Comparison between continuous and intermittent ozonation for remediation of soils contaminated with polycyclic aromatic hydrocarbons

Continuous ozonation can inactivate indigenous microbes due to the disinfection capability of ozone, which may affect subsequent bioremediation of soils. This study investigated the efficiency of removing polycyclic aromatic hydrocarbons from soils using intermittent ozonation technique, where ozone was sparged through the soil column every alternate day, resulting in shorter ozonation time for each ozonation circulation than continuous ozonation. The results showed that 85 % Phe, 94 % Ant, 76 % Flu, 87 % Pyr, and 91 % BaP were removed on 32 days in continuous ozonation treatment, while 90 % Phe, 84 % Ant, 78 % Flu, 81 % Pyr, and 96 % BaP were removed on 32 days in intermittent ozonation treatment, indicating both intermittent ozonation and continuous ozonation can effectively remove polycyclic aromatic hydrocarbons from soils. Fluorescein diacetate hydrolysis results indicated that the total microbial activity of intermittent ozonation was significantly (p<0.05) higher than that of continuous ozonation treatment at 8, 16, 24, and 32 days. The toxicity bioassay of soil extracts showed that the relative luminescence increased from 5 to 30 % at 8 days, without significant (p>0.05) increase at 32 days in continuous ozonation treatment, while it increased to 61 % at 32 days in intermittent ozonation treatment, indicating intermittent ozonation was more effective than continuous ozonation for the detoxification of soils contaminated with polycyclic aromatic hydrocarbons. It suggested that both treatments were equally effective at removing polycyclic aromatic hydrocarbons from soil, but intermittent ozonation was better than continuous ozonation for further detoxification and maintaining the total microbial activity of soil.

Keywords
Soil pollution; Soil remediation; Ozone; Detoxification; Microbial activity