Ozone membrane contactor for tertiary treatment of urban wastewater: Chemical, microbial and toxicological assessment

A membrane ozone contactor, operated under continuous mode, was applied to promote the tertiary treatment of urban wastewater (UWW), targeting the removal of contaminants of emerging concern (CECs), bacterial disinfection, and toxicity reduction. This system relies on the homogeneous radial distribution of ozone (O3) in the reaction zone by titration through a microfiltration borosilicate tubular membrane, while the UWW swirls around the membrane and drags the O3 microbubbles generated in the membrane shell-side. The membrane is coated with titanium dioxide (TiO2-P25) and radiation can be externally supplied via four UV lamps. The ozonation tests were carried out with secondary-treated UWW collected in different seasons (winter and summer) and spiked with a mix of 19 CECs (10 & mu;g L-1 each). For an O3 dose of 18 g m-3, the best performance was obtained by increasing the O3 concentration (maximum [O3]G,inlet of 200 g Nm-3) and decreasing the gas flow rate (minimum QG of 0.15 Ndm3 min-1), providing the highest ozone transfer yield (88 %) and, thus higher specific ozone dose (g O3 per g dissolved organic carbon). Under these conditions, removals >80 % or concentrations below the limit of quantification were obtained for up to 13 of the 19 CECs and reductions up to 5 log units for total heterotrophs and below the limit of detection for enterobacteria and enterococci. Tests including a UVC dose of 0.10 kJ L-1 enhanced disinfection ability but had no impact on CECs oxidation. After ozonation, the abundance of antibiotic resistant bacteria was reduced but not elimi-nated , microbial regrowth after 3-day storage was observed. No toxic effect was detected on zebrafish embryos using a dilution factor of 4 for the ozonized UWW , when granular activated carbon adsorption was subsequently applied the dilution factor decreased to 2.

Automated summary

A membrane ozone contactor was used for the tertiary treatment of urban wastewater, focusing on the removal of emerging contaminants, disinfection, and toxicity reduction. The system utilized a borosilicate tubular membrane coated with titanium dioxide and four UV lamps for radiation. By optimizing ozone concentration and gas flow rate, high removal rates of contaminants and disinfection efficacy were achieved. Antibiotic resistant bacteria were reduced but not eliminated after ozone treatment, and subsequent granular activated carbon adsorption further improved the water quality.