Effect of anthraquinone-2,6-disulfonate (AQDS) on anaerobic digestion under ammonia stress: Triggering mediated interspecies electron transfer (MIET)

The underlying mechanisms by which humic-like substrates affect anaerobic digestion under ammonia stress are insufficiently understood so far. In this study, anthraquinone-2,6-disulfonate (AQDS), a representative analogue of humic acid, was adopted at a 100 μM concentration as the exogenous additive during anaerobic digestion process along with 5.0 g NH4+-N/L stress. The results showed that AQDS could improve the cumulative CH4 production and the maximum CH4 production rate by 7.3 and 10.8%, respectively, and shorten the methanogenic lag phase by 13.8%. Acetate-related production and methanation were both facilitated, during which the biological rather than the chemical mechanism played a crucial role. The microbial diversity distribution revealed that electroactive Anaerolinea and Methanosaeta were significantly enriched in response to AQDS amendment. Herein, AQDS was presumed to serve as an electron shuttle to trigger a mediated interspecies electron transfer (MIET) network among electroactive consortia, thus accelerating acetate methanation and ameliorating methanogenesis under ammonia stress.