Hydrogen production from crude glycerol in an alkaline microbial electrolysis cell

Crude glycerol is an undesired by-product of biodiesel production with a low commercial value (i.e. a ton of biodiesel results in around 110 kg of crude glycerol) and, thus, glycerol needs valorization. In particular, there is a need of providing a benefit to alkaline wastewaters from biodiesel production with excess of glycerol. Bioelectrochemical systems (BES) are an emerging technique to recover the energy contained in a substrate either as electricity or as other added-value products such as hydrogen. Moreover, promising results have been reported with alkaline BES showing higher current intensities than neutral pH conditions. This study is the first experimental evaluation of alkaline bioelectrochemical production of hydrogen from real crude glycerol as sole carbon source. The results show that alkaline glycerol degradation is feasible under both microbial fuel cell mode (2 mA, 71.4 A/m3 and 55% of CE) and microbial electrolysis mode (maximum of 0.46 LH2/L/d and 85% of rCAT). The values obtained are promising since they are in the range of those obtained with other simpler carbon sources such acetate. A complex consortium involving fermentative bacteria (such as Enterococcaceae), alkaline exoelectrogens (such as Geoalkalibacter) and homoacetogens (such as Acetobacterium) was naturally developed in the anode of the MEC.