S122: Microbial conversion of biodiesel by-products to biofuel

In the following study, different cultures of sulfate-reducing bacteria (SRB) and methanogens were grown with crude glycerin as a means to convert the waste product into methane. The sulfate-reducing bacteria were grown syntrophically, in different combinations, with hydrogenotrophic methanogens.  Cultures were investigated for the ability to produce methane via the utilization of pure glycerol, fractionated glycerin, and crude glycerin as carbon and energy sources. In order to gain insight into cellular physiology, glycerol, acetate, free fatty acid, and methane concentrations were measured throughout growth. The cultures grew fastest on pure glycerol and experienced a lag-phase in growth on fractionated glycerin and longer lag-phases when transferred to crude glycerin. However, methane yields were similar on the three fractions.  Cultures growing on pure glycerol and fractionated glycerin displayed a decrease of methane production as growth rate increased. The opposite was observed with growth on crude glycerin. With most cultures, the addition of an aceticlasitc methanogen increased methane concentrations significantly.  Different methanogens displayed the capability of utilizing the by-product, acetate, from SRB oxidation of glycerol and the methanol layer from fractionated and crude glycerin.  Certain cultures appeared to interfere with particular culture combinations based upon decreased methane production, and some cocultures grew poorly and produced little methane when grown on the supernatant of other methanogens.  This is the first study to characterize the utilization of crude glycerin from biodiesel production by syntrophic cultures of SRB and methanogenic archaea.