The Optimization Studies on Selection of Carbon Sources for Photofermentative Hydrogen Production By Four New Isolates

Abstract

Hydrogen is an ideal  energy  alternative from  an  environmental  and  economic  point  of  view due to the facts that the combustion end product is only a water vapor and it is a clean energy carrier with a high  energy  yield.  Photofermentative bacteria are promising since they can carry out complete substrate conversion.  In this study four newly isolated photofermentative bacterial strains were tested in batch reactors in order to determine the optimum growth and hydrogen production conditions. The batch studies conducted by using different organic acids showed that acetate, butyrate, lactate and succinate are good sources for photofermentative biohydrogen production for these four new isolates. Theoretically, 5 g/L acetate should yield in 4 mol H₂/mol acetate. In this study, the yield values changed between 1.5-1.7 mol H₂/mol acetate. On the other hand, the hydrogen production rates were calculated to be between 0.46-0.60 L H₂/L reactor.day for acetate feed as the carbon source. The effluent of a dark fermentation process also includes high amounts of butyrate. The isolates 1, 2 and 3 produced up to 80 mL H₂ from butyrate except for the 4th isolate which was not able to use butyrate effectively. H₂ production rates of these 3 isolates were varied between 0.22 to 0.39 L H₂/L reactor.day were achieved. Succinate and lactate are also good sources for photofermentative H₂ production. Four of the isolates could use these carbon sources very effectively and about 50% of the theoretical yields were achieved.