Cornstalk, as an abundant renewable biomass resource, could be used for biocrude oil production through hydrothermal liquefaction (HTL), however, recalcitrant wastewater is released as the main byproduct. This study reported the degradation of recalcitrant wastewater and simultaneous hydrogen production via a continuous up-flow fixed-bed microbial electrolysis cell (MEC). Chemical oxygen demand removal rates were over 60% under different applied voltages and the highest reached 80.2% at 1.2 V. Specifically, GC-MS analysis identified recalcitrant organic matter in HTL wastewater like dimethyl phthalate and diethyl phthalate were significantly removed in a ratio of 95.3% and 79.3% via this MEC. A hydrogen production rate of 3.92 mL/L/d was achieved at 1.0 V in the cathode, whereas the maximum power density (305.02 mW/m(3)) was obtained at 0.6 V. Illumina MiSeq sequencing revealed that the content of phylum Proteobacteria in anodic biofilm (70.19%) was much higher than the inoculum (20.38%). The dominant genus Xanthobacter (58.17%) in anodic biofilm was probably associated with the degradation of dimethyl phthalate. This work suggested that it is feasible to efficiently degrade recalcitrant wastewater from HTL of cornstalk and simultaneously produce hydrogen through MEC. Copyright (C) 2016, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.