Key properties identification of biochar material in anaerobic digestion of sewage sludge for enhancement of methane production

Abstract

Owing to the intricate physicochemical characteristics of biochar material, a comprehensive understanding of their effects and mechanisms involved in anaerobic digestion still needs to be explored. In this study, the methane yield of sludge hydrolysate was inhibited by 13.3% after the addition of granular activated carbon (GAC), which was due to the predominance of non-selective adsorption by GAC. Whereas the shortened lag phase time (38.2%), the improved methane production rate (16.6%), and the increased methane yield (7.6%) were achieved after the algal biochar (ABC) addition. The methanogenic improvements by ABC were attributed to its redox capacity other than pH buffering capacity. Quantitative results showed that the content of phenolic and lactonic groups were 4.8 and 2.3 times higher than that of GAC, respectively, which endowed ABC with a stronger redox capacity, especially electron-donating capacity. Surface oxygen-containing functional groups like phenolic and lactonic groups of biochar material should be valued for the improvement of anaerobic digestion. The findings of this study provided a comprehensive insight into the connection between mechanisms and related biochar properties during the anaerobic digestion of sewage sludge, which also provided an important clue to selecting, even harnessing desirable biochar material for a given biotechnological process.