Effects of organic strength on performance of microbial electrolysis cell fed with hydrothermal liquefied wastewater

Microbial electrochemical technology has drawn increasing attention for the treatment of recalcitrant wastewater as well as production of energy or value-added chemicals recently. However, the study on the treatment of hydrothermal liquefied wastewater (HTL-WW) using microbial electrolysis cell (MEC) is still in its infancy. This study focused on the effects of organic loading rates (OLRs) on the treatment efficiency of recalcitrant HTL-WW and hydrogen production via the MEC. In general, the chemical oxygen demand (COD) removal rate was more than 71.74% at different initial OLRs. Specially, up to 83.84% of COD removal rate was achieved and the volatile fatty acids were almost degraded at the initial OLR of 2 g COD/L.d in the anode of MEC. The maximum hydrogen production rate was 3.92 mL/L.d in MEC cathode, corresponding to a hydrogen content of 7.10% at the initial OLR of 2 g COD/L.d. And in the anode, the maximum methane production rate of 826.87 mL/L.d was reached with its content of 54.75% at the initial OLR of 10 g COD/L.d. Analysis of electrochemical properties showed that the highest open circuit voltage of 0.48 V was obtained at the initial OLR of 10 g COD/L.d, and the maximum power density (1546.22 mW/m(3)) as well as the maximum coulombic efficiency (6.01%) were obtained at the initial OLR of 8 g COD/L.d. GC-MS analysis revealed the existence of phenols and heterocyclic matters in the HTL-WW, such as 1-acetoxynonadecane and 2,4-bis(1-phenylethyl)-phenol. These recalcitrant compounds in HTL-WW were efficiently removed via MEC, which was probably due to the combination effect of microbial community and electrochemistry in MEC anode.