Chemical Oxidation and Biological Attenuation Process for the Treatment of Contaminated Media

Abstract

Chemically oxidizing a wide range of targeted contaminants in soils, sludges, groundwater, process water, and wastewater and assisting in the eventual (over time) biological attenuation of the contaminants utilizing persulfates activated by trivalent metals, such as ferric iron. The use of trivalent metal activated persulfate results in a chemical oxidation process that yields degradation compounds which facilitate further attenuation via biological processes.

Claims

1. A method for chemical oxidation followed by a biological attenuation process of an environmental medium containing one or more contaminants, the method comprising: introducing a persulfate and one or more trivalent metals into the environmental medium, wherein the one or more trivalent metals activate the persulfate in order to chemically oxidize the one or more contaminants, wherein amount of the persulfate is selected to chemically oxidize the one or more contaminants and amount of the one or more trivalent metals is between approximately 20-25% of molecular weight of the persulfate so that at conclusion of the chemical oxidation sufficient residual sulfate and sufficient residual trivalent metals remain such that: naturally occurring facultative cultures utilize the residual sulfate and the residual trivalent metal as terminal electron acceptors to promote the biological attenuation process of the one or more contaminants; and the residual sulfate and the residual trivalent metal prevent formation and accumulation of hydrogen sulfide which is a toxin to the facultative cultures.

2. The method of claim 1, wherein the introducing one or more trivalent metals includes introducing the one or more trivalent metals via temporary or permanent wells.

3. The method of claim 1, wherein the introducing the persulfate includes introducing the persulfate via gravity feeding, induced gas stream, a pump, or a combination thereof.

4. The method of claim 1, wherein the introducing one or more trivalent metals includes introducing the one or more trivalent metals under pressure in either a gas or liquid stream.

5. The method of claim 1, wherein the persulfate and the one or more trivalent metals are combined before introduction into the environmental medium.

6. The method of claim 1, wherein the persulfate and the one or more trivalent metals are introduced into the environmental medium sequentially.

7. The method of claim 1, wherein the trivalent metal is ferric iron.

8. The method of claim 1, wherein the persulfate is sodium persulfate.

9. A method for oxidizing and biologically attenuating contaminants in an environmental medium containing one or more contaminants, the method comprising: introducing a composition including persulfate and one or more trivalent metals into the environmental medium, wherein the one or more trivalent metals activate the persulfate in order to cause oxidation of the one or more contaminants, wherein the oxidation of the one or more contaminants provides residual material, and wherein an amount of the persulfate is approximately 80-83% and an amount of trivalent metal is approximately 17-20% of a molecular weight of the composition so as to produce sufficient residual material such that: naturally occurring facultative cultures utilize the residual material as terminal electron acceptors to promote the biological attenuation process of the one or more contaminants; and the residual material prevents formation and accumulation of a toxin to the facultative culture.

10. The method of claim 9, wherein the introducing one or more trivalent metals includes introducing the one or more trivalent metals via temporary or permanent wells.

11. The method of claim 9, wherein the introducing the persulfate includes introducing the persulfate via gravity feeding, induced gas stream, a pump, or a combination thereof.

12. The method of claim 9, wherein the introducing one or more trivalent metals includes introducing the one or more trivalent metals under pressure in either a gas or liquid stream.

13. The method of claim 9, wherein the persulfate and the one or more trivalent metals are combined before introduction into the environmental medium.

14. The method of claim 9, wherein the persulfate and the one or more trivalent metals are introduced into the environmental medium sequentially.

15. The method of claim 9, wherein the trivalent metal is ferric iron.

16. The method of claim 9, wherein the persulfate is sodium persulfate.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The features and advantages of the various embodiments will become apparent from the following detailed description in which:

[0016] FIG. 1 is a table that outlines the MCL figures for various chemical contaminants;

[0017] FIG. 2 is a table that shows the elevated oxidation potential of the ferrate (Fe6+) species compared to other oxidants; and

[0018] FIG. 3 is table that demonstrates the ORP measurements for all three systems.

DETAILED DESCRIPTION

[0019] The current remediation process includes utilizing trivalent metals to activate persulfate (S.sub.2O.sub.8). The trivalent metals activate the persulfate in order to chemically oxidize a wide range of targeted contaminants and assist in the eventual (over time) biological attenuation of the contaminants. According to one embodiment, the trivalent metal is ferric iron (Fe.sup.3+). In alternate embodiments, another trivalent metal ion such as manganese (III) or manganic ion (Mn.sup.3+) may be used. Persulfate activation with ferric iron requires a lower activation energy than thermal activation, which makes iron activated persulfate a more efficient and rapid way of degrading contaminants. The trivalent metals may be applied, either concurrently or sequentially, with the persulfate.

[0020] Trivalent metal activated persulfate also has an increased oxidation reduction potential (ORP) over other activation mechanisms. Lab studies were performed to test the changes in ORP upon the activation of persulfate with ferric and ferrous iron species, as well as a caustic activator (Sodium Hydroxide). The experiments were performed at room temperature using deionized (DI) water and a 20% activator to persulfate amount. The materials were mixed for approximately 48 hours and the ORP values were measured. FIG. 2 is table that demonstrates the ferric iron/persulfate system was able to establish higher ORP measurements compared to its other two counterparts.

[0021] The contaminants that can be effectively treated with this technology include, but are not limited to, various man-made and naturally occurring volatile hydrocarbons including chlorinated hydrocarbons (e.g., volatile, semi-volatile and non-volatile organic compounds), non-chlorinated hydrocarbons, aromatic or polyaromatic ring compounds, brominated compounds, brominated solvents, 1,4-dioxane, insecticides, propellants, explosives (e.g., nitroaniline trinitrotoluene), herbicides, and petrochemicals. Examples of volatile organic compounds include chlorinated olefins such as PCE, TCE, cis-1,2-dichloroethane and vinyl chloride. Examples of non-volatile organic compounds include PCBs and dichlorobenzene. Examples of non-chlorinated compounds include total petroleum hydrocarbons (TPHs) such as benzene, toluene, xylene, methyl benzene and ethylbenzene, methyl tert-butyl ether (MTBE), tert-butyl alcohol (TBA) and polyaromatic hydrocarbons (PAHs) such as naphthalenepetrochemicals, chlorinated organics, pesticides, energetics, and perchlorates.

[0022] The technology may be used for treatment of contaminated soils, sediments, clays, rocks, sands and the like (hereinafter collectively referred to as “soils”), contaminated groundwater (i.e., water found underground in cracks and spaces in soil, sand and rocks), process water (i.e., water resulting from various industrial processes) or wastewater (i.e., water containing domestic or industrial waste, often referred to as sewage).

[0023] The activated persulfate effectively oxidizes the targeted contaminant(s) by initially oxidizing the contaminants in the subsurface and then promoting facultative biodegradation (biological remediation) of the contaminants. The introduction of sulfate free radicals allows for a long-lived oxidation, which further extends by utilizing the radical residual and stimulating the biological mineralization of the targeted contaminants.

[0024] During the chemical oxidation phase, sulfate free radicals attack the aromatic hydrocarbon bonds of organic compound contaminants. A residual of the oxidization process is sulfate (SO.sub.4.sup.−) as can been seen in equation 1. Equations 2-4 show the various persulfates (sodium, potassium, and ammonium) being initially broken down into the appropriate element and persulfate prior to the persulfate breaking down into sulfate.

S.sub.2O.sub.8.sup.2−.fwdarw.2SO.sub.4.sup.−  (Eq. 1)

Na.sub.2S.sub.2O.sub.8.sup.2−.fwdarw.2Na.sup.++S.sub.2O.sub.8.sup.2−.fwdarw.2SO.sub.4.sup.−  (Eq. 2)

K.sub.2S.sub.2O.sub.8.sup.2−.fwdarw.2K.sup.++S.sub.2O.sub.8.sup.2−.fwdarw.2SO.sub.4.sup.−  (Eq. 3)

(NH.sub.4.sup.+).sub.2S.sub.2O.sub.8.sup.2−.fwdarw.2NH.sub.4.sup.++S.sub.2O.sub.8.sup.2−.fwdarw.2SO.sub.4.sup.−  (Eq. 4)

[0025] In addition to direct oxidation, the activation of the persulfate with the trivalent metal (e.g., ferric iron) forms sulfate radicals (SO.sub.4..sup.2) as seen in equation 5. This provides free radical reaction mechanisms similar to the hydroxyl radical pathways generated by Fenton's chemistry. The sulfate radicals are used to further oxidize the contaminants. In addition, the oxidation of the ferric iron further results into the generation of the highly unstable ferrate species of iron (Fe.sup.6+)) which can more effectively address the targeted contamination. The ferrate iron is a transient species that has elevated oxidation potential compared to other oxidants. FIG. 3 is a table that shows the elevated oxidation potential of the ferrate iron compared to other oxidants.

S.sub.2O.sub.8.sup.−+Fe.sup.+3.fwdarw.Fe.sup.(+4 to +6)+SO.sub.4.sup.−2+SO.sub.4..sup.−2  (Eq. 5)

[0026] The chemical oxidation of the contaminants is followed by biological attenuation. The biological attenuation utilizes the byproducts of the chemical oxidation process (the sulfate formed and the residual ferric iron). The sulfate ion produced as a consequence of the decomposition of the persulfate allows for the attenuation of the targeted contaminants under sulfate reducing conditions. In addition, the iron present in the subsurface provides terminal electron acceptors for continued biological attenuation. As such, the term “biological attenuation” as used herein refers to degradation of compounds using biological processes and consequently the reduction of substances regarded to be contaminants in the substrate being treated.

[0027] 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 or sulfidogenesis and results in the production of sulfide. Sulfate concentrations may be used as an indicator of anaerobic degradation of 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 (C.sub.6H.sub.6), toluene (C.sub.7H.sub.8) and xylenes (C.sub.8H.sub.10) under sulfate reduction are presented in equations 6-8 respectively.

C.sub.6H.sub.6+3.75SO.sub.4.sup.−2+3H.sub.2O.fwdarw.0.37H.sup.++6HCO.sub.3.sup.−+2.25HS.sup.−+2.25H.sub.2S.sup.−  (Eq. 6)

C.sub.7H.sub.8+4.5SO.sub.4.sup.−2+3H.sub.2O.fwdarw.0.25H.sup.++7HCO.sub.3.sup.−+1.87HS.sup.−+1.88H.sub.2S.sup.−  (Eq. 7)

C.sub.8H.sub.10+5.25SO.sub.4.sup.−2+3H.sub.2O.fwdarw.0.125H.sup.++8HCO.sub.3.sup.−+2.625HS.sup.−+2.625H.sub.2S.sup.−  (Eq. 8)

[0028] Ferric iron is also used as an electron acceptor during anaerobic biodegradation of many contaminants after sulfate depletion, or sometimes in conjunction therewith. The basic reactions of the mineralization of benzene, toluene and xylenes using ferrous iron are presented in equations 9-11. During this process, ferric iron is reduced to ferrous iron (Fe.sup.+2), 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.

C.sub.6H.sub.6+18H.sub.2O+30Fe.sup.+3.fwdarw.6HCO.sub.3.sup.−+30Fe.sup.+2+36H.sup.+  (Eq. 9)

C.sub.7H.sub.8+21H.sub.2O+36Fe.sup.+3.fwdarw.7HCO.sub.3.sup.−+36Fe.sup.+2+43H.sup.+  (Eq. 10)

C.sub.8H.sub.10+24H.sub.2O+42Fe.sup.+3.fwdarw.8HCO.sub.3.sup.−+42Fe.sup.+2+50H.sup.+  (Eq. 11)

[0029] Ferrous iron formed as a result of the use of the ferric species as a terminal electron acceptor, under the same conditions the residual sulfate is utilized as a terminal electron acceptor by facultative organisms, generates sulfide (2S.sup.−2). Together, the ferrous iron and the sulfide promote the formation of pyrite (FeS.sub.2) as a remedial byproduct as seen in equation 10. Equation 11 provides a more complete equation identifying where the ferrous iron and the sulfide come from. The reduction of ferric iron to ferrous iron readily supplies electrons to exchange and react with the sulfide. The pyrite is an iron bearing soil mineral with a favorable reductive capacity.

Fe.sup.+2+2S.sup.−2.fwdarw.FeS.sub.2  (Eq. 10)

2Fe.sub.2O.sub.3+8SO.sub.4.sup.2−.fwdarw.FeS.sub.2+19O.sub.2  (Eq. 11)

[0030] 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. Pyrite acts as a tertiary treatment mechanism under the reducing conditions of the environment. 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.

[0031] 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.

[0032] 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.

[0033] The amount of tri-valent metal that should be utilized based on the amount of persulfate that is utilized can be calculated. Referring back to equations 2-4 shows that each persulfate molecule forms two sulfate molecules. We can determine the amount of sulfate that will be generated per amount of a specific persulfate by plugging the molecular weights into the equations.

[0034] The molecular weight are as follows: sodium persulfate (238 g), potassium persulfate (270 g), ammonium persulfate (228 g) and sulfate (96 g). Accordingly, 238 g of sodium persulfate, 270 g of potassium persulfate or 228 g of ammonium persulfate yields 192 g (2*96) of sulfate. Stated differently, approximately 1.24 g of sodium persulfate, 1.4 g of potassium persulfate or 1.19 g of ammonium persulfate is required to produce 1 g of sulfate. We can refer to these ratios as equations 2A-4A respectively.

[0035] Plugging molecular weights into equation 11 we can determine the amount of pyrite generated. The molecular weights are as follows: Fe.sub.2O.sub.3 (160 g), SO.sub.4.sup.2− (96 g) and FeS.sub.2 (120 g). Accordingly, 320 g (2*160) of Fe.sub.2O.sub.3 and 768 g (8*96) of SO.sub.4.sup.2− creates 480 g (4*120) of FeS.sub.2.

[0036] Using molecular weights we can calculate that 224 g of ferric iron (Fe.sup.3+) is required to produce the 320 g (2*160) of Fe.sub.2O.sub.3.

[0037] Utilizing equations 2A-4A, we can calculate that 952 g of sodium persulfate, 1080 g of potassium persulfate and 912 g of ammonium persulfate are required to produce 768 g of sulfate.

[0038] Accordingly, in order to produce the pyrite (e.g., 480 g) one would need to use 224 g of ferric iron and either 952 g of sodium persulfate, 1080 g of potassium persulfate or 912 g of ammonium persulfate. Simplifying the amount of the various persulfates to 100 g results in 23.53 g of ferric iron required per 100 g of sodium persulfate (23.53%), 20.74 g of ferric iron required per 100 g of potassium persulfate (20.74%) or 24.56 g of ferric iron required per 100 g of ammonium persulfate (24.56%). That is, for any of the three types of persulfate discussed one would want to utilize a molecular weight of ferric iron that is between approximately 20-25% of the molecular weight of the persulfate. So a mixture of ferric iron and persulfate would be between approximately 80% (100 g of persulfate/(100 g of persulfate+25 g of ferric iron)) to 83.3% (100 g of persulfate/(100 g of persulfate+20 g of ferric iron)) by weight of persulfate.

[0039] If we assumed a 25% range for the values of ferric iron, the amount of ferric iron would be between 17.65%-29.41% for sodium persulfate, 15.56%-25.93% of potassium persulfate or 18.42%-30.7% of ammonium persulfate.

[0040] Persons skilled in the art will appreciate that the conception, upon which this disclosure is based, may readily be utilized as a basis for the designing of other structures, methods, and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention.

[0041] The foregoing is considered as illustrative only of the principles of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, and accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.

[0042] Although the invention has been illustrated by reference to specific embodiments, it will be apparent that the invention is not limited thereto as various changes and modifications may be made thereto without departing from the scope. Reference to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described therein is included in at least one embodiment. Thus, the appearances of the phrase “in one embodiment” or “in an embodiment” appearing in various places throughout the specification are not necessarily all referring to the same embodiment.

[0043] The various embodiments are intended to be protected broadly within the spirit and scope of the appended claims.