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) (O3-BAF) treatment has become an alternative to reverse osmosis in potable wastewater reuse applications due to 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 (EBCT; 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 and 35 regulated and unregulated halogenated disinfection byproducts (DBPs) and 8 N-nitrosamines after chloramination. Conventional ozonation (without 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 post-chloramination. Regardless, the reduction in halogenated DBP formation during post-chloramination 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 (THMs), HAAs, NDMA, and bromate.