Influence of groundwater constituents on 1,4-dioxane degradation by a binary oxidant system

The influence of groundwater on the degradation of 1,4-dioxane (dioxane) by siderite-activated hydrogen peroxide coupled with persulfate was investigated through a series of batch experiments. The degradation of dioxane was considerably slower in groundwater compared to the tests conducted with ultrapure water. Additional tests were conducted to examine potential inhibitory effects of selected ions in isolation. The inhibition effect of anions on dioxane degradation, from strongest inhibition to weakest, was: bicarbonate (HCO₃^-) > sulfate (SO₄^2-) > chloride (Cl^-). The inhibition effect of cations on dioxane degradation, from strongest inhibition to weakest, was: calcium (Ca²⁺) > potassium (K⁺) > magnesium (Mg²⁺). Bicarbonate and calcium ions, which are the most abundant ions in the groundwater used herein, resulted in the greatest decrease in dioxane degradation rate compared to the other constituents. The results of experiments conducted to evaluate their impact over a range of concentrations showed that dioxane degradation was reduced asymptotically with the increase in their concentrations. The results of this study reveal a potential inhibitory effect caused by groundwater constituents during the application of activated binary H₂O₂-persulfate for in-situ treatment of organic contaminants in groundwater. This effect is attributed to radical scavenging, and its impact should be considered during the evaluation of total oxidant demand (TOD) prior to application.