The confluence of societally impacting forces such as climate change, overpopulation, and overdevelopment are stressing freshwater reserves (see figure 1) [1,2]. Beyond issues of scarcity, fresh water quality is increasingly affected by pollution derived from agriculture and industry. Water reuse addresses water scarcity [3][4][5][6]. By water reuse, we refer to the use of technology to directly or indirectly recycle treated wastewater effluent for potable and non-potable applications, thereby augmenting existing water supplies. In the US alone, water reuse, if implemented, could meet up to 30% of the current public water supply demand [7]. Advanced water treatment technologies are required to reduce contaminant levels in reused water to acceptable values [8]. These same technologies have the potential to also remove those contaminants not addressed by conventional water treatment systems. Advanced oxidation processes (AOPs) have been identified as the basis for the treatment of difficult water, addressing contaminants that are difficult to strip, absorb or biodegrade conventionally

Plasma-driven advanced oxidation represents a potential technology to safely re-use waters polluted with recalcitrant contaminants by mineralizing organics via reactions with hydroxyl radicals, thus relieving freshwater stress. The process results in some residual hydrogen peroxide, which can interfere with the standard method for assessing contaminant removal. In this work, methylene blue is used as a model contaminant to present a case in which this interference can impact the measured chemical oxygen demand of samples. Next, the magnitude of this interference is investigated by dosing de-ionized water with hydrogen peroxide via dielectric barrier discharge plasma jet and by solution. The chemical oxygen demand increases with increasing concentration of residual hydrogen peroxide. The interference factor should be considered when assessing the effectiveness of plasma to treat various wastewaters.

Per- and polyfluoroalkyl substances (PFAS) are contaminants of emerging concern owing to their ability to bioaccumulate in the body and subsequently cause cancer. PFAS, while recalcitrant to advanced oxidation, can be degraded by plasma action. In this work, we investigate the efficacy of two plasma reactors on degrading PFAS in ground water derived from two different contaminated sites. The reactors included an array of underwater plasma jets and a dielectric barrier discharge (DBD) with water dielectric barriers. While both reactors showed effectiveness in removing PFAS, the DBD with water barriers was most efficient with regard to the rate of degradation and power consumed. This better performance was attributed to the increased plasma–liquid contact area. Experiments indicate that air is a suitable working gas alternative to argon, and both AC and ns-pulsed power sources can generate the plasmas for these reactors. Furthermore, it was found that for both reactors, the removal rate for low and high PFAS concentration in ground water was the same, suggesting that the reactors are most efficient at treating heavily contaminated water. In this respect, a concentration step followed by plasma treatment may be a cost-effective means to treat the PFAS-contaminated water.

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