Microbial electrolysis using aqueous fractions derived from Tail-Gas Recycle Pyrolysis of willow and guayule

•Tail gas recycle pyrolysis aqueous phase from guayule and willow were used in MECs.•Substrate conversion was 71% for willow, while only 45% for guayule.•Ten compounds were identified by HPLC of which >80% were degraded in the MEC.•Mass spec showed unnatural peptides in substrate, which were partly degraded in MEC. This study investigated microbial electrolysis of two aqueous phase waste products derived from guayule and willow generated from Tail Gas Recycle Pyrolysis (TGRP). The highest average current density achieved was 5.0 ± 0.7 A/m2 and 1.8 ± 0.2 A/m2 for willow and guayule respectively. Average hydrogen productivity was 5.0 ± 1.0 L/L-day from willow and 1.5 ± 0.2 L/L-day for guayule. Willow also generated higher coulombic efficiency, anode conversion efficiency, and hydrogen recovery than guayule at most organic loading conditions. Compounds investigated exceeded 80% degradation, which included organic acids, sugar derivatives, and phenolics. Mass spectrometric analysis demonstrated the accumulation of a long chain amine not present in either substrate before treatment, and the persistence of several peptide residues resulting from the TGRP process. New biorefineries may one day capitalize on this otherwise discarded byproduct of TGRP, further improving the potential applications and value of microbial electrolysis towards energy production.