Generation and Decomposition of Reactive Oxygen and Nitrogen Species (RONS) in an Experimental Plasma Reactor for Wastewater Treatment

This study evaluates reactive species generation in two transient spark plasma reactors producing plasma-activated water from deionized water, tap water, and simulated wastewater. Plasma was applied above the liquid surface using a high-voltage source, and physicochemical changes were monitored during treatment and over two weeks post-treatment. Reactive species (nitrate, nitrite, ammonium, ozone, and hydrogen peroxide) were quantified, and tetracycline and Enterococcus faecalis were targeted. Complete pollutant removal was achieved in the 200 mL reactor across all water matrices, whereas the 1000 mL reactor required longer treatment times and exhibited reduced efficiency with wastewater. In the 200 mL reactor, energy efficiency per order was higher; ozone and hydrogen peroxide reached up to 1.5 ppm and 8 ppm, respectively; nitrate stabilized after 15 minutes, nitrite showed transient behavior, and ammonium increased continuously. The larger reactor exhibited similar but slower trends. Over two weeks, in both reactors, nitrate and ammonium remained stable, while ozone and hydrogen peroxide decayed rapidly. Plasma exposure caused an initial pH drop and an increase in conductivity, which subsequently stabilized. These findings underscore the critical role of reactor volume and water composition in PAW chemistry, pollutant removal, and reactive species stability, confirming plasma treatment as a sustainable, by-product-free technology for water remediation.