Formatted Title
Can Thermal Desorption be Converted to Achieve Destruction and Become a Sustainable Substitute for High Temperature Incineration?
Background/Objectives
How can thermal remediation be designed to be more than a simple separation of contaminants from soil?
High temperature thermal conductive heating (TCH) remediation at 300 to 350 ̊C has been utilized for decades to remediate contaminated soils both in situ and ex situ. TCH has a documented effect for a range of persistent organic pollutants like PAHs, dioxin, PCBs, chlorophenols, lindane and PFAS as well as mercury.
Approach/Activities
A common feature of the high temperature processes is that the thermal degradation forms more volatile degradation byproducts that more easily can be removed by simple evaporation. The degradation reactions can potentially be optimized to result in complete degradation or even mineralization if sufficient reaction time at elevated temperature is allowed for.
Tailoring the remediation process to favor thermal degradation of contaminants can greatly reduce the risk of operation, simplify the treatment system and associated costs and limit the need for disposal of waste products like spent activated carbon.
Results/Lessons Learned
Full-scale remediation projects have achieved significant thermal degradation of the contaminants in the soil during the heat treatment process, e.g. dioxins (99%) even where thermal degradation processes were not factored in as a major removal mechanism.
In order to reduce operator risk arising from the highly toxic pesticide parathion, a 40 ton pilot-scale project was designed to optimize thermal degradation. During operation 99.99% destruction of parathion in the soil was achieved.
Recently a lab-scale study has implemented a similar approach to PFOS remediation and has demonstrated near complete conversion of PFOS to inorganic (water soluble) fluoride 25% and insoluble species (75%) with only 0.05% left as PFOS. The investigation of the reactions and the insoluble fluorine species formed is ongoing.
These examples show how in situ or on-site thermal desorption can be operated towards thermal destruction in a far more sustainable way than traditional incineration, which consumes five to eight times more energy compared to thermal desorption due to the soil having no caloric value. However, the chemical reactions need to be controlled and monitored, to ensure that all reaction products are accounted for and included in the monitoring program and that the reaction products are not more hazardous than the original contaminants.
Using this approach it is likely to ease the stress on fixed incineration facilities as well as avoiding long and sometimes cross bordering transports of highly toxic substances.