The Mechanism Of Acid-Alkali Combined Pretreatment And Ethanol Fermentation From Waste Tobacco Stems

With the development of economic and social,the non-renewable fossil fuels on the earth are constantly being consumed and the energy crisis has become increasingly problematic.At the same time,the environmental problems caused by largely using of fossil fuels are becoming more and more serious,so it is necessary to find a renewable clean energy.The biomass is one of the most abundant renewable in the world,which is an ideal substitute.Yunnan Province is a largest area where tobacco is grown and a large amount of waste tobacco biomass is produced every year.If the waste tobacco biomass can be used effectively,the significant economic and ecological benefits will be produced.As so far,the research on biomass energy from waste tobacco biomass has been rarely reported.In present study,an acid-alkali combined pretreatment was used and the pretreatment sequence,concentration,temperature and solid to liquid ratio on pretreatment effect were optimized systematically.The results shown that the optimal pretreatment conditions are first pretreated by H₂SO₄(0.5%(w/w)with a 10%solid-liquid ratio(w/v))at 95?for 0.5 h and followed pretreated by Na OH(0.5%(w/w)with a 6%solid-liquid ratio(w/v))at 90?for 2.5 h.The enzymatic hydrolysis efficiency of substrate can be significant improved.After combined pretreatment,the surface structure of the tobacco stem was destroyed,the lignin removal rate could reach 30%,the crystallinity of the tobacco stem also increased significantly,and the zymolytic efficiency of the tobacco stem can be as high as 82.5%.In order to improve the feasibility of ethanol fermentation from pretreated tobacco stem,the effects of prehydrolysis time and substrate concentration on accumulation of reducing sugars for simultaneous saccharification and fermentation were researched.The effects of feeding period and mode on ethanol concentration at30%(w/v)tobacco stem were also optimized.The fermentation efficiency was highest when the rehydrolysis time is 24 h and feeding period is 24 h.The ethanol concentration reached 86.88 g/L at 30%(w/v)tobacco stem.After mass balance calculation,1 kg of tobacco stem raw material can be converted into 0.144 kg of ethanol by pretreatment and fermentation.The various inhibitors can be produced during the pretreatment and furan aldehyde is a kind of main inhibitors.The effect of furan aldehyde on growth of fusion yeast SHY07-1 was investigated by growth kinetics and the potential transcriptional regulatory mechanism was studied by transcriptomics.The results shown that the SHY07-1 has a better tolerance to furan aldehyde and there is no certain correlation between biomass and lag phase.After transcriptome analysis,the transformation of furan aldehyde by SHY07-1 was probably by improving the expression of aldehyde dehydrogenase(ALD)and alcohol dehydrogenase(ADH).At same time,the expressions of phosphate fructose kinase(PFK1)and phosphoglyceric kinase(PGK1)related to glycolytic cycle were also improved by furan aldehyde.