Optimizing red-blue light ratio enhances nutrient and antibiotic removal by an algal-based symbiotic consortium in...

Exploring effective techniques for the removal of nutrient and antibiotic contaminants is critical to addressing aquaculture wastewater pollution. A novel approach was adopted in this study, which aimed to optimize the red-blue light ratio specifically to enhance a three-member (algae-bacteria-fungi) symbiotic consortium for efficient pollutant removal. Four systems were evaluated: Chlorella vulgaris monoculture (Strain 1), Chlorella vulgaris + S395-2 (Strain 2), Chlorella vulgaris + Clonostachys rosea (Strain 3), and Chlorella vulgaris + S395-2 + Clonostachys rosea (Strain 4). Results demonstrated that a 5:5 red-blue light ratio provided optimal growth conditions, under which Strain 4 emerged as a stable and highly efficient dominant consortium. This system achieved the highest average removal rates for conventional pollutants, with COD (78.96 ± 3.21%), TN (82.37 ± 5.31%), NH₄⁺-N (63.16 ± 4.17%), and TP (84.51 ± 3.71%). Furthermore, under optimal lighting conditions at an antibiotic concentration of 0.25 mg L^-1, Strain 4 exhibited superior removal efficiency for oxytetracycline (OTC, 96.23 ± 2.01%), ciprofloxacin (CPFX, 79.62 ± 5.31%), and sulfamethoxazole (SMZ, 82.16 ± 4.76%). Density functional theory (DFT) calculations revealed that the exceptional degradation performance of OTC was attributed to its moderate amphiphilicity (ω = 1.23 eV, N = 2.79 eV), the narrowest HOMO-LUMO gap (4.28 eV), and abundant distribution of reactive sites. These findings provide valuable scientific insights into pollutant mitigation mechanisms in aquaculture environments.