Application of Ozone and Biological Media Filtration for Reclaimed Water

The ozonation and media filtration of secondary effluent from the Eastern Treatment Plant, a step-feed activated sludge facility, was piloted for over eighteen months. The media used was initially granular activated carbon and anthracite. The ozone dose was varied between a range of 7 – 15 mg/L but typically was operated at 10 mg/L.The ozone, biological media filtration system results are summarized as follows:Unexpectedly, ozone dosed between 8 and 12 mg/L is effective at achieving a tertiary effluent color between 10 and 20 Pt. Co units.Ozone dosed within the same range is effective at producing significant viral, protozoan and pathogen activation in contact times of under 10 seconds although a 2.5 minute contact time is being proposed for design purposes.Ozone hydrolyzed an additional 2 mg/L of dissolved organic carbon that was further degraded through the biological media filters (BMF).Final filtered effluent odor was significantly reduced through ozonation and BMF.Ozonation and BMF combined to fully nitrify ammonia in the final ETP effluent for almost 98% of expected conditions (ammonia less than 4.5 mg/L). During wet weather events when effluent may increase to 10 mg/L in NH3-N, ozone-BMF oxidizes 60 – 75% of this ammonia-nitrogen.Multiple solids stress tests were conducted on the ozone system where extreme solids events were simulated, or real high solids events were evaluated. Pathogen inactivation and color removal were not impacted by solids up to 50 mg/L in the effluent.Trace byproducts of ozonation have not been reliably analyzed although downstream BMF processes are expected to remove these byproducts to trace levels.Ozonation enhanced solids removal – preliminary results indicate ozone increases average BMF solids removal capacity by 46%.