Synergistic removal of pesticides and transformation products through optimization of ozonation and granular activated carbon filtration parameters toward achieving toxin-free drinking water

The escalating presence of emerging contaminants in drinking water sources, particularly pesticides and their transformation products (TPs), necessitates the development and implementation of advanced treatment strategies to safeguard human health. This study rigorously evaluates the synergistic efficacy of ozonation followed by granular activated carbon (GAC) filtration in mitigating the chemical and biological risks posed by target pesticides (atrazine, carbendazim, and thiophanate-methyl) and their derivatives. Bench-scale experiments, using influent pesticide concentrations representative of contaminated sources, demonstrated that ozonation effectively degraded benzimidazole (70–90 % removal) and triazine pesticides (20–70 % removal) within 10–15 min. However, comprehensive toxicity assessment (TCT) revealed that transformation products introduced dual effects during treatment: while increasing ozone dosage and contact time reduced overall toxicity, certain byproducts presented new toxicological risks. Subsequent GAC filtration (>100 mg/L) effectively removed both parent pesticides (>90 %) and their degradation products while significantly reducing TCT levels. Full-scale validation at a drinking water treatment plant corroborated these findings, highlighting the robustness of this combined approach. Critically, the study also revealed a significant decline in GAC's capacity to remove pesticides and TPs after 7–9 years of operation, despite sustained total organic carbon removal. This underscores the need for regular GAC replacement, ideally every two years, to maintain optimal treatment performance. By bridging laboratory-scale optimization with real-world application, this study establishes the combined ozone-GAC process as an effective strategy for mitigating the chemical and biological risks associated with pesticides and their TPs, ultimately ensuring the provision of safe and high-quality drinking water. • Ozone-GAC synergy mitigates pesticides and their transformation products in drinking water. • GAC filter lifespan critically impacts pesticide removal, requiring regular replacement. • Biological toxicity assessments reveal complex ozone-TP interactions and overall drinking water risk. • Bench-scale optimization informs full-scale treatment strategies for safer drinking water provision.