Publications

Selected publication  

Ahlawat K., Chithran A., Kimani B.G., Machala Z.: Decoupling nitrogen fixation from degradation: A dual-function DBD plasma-bubble system for sustainable wastewater treatment, Journal of Water Process Engineering 91, 110553 (2026).
citations: 0

Abstract

This study presents a novel off-gas-valorizing, dual-stage non-thermal plasma (NTP) configuration designed to overcome the energy efficiency and off-gas utilization limitations of conventional plasma-bubble reactors. The system couples a direct underwater double dielectric barrier discharge reactor (Reactor 1), operating at 50 W, with a secondary water treatment vessel (Reactor 2) powered solely by Recycled Plasma-Treated Air (RPTA). Spectroscopic characterization of the RPTA stream shows a mixed composition of ozone and nitrous oxide, alongside humidity-derived reactive species. This mixture initiated a vigorous in-situ peroxone reaction in Reactor 2, accelerating the hydroxyl radical generation rate to approximately 8 times higher than standard ozonation at identical dosages. Consequently, the RPTA-driven Reactor 2 achieved superior pollutant degradation without additional energy input. For the recalcitrant pollutant Coumarin (16 mg/L), the system achieved >99% degradation within 30 min, yielding an energy efficiency of 352 mg/kWh compared to only 141 mg/kWh for the direct plasma process. Similarly, Methylene Blue dye (10 mg/L) underwent >99% decolorization in just 1.5 min, with a kinetic rate constant of 3.1 min−1 and an energy yield of 3360 mg/kWh. For biological decontamination: The system achieved a 5-log reduction of Escherichia coli within 10 min, significantly outperforming the 3.6-log reduction of standard ozonation. Simultaneously, Reactor 1 served as a high-yield nitrogen fixation unit for plasma-activated water (PAW) production, accumulating 6.2 mM nitrate in 30 min (yield ~ 9.2 g/kWh). This dual-function approach successfully decouples agricultural resource recovery from wastewater treatment, maximizing chemical utility while minimizing energy waste.