Screeing Of High Efficient Fermentative Hydrogen-Producing Bacteria And Study On Hydrogen Production

There is currently a serious energy and environmental crisis that has been exacerbated by the limited availability of fossil fuels and pollution by industrial wastes. As an ideal clean energy carrier, hydrogen is regarded as one of the most promising substitutes for fossil fuels due to its high energy content and renewable and nonpolluting characteristics. When compared with traditional physicochemical methods of hydrogen production, biological hydrogen production has several unique advantages, including low-cost raw materials, operating at ambient temperatures and normal pressures, and expending no mineral resources.Among various approaches of biohydrogen production, dark fermentation has been considered an efficient approach because it enables the stable production of hydrogen without the need for light. Furthermore, this method can be used to produce hydrogen from industrial and agricultural wastes. Therefore, dark fermentation has the potential for large scale industrial production of hydrogen. In addition, anaerobic fermentation of organic freshwater waste, which is an environmentally friendly process that is less energy intensive than other forms of fermentation, has attracted extensive attention.Three strains of XA-2, BL, DA-1were isolated from activated sludge from a wastewater treatment plant. According to the Biolog Microbial Identification System and16S rDNA sequence analysis, the strainXA-2was determined to be Enterobacter cloacae XA-2. The cell growth was investigated at different conditions. The results indicated that the optimum culture conditions of the strain were a temperature of37℃, initial pH of9.0, an initial NaCl concentration of4%o and initial glucose of15g/L. In batch experiments, hydrogen evolution was observed during the late exponential phase. This strain was able to produce hydrogen over a wide range of pH values (5-12), with the optimum initial pH being pH5. The maximum cumulative hydrogen level and average rate of gas production were1767.80mL H2/L medium and445ml/L? h, respectively, with an initial glucose concentration of25g/1. A high cumulative hydrogen production (817.52ml/L) was obtianed When sucrose was used. In additon, This strain could produce hydrogen from various carbon sources such as monosaccharides (glucose, fructose), disaccharides (sucrose,maitose,lactose), alcohols (sorbitol) and inorganic carbon sources (citric acid).Moveover, this strain can tolerate a salinity two-fold higher than sea water and still produce hydrogen. The hydrogen production by E. cloacae XA-2in sea water was slightly higher than its production under fresh water conditions. Taken together, these results suggest that the strain has a strong salt-tolerance and potential ability for biohydrogen production and biological treatment of marine culture wastewater and organic waste. Based on its morphological characteristics and16S rDNA sequence analysis, the isolated strains BL and DA-2were determined to be Clostridium perfringens BL and Candida tropicalis DA-2, respectively. The former was obligate anaerobic productor, while the latter could not product hydrogen when cultured individually but it could improve hydrogen production when cultured with E. cloacae XA-2.