Poly-Aromatic Hydrocarbons
 
Creosote Contaminated Soil Treatment
 

Creosote was a common preservative used in the wood treating process. Creosote contains polynuclear aromatic hydrocarbons (PAHs), which are regulated under all State and Federal cleanup programs. Because of their complex molecular structure, PAHs are some of the most difficult compounds to degrade biologically. In the past, many creosote contaminated sites were remediated through expensive thermal methods. ETEC has developed a specialized bacterial consortium that provides rapid and consistent bioremediation of PAH contaminated soil and groundwater.
A Complex Problem
 
ETEC was hired by the owner of a former wood preserving facility located in Portland, Oregon to biologically remediate the PAH-contaminated soils. The site operated from 1944 to 1991, and used creosote in oil and water-based treatments. For years, waste oil and liquid process wastes containing creosote were applied to the site soil. Total PAH concentrations were required to be reduced from an initial average concentration of 1,862 parts per million (ppm) to less than 200 ppm.

ETEC initially approached the site using our conventional petroleum-degrading products. Because of the high initial PAH concentration, we first applied our biosurfactant (EZT-BSF), to reduce the toxicity of the soils and prepare them for biological treatment. ETEC then applied a proprietary multi-enzyme complex (EZT-MZC) to break down the PAH compounds, followed by our baseline bacteria for complete degradation. After 72 days of treatment, the total PAH concentration was reduced to 823 ppm. Although this 56% reduction was impressive, it did not achieve the 200 ppm target treatment level.
 
 
Turning Failure to Success
 
An article appearing in the November 6, 1995 edition of the Engineering News Record (ENR) reported that "...bioremediation can break down 95% of two, three or four-ring polyaromatic hydrocarbons, but only 60% of five and six-ring compounds." In addition, the article stated that it takes two to three years to achieve these levels of PAH degradation.
 
 
ETEC determined that PAH reductions achieved at our site were largely in the easily degradable two and three-ring PAHs. At this point in the treatment, our scientists completed isolation and culturing of a bacterial consortium specifically designed to degrade the four, five and six-ring PAH compounds. The result was a new generation of bacteria, the EZT-A3™. The EZT-A3™ is a bacterial consortium that uses a process called "co-oxidation" to degrade the more complex PAH compounds. The consortium includes four separate strains of bacteria that work in the following manner: two of the strains work together breaking down the PAH ring structure. The other two strains then complete the degradation of the residual compounds to carbon dioxide and water.
 
The Results Speak for Themselves
   
ETEC returned to the site and inoculated the PAH contaminated soil using the new EZT-A3 bacterial consortium. In only 16 days, the total PAH levels dropped dramatically, from 823 ppm to 157 ppm. The difference was attributed to degradation of the four, five and six-ring compounds, including a nearly 90% reduction of benzo(a)pyrene, one of the most biologically recalcitrant PAH compounds. The other 15 PAH compounds analyzed were reduced an even more impressive 90 to100 %.
 
Summary of PAH Concentrations in Soil (mg/kg)