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

Ozonation followed by biologically active filtration (BAF) (O-3-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 O-3-BAF at three specific ozone doses (0.5, 0.7, and 1.0 mg O-3/mg DOC) and different empty bed contact times (EBCTs; 15-45 min). The reaction of O-3 with granular activated carbon (GAC) (O-3/GAC) to promote the formation of hydroxyl radicals (OH) was evaluated at 1.0 mg O-3/mg DOC followed by BAF at 15-45 min EBCT. The efficacy of these techniques was compared for the removal of O-3 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 similar to 25%. O-3/GAC improved the removal of 1,4-dioxane to similar to 40%, while BAF increased the removal to similar to 50%. No bromate was detected during conventional ozonation. Although O-3/GAC formed 12.5 mu g/L bromate, this concentration was reduced during BAF treatment to <6.8 mu g/L. Even though conventional ozonation was more effective than O-3/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. O-3/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 similar to 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 O-3-BAF and (O-3/GAC) BAF met regulatory levels for trihalomethanes, HAAs, NDMA, and bromate.