Novel microbial-electrochemical filter with a computer-feedback pH control strategy for upgrading biogas into...

A novel microbial-electrochemical filter was designed and operated based on a combined microbial electrolysis cell and bio-trickling filter principles with the aim to maximize gas-liquid mass-transfer efficiency and minimize costs associated with bubbling biogas through liquid-filled reactor. CO₂/biogas feed to the MEF was done via a computer-feedback pH control strategy, linking CO₂ feed directly to the OH^- production. As a result current efficiency was constant at around 100% throughout the period of experiments. CO₂ from biogas was almost completely removed at cathodic pH setpoint of 8.5. Maximum CO₂ removal rate was 14.6 L/L/day (equivalent to 29.2 L biogas/L/day). Net energy consumption was around 1.28 kWh/Nm³CO₂ or 0.64 kWh/m³ biogas (maximum 49% energy efficiency). An ability to maintain a constant pH means elevated pH from increasing applied potential (current) is no longer an issue. The process can potentially be up-scaled and operated at a much higher current and therefore CO₂ removal rate.