低温等离子体降解污染土壤热脱附尾气中DDTs

为优化低温等离子体技术对污染土壤热脱附尾气的处理效果，采用脉冲电晕放电等离子体处理含DDTs（滴滴涕）的热脱附尾气，控制进气中的ρ（DDTs）为2.873 mg/m3，考察了载气φ（O₂）、等离子体温度、载气湿度和脉冲电压对DDTs降解效果的影响，分析了O₃在降解过程中的作用.结果表明:①当氮气/氧气混合载气中φ（O₂）分别为0、3%、6%、10%、21%和100%时，DDTs降解率分别为80.1%、76.5%、78.4%、81.1%、88.8%和94.6%，ρ（O₃）分别为0、0.20、0.25、0.40、0.99和1.93 mg/L.随着φ（O₂）的增加，ρ（O₃）逐渐增大，除氮气气氛外，DDTs降解率均逐渐增大，当φ（O₂）超过10%时，DDTs降解率较氮气气氛下更高.p，p'-DDD降解率均为100%，p，p'-DDE和o，p'-DDT的降解率随φ（O₂）的增加而增大.氮气气氛下p，p'-DDT降解率高于低浓度氧气气氛，除氮气气氛外，p，p'-DDT降解率随φ（O₂）的增加而增大.②当等离子体温度分别为80、100和150 ℃时，DDTs降解率分别为88.8%、83.2%和56.3%，ρ（O₃）分别为0.99、0.65和0.35 mg/L.当载气湿度为0、1.0、2.7和20.5 g/m3时，DDTs降解率分别为88.8%、81.6%、68.6%和30.0%，ρ（O₃）分别为0.99、0.73、0.56和0.32 mg/L.随着等离子体温度升高、载气湿度增大，反应器内ρ（O₃）逐渐减小，DDTs降解率也随之降低.③DDTs降解率随脉冲电压的升高而增大，当脉冲电压为24 kV、脉冲频率为50 Hz、等离子体温度为80 ℃、气体在反应器中的停留时间为10 s时，DDTs降解率达86.9%.研究显示，脉冲电晕放电等离子体能够快速、有效地去除热脱附尾气中的DDTs. 

Degradation of DDTs in Thermal Desorption Off-Gas by Non-Thermal Plasma

In order to optimize the treatment of thermal desorption off-gas by non-thermal plasma, pulsed corona discharge plasma was applied to remove DDTs in thermal desorption off-gas. The effects of oxygen concentration, plasma temperature, humidity and pulse voltage on DDTs removal were investigated. The important role of ozone in DDTs degradation was also analyzed. The results indicated that: (1) When the oxygen concentrations were 0, 3%, 6%, 10%, 21% and 100%, the DDTs degradation efficiencies were 80.1%, 76.5%, 78.4%, 81.1%, 88.8% and 94.6%, and the ozone concentrations were 0, 0.20, 0.25, 0.40, 0.99 and 1.93 mg/L, respectively. Ozone concentration increased with increasing oxygen concentration. The degradation efficiency of DDTs increased with the increase of oxygen concentration in the gas stream. When the oxygen concentration exceeded 10%, the degradation efficiency of DDTs was higher under oxygen atmosphere than under nitrogen atmosphere. With the increase of oxygen concentration, the degradation efficiency of p, p'-DDE and o, p'-DDT increased, and p, p'-DDD was degraded completely. The degradation efficiency of p, p'-DDT under nitrogen atmosphere was higher than that at low oxygen concentrations. The degradation efficiency of p, p'-DDT increased with the increase of oxygen concentration. (2) When the plasma temperatures were 80, 100 and 150 ℃, the DDTs degradation efficiencies were 88.8%, 83.2% and 56.3%, the ozone concentrations were 0.99, 0.65 and 0.35 mg/L, respectively. When the humidity was 0, 1.0, 2.7 and 20.5 g/m3, the DDTs degradation efficiencies were 88.8%, 81.6%, 68.6% and 30.0%, the ozone concentrations were 0.99, 0.73, 0.56 and 0.32 mg/L, respectively. The ozone was generated in the reactor and the DDTs degradation efficiency gradually decreased with the increase of the plasma temperature and the humidity of off-gas. (3) The DDTs removal efficiency increased with the increase of the pulse voltage. It was 86.9% when off-gas was treated by 80 ℃ plasma for 10 s at the pulse voltage of 24 kV and the pulse frequency of 50 Hz. In conclusion, the pulsed corona discharge plasma can effectively remove DDTs in thermal desorption off-gas.