Polyphenolic compounds mitigate the oxidative damage of anammox sludge under long-term light irradiation.

Continuous high-intensity light exposure can inhibit anaerobic ammonium oxidation (anammox) bacteria activity, though the specific impacts on anammox reactor performance remain unclear. This study investigates the effects of long-term light stress on anammox sludge reactors and explores the use of tea polyphenols as an engineering interventions to mitigate photo oxidation damage. The results showed that the nitrogen removal efficiency (NRE) of the reactor rapidly deteriorated to 41.4 % under 10,000 lx light conditions. However, reactors supplemented with 1 mg·L^-1 and 5 mg·L^-1 tea polyphenols sustained NREs of 75.2 % and 82.5 %, respectively. The addition of tea polyphenols alleviated oxidative stress by scavenging reactive oxygen species such as ·OH and H₂O₂, and by enhancing the activities of antioxidant enzymes including total superoxide dismutase and glutathione peroxidase. Candidatus Kuenenia was negatively impacted by light, while unclassified_f__Brocadiaceae thrived under light stress. These findings provide insights for the development of stable nitrogen removal systems under light exposure.