Enhanced production of hydroxyl radicals in plasma-treated water via a negative DC bias coupling

Hydroxyl radical (OH•) plays an important role in advanced oxidation processes (AOPs), which are employed to decompose organic pollutants in wastewater treatment. OH• is predominantly produced in AOPs for wastewater treatment via ultraviolet photolysis of hydrogen peroxide (H 2 O 2 ) or ozone, which is a costly and difficult process. This paper introduces an enhanced OH• production method based on microwave-driven atmospheric pressure plasma with negatively biased water. Fluorescence analysis using terephthalic acid and 2-hydroxyterephthalic acid showed that the OH• concentration in a DC coupled plasma-treated water (PTW) can be increased by 1–2 orders of magnitude compared to the case with microwave plasma only. In addition, we found that there exists an optimal concentration of H 2 O 2 in PTW for the ideal production of OH•. As a test case of AOPs, an Fe(III)-ethylenediaminetetraacetic acid solution containing H 2 O 2 was treated with a DC coupled plasma for 10 min, and more than 80% decomposition was recorded.