Aerobic cometabolism of tetrachloroethylene (PCE)


Source: CL Solutions, LLC

Tetrachloroethylene (PCE) is a problem contaminant because of its widespread use, potential toxicity and persistence in the environment. Like other chlorinated solvents, remediation of PCE in soil and ground water has proven to be very difficult. While there has been has been widespread success under anaerobic conditions, the application of bioremediation under aerobic conditions has not been as common. Aerobic sites have been managed by transformation to anaerobic conditions by introducing simple sugars or organic compound into aquifers to drive the conditions anaerobic by stimulating aerobic organisms. Once the site is anaerobic, anaerobic organisms are introduced or stimulated if already present in the aquifer. Aerobic cometabolism provides simple, reliable and sustainable approach because it is compatible with the existing aquifer conditions. Thus the application of aerobic bioremediation using CL-Out® is more cost effective because it requires less energy, effort and resources to implement.

Finding the Right Organisms

The presence of the contaminants in soil provides selective pressure to favor organisms that will tolerate the presence of the contaminants. One may also fortunately find organisms that have the capability of metabolizing the contaminants and benefiting from the presence of the contaminant. Vandenbergh and Kunka (1988) isolated P. fluorescens from contaminated soils that was capable of metabolizing a variety of chlorinated organic compounds including trichloroethylene (TCE). These organisms were capable of not only tolerating the contaminants, but could metabolize the contaminants.

Deckard, Willis and Rivers (1994) recognized that in the mammalian liver PCE is degraded by the hepatic cytochrome P-450. Recognizing that pseudomonads also have cytochrome P-450 oxygenase systems, pseudomonads isolated from contaminated soil samples were tested in a microcosm. The pseudomonads were able to grow with PCE or TCE as the sole carbon source. An increase in the chloride ion concentrations corresponded with the PCE degradation verifying the complete mineralization of the chlorinated solvents.

General Characteristics of Pseudomonas Metabolism

Pseudomonads are nutritionally diverse organisms that are well known for the beneficial application to degrade a wide range of organic chemicals. Some species are capable of using any one of 90 different organic chemicals as their sole carbon and energy source (Stanier, et. al., 1986). Pseudomonads also may degrade some chemicals by more than one pathway.

Pseudomonas organisms utilize metabolic enzymes that have a relaxed specificity, which means that an enzyme may react with different compounds with similar structures in their metabolism.

Pseudomonas organisms are generally aerobic organisms, but many may use nitrate as an electron acceptor.

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