Factors affecting biological reduction of CO₂ into CH₄ using a hydrogenotrophic methanogen in a fixed bed reactor

Abstract

Biological conversion of CO₂ was examined in a fixed bed reactor inoculated with anaerobic mixed culture to investigate influencing factors, the type of packing material and the composition of the feeding gas mixture. During the operation of the fixed bed reactor by feeding the gas mixture (80% H₂ and 20% CO₂ based on volume basis), the volumetric CO₂ conversion rate was higher in the fixed bed reactor packed with sponge due to its large surface area and high mass transfer from gas to liquid phase compared with PS ball. Carbon dioxide loaded into the fixed bed reactor was not completely converted because some of H₂ was used for biomass growth. When a mole ratio of H₂ to CO₂ in the feeding gas mixture increased from 4 to 5, CO₂ was completely converted into CH₄. The packing material with large surface area is effective in treating gaseous substrate such as CO₂ and H₂. H₂, electron donor, should be providing more than required according to stoichiometry because some of it is used for biomass growth.