Control of halogenated disinfection byproducts by non-thermal plasma in potable water reuse

Disinfection byproducts (DBPs), especially haloacetonitriles (HANs), are priority pollutants for potable water reuse facilities. Advanced oxidation processes (AOPs) are the final treatment barrier for DBPs, and there is interest in replacing UV/H₂O₂ AOPs with more effective options. We evaluate non-thermal plasma as an alternative AOP for reverse-osmosis (RO)-based reuse. Using a dielectric barrier discharge reactor selected because of scale-up potential, we show that non-thermal plasma removes 68% of 1,4-dioxane, a validation benchmark for AOPs, in phosphate buffer within 15 min, but removal declines to 39% in RO permeate. Within 15 min, plasma removed 49-63% of representative HANs. Volatilization dominated removal, highlighting the need for appropriate controls in the plasma water-contaminant field. We measured ∼100% bromide yield from the fraction of brominated HANs that were not volatilized showing that the technology is promising for DBP control if volatilization could be minimized. Hydroxyl radical (^•OH) played a minor role in degradation (<2% contribution). ^•OH is typically assumed to drive contaminant removal in plasma systems, motivating a re-evaluation of halogenated contaminant removal mechanisms by plasma. In RO permeate, the tested plasma lowered the concentration and formation potential of 19 priority DBPs, reducing calculated toxicity by >90%, but largely through volatilization. Preliminary analyses indicate that high energy costs are a barrier to implementation, but the technology is promising for decentralized reuse applications, where high energy inputs may be preferable to the costs associated with chemical acquisition.