Superfund Research Program
Pyrolytic Conversion of PAHs in Contaminated Sediments into Char to Eliminate Toxicity and Enhance Soil Fertility
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Project Summary (2020-2025)
There is a pressing need for technological innovation that leads to more efficient and sustainable remediation of contaminated sediments at Superfund sites. This project is developing a sustainable remediation technology to rapidly treat sediments and soils contaminated with polycyclic aromatic hydrocarbons (PAHs) and related polyaromatic compounds (PACs), including activated PAH byproducts of environmental transformations, in a manner that completely removes the associated health risks while adding value to the impacted media. The researchers' hypothesis is that pyrolysis of contaminated soils/sediments under carefully selected conditions reduces 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:
- Demonstrate that thermal pyrolysis reliably removes PAHs and PACs present in Superfund site sediments and eliminates their toxicity.
- Characterize the reaction mechanisms and end products to guide safe and cost-efficient application. Specifically, they are using thermogravimetry and evolved gas analyses to elucidate the physical and chemical processes occurring during pyrolysis. The possible catalytic effects of soil components like clays are being systematically studied, and surface analysis techniques are being used to determine the chemical composition and spatial distribution of pyrolysis products (like carbonaceous compounds). Finally, they are carefully characterizing 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, percent O2, moisture, etc.) to inform reaction mechanisms and guide reactor optimization efforts.
- Identify the operating conditions that maximize the benefits of soil pyrolysis (PAH & PAC removal and improved soil fertility) while minimizing associated costs.
Thus, these studies are building on their 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. They anticipate pyrolysis (a) rapidly and reliably decreasing PAH and PAC concentrations below regulatory thresholds, (b) adding agricultural value to the treated soils by improving fertility and drainage, and (c) contributing to a positive public image, facilitating regulatory acceptance of this novel technology from stakeholders such as the U.S. Environmental Protection Agency.