Enhanced anaerobic digestion of phenol via electrical energy input

In the present work, effects of direct interspecies electron transfer (DIET)-promoting condition on anaerobic treatment of phenol, in up-flow anaerobic sludge blanket reactors (UASB) were investigated. One reactor (C-UASB) was operated as a control, while two reactors (EA-UASBs) were operated with electrical energy input (EEI) at 0.3 V and 0.6 V. The organic loading rate was gradually increased from 0.5 to 14 kg COD/m(3)/d at a fixed hydraulic retention time of 1 d. A drastic decline in the biogas production was started to be seen from 7.0 kg COD/m(3)/d in C-UASB, while a stable performance was achieved up to 11 kg COD/m(3)/d with maintaining a CH4 production yield of 0.3 m(3)CH(4)/g CODadded in EA-UASBs. There was no difference in the performance between two voltages applied, but higher energy recovery value of 68% was achieved at 0.3 V (49% at 0.6 V). EEI changed the physicochemical properties of granules in a favorable way, increasing diameter, settling velocity, porosity, permeability, hydrophobicity, and integrity coefficient from 2.2, 1.4, 0.7, 0.0025, 23, and 87 to 2.7-2.9 mm, 1.9-2.0 cm/s, 0.9, 0.0039-0.0053 cm(2), 36-60%, and 94-95%, respectively. EEI also affected the microbial community, increasing the dominance of DIET-related microorganisms including Methanobacterium, Methanothrbc, and Syntrophorhabdus.