In-situ mineral CO₂ sequestration in a methane producing microbial electrolysis cell treating sludge hydrolysate

Microbial electrolysis cell (MEC) has excellent CH₄ production performance, however, CO₂ still remains in the produced biogas at high content. For achieving in-situ CO₂ sequestration and thus upgrading biogas, mineral carbonation was integrated into a MEC treating sludge hydrolysate. With 19 g/L wollastonite addition, in-situ mineral CO₂ sequestration was achieved by formation of calcite precipitates. CH₄ content in the biogas was increased by 5.1 % and reached 95.9 %, with CH₄ production improved by 16.9 %. In addition, the removals of polysaccharide, protein, and chemical oxygen demand (COD) of the MEC were increased by 4.4 %, 6.7 %, and 8.4 %, respectively. The generated precipitates rarely accumulated on bio-cathode, and did not significantly affect the morphology of cathode biofilm. However, integrating mineral carbonation resulted in a higher relative abundance of Methanosarcina on anode and slightly decreased the ratio of Methanobacterium to Methanosaeta on cathode, which should be noticed. In conclusion, integrating mineral carbonation is an attractive way to improve the performance of MEC by achieving in-situ CO₂ sequestration, accompanied with CH₄ production enhancement.