Light-driven oxygen supersaturation controls microbial resilience in microalgal-bacterial granular sludge systems:...

Microalgal-bacterial granular sludge (MBGS) enables carbon-neutral wastewater treatment by replacing aeration with photosynthetic oxygen. However, excessive light can induce dissolved oxygen (DO) supersaturation and triggering oxidative stress. This study investigated the effects of lighting mode (continuous vs. intermittent) and light intensity (400 and 800 μmol/m²/s) on MBGS performance over 96 days. At both light intensities, continuous light caused severe DO accumulation (>25 mg O₂/L), elevated reactive oxygen species (ROS), and reduced nutrient removal. Intermittent light effectively regulated DO, alleviated ROS stress, enhanced antioxidative enzyme activity, and restored microbial function. Under intermittent light, NH₄-N, TN, and PO₄-P removal efficiencies reached 99.2 %, 81.5 %, and 94.2 % (400 μmol/m²/s), and 89.7 %, 69.9 %, and 91.5 % (800 μmol/m²/s). Functional genera such as Dechloromonas, Pseudoxanthomonas and Pseudomonas were enriched under intermittent light mode. These results demonstrate that intermittent light is a feasible strategy to mitigate photo-oxygen stress and enhance nutrient removal in aeration-free MBGS systems.