(444e) Optimization of Advanced Oxidation Processes for Removal of 1,4-Dioxane from Water Influents

1,4-Dioxane is a synthetic cyclic ether that has been identified as a potentially harmful organic compound. As water quality testing procedures continue to advance, a growing number of valuable water resources around the world are being found to be contaminated with 1,4-dioxane. Historically, 1,4-dioxane was produced as a solvent stabilizer for the chemical degreaser 1,1,1-trichloroethane (1,1,1-TCA). In the early 2000s, 1,1,1-TCA was deemed an ozone depleting substance and its use was limited to essential applications. With the decline in 1,1,1-TCA production came the decline in 1,4-dioxane production. Unfortunately, 1,4-dioxane is formed as a by-product in several manufacturing processes used in the production of consumer goods. The polyester synthesis process and the ethoxylation process, which is utilized to manufacture surfactants found in detergents, shampoos, and cosmetics, are the two major processes that result in the formation of 1,4-dioxane as a by-product. 1,4-dioxane is considered a persistent organic pollutant as it does not readily degrade in the environment and instead accumulates. The USEPA has classified 1,4-dioxane as a Class 2B probable human carcinogen, but federal regulations for acceptable concentration levels in drinking water are not currently in place.

There is a critical need for effective treatment options to address water contamination caused by 1,4-dioxane. Due to its high solubility and affinity for water, adsorption processes have had challenges with treating 1,4-dioxane. Biotreatment methods are evolving, but more research is needed to yield a viable process. Surprisingly, little research has been applied toward the use of advanced oxidation processes for treating water contaminated with 1,4-dioxane. With 1,4-dioxane becoming an emerging pollutant of concern, more information is needed to characterize treatment process effectiveness and determine complimentary design parameters before these treatment systems can be properly applied in the field.

Advanced oxidation processes (AOPs) are a set of treatment processes that utilize hydroxyl radicals to degrade organic pollutants in water matrices. Various process configurations have been found to produce hydroxyl radicals. These configurations can be broken down into two main AOP groups: lighted (mainly UV photolytic-based) or dark (hydrogen peroxide and/or ozone based without photolysis). AOPs have a strong track record for treating a wide variety of organic pollutants in water matrices.

This study evaluated the comparative performance of various candidate AOPs (both lighted and dark) for the effective treatment of 1,4-dioxane within water matrices. Bench-scale AOP reactors were used to test the relative performance of the candidate AOPs for degrading 1,4-dioxane. Total organic carbon is used to evaluate the extent of mineralization along with the analytical tracking of key degradation products. Preliminary results indicated that 1,4-dioxane was easily degraded via oxidation. Efforts were then directed toward reducing oxidation system complexity and reagent cost without sacrificing treatment performance. Optimal dosing amounts and feed strategies have been optimized. Degradation kinetics coupled with completeness of oxidation reactions were also evaluated. Both lighted and dark systems were found effective with each type offering different benefits.