Operation strategies for biohydrogen production with a high-rate anaerobic granular sludge bed bioreactor

Long-term operation for biohydrogen production with an efficient carrier-induced granular sludge bed (CIGSB) bioreactor had encountered problems with poor biomass retention at a low hydraulic retention (HRT) as well as poor mass-transfer efficiency at a high HRT or under a prolonged operation period. This work was undertaken to develop strategies enabling better biomass retention and mass-transfer efficiency of the CIGSB reactors. Supplementation of calcium ion was found to enhance mechanical strength of the granular sludge. Addition of 5.4-27.2 mg/l of Ca ²⁺ also led to an over three-fold increase in biomass concentration and a nearly five-fold increase in the H ₂ production rate (up to 5.1 l H ₂/h/l). Two reflux strategies were utilized to enhance the mass-transfer efficiency of the CIGSB system. The liquid reflux (LR) strategy enhanced the H ₂ production rate by 2.2-fold at an optimal liquid upflow velocity of 1.09 m/h, which also gave a maximal biomass concentration of ca. 22 g VSS/l. Similar optimal H ₂ production rate was also obtained with the gas reflux (GR) strategy at a rate of 1.0-1.49 m/h, whereas the biomass concentration decreased to 2-7 g VSS/l and thereby the specific H ₂ production rate was higher than that with LR. The operation strategies applied in this work were effective to allow stable and efficient H ₂ production for nearly 100 days.