Meta-analysis of biogas upgrading to renewable natural gas through biological CO2 conversion

Biogas upgrading through CO2 conversion by hydrogenotrophic methanogenesis is receiving an increasing attention worldwide because of the demand for renewable natural gas. Herein, a holistic and statistical study of the operation conditions, driving forces, performances, and potential implementation of biogas upgrading via biological CO2 conversion was conducted. Based on a systematic review and meta-analysis of 46 existing pub-lications that were selected from 1475 papers, we have compiled a global dataset of CO2 bioconversion biogas upgrading, encompassing 308 study cases. Subsequently, we employed a rigorous analytical framework incor-porating data processing and mixed effects linear regression analysis to examine the dataset. This analysis revealed a significant positive relationship between the H2:CO2 ratio and the methane percentage in the upgraded biogas when using the study as a random effect. Furthermore, we performed meta-analysis on ob-servations taken when the ratio was close to 4:1 and found that ex situ reactors (91.93% [88.11%, 95.75%]) can perform better than in situ reactors (84.74% [80.69%, 88.80%]). No evidence of differential performance was found based on the present dataset between different temperature regimes or operation modes. Those findings establish a database that will contribute to a deeper understanding of the biogas upgrading via biological CO2 conversion.