Project 5: Pyolytic conversion of PAHs in contaminated sediments into char to eliminate toxicity and enhance soil fertility

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Project Summary There is a pressing need for technological innovation that leads to more efficient and more sustainable remediation of contaminated sediments at Superfund sites. This project will develop a sustainable remediation technology to rapidly treat sediments and soils contaminated with polycyclic aromatic hydrocarbons (PAHs) and related polyaromatic compounds (PACs), including activated PAHs byproducts of environmental transformations, in a manner that completely removes the associated health risks while adding value to the impacted media. Our hypothesis is that pyrolysis of contaminated soils/sediments under carefully selected conditions will reduce the concentration of all organic priority contaminants to below regulatory levels, thus completely eliminating toxicity, while restoring soil fertility to facilitate ecosystem restoration and re-greening efforts. Furthermore, different treatment objectives (e.g., regulatory compliance, detoxification, and soil fertility restoration) need not be mutually exclusive and could be simultaneously achieved by selecting appropriate pyrolytic treatment intensity (controlled through pyrolysis temperature and residence time). The Specific Aims of this project are: 1. Demonstrate that thermal pyrolysis will reliably remove PAHs and PACs present in Superfund site sediments and eliminate their toxicity. 2. 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 (like carbonaceous compounds). 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. 3. Identify the operating conditions that maximize the benefits of soil pyrolysis (PAH & PAC removal and improved soil fertility) while minimizing associated costs. Thus, the proposed studies will build on our recent discovery that pyrolysis can add value to soil contaminated with petrochemical wastes (including heavy petroleum hydrocarbons) by converting these pollutants to char-like material. The expected benefits are significant. We anticipate that pyrolysis will: (a) rapidly and reliably decrease PAH and PAC concentrations below regulatory thresholds; (b) add agricultural value to the treated soils by improving fertility and drainage; and (c) contribute to a positive public image, facilitating regulatory acceptance from stakeholders such as the EPA of this novel technology.