Enhanced anaerobic digestion of glycerol by promoting DIET reaction

This study was attempted to enhance anaerobic digestion efficiency of glycerol by promoting direct interspecies electron transfer (DIET) reaction. First, a batch test was performed in the presence of magnetite at various glycerol concentrations (2.5-10 g COD/L). The magnetite addition showed a little effect on CH4 production at 2.5 and 5.0 g COD/L, while it significantly enhanced the performance at 7.5 g COD/L (16% higher amount of CH4 production compared to the control) with shortening the lag period. To see the effect of promoting DIET reaction in the continuous operation, one reactor was operated with electrical energy (0.3 V) input, and the control was also operated at various organic loading rates (0.5-3.5 g COD/L/d, HRT = 20 d). The highest CH4 production rate achieved in the control was 520 mL CH4/L/d at 2.0 g COD/L/d, while the reactor with electrical energy input showed a stable performance up to 3.0 g COD/L/d with 820 mL CH4/L/d. The accumulation of propionate with pH decrease was accompanied with the drop of performance. The main change in bacterial community was the increased abundance of Pelobacter sp. (28% of total sequences) in the broth of electrical energy input, which was negligible in the control.