Optimization Of Ethanol Production By Saccharification And Fermentation From Water Hyacinth

As a kind of lignocellulosic biomass, water hyacinth could produce fuel ethanol efficiently after saccharification and fermentation processes. However, a lot of technologies in the process still need to be improved, including pretreatment method, enzyme cost and simultaneous saccharification and fermentation technology. In order to solve the key problems mentioned before, water hyacinth was chosen as substrate, optimization of pretreatment, enzyme hydrolysis and simultaneous saccharification and fermentation were investigated in this study.Dilute acid (H2SO4), dilute alkali (NaOH) and microwave combined alkali pretreatments were compared for their effects on the hydrolysis yield of reducing sugar from water hyacinth using the orthogonal test method. The result showed that acid pretreatment provided good results compared to others, and microwave combined alkali pretreatment was better than the single alkali pretreatment. By using SPSS 19.0, the optimist conditions of acid pretreatment were determined, which were acid concentration 1.00%, temperature 100℃, granularity 60 mesh, solid/liquid ratio 1:30, and saccharification time 30 min. The influence degree of these five factors on sugar production was temperature>solid/liquid ratio>saccharification time>acid concentration> granularity. The yield of reducing sugar could achieve 197.60 mg/g in the optimized condition, which improved 14.56%than before and was 37.91%of the maximum theoretical yield.To investigate the optimize conditions of enzyme hydrolysis after pretreatment, enzyme dosage, hydrolysis temperature and hydrolysis time were chosen as three factors by using single factor experimental analysis method. Under the condition of pH 4.5, enzyme dosage 0.05g/g water hyacinth, hydrolysis temperature 45 ℃ and the hydrolysis time 96h, the maximum reducing sugar yield could achieve 205.33 g/g water hyacinth.By using Response Surface Method, the optimum conditions of simultaneous saccharification and fermentation process were studied. Three factors, including fermentation temperature, fermentation time and inoculum dosage, were chosen to be investigated. Analyzed by Design-Expert software, the results showed that the optimal parameters were fermentation temperature 38.87℃, fermentation time 81.87h and inoculum dosage 6.11mL. In this condition, the ethanol production could achive 1.291 g-L-1. Meanwhile, the actual value of ethanol production was 1.289 g-L-1 (0.1289 g/g water hyacinth), which showed that the regression model was reliable..Based on the results above, the ethanol yield could achieve 0.1289 g/g water hyacinth under optimal condition when using water hyacinth as substrate, which could provide scientific guidance of ethanol production by fermentation of water hyacinth in future.