1,4-Dioxane is a probable human carcinogen and a widespread contaminant in Long Island, NY water supplies, with some of the nation’s highest concentrations detected (34 μg/L). As a result, New York State established the nation’s first drinking water standard for 1,4-dioxane at 1 μg/L. Advanced oxidation processes (AOPs), techniques that involve the generation of hydroxyl radicals, have been shown to be very effective in oxidizing 1,4-dioxane in drinking water. Although AOP technology has seen widespread applications, very few reports are available that evaluate their performance on larger scales (pilot- and full-scale systems) for the treatment of 1,4-dioxane. Toward this end, the New York State Center for Clean Water Technology (NYS CCWT), in collaboration with NYS Department of Health and Long Island water utilities, recently conducted a pilot program to test the performance of seven pilot-scale AOP systems including two UV/H₂O₂, two UV/chlorine, two UV/TiO₂, and one O₃/H₂O₂ across four different sites on Long Island. In addition to testing their performance as a function of UV power and oxidant dose to treat 1,4-dioxane, the source waters were modified to assess the impact of increased natural organic matter, bromide, and nitrate levels. Influent and effluent samples were analyzed for 1,4-dioxane, TOC, chlorinated solvents, disinfection byproducts, AOP byproducts (organic acids, aldehydes), and cell toxicity (MTT assay). Results reveal that although all AOP systems are capable of removing 1,4-dioxane to levels below the method detection limit (<0.02 μg/L), UV/H₂O₂ and O₃/H₂O₂ performed most efficiently with a mean electrical energy per order (EE/O) of 0.17 kWh/m³/order (range: 0.10 – 0.21) and 0.14 kWh/m³/order (range: 0.08 – 0.37), respectively. UV/TiO₂ showed high variability in its performance (EE/O range: 0.37 – 25.8 kWh/m³/order) and showed the highest energy consumption to achieve complete removal of 1,4-dioxane compared to other technologies. The general trend in performance to remove 1,4-dioxane in terms of EE/O was UV/H₂O₂ ≥ O₃/H₂O₂ > UV/chlorine > UV/TiO₂. This presentation will additionally discuss byproducts formation, preliminary cost analysis, pilot testing challenges, and research needs with regards to AOP treatment of 1,4-dioxane.

Cheng-Shiuan Lee

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