Immobilized exogenous electron shuttle-mediated anaerobic ammonia oxidation (anammox) process: Performance and mechanism

This investigation focused on assessing the impact of exogenous electron shuttle-mediated anaerobic ammonia oxidation (anammox) process under varying anthraquinone-2,6-disulfonate (AQDS) concentrations (0, 0.1 mM, 0.5 mM, and 1 mM). It was observed that a 0.1 mM concentration of AQDS notably amplified the metabolic function of anammox bacteria, leading to a significant enhancement in specific anammox activity, which peaked at 1.9 mg N/ (g VSS h). Employing the 15N stable isotope tracing technique, it was discerned that 0.1 mM AQDS was the most efficacious concentration for optimizing the anammox rate. Fulvic acid, humic acid-like substances and tryptophan-like proteins in the soluble microbial products observed in 3D-EEM demonstrated a marked elevation in fluorescence intensity in reactors A2 (0.1 mM AQDS), A3 (0.5 mM AQDS), and A4 (1 mM AQDS) compared to the control group (A1). Metagenomic and transcriptomic analyses were meticulously performed to dissect the composition of microbial communities and the expression of functional genes in different AQDS-treated environments. A marked influence of AQDS (0.1 mM) was observed on the transcriptional activities of heme C-, NADH dehydrogenase- and ABC transporters-related genes (hdh, hzs, ccmF, fdoG and ETFDH), which were integral to nitrogen metabolism and electron transfer processes. Electron transfer mechanisms in the AQDS-mediated anammox process revealed that AQDS could act as an electron shuttle, bolstering the activity of essential genes (amt, nrt, rnf) and transporter proteins. Ultimately, this research elucidated the prospective potential role of AQDS in enhancing anammox nitrogen removal performance.