Biohydrogen Production From Glycerol in Microbial Electrolysis Cells and Prospects for Energy Recovery From Biodiesel Wastes

The manufacture of biodiesel generates 10 wt% of glycerol as a byproduct. Currently, the majority of this waste glycerol is treated in wastewater treatment plants or incinerated. In this study, single chamber, membrane-free microbial electrolysis cells (MECs) was evaluated to produce hydrogen from pure glycerol and waste glycerol. At an applied voltage of 0.6 V, a maximum current density of 7.5 ± 0.4 A/m² (238.6 ± 12.7 A/m³) was observed, the highest reported current density for a microbial electrochemical system operating on glycerol. Maximum current densities on 0.5% waste glycerin were 0.1–0.2 A/m², much lower than those on pure glycerol, possibly due to the high salt and soap concentration in the waste glycerol. The maximum hydrogen yield on 50 mM glycerol was 1.8 ± 0.1 mol hydrogen/mol glycerol at a hydrogen production rate of 1.3 ± 0.1 m³/day/m³. The presence of methanol in the waste glycerin reduced hydrogen yield by nearly 30%. The energy efficiency on 0.5% of waste glycerol reached 200% at an applied voltage of 0.6 V. Conversion of all of the waste glycerol currently generated annually in global biodiesel manufacture to hydrogen using optimized MEC technology could generate ∼ 180 million kg of H₂, representing a value of nearly $540 million, or the amount of H₂ required for the production of 4.8 billion kg of green diesel. This study indicates that the generation of useful products (such as hydrogen) from waste glycerol will greatly increase the viability of the growing biodiesel industry.