In situ remediation of oil-contaminated soils by ozonation: Experimental study and numerical modeling

The goal of the present work is to quantify the performance of ozonation as a method for the in situ remediation of soils polluted at varying degree with different types of hydrocarbons, and assess its applicability, in terms of remediation efficiency, cost factors, and environmental impacts. Ozonation tests are conducted on dry soil beds, for three specific cases: sandy soil contaminated with low, moderate and high concentration of a non-aqueous phase liquid (NAPL) consisting of equal concentrations of n-decane, n-dodecane, and n-hexadecane; sandy soil polluted with diesel fuel; oil-drilling cuttings (ODC). The transient changes of the concentration of the total organic carbon (TOC), total petroleum hydrocarbons (TPH), polycyclic aromatic hydrocarbons (PAHs), and soluble chemical oxygen demand (SCOD) in soil and carbon dioxide (CO₂), carbon monoxide (CO), volatile organic compounds (VOCs), and ozone (O₃) in exhaust gases are recorded. A numerical model is suggested where the ozone is adsorbed on solid grains, reacts with adsorbed organic species, and desorbed CO₂, CO along with unconsumed O₃ are released. The model is used to estimate the ozonation kinetic parameters, upscale the process, and estimate the cost and gas emissions per 1 tn of treated soil. Experiments reveal that after 4h of treatment, the TOC decreases profoundly only for the low NAPL concentration (76.4%), the highest and fastest TPH removal efficiency occurs for the moderate NAPL concentration (∼88%), and diesel fuel (87%), while the TPH removal efficiency becomes high enough for oil-drilling cuttings (80%) after 8h of treatment. In all cases, mainly CO₂ is detected in exhaust gases, its cumulative mass is fully consistent with the TOC losses, while the O₃ consumption is enhanced for heavily polluted soils. The concentration of PAHs is reduced profoundly for both the diesel fuel and ODC. The lowest energy consumption per unit mass of degraded TPH or TOC occurs for the heavily polluted soils. The cost of soil treatment increases with the initial TPH concentration and pollutant complexity increasing.