Hydrogen production from starch by co-culture of Clostridium acetobutylicum and Rhodobacter sphaeroides in one step hybrid dark- and photofermentation in repeated fed-batch reactor.

Hydrogen production from starch by a co-culture hybrid dark and photofermentation under repeated fed-batch conditions at different organic loading rates (OLR) was studied. Effective cooperation between bacteria in co-culture during initial days was observed at controlled pH 7.0. However, at pH above 6.5 dark fermentation phase was redirected from H2 formation towards production of formic acid, lactic acid and ethanol (which are not coupled with hydrogen production) with simultaneous lower starch removal efficiency. This resulted in decrease in the hydrogen production rate. The highest H2 production in co-culture process (3.23LH2 /Lmedium - after 11days) was achieved at OLR of 1.5gstarch /L/day, and it was twofold higher than for dark fermentation process (1.59LH2 /Lmedium ). The highest H2 yield in the co-culture (2.62molH2 /molhexose ) was obtained at the OLR of 0.375gstarch /L/day. Different pH requirements of bacteria were proven to be a key limitation in co-culture system.