Pretreatment and upward liquid velocity effects over granulation in hydrogen producing EGSB reactors

• Seeding EGSB reactors with heat treated anaerobic sludge led to consolidated granules.
• Upward liquid velocity (ULV) influences settling velocity and density of granules.
• Increasing ULV promoted bigger granules leading to greater biomass retention.
• ULV promoted selective wash-out of propionate-producing bacteria.
• ULV prompted granules development with increased specific hydrogenogenic activity.

Hydrogen production by fermentation with granular anaerobic biomass has been regarded as one alternative to obtain clean energy. However critical aspects such as process conditions to obtain hydrogenogenic granules have been scarcely investigated. In this work two inoculum pretreatments and different upward liquid velocities (ULV) in expanded granular sludge bed (EGSB) reactors were applied to determine the influence of these parameters on the formation, structure and specific hydrogenogenic activity (SHA) of the granules. Heat pretreated inoculum produced granules with greater manipulation resistance compared to those produced with wash-out pretreatment. Furthermore, the increase of ULV (2.5–4.5 m/h) generated bigger granules with a granule size distribution with a trend to a normal distribution and higher protein to carbohydrate ratios. Mass balances showed that propionate was the main metabolite, nonetheless, its production decreased substantially as the ULV applied increased, indicating a selective wash-out of propionate-producing bacteria. In the opposite way, SHA values were higher as the ULV applied increased as a result of selective enrichment and better mass transfer conditions. The whole results indicated that the inoculum pretreatment and hydrodynamic conditions play a key role in the formation, structure and in the biological properties of hydrogen-producing granules in EGSB reactors.

Figure optionsDownload as PowerPoint slide