An operational strategy to produce Bio-hydrogen : the use of digestate for process control

A semi-continuous digester was fed twice a day with a concentrated solution of glucose (100 g l-1) and monitored for a 30-days period, with the aim of testing the possibility of utilizing the digestate of a traditional biogas plant, after a heat-shock at 100ºC, for controlling process parameters (organic loading rate OLR, pH, volatile fatty acids VFA concentration), by adding it to the fresh substrate at a ratio R of the total feeding volume. The process resulted instable for OLR=10 gVS L-1and R=0.7, while more stable for OLR of 5 gVS L-1and R=0.85. The maximum bio-hydrogen production rate in stable conditions was 100 NmLH2 h-1 and the conversion yields were 1.7 - 1.8 molH2 mol-1glucose. The produced biogas showed always complete absence of methane.