Evaluation of H2 supplementation in in situ biomethanation using fed batch reactors for paper industry wastewater treatment

This study investigated in situ biomethanation as a biogas upgrading strategy by injecting hydrogen (H2) into anaerobic fed-batch reactors treating wastewater from the pulp and paper industry. Granular sludge was used as inoculum and H2 was supplied at two pressures (0.6 and 0.9 bar overpressure in CB and CC assays, respectively) to evaluate its impact on treatment efficiency, methane (CH4) production, and microbial community dynamics compared to control reactors (CA sets) after an adaptation phase with feeding wastewater only.The CH4 production increased during the first two feeding cycles with H2 supplementation accompanied by a reduction in CO2 emissions. However, this was transient and at the end of cycle 7 acid accumulation (mainly acetic and propionic acids) and reduced CH4 production was observed in both H2-supplemented assays.Microbial community structure changed first as a function of new stirred reactor conditions and later according to amount of H2 addition resulting in three clearly separated groups of communities. Although the process demonstrated potential for simultaneous biogas upgrade and wastewater treatment, the overall performance was negatively influenced by increased H2 pressure. This highlights that proper H2 dosing and microbial monitoring are critical to ensure process stability for in situ biomethanation systems. Considering the fragile balance of the investigated wastewater treatment process an ex situ upgrade using a separate reactor is recommended.