Ozonation of wastewater effluent by the MEMBRO3X contactor: Micropollutants abatement and bromate mitigation

Wastewater treatment plants (WWTPs) are significant sources of micropollutants, potentially adversely affecting freshwater ecosystems. Ozonation is an effective way to abate micropollutants during treatment of wastewater effluent, however, the presence of bromide may lead to bromate, a potentially carcinogenic byproduct. The applicability of a hollow fiber porous membrane-based ozone contactor (MEMBRO₃X) was assessed for wastewater effluent treatment for the simultaneous abatement of micropollutants and bromate mitigation by investigating the effects of operating conditions (e.g., hydraulic retention times, gas phase concentrations of ozone and hydrogen peroxide dosing) and water quality parameters (concentration of dissolved organic matter (DOM) and level of alkalinity). In synthetic water containing Suwannee River Natural Organic Matter and bromide, MEMBRO₃X showed better performance for relative micropollutant abatement with minimal bromate formation compared to the conventional ozonation in the presence of high DOC concentration and high alkalinity for ozone gas phase concentrations of ≤ 10 gO₃ Nm^-3. Key ozone mass transfer parameters, including liquid velocity and membrane length, were also investigated to support interpretation of treatment performance. Adding H₂O₂ improved ozone mass transfer at the membrane interface, but also elevated bromate formation, making this an unfavorable option. Three secondary wastewater effluent samples were investigated, and a similar trend as for synthetic DOM-containing water was observed regarding water quality and process operating conditions. The calculated required membrane surface areas for the MEMBRO₃X process are 15 to 60 m² per cubic meter of treated water per hour, which aligns with typical membrane-based filtration systems. This suggests that the MEMBRO₃X process is a practical solution for effective micropollutant abatement with minimized bromate formation.