Study On Process Conditions And Influence Law Of Bio-hydrogen Production From Biomass By Fermentation

With the increasingly stringent of environmental requirements and the increasingly exhausted of world fossil energy sources, hydrogen, as a clean energy that can replace conventional fossil fuels, is being paid more and more attention. Meanwhile, anaerobic fermentation hydrogen production with biomass solid wastes is a biotechnology that uses the physiological metabolism of microorganisms which decompose organic substances to product hydrogen. During production of the clean energy, it also reduces environmental pollution problems that are caused by the stacking and burning of the biomass solid wastes, changing waste into valuables. The fermentation hydrogen production is a clean production mechanism that conforming with sustainable development strategy. In this paper, on the basic of the previous research, a detail research of hydrogen production by anaerobic fermeniation from corn straw was carried out.First of all, optimize the pretreatment process of the cow compost that was taken as bacteria source. After comparing the ways among directly forced aeration, directly boiling and the combination of boiling and forced aeration-forced aeration, the combination of boiling and forced aeration-forced aeration was chosen as the pretreatment process according to the hydrogen production potential. The effects of boiling time and amount of bacteria source on hydrogen production potential were examined. The optimum boiling time was 18min, the optimum amount of bacteria source is 50g/L. Under these conditions, the hydrogen production potential of the sucrose simulated wastewater and corn straw reaches the maximum, was respectively 241.35mL/g, 138. 57mL/g.One of key factors of Bio-hydrogen prodution by biomass was to improve the system stability. And this depends on the stability of microorganisms in the fermentation broth to a larger degree. Preliminary study was carried out on microbial ecology of the fermentation broth. The effects of boiling time and amount of bacteria source on hydrogen production potential were examined. The growth of the microorganism of the 5L and 30L reactors were examined. Both growth curve of the tow reactors accorded with the typical microbic growing law. In stationary phase, the concentration of hydrogen-producing bacteria reached the maximum , was respectively 3.32g/L, 3.90g/L. Meanwhile, purification and anaerobic culture were carried out on the strain in the stationary phase, a pure strain was obtained. By means of the Gram Stain and scanning electron microscope, a preliminary judgement was preliminary made that the strain was Clostridium.The pretreatment result of substrate was also a key factors of Bio-hydrogen prodution. Basing on the basic of previous experiments, the corn straw was pretreated by combination of mechanical grinding, steam explosion and dilute acid hydrolysis. The effect of particle size of corn straw and the liquid-solid ratio during the acidolysis to the result of acidolysis and hydrogen-producing were examined. The optimum particle size of corn straw is less than 0. 850mm, the optimum liquid-solid ratio was 10. Under these conditions, the sugar content of the corn straw after acidolysis reached maximum at 19. 76%. Hydrogen-prodution culture experiment was carried out by the optimum mean of pretreatment, the maximum hydrogen production potential of corn straw was 128. 79ml/g.Factors in the fermentation process of hydrogen production were studied, and then they were optimized in 5L and 30L reactor. The most appropriate control conditions are as follows: temperature 37℃; pH 5. 0±0. 2; the optimum substrate concentration: 10g/L in 5L reactor, 15g/L in 30L reactor, substrate residence time 12h; stirring speed: 120r/min in 5L reactor, 100r/min in 30L reactor. Effects of metal ions on the hydrogen fermentation were mainly studied. The effects of Fe²⁺ and Mg²⁺ on hydrogen production potential and rate were examined. The optimum ion concentration was at Fe²⁺200mg/L, Mg²⁺10mg/L.At this condition, the maximum hydrogen production potential and rate in 5L reactor is 112.37mL/g and 115. 68mL/(L·h) respectively; while in 30L reactor was 193. 85mL/g, 373. 92mL/(L·h) respectively.At the optimized experimental conditions obtained in the earlier experiments, conducting the hydrogen production contrast experiment in 5L and 30L reactors, and obtained the desired experimental results. The results got from the two size reactors about hydrogen production potential, maximum hydrogen production rate, delay time of hydrogen production and the maxmum of H₂ concentration in bio-gas showed that the hydrogen production potential, the maximum hydrogen production rate for corn stalk in the 30L reactor were 1. 7 times, 3.22 times of 5L reactor, respectively. The delay time of hydrogen production was shorter and the maxmum concentration of H₂ in bio-gas was higher in the 30L reactor. The metabolic pathways of microorganisms were also compared with the two size reactors, the experimental results showed that the maximum concentration of H₂ in the bio-gas was 55% in the 5L reactor and 61% in the 30L reactor, wheares, no methane was detected in the reaction process. The concentration of H₂ and the content of the main liquid end products in the 30L reactor were higher than those parameters in the 5L in the whole butyric acid type fermentation reaction process. All of the above results showed that the fermentation performance in the 30L reactor was more superior than that in the 5L reactor.