Light wavelength modulation and emerging contaminant stress: Deciphering adaptive responses in microalgal-bacterial granular sludge systems

The escalating global water crisis, intensified by antibiotic contamination, presents urgent threats to ecological security and public health. Microalgal-bacterial granular sludge (MBGS) emerges as a sustainable wastewater treatment technology with inherent capabilities for phototrophic energy utilization. This study systematically investigated the treatment efficiency of MBGS and the evolution of its microbial community under different light wavelengths and the stress of emerging contaminants, amoxicillin (AMX) and ciprofloxacin (CF). Experimental results reveal that red light irradiation (620–650 nm) significantly enhances photosynthetic performance through elevated chlorophyll accumulation (26.1 mg/g) and dissolved oxygen production (21.7 mg/L). Simultaneously, it stimulates extracellular polymeric substance (EPS) biosynthesis (144.5 mg/g), thereby improving system stability and contaminant removal efficacy. In contrast, blue light conditions result in lower processing efficiency compared to alternative wavelengths. Furthermore, under high-concentration antibiotic conditions, MBGS exposed to red light showed superior contaminant removal capacity due to the adsorption and shielding effect of EPS on antibiotic toxicity. Additionally, microbial community analysis reveals that red light significantly increases the abundance of Cyanobacteria (52.6 % abundance), AMX favors the proliferation of Cyanobacteria, while CF promotes the growth of Acidobacteriota. These findings establish red light optimization as an effective strategy for enhancing MBGS performance in antibiotic-laden wastewater treatment, providing crucial theoretical foundations for process optimization in sustainable water remediation.