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Evaluation of Enhanced Ozone–Biologically Active Filtration Treatment for the Removal of 1,4-Dioxane and Disinfection Byproduct Precursors from Wastewater Effluent

Vatankhah, Hooman, Szczuka, Aleksandra, Mitch, William A., Almaraz, Nohemi, Brannum, Jacob, Bellona, Christopher
Environmental science & technology 2019 v.53 no.5 pp. 2720-2730
N-nitrosodimethylamine, activated carbon, byproducts, dioxane, disinfection, filtration, haloacetic acids, hydroxyl radicals, membrane bioreactors, ozonation, ozone, reverse osmosis, wastewater, water reuse
Ozonation followed by biologically active filtration (BAF) (O₃–BAF) treatment has become an alternative to reverse osmosis in potable wastewater reuse applications because of the ability to produce a high-quality effluent while reducing brine production and disposal. In this study, effluent from a sequencing batch membrane bioreactor (SBMBR) was treated by O₃–BAF at three specific ozone doses (0.5, 0.7, and 1.0 mg O₃/mg DOC) and different empty bed contact times (EBCTs; 15–45 min). The reaction of O₃ with granular activated carbon (GAC) (O₃/GAC) to promote the formation of hydroxyl radicals (·OH) was evaluated at 1.0 mg O₃/mg DOC followed by BAF at 15–45 min EBCT. The efficacy of these techniques was compared for the removal of O₃ refractory 1,4-dioxane and the reduction in the formation of bromate, 35 regulated and unregulated halogenated disinfection byproducts (DBPs), and 8 N-nitrosamines after chloramination. Conventional ozonation (without the presence of GAC during ozonation) removed 6–11% of 1,4-dioxane, while BAF increased the removal to ∼25%. O₃/GAC improved the removal of 1,4-dioxane to ∼40%, while BAF increased the removal to ∼50%. No bromate was detected during conventional ozonation. Although O₃/GAC formed 12.5 μg/L bromate, this concentration was reduced during BAF treatment to <6.8 μg/L. Even though conventional ozonation was more effective than O₃/GAC for the reduction in chloramine-reactive N-nitrosodimethylamine (NDMA) precursors, BAF treatment after either conventional or enhanced ozonation reduced NDMA formation during chloramination to <10 ng/L. O₃/GAC was more effective at reducing halogenated DBP formation during postchloramination. Regardless, the reduction in halogenated DBP formation during postchloramination achieved by BAF treatment was ∼90% relative to the formation in the SBMBR effluent after either conventional or enhanced ozonation. The reduction of haloacetic acid (HAA) formation improved moderately with increasing BAF EBCT. Both O₃–BAF and (O₃/GAC)–BAF met regulatory levels for trihalomethanes, HAAs, NDMA, and bromate.