ANAEROBIC FERMENTATION OF CRUDE GLYCEROL TO PRODUCE VALUE-ADDED PRODUCTS

Crude glycerol (CG) from biodiesel production was fed to anaerobic fermentations by Enterobacter aerogenes and a mixed culture of microorganisms from an industry biogas production unit. The major contaminant removed from the CG is a mixture of matter organic non-glycerol (MONG), which has the potential to reduce the efficiency of converting crude glycerol to value-added products. Removal of MONG from CG was a simple and inexpensive process that was done by the acidification of CG to a pH of 2.0 or less. This resulted in a MONG recovery of 75% and produced CGMR (Crude glycerol with MONG removed) with a MONG content of 6.43%. The effect of substrate inhibition was found from the anaerobic fermentations. Ethanol was the main product from the fermentation with E. aerogenes. When refined glycerol and CGMR were used with an initial glycerol concentration of less than 30 g/L, anaerobic digestions by E. aerogenes produced comparable results for glycerol conversion and ethanol yield. Fermentation of CG did not produce competitive values of glycerol conversion and ethanol yield. Meanwhile, fermentation of CGMR using the mixed culture of microorganisms was studied with an initial glycerol concentration of about 12 g/L in tap water, and no additional supplement nutrition was applied. As a result, valuable products were found in both liquid and gas phases. A heat-pretreating process was applied to enrich the hydrogen-producing bacteria and enhance the hydrogen content in the gas product to about 83%. Methane was the main gas phase component (71%) when the sludge was not heat-pretreated. In addition, the ethanol yield increased approximately two times using the heat-pretreated sludge, while the 1.3-propanediol yield increased about two times with the non heat-pretreated sludge. In conclusion, the fermentation of CGMR introduced the possibility of using CGMR during the biological process of converting glycerol to value-added products. Moreover, if the recovered MONG is a regained biodiesel feedstock, the use of CGMR could help to increase the efficiency of natural resource usage.