Patent Application Focused on Optimizing CVOC Degradation via Limiting Methanogenesis

PHILADELPHIA - March 12, 2013 - PRLog -- In our most recent advance, IET has identified a mechanism for addressing chlorinated solvent impacts that optimizes the utilization of evolved hydrogen.  Nearly all remedial processes targeting chlorinated solvents rely on evolved hydrogen, generally from fermented sugars, carbohydrates or other organic compounds.  The competition for the hydrogen by methanogenic processes results in loss of efficacy and a loss of alkalinity due to the conversion of carbon dioxide to methane.  The ability to target and block the enzyme system that is responsible for the methane production will significantly change the way soil and groundwater remedial programs are implemented.  Regardless of the organic hydrogen donor, this patent application will greatly extend the life of those donors in-situ.  With the addition of these inhibitors all remedial processes for reductive dechlorination will benefit.  IET has again demonstrated that as a remedial contractor facing challenges placed on us by our customers we can offer unique and innovative solutions.

The present invention relates to the use of various inhibitors of different enzymes and coenzymes systems that are responsible for the production of methane and therefore compete with halo-respiring bacteria during the anaerobic reductive dechlorination process.  The present invention utilizes various compounds such as but not limited to red yeast rice, vitamin B10 derivatives, and ethanesulfonates to disrupt enzyme and coenzyme systems and limit the productivity of methanogens in producing methane.  The inhibition of methanogenesis will result in lower methane production, which positively affects numerous environmental aspects of major concern, and will also help dehalogenating bacteria to more effectively utilize the environmental conditions that promote reductive dechlorination of chlorinated volatile organic compounds (CVOCs), in in-situ remediation processes.

A wide variety of organic substrates will stimulate reductive dechlorination including acetate, propionate, butyrate, benzoate, glucose, lactate and methanol.  Inexpensive, complex substrates such as molasses, cheese whey, corn steep liquor, corn oil, hydrogenated cottonseed oil beads, solid food shortening, beef tallow, melted corn oil margarine, coconut oil, soybean oil, and hydrogenated soybean oil have the potential to support complete reductive dechlorination.

Reductive dechlorination only occurs in the absence of oxygen; and, the chlorinated solvent actually substitutes for oxygen in the physiology of the microorganisms carrying out the process. As a result of the use of the chlorinated solvent during this physiological process, it is at least in part dechlorinated.  Remedial treatment technologies usually introduce an oxygen scavenger to the subsurface in order to ensure that this process would occur immediately.  

Heterotrophic bacteria are often used to consume dissolved oxygen, thereby reducing the redox potential in the ground water.  In addition, as the bacteria grow on the organic particles, they ferment carbon and release a variety of volatile fatty acids (e.g., acetic, propionic, butyric), which diffuse from the site of fermentation into the ground water plume and serve as electron donors for other bacteria, including dehalogenators and halorespiring species.  An iron source usually provides substantial reactive surface area that stimulates direct chemical dechlorination and an additional drop in the redox potential of the ground water via chemical oxygen scavenging.

Bacteria generally are categorized by: 1) the means by which they derive energy, 2) the type of electron donors they require, or 3) the source of carbon that they require.  Typically, bacteria that are involved in the biodegradation of CAHs in the subsurface are chemotrophs (bacteria that derive their energy from chemical redox reactions) and use organic compounds as electron donors and sources of organic carbon (organoheterotrophs).  However, bacteria are classified further by the electron acceptor that they use, and therefore the type of zone that will dominate in the subsurface.  A bacteria electron acceptor class causing a redox reaction generating relatively more energy, will dominate over a bacteria electron acceptor class causing a redox reaction generating relatively less energy.

Halophiles are salt-loving organisms that inhabit hypersaline environments.  They include mainly prokaryotic and eukaryotic microorganisms with the capacity to balance the osmotic pressure of the environment and resist the denaturing effects of salts.  Among halophilic microorganisms are a variety of heterotrophic and methanogenic archaea; photosynthetic, lithotrophic, and heterotrophic bacteria; and photosynthetic and heterotrophic eukaryotes.

One the other hand, methanogens, play a vital ecological role in anaerobic environments, since they remove excess hydrogen and fermentation products that have been produced by other forms of anaerobic respiration.  Methanogens typically thrive in environments in which all electron acceptors other than CO2 (such as oxygen, nitrate, trivalent iron, and sulfate) have been depleted.

Based on thermodynamic considerations, reductive dechlorination will occur only after both oxygen and nitrate have been depleted from the aquifer since oxygen and nitrate are more energetically favorable electron acceptors than chlorinated solvents.  Almost any substrate that can be fermented to hydrogen and acetate can be used to enhance reductive dechlorination since these materials are used by dechlorinating microorganisms.  However, hydrogen is also a substrate for methanogenic bacteria that convert it to methane.  By utilizing hydrogen, the methanogens compete with dechlorinating microbes.

This invention provides different methods of inhibition of methane production from methanogenic bacteria by depressing the action of various enzymes and coenzymes that play a key role in the methane production.  Various enzymes and coenzymes are targeted in the current invention.  The inhibitors used, are found to be harmless for the rest of the bacteria that are present in the system.

The method of restricting methane production in methanogenic bacteria, by the use of the enzyme inhibitors, can be very useful during in-situ remediation of chlorinated solvents.  This method is expected to positively affect the competition of the methanogen and halo bacteria for the organic hydrogen donors that are injected in the soil and groundwater system during the remediation process.  The method also provides an alternative approach for the decrease of the emission levels of methane, which is considered a major greenhouse gas.