Research On Enzymatic Hydrolysis And Fermentation Of Large Algae To Produce Bio-ethanol

With the population explosion and the gradual depletion of the non-renewable fossil fuels such as coal,oil and natural gas,the energy shortages will seriously threaten the long-term development of human beings.Meanwhile,a series of environmental problems such as global warming,air pollution and water pollution have forced people to explore environmental-friendly renewable sources of energy.Biomass is an organic matter which is directly or indirectly formed by the photosynthesis of green plants in different ways.It can be transformed into different types of sustainable energy through a variety of ways,which can not only ease the excessive dependence on traditional fossil fuels,but also can reduce environmental pollution to some extent.The conversion of biomass into new energy mainly includes physical conversion,chemical conversion and bioconversion.Thermochemical conversion in chemical conversion and biological fermentation in bioconversion are the main methods to produce liquid fuels.Bioethanol as a kind of fungible liquid fuel fermented from biomass shows a promising prospect.It not only has good environmental protection and antiknock abilities,but also can enhance the degree of gasoline combustion when it is blended with gasoline.Biomass can be divided into terrestrial biomass and marine biomass.Compared with the former,marine biomass has the advantages of wide source,high photosynthetic efficiency and no occupation of cultivated land,which has received more and more attention in biomass conversion to new energy sources.In this work,Enteromorpha prolifera which outbreaks in Qingdao seaside was used as the raw material for enzymatic hydrolysis and fermentation to produce bioethanol.The effects of substrate concentration,enzyme dosage,enzymolysis time,temperature and p H value on enzymatic hydrolysis were studied.The results showed that the optimum enzymatic hydrolysis conditions were material liquid ratio of 5%,cellulase dosage of 80 mg,enzymolysis time of 48 h,enzymolysis temperature of 60 oC and the p H value of 4.8.In addition,the effects of time,temperature and yeast dosage on fermentation were also discussed.The ethanol has the highest yield under the condition of the fermentation time of 48 h,the temperature of 30 oC and the yeast dosage of 2.1 g.The macroalgaes are divided into green algae,brown algae and red algae.Although their main components are polysaccharides,fat and protein,the compositions and contents of each component are different.Especially,polysaccharides are the main components involved in hydrolysis.Therefore,there aregreat differences in the processes of enzymatic hydrolysis and fermentation.We selected the Enteromorpha(green algae),Undaria pinnatifida(brown algae)and Porphyra tenera(red algae)as raw materials,respectively,for enzymatic hydrolysis and fermentation under the same conditions.The characterizations of SEM and FTIR for the raw materials and residue after enzymatic hydrolysis have been performed.The reducing sugar yields and fermentation efficiencies have also been compared.The result showed that the reducing sugar yield of Porphyra tenera is the highest.Moreover,we also found that the yield of ethanol is proportional to that of reducing sugar.For the three kinds of macroalgaes,Porphyra tenera has the highest ethanol conversion of 13.17%,so it is the most promising bioethanol fermentation biomass feedstock.At present,the main feedstocks for bioethanol production are lignocellulosic biomass and algae biomass.There are great differences in their main components.The former mainly includes cellulose,hemicellulose and lignin,while the latter contains polysaccharide,fat and protein.These great differences in the components can lead to differences in ethanol yield.Cellulose in lignocellulosic biomass and polysaccharide in algae biomass are the main components involved in fermentation.The internal structures between them are completely different.So,we selected microcrystalline cellulose as the model of cellulose and sodium alginate as the model of macroalgae polysaccharide as well as sweet potato straw and Undaria pinnatifida to hydrolyze and ferment to produce bioethanol.The result showed that macroalgae biomass was better than terrestrial biomass in both the reducing sugar and the bioethanol yield in spite of some differences.Therefore,considering the higher preprocessing cost of terrestrial biomass and the competition with food,marine biomass has greater potential and broader prospect in the production of bioethanol.