Full-scale multipurpose ozonation in urban wastewater with strong textile input: removal of colour, micropollutants, pathogens and antimicrobial resistance indicators

Abstract

Understanding multipurpose ozonation performance under realistic and variable wastewater conditions is critical for investment decisions under the revised EU Urban Wastewater Treatment Directive (EU-UWWTD). As most studies focuses on single treatment objectives or homogeneous municipal effluents, integrated evaluations are particularly needed for industry-influenced wastewaters, where ozone reactivity and process efficiency can differ markedly. This study aims to provide a holistic assessment of full-scale ozonation by simultaneously investigating the responses of chemical and biological contaminants, as well as microbial community dynamics, variable ozone doses applied primarily for textile colour control. To our knowledge, this is one of the first integrated full-scale studies of ozonation in a strongly textile-influenced urban WWTP (51% of total inflow). Ozonation performance was assessed through three full-scale experimental campaigns, each evaluating three ozone doses in the range of 0.4–1.0 mg O₃/mg TOC. The study evaluated colour removal, micropollutant abatement, pathogen and antimicrobial resistance (AMR) indicators reduction, by-product formation, acute toxicity and surrogate parameters for process monitoring. Ozonation had little effect on bulk organic parameters but achieved 50–84% colour removal and near-complete elimination of terrestrial humic-like fluorescence. High organic matter content and colour constrained ozone exposure, shifting micropollutant abatement towards predominantly •OH-driven oxidation. Nevertheless, ozonation alone achieved ≥80% removal of the monitored micropollutants at ozone doses ≥0.65 mg O₃/mg C, indicating its major contribution towards EU-UWWTD compliance targets. Somatic coliphages and bacteria log-reductions ranged from 0.9 to >2.3 and from 0.2 to 1.2, respectively. Acute toxicity was reduced, whereas AMR gene abundance showed limited sensitivity to ozone dose. Post-treatment microbial regrowth was observed, particularly at higher ozone doses, including bacterial groups carrying resistance genes, suggesting a selection-like process. Operational surrogate indicators (A254, A436, colour-scan and PARAFAC components) were identified/validated to support process monitoring and EU-UWWTD implementation in complex wastewater matrices.