Synergistic effect of anthraquinone and biochar on anaerobic ammonia oxidation system initiation and functional microorganism enrichment.

This study explored the effects of anthraquinone concentration gradients (0.025-0.075 mmol/L) in combination with biochar (10 g/L) on the initiation of an anaerobic ammonia oxidation (anammox) system and the dynamics of associated functional microorganisms. At the low anthraquinone concentration (0.025 mmol/L), biochar effectively safeguarded core functional bacterial activity by adsorbing toxic substances and providing attachment sites for microorganisms, thereby enhancing NH-N removal efficiency to 98.6 % and significantly enhancing the system stability. At the medium concentration (0.05 mmol/L), anthraquinone inhibited core functional bacteria, leading to NO-N accumulation. Biochar maintained nitrogen removal functionality through promoting synergistic metabolism between denitrifying bacteria and anammox bacteria, achieving 75.4 % of NH-N removal efficiency. At the high anthraquinone concentration (0.075 mmol/L), the relative abundance of the core functional bacterium Candidatus Brocadia dropped to 1.03 %, leading to the irreversible collapse of the nitrogen removal function. Within the concentration range established in this study, the safe control threshold for anthraquinone was determined to be below 0.05 mmol/L, with biochar's synergistic adsorption effect being effective only under low-to-medium anthraquinone concentrations.