Fei Juntao

Yield of Ozone, Nitrite Nitrogen and Hydrogen Peroxide Versus Discharge Parameter Using APPJ Under Water ⁄

Discharge plasma in and in contact with water can be accompanied with ultraviolet radiation and electron impact, thus can generate hydroxyl radicals, ozone, nitrite nitrogen and hydrogen peroxide. In this paper, a non-equilibrium plasma processing system was established by means of an atmospheric pressure plasma jet immersed in water. The hydroxyl intensities and discharge energy waveforms were tested. The results show that the positive and negative discharge energy peaks were asymmetric, where the positive discharge energy peak was greater than the negative one. Meanwhile, the yield of ozone and nitrite nitrogen was enhanced with the increase of both the treatment time and the discharge energy. Moreover, the pH value of treated water was reduced rapidly and maintained at a lower level. The residual concentration of hydrogen peroxide in APPJ treated water was kept at a low level. Additionally, both the efficiency energy ratio of the yield of ozone and nitrite nitrogen and that of the removal of p-nitrophenol increased as a function of discharge energy and discharge voltage. The experimental results were fully analyzed and the chemical reaction equations and the physical processes of discharges in water were given.

Atmospheric Pressure Plasma Jet in Organic Solution: Spectra, Degradation Effects of Solution Flow Rate and Initial pH Value

The organic compounds of p-nitrophenol (PNP) solution was treated by the active species generated in a stirred reactor by an atmospheric pressure plasma jet (APPJ). The emission intensities of hydroxyl (OH), oxygen (O), nitric oxide (NO), hydrogen (H) and molecular (N2) were measured by optical emission spectroscopy (OES). The relations between the flow rates of the PNP solution and degradation, the degradation effects and initial pH value of the solution were also investigated. Experimental results show that there exist intense emissions of O (777.1 nm), N2 (337.1 nm), OH (306–310 nm) and NO band (200–290 nm) in the region of plasma. Given the treatment time and gas flow rate, the degradation increased as a function of discharge energy and solution flow rate, respectively. The solution flow rate for the most efficient degradation ranged from 1.414 m/s to 1.702 m/s, and contributed very little when it exceeded 2.199 m/s. This indicates the existence of diffusion-controlled reactions at a low solution flow rate and activation-controlled reactions at a high solution flow rate. Moreover, increasing or decreasing the initial pH value of neutral PNP solution (pH=5.95) could improve the degradation efficiency. Treated by APPJ, the PNP solutions with different initial pH values of 5.95, 7.47 and 2.78 turned more acidic in the end, while the neutral solution had the lowest degradation efficiency. This work clearly demonstrates the close coupling of active species, photolysis of ultraviolet, the organic solution flow rate and the initial pH value, and thus is helpful in the study of the mechanism and application of plasma in wastewater treatment.

Water Content Effect on Oxides Yield in Gas and Liquid Phase Using DBD Arrays in Mist Spray

Electric discharge in and in contact with water can accompany ultraviolet (UV) radiation and electron impact, which can generate a large number of active species such as hydroxyl radicals (OH), oxygen radical (O), ozone (O3) and hydrogen peroxide (H2O2). In this paper, a nonthermal plasma processing system was established by means of dielectric barrier discharge (DBD) arrays in water mist spray. The relationship between droplet size and water content was examined, and the effects of the concentrations of oxides in both treated water and gas were investigated under different water content and discharge time. The relative intensity of UV spectra from DBD in water mist was a function of water content. The concentrations of both O3 and nitrogen dioxide (NO2) in DBD room decreased with increasing water content. Moreover, the concentrations of H2O2, O3 and nitrogen oxides (NOx) in treated water decreased with increasing water content, and all the ones enhanced after discharge. The experimental results were further analyzed by chemical reaction equations and commented by physical principles as much as possible. At last, the water containing phenol was tested in this system for the concentration from 100 mg/L to 9.8 mg/L in a period of 35 min.

Yield of hydrogen peroxide, ozone and nitrite nitrogen with DBD arrays in water mist spray

Summary form only given. Electric discharge in water can accompany UV radiation and electron impact, and can generate oxidants such as hydroxyl radicals, ozone and hydrogen peroxide. Here, a non-thermal plasma processing system was established by means of dielectric barrier discharge (DBD) arrays in water mist spray. The yield of hydrogen peroxide (H₂O₂), ozone (O₃) and nitrite nitrogen (NO_x) were both enhanced after discharge in water. The effects of water-air flow ratio, discharge time and high voltage power were investigated. The intensities in the ultraviolet region were measured by optical emission spectroscopy (OES) with different power input and moisture content. Experimental results show that there exist intense emissions of OH (309-317.8 nm), O⁺ (372.3, 375.1, 394.7, 397.6 nm), N₂ (335.5, 352.1 nm), and NO (296, 357.7, 378.9 nm) in the plasma and the intensity increases with both increasing input power and moisture. The concentration of H₂O₂, O₃ and NO_x was measured after discharge. The yield of H₂O₂, O₃ and NO_x in water and O₃ and NO₂ in DBD changed as a function of water-air flow ratio and treatment time. For same treatment time, the yield of O₃ and NO₂ in the DBD increased initially and then decreased with increasing water-air flow ratio, and the yield of H₂O₂, O₃ and NO_x in water decreased slowly with increasing water-air flow ratio. For same water-air flow ratio, the yield of O₃ and NO_x in water increases initially then remains constant with increasing treatment time; the yield of H₂O₂ in water increases significantly and sustained with increasing treatment time, and the pH value of treated water slightly decreases with increasing treatment time. The experimental results were fully analyzed by the chemical reaction equations and commented by the physical principles as much as possible. Finally, the water containing phenol was tested in this system. The degradation rate came to 86% in 30 min.