(173c) Integrated Biogas Upgrading and Bicarbonate Production for Microalgal Cultivation Using Electrochemical pH Swing Technology

Bioenergy with Carbon Capture, Utilization, and Storage (BECCUS) is as emerging strategy that integrates low-carbon energy production with negative emissions. Biogas, a renewable energy carrier with several environmental benefits. It is primarily produced by anaerobic digestion of organic matter, such as agricultural waste and manure. It is considered a gaseous-phase biomass resource and typically consists of methane (CH₄), carbon dioxide (CO₂), and a few trace gases, like hydrogen sulfide (H₂S). While the high methane content contributes to its heating value, the presence of CO₂ and other impurities significantly reduces its overall heating efficiency. Therefore, upgrading biogas through CH₄ separation is essential to improve its energy quality and enable broader utilization within clean energy systems. As a minor component in biogas, CO₂ presents a key challenge for effective capture and utilization. This study develops an integrated biogas upgrading system based on an electrochemical pH swing, incorporating CO₂ capture and utilization technologies, and evaluates the performance of the electrochemical system. The pH swing mechanism generates a strong alkaline solution, which enhances CO₂ solubility and facilitates its conversion into bicarbonate. This resulting bicarbonate-rich solution can serve as an auxiliary carbon source for algae cultivation, thereby improving both biomass productivity and lipid content. Algae have emerged as a promising biofuel resource due to their high energy density and exceptional carbon sequestration capabilities. By absorbing bicarbonate as a carbon source and producing energy-rich biomass, algae offer a forward-looking solution for carbon capture and utilization. This approach aligns with BECCUS, enabling not only bioenergy production but also the transformation of captured carbon into valuable bioproducts. The electrochemical pH-swing module was conducted using synthetic water samples and model biogas composed of 60% CH₄ and 40% CO­₂, and 100 ppm H₂S. The system was operated under semi-batch conditions with continuous gas injection, and the influence of key operational parameters, including applied cell voltage, optimal operation time, and gas-to-liquid ratio, was systematically analyzed. Using a 2 L aqueous phase and a controlled inlet gas containing 20% CO­₂, the cell voltage was varied to determine its impact on CO­₂ capture efficiency and energy demand, the cost-benefit analysis was also conducted. Experimental findings confirm that the proposed electrochemical system enables efficient transformation of CO­₂ from biogas into an aqueous bicarbonate solution. This bicarbonate-enriched medium was subsequently applied in microalgal cultivation, with species such as Chlorella showing improved biomass productivity under these conditions. By coupling CO­₂ removal with downstream biological utilization, the process offers a closed-loop strategy for renewable energy generation and carbon valorization. These results highlight a practical pathway toward BECCS, supporting the broader goals of circular bioeconomy development.