Portrait | Kyriacos Zygouakis

Kyriacos Zygourakis

Chemical and Biomolecular Engineering

Pyrolytic Treatment of Soils Contaminated with Heavy Petroleum Hydrocarbons

Plants show significantly higher germination and growth in pyrolyzed soils when compared to contaminated or incinerated soils.

Untreated Soil A

TPH: 18,000 mg/kg

Soil A Pyrolyzed in rotary kiln at 420ºC and 15 min residence time

TPH: Not Detectable

Turning Oil Spills into

Fertile Soil

Almost 98% of crude oil spills occur on land with an average of 70 spills per day. Without an adequate response, the effects of major spills could last for decades. Although bioremediation can contribute to the cleanup of terrestrial spills, it is very difficult to biodegrade weathered heavy hydrocarbons. While current thermal technologies can quickly remove over 99% of the total petroleum hydrocarbons (TPH), they also destroy key soil constituents and adversely affect soil properties such as organic carbon content, water retention, stability, and microbial activity. Thus, treated soils become unsuitable for reuse since they cannot support vegetative growth or even provide erosional stability.

To overcome these problems, we have developed a new pyrolysis process that treats soils contaminated with heavy petroleum crudes at temperatures between 400 and 450 C in anoxic atmospheres. The new process reduces TPH and PAH levels to well below regulatory standards by desorbing low molecular weight hydrocarbons and converting the heavy recalcitrant hydrocarbons to char. For example, treatment at 420 C with only 15 min of residence time in a rotary kiln resulted in high removal efficiencies for both total petroleum hydrocarbons (TPH) (99.9%) and polycyclic aromatic hydrocarbons (PAHs) (94.5%). Viability assays with a human bronchial epithelial cell line showed that pyrolytic treatment effectively achieved the detoxification of contaminated soil extracts.

Most importantly, however, plant growth studies with Arabidopsis thaliana and Lactuca sativa (Simpson black-seeded lettuce) showed that soils treated with pyrolysis were much more fertile than either the original contaminated soils or soils treated with incineration. Biomass production rates for pyrolyzed soils were 80-900% higher than the rates we measured for contaminated or incinerated soils. These results suggest that soil pyrolysis could become a viable thermal treatment to quickly remediate soils impacted by weathered crude oil while improving their fertility and potentially enhancing revegetation.

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