| Summary: | Fast energy consumption and global climate change is pushing people to seek alternative and renewable energy resources. Hydrogen is the most promising alternative energy and can be produced from a variety of inexpensive renewable resources by fermentation. Caproate is an important precursor for the synthesis of fine chemicals in industry. It can be formed from ethanol and acetate or butyrate by anaerobic bacterium Clostridium kluyveri in the fermentative hydrogen production process. The roles of ethanol and acetate as the products of fermentative hydrogen production by hydrogen-producing Clostridium species and also the essential substrates for caproate formation by C. kluyveri indicated the possibility of coculturing them with sugar and ethanol as substrates to produce caproate and hydrogen as the end products. Suitable source of sludge for isolation of C. kluyveri was identified by analyzing the composition of hydrogen and concentration of caproate. Isolation and cultivation of bacteria was carried out by serial dilution and transferring of cultures between liquid medium and solid medium repeatedly. In the cultures of C. kluyveri with synthetic medium, samples which consumed more ethanol during the same period produced more caproate, as much as 1/3 of the total VFA. More caproate was produced in terms of quantity and proportion when the ethanol/acetate ratio was larger. Butyrate composition of the total VFA was maintained at a stable range of 28~30% and ethanol/butyrate ratio was maintained around 12~14. In an enrichment culture, large reduction in ethanol and acetate with formation of butyrate and caproate was observed indicating ethanol and acetate were the two essential substrates for C. kluyveri. Around 60% of carbon source was consumed by C. kluyveri to form acid and it also consumed a large part of carbon for biomass growth. Hydrogen-producing Clostridium species were cultured separately with glucose or starch substrate. By comparing the biogas and acids accumulation, glucose generally was easier to be fermented to form acids than starch in terms of total production and maximum concentration. It always resulted in a lower final pH than using starch as substrate.
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