Two-stage conversion of crude glycerol to energy using dark fermentation linked with microbial fuel cell or microbial electrolysis cell

•Crude glycerol was converted to energy by connecting dark fermentation with MFC/MEC.•Dark fermentation obtained high H2 production rate and yield.•MFCs and MECs produced electricity or H2 using different fermentation metabolites.

Crude glycerol is a main byproduct of the biodiesel industry, and the beneficial use of waste glycerol has been a major challenge. This study characterises the conversion of crude glycerol into bioenergy such as H2 and electricity using a two-stage process linking dark fermentation with a microbial fuel cell (MFC) or microbial electrolysis cell (MEC). The results showed that fermentation achieved a maximum H2 rate of 332 mL/L and a yield of 0.55 mol H2/mol glycerol, accompanied by 20% of organic removal. Fed with the raw fermentation products with an initial COD of 7610 mg/L, a two-chamber MFC produced 92 mW/m2 in power density and removed 50% of COD. The Columbic efficiency was 14%. When fed with 50% diluted fermentation product, a similar power output (90 mW/m2) and COD removal (49%) were obtained, but the CE doubled to 27%. Similar substrates were used to produce H2 in two-chamber MECs, and the diluted influent had a higher performance, with the highest yield at 106 mL H2/g COD and a CE of 24%. These results demonstrate that dark fermentation linked with MFC/MEC can be a feasible option for conversion of waste glycerol into bioenergy.