Iron-ozone catalytic oxidation reactive filtration of municipal wastewater at field pilot and full-scale with high-efficiency pollutant removal and potential negative CO2 e with biochar.

Abstract

Iron-ozone catalytic oxidation (CatOx) shows promise in addressing challenging wastewater pollutants. This study investigates a CatOx reactive filtration (Fe-CatOx-RF) approach with two 0.4L/s field pilot studies and an 18-month, 18L/s full-scale municipal wastewater deployment. We apply ozone to leverage common sand filtration and iron metal salts used in water treatment into a next-generation technology. The process combines micropollutant and pathogen destructive removal with high-efficiency phosphorus removal and recycling as a soil amendment, clean water recovery, and the potential for carbon-negative operation with integrated biochar water treatment. A key process innovation is converting a continuously renewed iron oxide coated, moving bed sand filter into a "sacrificial iron" d-orbital catalyst bed after adding O3 to the process stream. Results for the Fe-CatOx-RF pilot studies show >95% removal efficiencies for almost all >5× LoQ detected micropollutants, with removal rates slightly increasing with biochar addition. Phosphorus removal for the pilot site with the most P-impacted discharge was >98% with serial reactive filters. The long-term, full-scale Fe-CatOx-RF optimization trials showed single reactive filter 90% TP removal and high-efficiency micropollutant removals for most of the compounds detected, but slightly less than the pilot site studies. TP removal decreased to a mean of 86% during the 18L/s, 12-month continuous operation stability trial, and micropollutant removals remained similar to the optimization trial for many detected compounds but less efficient overall. A >4.4 log reduction of fecal coliforms and E. coli in a field pilot sub-study suggests the ability of this CatOx approach to address infectious disease concerns. Life cycle assessment modeling suggests that integrating biochar water treatment into the Fe-CatOx-RF process for P recovery as a soil amendment makes the overall process carbon-negative at -1.21 kg CO2 e/m3 . Results indicate positive Fe-CatOx-RF process performance and technology readiness in full-scale extended testing. Further work exploring operational variables is essential to establish site-specific water quality limitations and responsive engineering approaches for process optimization. PRACTITIONERS POINTS: Adding ozone to WRRF secondary influent flows into tertiary ferric/ferrous salt dosed sand filtration amplifies a mature reactive filtration technology into a catalytic oxidation process for micropollutant removal and disinfection. Expensive catalysts are not used. Iron oxide compounds used to remove phosphorus and other pollutants act as sacrificial catalysts with ozone, and these rejected iron compounds can be returned upstream to aid in secondary process TP removal. Biochar addition to the CatOx process improves CO2 e sustainability and phosphorus removal/recovery for long-term soil and water health. Short duration field pilot scale and 18-month full-scale operation at three WRRFs with good results demonstrate technology readiness.