Hvdrogen Production From Biomass By Combination Of Dark And Photo Fermentation

Hydrogen is a new type of clean energy with high energy density. Hydrogen production from recyclable biomass by bacterial fermentation is attracting more and more attention and becoming the focus of research field and high technology competition. In this paper, the mechanism of hydrogen production by combination of dark and photo fermentation was studied with recyclable biomass as substrates which are rich in glucose, starch and cellulose. In the pretreatment, a novel method of combining microwave heating and acid/alkali solution at high temperature and high pressure was used to promote the hydrolysis of the cellulosic biomass. In dark and photo fermentation, mixed bacteria were used to produce hydrogen instead of the pure bacteria, which can greatly enhance the hydrogen yield. By combination of dark and photo fermentation, hydrogen yield form cellulosic biomass reached the international advanced level.In this study, glucose was used as substrate for hydrogen production by combination of dark and photo fermentation in a two phase process. The inoculum in dark and photo fermentation are Clostridium butyricum (C. butyricum) and Rhodopseudomonas palustris (R. palustris) respectively. In the first phase of dark fermentation, the maximum hydrogen yield (HY) of1.72mol H2/mol glucose and the maximum hydrogen production rate (HPR) of100ml J2/l/h were obtained with acetate and butyrate as the main liquid byproducts. In the sencond phase of photo fermentation, R. palustris could use the residual liquid of dark fermentation to further produce hydrogen. The maximum HY and HPR could reach4.16mol H2/mol glucose and118ml H2/1/h respectively. By combination of dark and photo fermentation, hydrogen yield from glucose could be greatly increased from1.72to5.48mol H2/mol glucose.Hydrogen production from starchy biomass such as cassava starch by combination of dark and photo fermentation was studied. In dark fermentation, the mixed hydrogen-producing bacteria was isolated and enriched from acitivated sludge and then domescated with cassava starch. When raw cassava starch was hydrolyzed by α-amylase&glucoamylase and then used for hydrogen production, the maximum HY was increased from240.4to276.1ml H2/g starch and maximum Roverall from72.5to229.3ml H2/1/h respectively. In photo fermentation, R. palustris was used as the inoculum to produce hydrogen from the residual liquid of dark fermentation. The maximum HY and HPR were131.9ml H2/g starch and16.4ml H2/1/h, respectively. The maximum HY form cassava starch was enhanced from240.4to402.3ml H2/g starch by combiantion of dark and photo fermentation. In further study, the HY was further enhanced to840ml H2/g starch by optimizing the culture conditions of dark fermentation with response surface methodology (RSM) and improving hydrogen production in photo fermentaiton with immobilized mixed photosynthetic bacteria.A novel method to pretreat and degrade cellulosic biomass was studied. Rice straw was pretreated by microwave-assisted alkali to improve the saccharification of enzymatic hydrolysis and HY in dark and photo fermentation. A maximum reducing sugar yield of69.3g/100g TVS was obtained when50g/1rice straw was pretreated by microwave heating for15min at140℃in0.5%NaOH solution and then enzymatically hydrolyzed for96h. When hydrolyzed rice straw was used for hydrogen production by anaerobic bacteria in dark fermentation, a maximum HY of155ml H2/g TVS was obtained at60g/1rice straw. The residual solution (mainly acetate and butyrate) of dark fermentation was reutilized for hydrogen production by immobilized mixed photosynthetic bacteria in photo fermetation, and the maximum HY of328ml H2/g TVS was obtained at50g/1rice straw. By combination of dark and photo fermentation, the maximum HY was greatly enhanced to463ml H2/g TVS (at50g/1rice straw).Water hyacinth, which is a typical cellulosic biomass, was used as substrate to compare the effects of different pretreatmen method on reducing sugar and hydrogen production.(1)20g/1water hyacinth was first pretreated with1.0%(w/v) NaOH solution for24h at45℃C and heated for1.0min at420W in a microwave oven at normal pressure, then pretreated water hyacinth solution was hydrolyzed by cellulase for48h at45℃and used for hydrogen production. In dark fermentation, the maximum HY and HPR were76.7ml H2/g TVS and223.1ml/l/h. The maximum HY in photo fermentation was522.6ml H2/g TVS. By combination of dark and photo fermentation, the maximum HY could be improved from76.7to596.1ml H2/g TVS.(2) When20g/lwater hyacinth was pretreated by microwave heating for15min at140℃in1.0%H2SO4solution and then enzymatically hydrolyzed for72h, a maximum reducing sugar yield of64.4g/100g TVS was obtained. Then the pretreted water hyacinth solution was used for hydrogen production in dark fermentation, a maximum HY of112.3ml H2/g TVS was obtained. The maximum HY in photo fermentation was639.3ml H2/g TVS. By combination of dark and photo fermentation, the maximum HY from water hyacinth could reach751.5ml H2/g TVS. Finally, semicontinous fermentation experiments in two serial5-L reactors were carried out and a HY of335.7ml H2/g TVS was obtained, which could lay a foundation for the indudtrial application of hydrogen production from water hyacinth.