CO2 sequestration in microbial electrolytic cell-anaerobic digestion system combined with mineral carbonation for sludge hydrolysate treatment

Abstract

The combination of microbial electrolytic cells and anaerobic digestion (MEC-AD) became an efficient method to improve CO₂ capture for waste sludge treatment. By adding CaCl₂ and wollastonite, the CO₂ 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 CaCl₂ exhibited different CO₂ sequestration performances due to different Ca²⁺ release characteristics. Wollastonite appeared to have a better CO₂ sequestration effect and provided a wide margin of pH change, but CaCl₂ released Ca²⁺ 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 CO₂ content of biogas is only 12.40 % and 2.22 % under 0.8 V with CaCl₂ and wollastonite addition, respectively. Finally, the contribution of chemical CO₂ sequestration by mineral carbonation and biological CO₂ sequestration by hydrogenotrophic methanogenesis was clarified with CaCl₂ addition. The chemical and biological CO₂ sequestration percentages were 46.79 % and 53.21 % under 0.8 V, respectively. With the increased applied voltage, the contribution of chemical CO₂ sequestration rose accordingly. The findings in this study are of great significance for further comprehending the mechanism of calcium addition on CO₂ sequestration in the MEC-AD system and providing guidance for the later engineering application.

Keywords: Anaerobic digestion; CO(2) sequestration; Calcium addition; Microbial electrolytic cell; Wollastonite.