Transport characteristics of gas phase ozone in soil during soil remediation by pulsed discharge plasma

In order to investigate transport characteristics of chemically active species in soil during soil remediation by pulsed discharge plasma, gaseous ozone, as a model active species, was chosen in the present research. Ozone transport characteristics in soil were investigated by laboratory column experiments. Effects of soil organic matter, metal oxides, soil pH, soil moisture, and ozone initial concentration on the fate and transport of ozone were evaluated. The experimental results showed that ozone transport velocity was inversely proportional to soil organic matter. Metal oxides could decompose ozone by catalytic reactions, and thus exhibited negative effect on ozone transport. Alkaline soil was not beneficial for ozone transport, due to reactions of ozone with OH− ions. Water molecules could cover on soil particles to form water film, which interfered with reaction of ozone with soil organic matter and also blocked the catalytic ozone decomposition over metal oxides, and thus a certain amount of water in soil could quicken ozone transport. The relationship of p-nitrophenol (PNP) removal in soil column and ozone transport was also studied. Compared with clean soil, ozone transport velocity in PNP contaminated soil was obviously retarded, and more ozone was consumed by PNP molecules. After 30 min of ozone treatment, the maximum PNP degradation efficiency (73.5%) was achieved in the column packed with quartz sand, and followed in descending order, with sand (65.2%), with sandy soil (51.8%) and with clay soil (45.6%). Organic matter and metal oxides resulted in the different PNP removal characteristics in these porous media.