In-situ Biomethane Enrichment by Recirculation of Biogas Channel Digester Effluent Using Gas Stripping Column

This study was conducted to examine the in-situ methane enrichment in a biogas system by continuously stripping carbon dioxide from the effluent and recirculating back to the system. A laboratory-scale biogas digester with 1,000-liter working volume was coupled with a 110-liter stripping column and was operated using chicken manure as the substrate. It was found that the carbon dioxide stripping performance depended on the ratio between liquid and gas flow rates (L/G Ratio) in the column. The optimum L/G ratio was indicated to be 0.83 times. In a continuous experiment, the effluent recirculation rate was varied from 200%-400% of the digester volume. The higher recirculation rate resulted in the higher methane enrichment. The methane enrichment was in a range of 10-23% while the methane loss was between 3.7% to 16.0% for the system with 200% and 400% recirculation rate, respectively. The overall mass transfer coefficients were in the range of 1.4-6.9 x 10-4 s-1.