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"Chemical Oxidation and Biological Attenuation Process for the Treatment of Contaminated Media"
Innovative Environmental Technologies, Inc. (IET) received notification on May 27th that our patent application titled, "Chemical Oxidation and Biological Attenuation Process for the Treatment of Contaminated Media" is assigned application # 13891934
Divalent metal activation: The utilization of ferrous iron, usually as a chelated cation consumes the oxidant (persulfate)
Caustic Activation: The utilization of caustic (high pH) activation of persulfate presents inherit health and safety issues while creating an unsuitably high pH environment for biological attenuation. Further, within this activation mechanism is a self limiting biological attenuation process once the pH returns to suitable levels. The sulfate, when used as a biological terminal electron acceptor, transitions to sulfite and finally sulfide. This final product forms hydrogen sulfide which inhibits further biological activity.
Heat Activation: The utilization of heat as an activation mechanism is generally difficult to implement, incurs high implementation costs while not addressing the hydrogen sulfide issue.
Hydrogen Peroxide Activation: The use of peroxide as an activating mechanism again does not address the hydrogen sulfide generation problem while having limited efficacy on many targeted compounds.
Under the IET approach, persulfate activation with ferric iron requires a lower activation energy than alternative mechanisms while not consuming the persulfate oxidant. The mechanism is believed to elevate the oxidation state of the iron transiently to a supercharged iron ion which in itself may act as an oxidant. As this supercharged iron cation is consumed the resulting ferric species may act as a terminal electron acceptor for biological attenuation. Coincidentally, the generated sulfate ion from the decomposition of the persulfate provides a terminal electron acceptor for sulfate reducers which may further remediate the targeted compounds in the groundwater and soils. The reactions that occur in the chemical oxidation can be seen below:
Oxidation Chain Reactions
H2O2 + Fe+2 (Indigenous)
H2O2 + Fe0 (Added ZVI) -------->
S2O8 + Fe+3 --------->
Direct oxidation of NaS2O8 and H2O2.
It has now been discovered, in a surprising way, and this is the basis of the invention, that the use of persulphate as oxidizing agent in the synthesis of ferrates brings about a solution to the problems set forth above.
After dissolved oxygen has been depleted in the treatment area, sulfate (by-product of the persulfate oxidation) may be used as an electron acceptor for anaerobic biodegradation. This process is termed sufanogenesis and results in the production of sulfide. Sulfate concentrations may be used as an indicator of anaerobic degradation f fuel compounds. Stoichiometrically, each 1.0 mg/L of sulfate consumed by microbes results in the destruction of approximately 0.21 mg/L of BTEX. Sulfate can play an important role in bioremediation of petroleum products, acting as an electron acceptor in co-metabolic processes as well. The basic reactions of the mineralization of benzene, toluene and xylenes under sulfate reduction are presented in equations below:
C6H6 + 3.75 SO42- + 3 H2O --> 0.37 H+ + 6 HCO3- + 2.25 HS- + 2.25 H2S-
C7H8 + 4.5 SO42- + 3 H2O --> 0.25 H+ + 7 HCO3- + 1.87 HS- + 1.88 H2S-
C8H10 + 5.25 SO42- + 3 H2O --> 0.125 H+ + 8 HCO3- + 2.625 HS- + 2.625 H2S-
Ferric iron is also used as an electron acceptor during anaerobic biodegradation of many contaminants after sulfate depletion, or sometimes in conjunction with sulfate. During this process, ferric iron is reduced to ferrous iron, which is soluble in water. Ferrous iron may then be used as an indicator of anaerobic activity. As an example, stoichiometrically, the degradation of 1 mg/L of BTEX results in the production of approximately 21.8 mg/L of ferrous iron.
Ferrous iron formed as a result of the use of the ferric species as a terminal electron acceptor, under these same conditions the residual sulfate is utilized as a terminal electron acceptor by facultative organisms, generating sulfide. Together, the ferrous iron and the sulfide promote the formation of pyrite as a remedial byproduct. The mechanism described herein combats the toxic effects of sulfide and hydrogen sulfide accumulation on the facultative bacteria, while also providing a means of removing target organics through soil mineral (pyrite) suspension.
This technique utilizes the interaction between the occurring sulfate and ferric iron. Ferric iron (Fe3+) is reduced to ferrous iron (Fe2+); readily supplying electrons to exchange and react with sulfide. Together, sulfide and iron form pyrite, an iron bearing soil mineral with a favorable reductive capacity.
Fe2+ + 2S2- --> FeS2
Pyrite possesses a finite number of reactive sites that are directly proportional to both its reductive capacity and the rate of decay for the target organics. The reductive capacity of iron bearing soil minerals (like pyrite) initially results in a rapid removal of target organics by minimizing the competition between contaminants and sulfate as a terminal electron acceptor. Preventing these unfavorable interactions with ferric iron provides a continual source for electron exchange resulting in the timely removal of contaminants through pyrite suspension.
Once the reductive capacity of pyrite is met, the bound organic contaminants tend to precipitate out, removing the contaminants rapidly and without the production of daughter products.