Synergistic 1,4-dioxane removal by non- thermal plasma followed by biodegradation

In this work a water film non-thermal plasma reactor is combined with an aerobic biological reactor to treat water contaminated by 1,4-dioxane. The plasma reactor converted 1,4-dioxane to organic products including ethylene glycol, ethylene glycol monoformate, ethylene glycol diformate, 1,4-dioxan-2-one, 1,4-dioxan-2-ol, and formic, oxalic, glycolic, and methoxyacetic acids. The detection of these organic products led to a proposed novel 1,4-dioxane degradation pathway. The plasma reactor primarily utilized OH radicals formed directly from water to degrade 1,4-dioxane at an energy efficiency comparable to, but with a reaction rate over three orders of magnitude higher than that in other advanced oxidation processes (AOPs), which might be due to the significant local OH radical production. The concentration and composition of the organic products exiting the plasma reactor varied with hydraulic retention time (HRT) and affected the following biological treatment time. At the optimum HRT for the plasma reactor (i. e., 1 s), similar to 25% of 1,4-dioxane was mineralized to CO2, and similar to 75% was converted to organic products, which were further degraded in the following biological reactor.