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

• Applied voltage and calcium addition increased biogas yield and CO 2 sequestration. • Wollastonite and CaCl 2 exhibited different CO 2 sequestration performances. • Wollastonite showed a better CO 2 sequestration effect with 2.22% CO 2 in biogas. • The contribution of chemical and biological CO 2 sequestration was clarified. The combination of microbial electrolytic cells and anaerobic digestion (MEC-AD) became an efficient method to improve CO 2 capture for waste sludge treatment. By adding CaCl 2 and wollastonite, the CO 2 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 2 exhibited different CO 2 sequestration performances due to different Ca2+ release characteristics. Wollastonite appeared to have a better CO 2 sequestration effect and provided a wide margin of pH change, but CaCl 2 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 CO 2 content of biogas is only 12.40 % and 2.22 % under 0.8 V with CaCl 2 and wollastonite addition, respectively. Finally, the contribution of chemical CO 2 sequestration by mineral carbonation and biological CO 2 sequestration by hydrogenotrophic methanogenesis was clarified with CaCl 2 addition. The chemical and biological CO 2 sequestration percentages were 46.79 % and 53.21 % under 0.8 V, respectively. With the increased applied voltage, the contribution of chemical CO 2 sequestration rose accordingly. The findings in this study are of great significance for further comprehending the mechanism of calcium addition on CO 2 sequestration in the MEC-AD system and providing guidance for the later engineering application. [ABSTRACT FROM AUTHOR]