Selectivity Control in an Atmospheric Pressure Plasma Source for Point-of-Use Water Disinfection

In parts of the world where water treatment infrastructure is lacking, the WHO estimates that 2 billion people are drinking water from a contaminated source and that nearly half a million people die annually from waterborne illnesses. To address this need, we are developing a solar powered point-of-use plasma disinfection applicator. Preliminary results show that over short treatment periods 6 log reduction in E. Coli is realizable in modest sized treatment volumes. An important consideration is that the final product is safe to drink. This apparatus allows for internal plasma chemistry to be tuned, thereby allowing for the reduction in undesired products, NO2- and NO3-, and maximization of the high-disinfection products, O3, H2O2, and OH- radicals. Here we study the species selectivity of the plasma system; emission spectroscopy is used to monitor relative production rates for a range of reactive species generated by the device over a broad parameter space, including gas flow, applied voltage, and excitation frequency. We also present operation data featuring a low cost power supply. This work aims to lay the foundation for modeling the gas phase chemistry of this device and the resulting activation of the liquid water.