What question did this study set out to answer?

This research aims to assess the effectiveness of hydrogen supplementation in enhancing biomethanation processes for treating wastewater from the paper industry.

April 28, 2026Open Access

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

Key Points

This research aims to assess the effectiveness of hydrogen supplementation in enhancing biomethanation processes for treating wastewater from the paper industry.
Used anaerobic fed-batch reactors with granular sludge as inoculum and supplied H2 at two pressures (0.6 and 0.9 bar)
Compared H2 supplemented reactors to controls after an adaptation phase with only wastewater feeding
Monitored changes in methane production and microbial community dynamics over seven cycles.
Methane production increased in the initial cycles with H2 addition but reduced significantly by cycle 7 due to acid accumulation (acetic and propionic acids).
Microbial community structure evolved with H2 supplementation, showing new enrichments, especially in Ethanoligenenaceae and Methanobacterium.
Despite initial benefits, higher pressures negatively affected overall treatment performance.

Abstract

Background This study investigated in situ biomethanation as a biogas upgrading strategy by injecting hydrogen (H 2 ) into anaerobic fed-batch reactors treating wastewater from the pulp and paper industry. Methods Granular sludge was used as inoculum and H 2 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 (CH 4 ) production, and microbial community dynamics compared to control reactors (CA sets) after an adaptation phase with feeding wastewater only. Results The CH 4 production increased during the first two feeding cycles with H 2 supplementation accompanied by a reduction in CO 2 emissions. However, this was transient and at the end of cycle 7 acid accumulation (mainly acetic and propionic acids) and reduced CH 4 production was observed in both H 2 -supplemented assays. Microbial community structure changed first as a function of new stirred reactor conditions and later according to amount of H 2 addition resulting in three clearly separated groups of communities. The family Syntrophobacteraceae responsible for propionate degradation declined in all reactors due to operational changes and following microbial succession. In control reactors it was out-competed by members of Geobacteraceae and Desulfobulbaceae. In CB and CC assays, Ethanoligenenaceae, Bacillaceae, Kosmotogaceae, Anaerolineaceae, and Anaerolineaceae families were enriched as a result of H 2 supplementation. The most abundant methanogens were affiliated to the acetotrophic Methanothrix and the hydrogenotrophic Methanobacterium in all batch reactors. Upon H 2 addition the relative abundance of Methanobacterium increased and became predominant in later cycles of CB and CC sets. Despite this shift, both genera coexisted throughout the experiments, suggesting that multiple metabolic pathways contributed to CH 4 production under H 2 -enriched conditions. Conclusions Although the process demonstrated potential for simultaneous biogas upgrade and wastewater treatment, the overall performance was negatively influenced by increased H 2 pressure. This highlights that proper H 2 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 of biogas using a separate reactor is recommended.

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