Development and validation of a comprehensive model for biotrickling filters upgrading biogas

This paper details the development, validation, and analysis of a conceptually correct mathematical model for biogas upgrading biological trickling filter (BTF) reactors. The model considers convective transport and dispersion of gases through the fixed bed and mass transfer and reaction of absorbed gases in immobilized biofilms. Wetted and non-wetted biofilms, gas volume contraction through the bed as hydrogen and CO2 are converted to methane, and axial dispersion were all included in the model. The model successfully predicted the performance of a laboratory scale BTF upgrading various raw biogas compositions. A parametric sensitivity analysis revealed that the influent gas flow rate, biofilm specific surface area, and maximum rate of reaction (Rmax) were the most sensitive parameters. Furthermore, reducing the wetted biofilm ratio by 54% (12% wetted) was the easiest optimization measure for achieving renewable natural gas standards (>97% effluent methane). Practically, this could be achieved e.g., by applying an intermittent trickling regime. The liquid-film mass transfer coefficient (kLa) was not a sensitive parameter. This was because the model predicted that a majority of substrate conversion was occurring in the non-wetted biofilm, a finding that further supports the importance of reducing biofilm wetting in these BTFs. Overall, the model provides a strong conceptual framework for future studies modeling biogas upgrading processes. Additionally, it has the potential to be a useful tool in scaling and optimizing BTF bioreactors for biogas upgrading applications.

Duke Scholars

Author Marc Deshusses Civil and Environmental Engineering