| Lignocelluloses are the most promising feedstocks for biorefinery, but the requirement for depolymerisation of cellulose makes cellulosic bioconversion cost-inefficient. In this study, industrial wastes, including cassava residues (CR) and furfural residues (FR), with corn were bio-converted into ethanol and L(+)-lactic acid. Integration process using multiple materials and producing multiple products were developed to cost-efficiently use these wastes. The main conclusions were as follows:A fermentation system using the mixed cultures of yeast and lactic acid bacteria (MSSF) was designed to mainly produce ethanol before54h and lactic acid after54h from FR. The substrate loading and temperature influence the acid/alcohol molar ratio. However, substrate loading, temperature and the cell mass ration have effect on the cellulose conversion ratio of MSSF, which is always higher than those of sole SSF. MSSF obtained9.02g/L of ethanol and18.9g/L of lactic acid at120h using substrate loading of9%, corresponded to1.07of acid/alcohol molar ratio and86.8%of cellulose conversion ratio. One bottleneck of MSSF is the need of nutrient addition. The sequential production of ethanol and lactic acid can be improved by using starchy materials and cellulosic materials. Some treatment added between ethanol fermentation and lactic acid fermentation makes nutrient addition unnecessary. Under the selected conditions, the integrated process using mixed materials coproduce22.4g/L ethanol and47.6g/L lactic acid at120h, corresponded to acid/alcohol ratio of1.08and a polysaccharide utilization ratio of86.9%.Delignification and surfactant additions are two ways of reducing the negative effect of lignin on bioconversion. For Alkaline peroxide, a delignification degree of80.2%and37.3%were the optimum delignification degree for ethanol SSF and lactic acid SSF, respectively. Gleditsia Saponin had a better performance in improving ethanol SSF than Tween-20. Protein surfactants can be produced from yeast by hydrothermal treatment. After hydrothermal treatment at121℃for30min,64.4%of yeast nitrogen and83%of yeast carbonhydrate remained in YHS while only2.28%of yeast nitrogen was non-enzymatic proteins dissolved in YHL, which have close molecular weight with cellulases. Competitive adsorption of non-enzymatic proteins and cellulases on lignin is the reason for the enhancement of glucose yield by YHL. The optimum protein loading of FRs was ranged from11.8mg/g FRs to23.5mg/g FRs, resulting in that0.63mg of nitrogen in YHL was absorbed on1gram of lignin and the enzymatic hydrolysis of FRs was increased by14.4%.Different interactions exist between lignin, cellulases and microorganisms. The effect of yeast on cellulases is not significance while lactic acid bacteria(LAB) consumed cellulases as nutrients. Extra nutrients and lignin reduce the negative effect of LAB on cellulases. Yeast are more tolerated to phenolic components than LAB. LAB and yeast compete with each other in the fermentation by mixed culture, but dead yeast cells provide nutrients for LAB. Though LAB and yeast did not consume ethanol and lactic acid, the two products inhibit lactic acid fermentation and ethanol fermentation.Using multiple materials obviously increased the yield and the final product concentration of bioconversion process. Whatever the product is ethanol or lactic acid, substrate composition is one of main factors influencing processes using multiple materials. Under optimized conditions of ethanol fermentation using multiple materials, final ethanol concentration and polysaccharide utilization were ranged from66.0g/L to73.1g/L and from73.3%to90.3%, respectively. Nutrients, substrate composition and carbon/nitrogen ratio were the main factors influencing lactic acid fermentation using multiple materials. Yeast treated by hydrothermal treatment was proven to be an effective nitrogen sources. When carbon/nitrogen ratio was between20～63, final lactic acid concentration was ranged from40.7g/L to79.5g/L and polysaccharide utilization was ranged from81.5%to87.1%. |
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