Detoxification of atrazine-contaminated wastewater by granular sludge

Atrazine (ATZ) is a widely used herbicide associated with ecological and human health risks, making its removal from wastewater a priority. This study evaluates, for the first time, the performance of an aerobic granular sludge sequencing batch reactor (AGS-SBR) for the detoxification of ATZ-contaminated wastewater. The system consistently achieved high removal efficiencies (≥95%) of organic matter and phosphate. Nitrifying bacteria, on the other hand, were inhibited during ATZ exposure but rapidly recovered their metabolic activity every time ATZ supply was suspended, reaching 97% ammonium uptake. Despite fluctuations in ATZ removal (−4–45% removal efficiency), the system was able to reduce the contaminated wastewater by up to 78%, supported by stable and compact granules with excellent settling properties. Increased production of extracellular polymeric substances (EPS) possibly contributed to microbial protection and prevented granule disintegration under toxic stress. Prolonged ATZ exposure led to a marked reduction in microbial diversity, with a final community dominated by Corynebacterium (80% of total microbial population) . 16S rRNA sequencing combined with in silico inspection suggests that this genus may play a key role in ATZ biotransformation. Overall, the findings of this study demonstrate the robustness and bioremediation potential of AGS technology for treating wastewater containing persistent pesticides, even under elevated toxic concentrations, as well as the potential of Corynebacterium genus form enhancing ATZ removal in biological systems. More research should focus on the specific contributions of this genus to ATZ degradation pathways. • An AGS system was employed to treat ATZ-contaminated wastewater. • Stable granules and EPS overproduction protected microbes from ATZ and biomass. • Despite limited ATZ removal, wastewater toxicity was reduced by up to 78%. • Excellent organic matter and phosphate removal (> 95%) were achieved throughout. • Corynebacterium dominated (80%) and is a promising candidate for ATZ removal.