Magnetite doped granular activated carbon as an additive for high-performance anaerobic digestion

Abstract In recent years, granular activated carbon (GAC) has been extensively investigated as an additive for promoting electroactive microbiome to enhance anaerobic digestion performance. This study first demonstrates that GAC particles doped with magnetite can significantly improve the syntrophic degradation of propionate, a substrate that is not readily degraded by microbial communities in the anaerobic digestion process. The bioreactor amended with magnetite doped GAC achieved the highest methane production (220 mL/g COD) and COD removal (70%) in fed-batch tests, which were 1.5 and 1.2 times of those in control and GAC amended bioreactors, respectively. The acetate accumulation was found to be correlated with methane production. Quantitative comparison of microbial communities suggested that the addition of GAC or doped GAC didn’t achieve higher microbial biomass compared to control. Instead, multiple known electroactive bacterial genera (Shewanella, Pseudomonas, Geobacter, and Desulfuromonas) were selectively enriched along with higher levels of heme-binding proteins in the bioreactors amended with magnetite doped GAC (1.1 × 105 cells/µL) and GAC (8.4 × 104 cells/µL) in comparison to control (2.5 × 104 cells/µL). Thus, our results suggest that tailoring GAC particles though doping with magnetite can provide an efficient method to achieve high-performance anaerobic digestion.