Remediation Of PNP Contaminated Soil Using Needles-Plate Discharge Plasma

As the soil pollution problem is getting worse, the research for rapid soil remediation method is becoming a necessity in environment field. Recently, non-thermal discharge plasma has been widely exploited in remediation of contaminated soils, due to its advantages: efficiency, wider range and no secondary pollution.In this paper, the typical needles-plate electrode structure was employed to produce low-temperature plasma for remediation PNP contaminated soil. There are two parts in the experiment:one is choosing the needles-plate dielectric barrier discharge (DBD) to remedy PNP contaminated soil, another is the needles-plate corona discharge, which is used to repair PNP contaminated soil with moisture content is100%. The aim of this study is to investigate the impact factors on PNP degradation,exploring the feasibility of needles-plate electrode discharge plasma to repair PNP contaminated soil, as a reference role for following research work. The following works were carried out and the main results are summarized as follows:(1) Needles-plate DBD can generate moderate power density plasma at atmospheric pressure. Investigating discharge voltage and soil filling that effect discharge characteristics of reactor, and the effects of some factors, such as electrical parameters and soil parameters on PNP removal. About82%of PNP could be removed after60min DBD decomposition under discharge voltage15kV, frequency50Hz, discharge gap4.5mm, the power efficiency0.020g/kWh. The degradation rate will increase with the longer discharge time and higher discharge voltage; simultaneously it will enhance electric field intensity and improve the input power. The degradation rate increases from74.6%to87.3%when improving the discharge voltage from12kV to18kV, after treatment60min. Soil filling could affect the allocation ratio of the gas phase and reduce gas gap, then increase the electric field strength, the input power of the reactor is enhanced. The experiment would also show good results if there is no additional input gas when the reactor is in the air; when the soil moisture content is10%the degradation of PNP is82%; alkaline conditions and the lower initial concentration of PNP will be conducive to degradation.(2) Needles-plate pulse corona discharge plasma was employed to remedy PNP contaminated soil with moisture content is100%. Studying the applied voltage and frequency which affect the characteristics of the reactor. And the impact factors of degradation of PNP are investigated. After60min treatment.86.3%of PNP was removed under the optimum condition, discharge voltage21.6kV, frequency70Hz, the air flow rate0.4L/min,discharge gap10mm,energy efficiency is0.20g k/Wh. Increasing the discharge voltage and frequency could both improve the degradation efficiency; with air flow rate0.4L/min, the degradation rate could reach86.3%; the concentration of H2O2produced in clean soil is obvious higher than that in PNP contaminated soil with water content100%;there is an obvious mineralization effect in this experimental system, the value of COD and TOC was reduced by extending the time of discharge.