[Effect of Adding Granular Activated Carbon (GAC)/Manganese Dioxide (MnO2) for the Anaerobic Digestion of Waste Activated Sludge].

The addition of conductive materials or metal oxide nanoparticles to an anaerobic system is an attractive strategy to enhance anaerobic digestion. The effect of granular activated carbon (GAC) and/or manganese dioxide (MnO2) on waste activated sludge (WAS) anaerobic digestion was investigated by batch experiments. The experiments were provided in control, GAC, MnO2, and GAC/MnO2 groups, which were named R0, R1, R2, and R3, respectively. The sludge characteristics, microbial activity, and microbial community structure were systematically investigated. Results showed that CH4 yield rate was evidently increased by 68.18% and 51.35% in R1 and R3, respectively, whereas the cumulative CH4 production decreased by 21.25% in R2, compared with R0. Moreover, the fermentation process could be promoted with the addition of GAC and/or MnO2. The phosphate precipitation generated by Mn2+ and phosphate released from WAS blocked the anaerobic metabolic channel and then decreased the production of CH4 in R2. The increase in CH4 yield rate in R3 was mainly attributed to the conductivity and adsorption of GAC and the catalysis of MnO2. Additionally, the microbial activity could be promoted with the addition of GAC, MnO2, and GAC/MnO2 in anaerobic digestion. Microbial community structure analysis showed that the abundance of the Methanobacterium and Methanosaeta increased with the addition of GAC and MnO2, which could enhance the interspecies electron transfer between fermenting bacteria and methanogens and boost fermentation and CH4 production.