| Recently, the amount of organic pollutants in water has risen quickly led by the increase of population and the rapid development of industry. Based on the universality and harmfulness of organic pollutants in water, a pulsed discharge plasma(PDP) system with multi-needle-to-plate electrode geometry combined with activated carbon(AC) was set up in the paper and used to degrade organic contaminants in water. The degradation rate of organic contaminants improved and the energy efficiency of PDP enhanced as well. Firstly, the operating conditions of the combined system of PDP and AC was optimized according to the formation of H2O2 under different experimental conditions; Secondly, acid orange 7(AO7) and bisphenol A(BPA) were selected as the targeted contaminants, the degradation rate of the two organic compounds in the combined PDP/AC system was investigated by varying different parameters and the corresponding degradation mechanism was analyzed;Lastly, the production and variation of major radicals(?OH and ?O) in the PDP/AC system were investigated using spectroscopy detection technique, the synergistic effect of PDP/ AC and the oxidation of radicals on the contaminants were confirmed.Main conclusions of the research are summarized as follows:(1) A PDP system with seven-needle-to-plate electrode geometry was firstly established in the study, H2O2 concentrations under different conditions of pulse peak voltage, air flow rate, initial pH value of the solution and AC additive amount were investigated to optimize the operating conditions of the combined system of PDP/AC.The obtained experimental results showed that the formation of H2O2 was highest when the pulse peak voltage, the air flow rate, the initial pH value and the additive amount of AC were 20 kV, 2 L/min, 6.9 and 4 g, respectively. The highest H2O2 formation was 0.30573 mmol/L and corresponding energy efficiency was 0.022505mmol/J.(2) The AO7 was selected as the targeted contaminant, the effect of AC addition and particle size of the AC, electrode gap, solution conductivity, initial pH value of solution and variety and rate of carrier gas on the decoloration of AO7 was investigated and the kinetic analysis of was also carried out. The optimal parameters in PDP/AC system were obtained as follows: 4 g AC addition and 2-3 mm particlesize of the AC, 15 mm electrode gap, 3 initial pH value of solution and 2 L/min oxygen flow rate; UV-Vis spectrum analysis of solution at different reaction time indicated the degradation of AO7 in the PDP/AC system; the removal of TOC achieved 30.3% at the optimal conditionl; intermediates of AO7 degradation were identified by the GC-MS analysis, and the intermediates were 1,4-Benzoquinone,phthalic anhydride, 2H-1-Benzopyran, 2-Formyl-Benzoic acid, 2-Naphthalenol1,2-Naphthalenedione, and the degradation pathway of AO7 was also proposed; the result of scanning electron microscope(SEM) analysis indicated that the surface of the AC after PDP treatment was smoother, the volume of micropore and mesopore decreased and macropore appeared.(3) The BPA was selected as the targeted contaminant, the effect of initial concentration of the solution, the addition of the radical scavenger and the gas varieties on the BPA degradation was investigated. The results indicated that the degradation rate of BPA increased first and then decreased with the increase of initial concentration of the BPA; the addition of ?OH scavenger was not beneficial to the BPA degradation, which confirm the important effect of the ?OH; compared to air and nitrogen, the degradation rate of BPA was highest when oxygen was bubbled into the reaction system. The detected change of the pH value and conductivity of the solution during the reaction process demonstrated that the pH value of solution decreased and conductivity of solution increased with the increase of discharge time. Analysis of UV-Vis spectrum indicated a lot of intermediates could be generated during BPA degradation in the PDP/AC system.(4) The effect of different parameters on the emission spectrum intensities of the?OH and the ?O were investigated using the spectroscopy detect technique. The emission spectrum intensities of the ?OH and the ?O in deionized water, AO7 solution and BPA solution in both the sole PDP system and the PDP/AC system were detected.The obtained results indicated that the relative emission intensity of the ? OH increased with the increase of additive amount of the AC, whereas the relative emission intensity of the ? O was almost invariant; higher pulse voltage peak and lower electrode gap were benefit to the generation of the ?OH and the ?O; The formation of the ?OH and the ?O generated in the PDP/AC system was higher than those in the sole PDP system no matter the distilled water or the AO7 solution or BPAsolution was used as the solution phase, which confirmed the synergetic effect of the PDP and the AC; both in the sole PDP system or the PDP/AC system, the formation of?OH and ?O in the distilled water was higher than those in the AO7 solution, which confirmed the oxidation of the two radicals on the organic compounds. |
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