Enhancing Biogas Purity from Livestock Manure Using Desulfurization and CO₂ Scrubbing System

Aims: This study was aimed at increasing the quality of CH4 thereby reducing the quantity of H2S and CO2 using the desulphurisation and decarboxylation scrubbers respectively.

Study Design: This study employed an experimental research design to evaluate the effectiveness of desulphurization and Decarboxylation scrubbers in enhancing biogas quality by reducing H₂S and CO₂ concentrations.

Place and Duration of Study: Waste-to-resource project laboratory of the Department of Environmental Science of the University of Buea, Cameroon between May and July 2023.

Methodology: The scrubbers were made up of locally available materials with the desulphurization scrubber constituting of 20 cm long PVC pipes with a diameter of 0.45 cm and a stopcock at both ends of the pipe making it air tight and contain within its iron fillings mesh with a mass of 25 g. While one of the Decarboxylation scrubbers was made up of the same material as desulphurization but contain within it particle size of 2 mm and mass of 50 g activated carbon and the other consisted of a cylindrical plastic container with a height of 20 cm and diameter of 16 cm, containing 4 M Ca (OH)2 (lime water). The different scrubbers were evaluated and optimized and efficiencies calculated for each.

Results: Result from the Decarboxylation scrubber showed highest efficiency of CO2 absorption in activated carbon (86.41 %) and least in 4M Ca (OH)2 (85.32 %). The desulphurization scrubber had an efficiency of 98.93 % removal of H2S by the iron fillings. The combination of desulphurization and Decarboxylation scrubbers had an outstanding result in increasing the quality of CH4 produced (0 % to 80.8 %). It can be concluded from this studies that, Ca (OH)2 and Iron fillings should be connected in series in any biogas outlet stream to enhance biogas production. Also, activated Carbon is discouraged to be used as a scrubber because it produces CO which is a very poisonous gas to human health.

Conclusion: This study showed that using iron fillings and Ca (OH)₂ scrubbers significantly improved biogas quality, achieving 80.8% methane purity. Activated carbon is discouraged due to CO production. Future research should explore varying Ca (OH)₂ concentrations and use FTIR, XRD, and SEM analyses to assess activated carbon’s structural changes. This study recommends testing various Ca (OH)₂ concentrations for efficiency and using FTIR, XRD, and SEM to analyze structural and morphological changes in activated carbon before and after use.