Impact of Supplemental Hydrogen on Biogas Enhancement and Substrate Removal Efficiency in a Two-Stage Expanded Granular Sludge Bed Reactor

In two-stage anaerobic expanded granular sludge bed (EGSB) reactors, up to one-third of the chemical oxygen demand (COD) content is naturally preacidified in a first stage preacidification (PA) tank and then fed to a second stage digester for conversion to methane. Hydrogen, an intermediate product of the first stage, could be theoretically captured escaping from the PA tank and sent to the digester to biologically convert the carbon dioxide to methane for biogas enhancement. Pilot-scale tests were conducted to assess the impact of introducing hydrogen gas on biogas quality enhancement and substrate removal efficiency in an EGSB digester fed with distillery wastewater at mesophilic temperature (35[degrees]C). The amount of hydrogen introduced, 0.15 or 0.30 L/(L sub(biogas) times day), was less than what could be theoretically captured escaping from the PA tank. Biogas quality was enhanced by ~10% to 20% and the energy yield increased by ~33-42% depending on the hydrogen injection rate. COD removal efficiency remained constant at about ~98% with and without hydrogen. The Monod model maximum substrate removal rate constant slightly increased, while the half-saturation coefficient slightly decreased with the added hydrogen, both indicating that hydrogen injection did not negatively affect substrate removal efficiency or biomass culture stability.