Project 4: Pyolytic conversion of PAHs in contaminated sediments into char to eliminate toxicity and enhance soil fertility

There is a pressing need for more reliable, broadly applicable and cost-effective remediation of contaminated soils and sediments at Superfund sites. Building on our recent discovery that pyrolysis can efficiently remediate soil contaminated with petrochemical wastes and restore soil fertility, this project will develop a sustainable remediation technology to rapidly treat soils contaminated with polycyclic aromatic hydrocarbons (PAHs) and other lipophilic contaminants (including more toxic PAH byproducts of environmental transformations), in a manner that completely removes the associated health risks while enhancing restoration efforts.

Our hypothesis is that pyrolysis of contaminated soils/sediments under carefully selected conditions will reliably achieve regulatory compliance of organic priority contaminants and completely eliminate toxicity, while increasing soil fertility to facilitate ecosystem restoration and re-greening efforts.

• Demonstrate that pyrolytic treatment will consistently remove all PAHs and other organic pollutants present in Superfund site sediments and eliminate their toxicity.
• Characterize the reaction mechanisms and end products to guide safe and cost-efficient application. Specifically, we will use thermogravimetry and evolved gas analyses to elucidate the physical and chemical processes occurring during pyrolysis. The possible catalytic effects of soil components like clays will be systematically studied, and surface analysis techniques will be used to determine the chemical composition and spatial distribution of pyrolysis products. Finally, we will carefully characterize the treated soils to determine how their key properties (like surface chemistry, chemical stability, porosity, density, water-holding capacity, and ability to hold plant-available water) are affected by the chosen pyrolysis conditions (contact time, temperature, %O2, moisture, etc.) to inform reaction mechanisms and guide reactor optimization efforts.
• Identify operating conditions that maximize the benefits of soil pyrolysis while minimizing associated costs. Whereas ensuring a minimum treatment intensity (controlled by pyrolysis temperature and solids residence time) is critical for efficient remediation, there is a maximum intensity beyond which pyrolytic treatment becomes detrimental with regards to soil damage and excessive energy usage. Accordingly, we will minimize treatment costs per unit mass of contaminated soil by lowering both the pyrolysis times (thus enhancing processing capacity) and the temperatures (thus reducing energy requirements and carbon footprint).

We anticipate that pyrolysis will:

• Rapidly and reliably achieve regulatory compliance in a broad range of soil contamination scenarios
• Simultaneously add agricultural value to the treated soils by improving fertility and drainage
• Contribute to a positive public image, facilitating regulatory acceptance from stakeholders such as the EPA of this novel technology