Intermittent nighttime lighting enhances microalgal-bacterial granular sludge in synthetic wastewater treatment

The microalgal-bacterial granular sludge (MBGS) system is a promising technology due to its low energy demand and high treatment efficiency under illumination. However, its performance declines at night owing to the absence of light, reducing dissolved oxygen and microbial activity. This study proposes and evaluates an intermittent nighttime lighting strategy (12 h-light/3 h-dark/6 h-light/3 h-dark using LEDs) to enhance MBGS performance for treating synthetic wastewater. Supplemental lighting improved removal efficiencies of chemical oxygen demand, ammonia nitrogen, and phosphate by 7.5 %, 27.7 %, and 27.1 %, respectively. Metagenomic analysis revealed an increased genetic potential for pollutant degradation, evidenced by a higher abundance of genes involved in key metabolic pathways (e.g., GLU, ppa). Microbial community structure shifted, with increased abundances of Cyanobacteria and Verrucomicrobia and a decreased abundance of Proteobacteria. Genetic potential analysis suggested enhanced nitrogen assimilation, ATP cycling, and glycogen synthesis, alongside reduced lactate metabolism, indicating a shift toward aerobic pathways. These results demonstrate that intermittent nighttime lighting enables sustainable round-the-clock wastewater treatment.