Surface-Adhered\nMicrobubbles Enhance the Resistance\nof ANAMMOX Granular Sludge to Sulfamethoxazole Stress

The granule-based anammox process has been reported to\nbe more\nresistant to the stress of antibiotics; however, the underlying resistance\nmechanism is still not fully understood. In this study, we found that\nmore microbubbles stably adhered to the surface layer of anammox granular\nsludge (AnGS, Gs) operating under long-term sulfamethoxazole (SMZ)\nstress of 2 mg/L, compared to that in the control reactor (Gc). The\ndifference in covering content can be up to over three times (1.0\n± 0.1% vs 0.3 ± 0.0%). Batch tests showed that the coverage\nratio of microbubbles on Gs reached approximately 32.5%, which significantly\nreduced SMZ transfer into AnGS due to the adsorption of SMZ by bubbles,\nthus alleviating the inhibition of anammox bacterial activity by 36.5%.\nThe adhesion force between the microbubbles and the surface layer\nof Gs was found to be largely enhanced by 75.0% compared to that of\nGc. The increased hydrophobicity of surface layer due to the increased\nextracellular polymer substance (EPS, mainly proteins) content, and\nthe larger capillary force of surface layer, owing to the unique micronano\nstructure, were identified as key factors responsible for the stable\nadhesion of microbubbles on the Gs. Consequently, this study demonstrated\nthe vital roles of the surface-adhered microbubbles in resisting the\nstress of SMZ and shed light on the regulation and development of\nrobust granule-based anammox processes.