Efficiency of Photobioreactor with Microalgae Strains Monoraphidium griffithi and Desmodesmus sp. for Biogas Upgrading

Monoraphidium griffithii and Desmodesmus sp. microalgae cultures were exploited to examine the CO2 fixation efficiency in a bubble column photobioreactor (PBR). Two medium were used as the control groups to compare the effect of CO2 solubility in modified woods hole (MWH) medium and distilled water. Experiments were performed indoors using experimental apparatus consisting of 4 vertical bubble columns in total and injecting real biogas with 36% of CO2 and 56% of CH4 taken from wastewater treatment plant. As a result, system using Monoraphidium griffithii and Desmodesmus sp. cultures improved CO2 removal efficiency by 11.2% and 5.5% compared to MWH medium, respectively. In addition, 86.1% of the CO2 in the biogas could be captured by the Monoraphidium griffithii culture and 80.4% - by the Desmodesmus sp. culture. CH4 content in the effluent biogas increased from 56.1% to 66.4% using Monoraphidium griffithii culture. CH4 concentration in distilled water increased from 56.1% to 63.2% because CO2 is soluble in water, whereas CH4 has low solubility. Consequently, the volume of CH4 increased. After 32-36 hours, all media reached their saturation point, and the CO2 concentration returned to its starting value. The established microalgae culture system with intermittent operation could be efficiently used as a CO2 capture technology for biogas upgrading.