Photofermentation of crude glycerol from biodiesel using Rhodopseudomonas palustris: Comparison with organic acids and the identification of inhibitory compounds

The growth of the biodiesel industry, and its concurrent production of glycerol, has lowered the price of glycerol 20-fold. While many options for using this glycerol have been proposed, the size of the waste stream means that generation of fuels is likely to be the only viable route. One such fuel is hydrogen, production of which can be achieved biologically. The photofermentation of glycerol to hydrogen using Rhodopseudomonas palustris was investigated by exploring the growth rate, hydrogen production rate and hydrogen yield. R. palustris grows on glycerol at a rate of 0.074 h−1, and photoferments glycerol into 97 mol% hydrogen at a conversion efficiency nearing 90% of the 7 mol H2 theoretical maximum at a rate of 34 ml H2/gdw/h. Some inhibition of growth by crude glycerol was seen. This was determined to be caused by saponified fatty acids, removal of which yielded a treated crude glycerol which showed no inhibition.