Effects of Thermal Desorption on Soil Physical and Hydraulic Characteristics.

Given the recent increase in oil production in regions with predominantly agricultural economies, the determination of effective methods for remediating oil contamination in these areas is increasingly relevant.  Thermal desorption (TD) is a technique for treating petroleum hydrocarbon (PHC) soil contamination wherein the soil is heated to enhance contaminant vaporization; clean soil is separated from PHCs via volatilization.  Biochar is a byproduct of this process when oxygen limiting conditions occur within the primary drum desorber.  Although TD is effective in reducing PHC concentrations in soil, the viability of using TD treated soils for agricultural production has yet to be thoroughly studied. The objectives of this research were to determine the extent to which TD treatment at 350 C alters soil physical and hydraulic characteristics in native, non-contaminated topsoil and subsoil used for agricultural production.  In samples subjected to TD treatment, soil specific surface area decreased by 15-20%, which corresponded with a slight decrease in clay-sized particles. In the topsoil, TD treatment caused soil organic carbon to decrease by almost 30% and aggregate stability to decrease by 20%.  Saturated hydraulic conductivity increased by over 400% in both the topsoil and subsoil after TD treatment.  Water retention decreased as pressure increased in treated samples, but plant available water remained unchanged.  These results suggest that water balances should be monitored closely in TD treated soils, and further management may be required before being returned to agricultural use.