In this study, an electro-coagulation treatment is performed to remove phenolic compounds, 5-hydroxymethylfurfural (5-HMF), and furfural from hydrolysates obtained by pilot-scale supercritical water hydrolysis (SCWH) of lignocellulosic biomass. The treatment used aluminum electrodes under various conditions (initial pH: 2.5-11, voltage: 0-10 V, and electrolyte (NaCl) concentration: 0-1.6% (w/v)). Changes in the treatment parameters resulted in more than 40% of phenolic compounds and most of the 5-HMF and furfural being removed from the hydrolysates at the optimal condition (pH 5/10 V/0.8% NaCl/180 min) while the initial sugar (glucose and xylose) concentrations were maintained. Therefore, the electro-coagulation treatment may provide a more effective purification process for sugar production compared to the conventional activated charcoal treatment process, which causes sugar loss (>25%). (C) 2019 Elsevier Ltd. All rights reserved.