Production of value-added products from biodiesel derived crude glycerol

Abstract

Crude glycerol, a by-product of biodiesel production which contain impurities such as methanol, triglycerides and catalysts, would represent a huge challenge to the environment if disposed. Thus the best opportunity is to convert crude glycerol into valuable products. While a number of microorganisms are able to utilize glycerol as a sole carbon source to yield a range of organic acids and alcohols, the fermentation process has not been optimized. The main objective of the study was to evaluate the application of ultrasound to enhance the production of value-added acids and alcohols by anaerobic fermentation of crude glycerol. By a method of screening, Clostridium diolis was selected and used in batch fermentation experiments at 37 oC, pH of 6.8 - 7 and 150 rpm on anaerobic environment by N2 sparging. Prior to each experiment, crude glycerol was washed three (3) time with diethyl ether and a series of glycerol concentrations (50-150 g/L) was fermented for 48 hours with samples taken every 3 hours for analyses. The high-performance liquid chromatography (HPLC) and a light microscopy were used to analyze samples before and after the fermentation process. Interestingly, very low amounts of methanol and free fatty acids were observed in the washed glycerol after HPLC analysis compared to crude glycerol. Results also demonstrated the production of 1, 3-Propanediol (1, 3-PD) and acetic acid when the fermentation liquor was analyzed by HPLC after 48 hours. Moreover, other solvents such as butanol and lactic acid were obtained in very low quantities. Subsequently, the effect of ultrasound on the growth of Clostridium diolis was evaluated and lead to enhanced yields by promoting rapid cellular growth rate. The results thereby indicate that better product yields can be achieved when microorganisms are stimulated with low intensity ultrasonic irradiations