Production of Reactive\nOxygen Species during Redox\nManipulation and Its Potential Impacts on Activated Sludge Wastewater\nTreatment Processes

Reactive oxygen species (ROS) are ubiquitous in redox-fluctuating\nenvironments, exerting profound impacts on biogeochemical cycles.\nHowever, whether ROS can be generated during redox manipulation in\nactivated sludge wastewater treatment processes (AS-WTPs) and the\nunderlying impacts remain largely unknown. This study demonstrates\nthat ROS production is ubiquitous in AS-WTPs due to redox manipulation\nand that the frequency and capacity of ROS production depend on the\noperating modes. The anaerobic/oxic continuous-flow reactor showed\npersistent ROS generation (0.8–2.1 μM of instantaneous\nH<sub>2</sub>O<sub>2</sub>), whereas the oxic/anoxic sequencing batch\nreactor (0.21–0.28 mM of H<sub>2</sub>O<sub>2</sub> per cycle)\nand the anaerobic/anoxic digestion reactor (0.27–0.29 mM of\nH<sub>2</sub>O<sub>2</sub> per cycle) exhibited periodic ROS production.\nOur results illustrated that ROS generated during redox manipulation\ncan contribute to the removal of organic micropollutants. Due to their\nhigh activity, ROS can directly accelerate the abiotic oxidation of\norganic phenolics and Fe(II) minerals in sludges. ROS could also affect\nbiotic nitrification by changing the microbial community composition\nand regulating the relative expression of functional genes, such as <i>amoA</i>, <i>nrxA</i>, and <i>nrxB</i>.\nThis research demonstrates the ubiquitous production of ROS during\nredox manipulation in AS-WTPs, which provides new insights into pollutant\nremoval and the abiotic and biotic elemental transformation in AS-WTPs.