High yield conversion of a crude glycerol fraction from biodiesel production to hydrogen by photofermentation

Present biodiesel manufacturing processes inevitably produce a crude glycerol side fraction. Projected future volumes of biodiesel will generate enormous quantities of glycerol of a magnitude suggesting that conversion to a fuel is the only viable route. Here we have shown that the photosynthetic bacterium Rhodopseudomonas palustris is capable of the photofermentative conversion of glycerol, both pure and a crude glycerol fraction, to hydrogen, a proposed future fuel. Relatively high yields, up to 6 moles H2/mole glycerol (75% of theoretical, 8 moles of H2/mole glycerol) were obtained. Even the crude glycerol fraction, at the concentrations used here, was readily converted to hydrogen with no apparent evidence of inhibition or toxicity. We show that the concentration of added nitrogen can be used to modify both rates and yields of hydrogen production with an apparent trade-off between the two. Finally, some factors are identified that might be examined in future studies in attempts to increase rates and/or yields.