentation significantly,the batch fermentation using microbial mix-cultures A-fm4 obtained by enrichment and purification in laboratory and abroad strains C.jungdahlii,C.autoethanogenum DSM10061 feeding biomass generated syngas was conducted under different fermentation conditions.The results show that ethanol concentrations and cell growth were effected by initial medium pHs significantly.Lower initial medium pH?4.0⁵.0?could inhibit cell growth and ethanol fermntation.The optimal initial pH?7.0?was got after the batch fermentation experiments by microorganisms A-fm4,C.jungdahlii and C.autoethanogenum DSM10061.The optimal initial pH could promote the cell growth and ethanol production at a significant level,and the maximal dry cell weights of strains A-fm4,Clostridium.ljungdahli iand C.autoethanogenum DSM10061 wre 0.048,0.171,0.087g/L DCW respectively,the maximal ethanol concentrations compared with lower initial medium pH were more than 2.4 fold,2.2 fold and 4.6 fold respectively,also,the levels of ethanol producivity were more than 5.1 fold,2.9 fold and 4.7 fold respectively.And the optimal initial pH could raise the standards of the four key enzymes?activities significantly,but difference would exist in different strains.Lower concentration of NH₄⁺ stimulates cell growth and acetate fermentation,while the concentration of higher than 9.35mmol/L significantly inhibits the cell growth and ethanol fermentation,and the concentration of NH₄⁺ stimulates the ethanol fermentation at 18.7mmol/L⁷8.8mmol/L.Based on the research of enzymatic mechanism during growth period and ethanol or acetate period,it proves that the key enzymes?H2ase,CODH,ADH and ACK?existed in metabolic pathway are all inhibited by higher concentration of NH₄⁺?149.6mmol/L?,and the levels of enzyme activity of growth period are higher than the levels of enzyme activity of fermentation period.The enzyme activity of H2 ase,CODH,ADH decreases significantly along with the elevating concentration of NH₄⁺,while the enzyme activity of ACK increases when the concentration of NH₄⁺ is 18.7mmol/L³7.4 mmol/L.These show that lower concentration or none of NH₄⁺ will improve the utilization efficiency of carbon source by stimulating reducing power production as well as benefit for ethanol production,the higher concentration of NH₄⁺ will inhibit cell growth and ethanol fermentation process and then the metabolic pathway is restrained.Moreover,the research also shows that the Ki level of C.ljungdahlii and C.autoethanogenum is 208.131 mmol/L and 240.373 mmol/L respectively,both of them have a stronger ability of resistance to NH₄⁺,this will provide microorganism resources for domestication of resistance to NH₄⁺,slao lay the foundation for reducing industrial production costs and simplifying the gas purification procedure in syngas fermentation.Moreover,the demand for nitrogen source mainly comes from amino nitrogen during syngas fermentation,and these microorganisms feed inorganic nitrogen source bad.So we can make amino nitrogen become an indicator to reflect the change of the nitrogen source in fermentation,the amino nitrogen also does not change significantly in the middle and later periods of fermentation.The concentration of Ca²⁺ stimulates the growth and ethanol/acetate fermentation at 1.80mmol/L,and it is better for ethanol production.Under the same concentration of Ca²⁺,the activity levels of the four key enzymes in ethanol fermentation period are lower than the levels in growth period?except the strain C.autoethanogenum DSM10061?.The different concentrations of Ca²⁺could influence enzyme activity levels and then influence the fermentation process,especially arise the activity level of ACK.6.25mmol/L Mg²⁺ stimulates growth and shorten the time of adaptive phase during fermentation.Lower concentration of Mg²⁺ stimulates ethanol fermentation,while higher inhibits acetate fermentation.Ethanol and acetate fermentation would be stimulated differently under 6.25mmol/L Mg²⁺ by different strains,6.25mmol/L Mg²⁺ benefits ethanol fermentation for A-fm4,and benefits acetate fermentation for C.autoethanogenum DSM10061,while inhibits acetate fermentation for C.ljungdahlii.Key enzymes H2 ase and CODH would be stimulated in both period time under 6.25mmol/L Mg²⁺?except A-fm4?.In ethanol fermentation period,6.25mmol/L Mg²⁺ arises significantly the activity level of ACK,while higher activity level of ADH was got under 1.25mmol/L Mg²⁺,Ca²⁺ and Mg²⁺ possessed obvious interaction in fermentation,but it does not work for the growth of A-fm4,and the interaction would display significantly for ethanol/acetate fermentation,while it will be antagonistic for acetate production.The optimal concentrations of Ca²⁺ and Mg²⁺ were 1.80mmol/L and 6.25mmol/L respectively by Minitab soft.The interaction could stimulate growth and ethanol/acetate fermentation,also improve ethanol/acetate production capacity per cell,it can promote two metabolic pathways of A-fm4 together,and it also stimulates the metabolic pathways of ethanol/acetate fermentation of stains C.ljungdahlii and C.autoethanogenum DSM10061.Finally,the optimal values of various factors influenced the syngas fermentation process significantly,ethanol fermentation was most effective under the optimal values of various factors : NH₄⁺0mol/L,Mg²⁺ 6.25mmol/L,Ca²⁺1.80mmol/L,pH 7.0,which should be supposed to be an efficient experimental scheme.