Nitrogen Fixation in Water Using Air Phase Gliding Arc Plasma

Abstract

Treatment of irrigation water using plasma involves a series of electrochemical reactions that forms NO x − in water working as a fertilizer in plant cultivation. Here we report the results of an experimental study of the effects of different discharge conditions especially discharge frequency on air phase gliding arc discharge. The results show that, the low-frequency system consumed nearly three times more energy than the high-frequency system when generating the same NO x − production rate in water; gas flow rate has strong influence on the low-frequency system while slight influence on the high-frequency system; high-frequency discharge can generate much larger plasma area to promote electrochemical reactions resulting more NO x − produced in water. Frequency from 5 kHz to 80 kHz does not significantly influence on the nitrogen fixation of gliding arc. Nitrogen is an essential element in chlorophyll, DNA, RNA, and amino acids of plants.1 Nitrogen fertilizer, a much needed nutrient for growing crops, is made from ammonia produced by the Haber-Bosch ammonia synthesis process.2 Nitrogen fixation via the traditional Haber-Bosch method represents an energy-intensive and environmental-destructive process, and ammonia has been identified as one of the 18 chemical compounds contributing to 75% of greenhouse gas (GHG) emissions.3 To reduce negative environment footprints by the traditional Haber-Bosch process, the fertilizer industry has been long looking for alternative options of producing ammonia as nitrogen fertilizers in agriculture application. Industrial plasma processing is one novel method demonstrating a great potential to be developed as an alternative technique for nitrogen fixation. 4 In more recent years, generation of nitrogen in aqueous solution has been demonstrated with various discharges, including spark, gliding arc, glow, corona, and dielectric barrier discharge.5-10 Oxygen nitrogen water mixture used in irrigation significantly influences plant growth phase working as a fertilizer in plant cultivation. Takaki et al. applied a magnetic pulse power generator with 250 pps repetition rate as the power supply and found the growth rate of Chinese cabbage increased significantly by treating drainage water with underwater discharge.5 Alex Lindsay et al. developed a unique low-voltage largevolume glow discharge with 162 MHz frequency power supply. The method was capable of generating plasma activated water, demonstrating statistically significant positive effects on plant height, sprouts per pot, leaf span and shoot mass on the growth of radishes, marigolds, and tomatoes.7 Park et al. compared three discharge methods: submerged spark discharge at an average frequency of 5 Hz; transferred gliding arc discharge and gliding arc plasmatron powered with DC supply. Their results showed that most plants grew better with the non-thermal gliding arc plasmatron discharge than submerged spark discharge and transferred gliding arc discharge.11 However, considering limited pressure and power levels, conventional glow...

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