Streamer-spark discharge at the water surface as a source of plasma-activated water: nitrogen fixation yields and biocidal efficiency

Abstract

The plasma filaments propagating along the air–water interface offer a useful approach to enhance the transport of reactive species from plasma into the liquid medium. In this work, we investigated the novel streamer-spark discharge geometry, where both electrodes are submerged in water, inside a continuous flow-through reactor as a source of plasma-activated water (PAW) that can be used as a nitrogen-enriched water fertilizer and/or antimicrobial agent. We have inspected the efficiency of nitrogen fixation by varying the external parameters such as airflow and discharge repetition rate at fixed water flow through the reactor. The concentrations of generated NO_x species exhibit linear dependence on input power in both gaseous and dissolved forms, with the production rate of NO_x⁻ reaching as high as 48.5 μmol min⁻¹ with standard energy efficiencies of around 16 mmol MJ⁻¹. Biocidal efficiency was tested on three selected fungal species (Botrytis cinerea, Penicillium italicum, Aspergillus carbonarius), which are usually more resilient than bacteria. The best efficacy in conidia germination inhibition has been achieved for Penicillium italicum (nearly 40%). The results presented also indicate that the energy efficiency of NO₃⁻ synthesis is tied to the characteristics/parameters of individual streamer-spark discharge events, while the total NO₃⁻ concentration and production throughput are determined by the overall discharge power.