Biodegradability and methane production potential of glycerol generated by biodiesel industry

Crude glycerol, the main by-product of the biodiesel industry, is a material containing compounds considered recalcitrant to microorganisms. The aims of this study were to determine the anaerobic biodegradability and the methane production potential (MPP) of different crude glycerols generated from the transesterification of oils from several kinds of seeds and/or beans, and the anaerobic toxicity of crude glycerol obtained from a mixture of soybean and cottonseed oils. All tests were based on specific methanogenic activity assays (SMA). The biodegradability tests and the MPP assays lasted 30 days. Toxicity was evaluated through the statistical technique of factorial design and a response surface was generated in which the concentrations of crude glycerol and glucose were the independent variables and SMA was the dependent variable. The results showed that the type of seed or bean, as well as the transesterification process, affected the anaerobic biodegradability. Biodegradability ranged between 65.9 and 85.6% and MPP, between 0.220 and 0.322 m3 CH4/kg crude glycerol. The toxicity test showed that crude glycerol was not toxic to anaerobic sludge.