Pulse Discharge Plasma Treatment Refractory Organics

Pulsed discharge plasma is a recently developed advanced oxidation process for removing hazardous recalcitrant organic pollutants from wastewaters. Its promising feature lies in its multiple oxidative effects, including high energy electrons, hydroxyl radicals, UV, ozone, etc. It can degrade almost all sorts of organic compounds without selectivity and has the advantage of high efficiency, good fidelity. The fission of chemical bonds could be efficiently realized by the discharge in room temperature without any reagents added in. Therefore, it has the potential in industrial application.In this dissertation, the principal of water treatment by pulsed discharge plasma was introduced. Simulated wastewater formed by rhodamine b dilute into deionized water was treated and the following works have been done:1. A new type of plasma processing system for water treatment was established. The electrode section is an array of parallel metal rods placed into dielectric tubes. Waste water was sprayed into the reactor through an atomizing nozzle. Large area of discharge plasma which was locally homogeneous was generated in the liquid-gas mixed phases. The reactor matches with the pulsed power supply to get a fast rise flank of the pulse (<100ns), and the pulse width is 200ns.2. An equivalent model of the discharge circuit was set up. The discharge waveform was in correspondence with its physical processes. The rise time, fall time and width of the pulse which may influence the energy efficiency of the discharge were discussed. The energy efficiency and energy distribution of the pulses were analyzed and calculated. Under the condition of 20kV peak pulsed voltage,250Hz pulse frequency, the energy of a single pulse obtained 0.25J, the average discharge power reached 63W and the actual plasma dissipating power reached 35W.3. Based on the analysis of the ultraviolet (UV) spectra of the solution, chemical oxygen demand, total organic carbon and total nitrogen variation, the reaction pathways and the possible intermediate products of rhodamine b were proposed. And some other typical persistent pollutants were also treated.4. Different experimental parameters, such as peak pulsed voltage, pulse frequency, initial pH and initial conductivity of the solution, diverse gas sources and initial concentration were studied to see their effects on the degradation rates. The obtained results showed that the removal rate of rhodamine b could be improved either by increasing the peak pulsed voltage and pulse frequency or by increasing the discharge time; The initial pH value of the solution had little effect on the process; The initial conductivity of the solution affected the degradation rate greatly and higher initial conductivity was a disadvantage for the discharge; The nature of the gas introduced would influence the reaction process considerably and the efficiency increased in the order of oxygen>air>nitrogen; For higher initial concentration, the degradation rate decreased, but the yield increased. Under the condition of 20kV peak pulsed voltage,250Hz pulse frequency,90mg/L initial concentration,6.4 initial pH, 12.0L/min oxygen pumped in, the removal rate of rhodamine b reached 99.1% after 12min treatment time.