Method of smoldering combustion for the treatment of oil sludge-contaminated soil

There is an urgent need to globally remediate oil sludge-contaminated soil (OSS). Smoldering combustion is a new low-energy approach for the treatment of organic waste. Therefore, the feasibility of smoldering combustion for the treatment of OSS was investigated in this study using a series of laboratory-scale experiments. The effective remediation of OSS was found to be achievable when the mass ratio of oil sludge in the sample reached 1/12 and above. Experimental results showed that smoldering at peak temperatures above 500 °C was found to completely remove petroleum hydrocarbons from the samples. The mass ratio of oil sludge in the sample had little effect on the distribution of the major elements (Si, Al, and Ca) in the smoldering products, and most of the minerals in the oil sludge adhered to the surface of the soil particles after smoldering. The smoldering heating environment is detrimental to the reusability of the soil, increases soil pH and available phosphorus content, and decreases organic carbon and total nitrogen content. Moreover, the influence of the airflow rate and material height on smoldering characteristics was investigated. Matching the appropriate airflow rate can help maintain optimal smoldering conditions, and smoldering remains stable with increasing material height. The addition of recovered oil to a sample with a low mass ratio of oil sludge can help with smoldering ignition and improve the removal efficiency of petroleum hydrocarbons. This study has confirmed that smoldering can be used to treat OSS within a broad range of oil sludge concentrations without pretreatment.