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H2 addition through a submerged membrane for in-situ biogas upgrading in the anaerobic digestion of sewage sludge

Alfaro, Natalia, Fdz-Polanco, María, Fdz-Polanco, Fernando, Díaz, Israel
Bioresource technology 2019 v.280 pp. 1-8
Methanobacterium, Methanoculleus, acetogens, anaerobic digesters, anaerobic digestion, biogas, carbon dioxide, hydrogen, liquids, methane, methane production, methanogens, pH, sewage sludge, waste treatment
In-situ upgrading of biogas in a mesophilic anaerobic digester of sewage sludge by sparging H₂ through a membrane was studied. Large gas recirculation rates were required to facilitate H₂ transfer to the bulk liquid phase; at ∼200 L Lᵣₑₐcₜₒᵣ⁻¹ d⁻¹, H₂ utilization efficiency averaged 94% and the specific CH₄ production increased from 0.38 L Lᵣₑₐcₜₒᵣ⁻¹ d⁻¹, during conventional digestion, to 0.54 L Lᵣₑₐcₜₒᵣ⁻¹ d⁻¹. Sludge digestion was not compromised by elevated H₂ partial pressure nor by the associated rise in the pH (8.1) because of CO₂ removal. In this regard, VFA accumulation was not detected and the performance of VS removal was similar to the observed without H₂ supply. Microbial analysis revealed that homoacetogens were outcompeted by hydrogenotrophic methanogens. Methanoculleus sp., Methanospirillum sp., Methanolinea sp. and Methanobacterium sp. were the hydrogenotrophic archaea present over the experiment.