Low-chlorine pretreatment enables microalgae to reduce multi-target pollutants in livestock wastewater: Focus on ARG attenuation via host-community shifts.

Microalgae exhibit unique advantages in ARG removal, yet their growth and efficacy are often constrained by complex organic matter and microorganisms in wastewater. To address this issue, this study employed chemical pretreatment to synergistically enhance microalgal treatment and, for the first time, developed a novel coupled process to tackle ARGs in livestock wastewater. The results indicate that low-chlorine (1 mg/L) pretreatment combined with the indigenous filamentous alga (S2) significantly removed pollutants (TN: 81.50%, COD: 70.71%) and reduced the total abundance of ARGs by 81.73%. The core mechanism lies in low-chlorine pretreatment shaping a mutually beneficial algae-bacteria system, which achieves efficient ARG control by altering the host bacterial. The study formalized the operating condition with a multi-objective desirability index combining nutrient removal, ARG reduction, and algal growth, which identified 1 mg/L as the overall optimum. The combined treatment process at a low chlorine dosage demonstrated both high efficiency and feasibility, providing an innovative strategy for livestock wastewater treatment.