Experimental Evaluation of Continuous In-Situ Biomethanation of CO2 in Anaerobic Digesters Fed on Sewage Sludge and Food Waste and the Influence of Hydrogen Gas–Liquid Mass Transfer

In-situ biomethanation combines conventional biogas production from the anaerobic digestion (AD) of organic matter with addition hydrogen to produce a higher quality biomethane gas. However, challenges surrounding its performance and control could hinder uptake. To investigate this, an automated rig was designed operated study in-situ sewage sludge (SS) food waste (FW) feedstocks. The effects that were experimentally investigated included recirculation rate, stirring intensity, loading rate (OLR). All results highlighted rate-limiting effect H2 gas–liquid mass transfer (measured kLa in range 43–82 day−1), which implied by lack evidence hydrogen-induced biological inhibition high average equilibrium content (a volume 7–37%). At OLR 2 g VS L−1day−1, increasing mechanical rates improved methane evolution up 0.17 0.23 L L−1day−1 conversion 80 66% for waste, respectively. A lower 1 allowed increased but at level productivity. process model, validated on experimental data, predicted improving least 240 day−1 would be required OLRs common AD systems order achieve drop-in terms biogas, further downstream treatment certain applications.