Degradation of Pyraclostrobin in Water Using a Novel Hybrid Gas–Liquid Phase Discharge Reactor

In this paper, the hybrid gas–liquid discharge plasma can efficiently degrade pesticide residues in water driven by nanosecond pulse power, which can achieve the simultaneous discharge process in the liquid and gas phases. The relevant factors are systematically investigated, including the waveforms of discharge current and pulse voltage, discharge images, and optical emission spectra during the discharge process. The Stark broadening of Hα calculates the electron density. The effects of the pulse peak voltage and discharge time on the emission intensities of OH (A2∑ → X2∏), N2 (C3∏u → B3∏g), Hα, and O (3p5P → 3s5S0) are discussed in-depth by the optical emission spectra. The gas–liquid discharge plasma with an electron density of 7.14 × 1017 cm−3 was found. The emission intensities of OH (A2∑ → X2∏), N2 (C3∏u → B3∏g), Hα, and O (3p5P → 3s5S0) present the rising trend by increasing the pulse peak voltage and discharge time. In addition, pyraclostrobin is adopted as the research object to study the removal efficiency of pollutants. The results confirm that pyraclostrobin can be completely degraded after 10 min of plasma treatment with the pulse peak voltage of 28 kV, and the degradation rate and energy yield was 0.323 min−1, and 1.91 g/kWh, respectively. The intermediate products and the possible degradation mechanism of pyraclostrobin are further explored by combining the results of high-performance liquid chromatography–mass spectrometry (HPLC-MS/MS) and density functional theory (DFT), the developmental toxicity of the intermediate products was analyzed, which provided a scheme for the treatment of pesticide wastewater by gas–liquid discharge plasma technology.