Low-temperature thermal desorption

Abstract: Effects of low-temperature thermal desorption (LTTD) treatment on the ecological properties of soil contaminated by petroleum hydrocarbons were assessed. For this purpose, various ecological properties related to soil health and physicochemical properties of the oil-contaminated soil before and after LTTD treatment were investigated. Total petroleum hydrocarbon concentration, electrical conductivity, organic matter, and total nitrogen decreased while water-holding capacity and available P2O5 increased. The soil color was also changed but textural class was not changed after LTTD. The microbial number and dehydrogenase activity increased following LTTD, but there was no significant difference in the β-glucosidase and acid phosphatase activities. Seed germination succeeded after LTTD, but the germination rate was still lower than that in non-contaminated soil as the growth of plants and earthworms was. The results showed that overall soil health related to biological productivity and environmental functions was improved after LTTD and suggested that LTTD could be a better alternative to other harsh remediation methods. However, ecological indicators still show differences to the adjacent non-contaminated level. Therefore, to ensure safe soil reuse, the change in eco-physiochemical properties as well as contaminant removal efficiency during the remediation process should be considered.

Abstract: A process and apparatus are provided for removing organic and inorganic contaminants from solid media such as drill cuttings, tank bottoms or contaminated soils. The process is conducted in at least one thermal screw conveyor (12, 22, 32) which provides two or more separate temperature zones which can be operated as one or more of low temperature thermal desorption, high temperature thermal desorption and pyrolysis. Preferably the process is conducted in three interconnected thermal screw conveyors (12, 22, 32) which each provide a separate temperature zone. The process is conducted such that the solid media in each of the temperature zones is held under a vacuum. Direct and indirect heating of the solid media in each of the temperature zones is provided. In the pyrolysis zone, an organic binder may be added to encapsulate inorganic contaminants such as metals.