Sustainable valorization of waste glycerol into bioethanol and biodiesel through biocircular approaches: a review

Abstract

Liquid biofuels like biodiesel and bioethanol are crucial in the transition to low-carbon and high-energy alternatives to fossil fuels. One significant by-product of biodiesel production is glycerol, which accounts for about 10% of the total conversion output. While waste glycerol poses challenges due to its impurities and contaminants, it also holds potential as a metabolic resource for essential cellular components in microorganisms. Crude glycerol production is reviewed, highlighting relevance in current biodiesel technologies and its biochemical composition. To efficiently utilize waste glycerol, co-valorization with low-cost substrates through biocircular platforms using various microorganisms or insects for second and third-generation oxy-biofuels has been explored. Among these, the black soldier fly larvae have demonstrated higher competitiveness for lipid contents (35–43%), making them a promising organism for recycling waste glycerol into biodiesel production, alongside microalgae and oleaginous yeast. The microbial biodiesel productivity from oleaginous yeast is notably higher (3546 kg ha−1 y−1) than soybean biodiesel (562 kg ha−1 y−1), while microalgal biodiesel productivity surpasses palm biodiesel by more than 25 times. Remarkably, black soldier fly larvae biodiesel productivity was reported to be ~ 1.7 times higher than microalgae and an impressive ~ 43 times higher than palm biodiesel. Despite their potential for biodiesel production, waste glycerol from biodiesel industry still represents a challenge because of high impurities, high viscosity, and limited direct applications in existing processes. To further enhance energy sustainability and address the challenge of waste glycerol, biocircular platforms are discussed for waste glycerol utilization with domestic wastewater sludge, lignocellulosic biomass, and protein-rich wastes. These platforms offer opportunities to create other sustainable agricultural products while minimizing their environmental footprint.

A Response Surface Methodology Study for Chlorella vulgaris Mixotrophic Culture Optimization

“…Thus, to scale up the mixotrophic culture, it is necessary to use cost-effective nutrient sources, i.e., low-cost nitrogen and organic carbon substrates. Possible sources include urea, a cheap nitrogen source supplied as fertilizer in agriculture, and glycerol, a carbon source coproduct of the biodiesel industry [ 4 , 5 ].…”

Enhancing Recovery Yield of Vegetable Oil Methyl Ester for Bioresin Production: A Comparison Study Using Acid Neutralization

“…In contrast, heterogeneous catalysts need extreme reaction conditions (high temperature and pressure) that do not favor industrial applications, although heterogeneous catalysts can be used repeatedly. However, homogenous base catalysts initiate a saponification reaction, making the separation of methyl esters from the glycerol phase difficult [10][11][12]. Sodium ions, which are formed by a reaction between sodium hydroxide and methanol (Equation (1)), initiate soap formation.…”

The Biosynthesis of Liquid Fuels and Other Value-Added Products Based on Waste Glycerol—A Comprehensive Review and Bibliometric Analysis

“…According to Organisation for Economic Co-operation Development and the Food and Agricultural Organization (OECD-FAO) estimates, global biodiesel production currently stands at around 47.1 billion litres, and waste glycerol accounts for 12% of the total esters produced [10]. Waste glycerol is also produced during alcoholic fermentation and accounts for about 10% of the total sugar used to produce bioethanol [11]. A significant oversupply of crude glycerol from the biofuel industry is causing glycerol prices to fall from USD 480/t in 2002 to USD 110/t in 2021.…”