The paper reports an experimental investigation into the transient performance during the start-up of a pilot-scale two-phase anaerobic digestion (TPAD) process demonstration unit (PDU) treating food waste with biochar addition. Hydrogen (H-2) was produced in the first phase (R1) and methane (CH4) was produced in the second phase (R2). A fed-batch operation strategy was applied to the start-up of both phases, followed by semi-continuous operation. Production rates and yields of H-2 and CH4 and volatile fatty acids (VFA) were measured while the pH and temperature were monitored throughout the process. Fed-batch operation allowed microbe enrichment and gradual VFA production in both phases, which was observed to be efficient in starting up the TPAD PDU. Under semi-continuous operation, R1 produced biogas with composition up to 49% of H-2 and at a yield of 46 L H-2.kg(-1) VS. CH4 composition and yield reached up to 59% and 301 L CH 4 .kg(-1) VS in the R2. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.