Controlling contaminants using a far-UVC-based advanced oxidation process for potable reuse

Increasing the efficiency of the processing units used to purify municipal wastewater to potable quality would enhance the sustainability of potable reuse. Conventional advanced oxidation processes using 254 nm UV light degrade contaminants by both direct photolysis and reaction with radicals produced by hydrogen peroxide photolysis. Treatment goals include 0.5-log removal of 1,4-dioxane, reducing N-nitrosodimethylamine to <10 ng l−1 and 6-log virus inactivation. Using three potable reuse waters, we demonstrate here that a switch from 254 to 222 nm (far-UVC) achieved all three treatment goals at ~320 mJ cm−2 UV fluence, which is around four-fold less than is needed at 254 nm. Developing and validating a kinetic model, we determined that the increased energy efficiency arises from a 2.1- to 7.5-fold increase in direct photolysis and a 3.6-fold increase in radical concentrations. Compared with switching to far-UVC wavelengths, alternative efforts to switch from H2O2 to chlorine have been frustrated by the need to increase UV fluence to control N-nitrosodimethylamine. Enhancing the advanced oxidation processes used in potable reuse treatment trains represents an attractive target for reducing the energy intensity of the train. Switching the UV wavelength from 254 nm to 222 nm improves contaminant degradation by both direct photolysis and reaction with radicals, offering substantial efficiency gains.