Residual Glycerol from Biodiesel Manufacturing, Waste or Potential Source of Bioenergy: A Review

Abstract

This review provides a summary of the research conducted on the use of crude glycerol, the major byproduct of the biodiesel industry, as substrate for anaerobic co-digestion and production of biogas. In general, for every 100 kg biodiesel produced, approximately 10 kg crude glycerol is generated. Because this glycerol is expensive to purify for use in food, pharmaceutical, or cosmetic industries, biodiesel producers must seek alternative methods for its disposal. Several studies have demonstrated that the use of crude glycerol as a C source for fermentation and biogas generation is a promising alternative use for this waste material. The high C content of glycerol increases the C:N ratio in the mixture, avoiding the inhibition of the process by the excess of N increasing methane production of digesters by 50 to 200%. Anaerobic codigestion of glycerol and a variety of residual biomasses may be a good integrated solution for managing these wastes and simultaneously producing a source of bioenergy in an environmentally friendly way. On the other hand, after anaerobic treatment of glycerol, an organic matter-rich solid waste is generated (digestate). The incorporation of digestates from glycerol co-digestion to soils constitutes an important source of organic matter and nutrients for plants. However, the potential of digestates as an organic soil amendment has not been sufficiently studied. The utilization of glycerol as a potential source of energy, rather than as a waste, seems to be a convenient way of lowering the costs of biodiesel production and making this emerging industry more competitive.

Progress, prospect and challenges in glycerol purification process: A review

“…It was found that for initial concentration of 70 g/L crude glycerol, certain impurities inhibited the cell growth. Soap and methanol have been found to negatively influence the algae production of DHA from crude glycerol [60] and the high salinity (Na or K) of crude glycerol can largely inhibit the microbial activity in the anaerobic digestion of crude glycerol [61]. Studies also show that saponified fatty acids (SFA) have inhibitory effect on photofermentative growth of Rhodopseudomonas palustris on crude glycerol to produce hydrogen [12].…”

<b>Co-digestion of crude glycerin associated with cattle manure in biogas production in the State of Paraná, Brazil

“…However, glycerin obtained from the process of production and the obtainment of esters (approximately 10 kg of glycerin are generated for every 100 L of biodiesel produced) has several impurities such as water, fatty waste, catalyst residues and a high chemical oxygen demand (Santibañez, Varnero, & Bustamante, 2011).…”

Hydrogen biorefinery: Potential utilization of the liquid waste from fermentative hydrogen production

“…Therefore, liquid waste generated during fermentative hydrogen production using pure/crude glycerol could be considered as a potential renewable source of PD. Crude glycerol is a byproduct of biodiesel manufacturing by trans-esterification process and nearly 10 kg of crude glycerol is generated for every 100 kg of biodiesel produced [35]. Although it is an expensive process [35]; glycerol can be recovered from crude glycerol [36].…”