Thermophilic Biogas Upgrading via ex Situ Addition of H(2) and CO(2) Using Codigested Feedstocks of Cow Manure and the Organic Fraction of Solid Municipal Waste

[Image: see text] Bioconversion of renewable H(2) and waste CO(2) using methanogenic archaea is a promising technology for obtaining high-purity CH(4), which can serve as an alternative for natural gas. This process is known as ex situ biogas upgrading. This work highlights the pathway toward the bioconversion of renewable H(2) and CO(2) into high-purity biomethane by exploiting highly accessible agro-municipal residues: cow manure (CM) and the organic fraction of solid municipal waste (OFSMW), which used to be called “waste materials”. More specifically, an ex situ thermophilic (55 °C) biogas upgrading process was conducted by CM and OFSMW codigestion at different mass proportions: 100:0, 80:20, 70:30, 60:40, and 50:50. Maximum CH(4) concentrations of 92–97 vol % and biogas volumetric production rates of 4954–6605 NmL/L.d were obtained from a batch reactor of 3 L working volume. Feedstock characterization, pH monitoring, and the carbon-to-nitrogen ratio were critical parameters to evaluate during biogas upgrading experiments. In this work, the usefulness of agro-municipal substrates is highlighted by producing high-purity biomethane—an energetic chemical to facilitate renewable energy conversion, which supports various end-use applications. This process therefore provides a solution to renewable energy storage challenges and future sustainable and green energy supply.