CO sequestration in microbial electrolytic cell-anaerobic digestion system combined with mineral carbonation for sludge hydrolysate treatment.

The combination of microbial electrolytic cells and anaerobic digestion (MEC-AD) became an efficient method to improve CO capture for waste sludge treatment. By adding CaCl and wollastonite, the CO sequestration effect with mineral carbonation under 0 V and 0.8 V was studied. The results showed that applied voltage could increase dissolved chemical oxygen demand (SCOD) degradation efficiency and biogas yield effectively. In addition, wollastonite and CaCl exhibited different CO sequestration performances due to different Ca release characteristics. Wollastonite appeared to have a better CO sequestration effect and provided a wide margin of pH change, but CaCl released Ca directly and decreased the pH of the MEC-AD system. The results showed methane yield reached 137.31 and 163.50 mL/g SCOD degraded and CO content of biogas is only 12.40 % and 2.22 % under 0.8 V with CaCl and wollastonite addition, respectively. Finally, the contribution of chemical CO sequestration by mineral carbonation and biological CO sequestration by hydrogenotrophic methanogenesis was clarified with CaCl addition. The chemical and biological CO sequestration percentages were 46.79 % and 53.21 % under 0.8 V, respectively. With the increased applied voltage, the contribution of chemical CO sequestration rose accordingly. The findings in this study are of great significance for further comprehending the mechanism of calcium addition on CO sequestration in the MEC-AD system and providing guidance for the later engineering application.