Liquid purification or separation – Processes – Chemical treatment
Reexamination Certificate
1998-09-17
2001-03-06
Simmons, David A. (Department: 1724)
Liquid purification or separation
Processes
Chemical treatment
C210S765000, C210S908000
Reexamination Certificate
active
06197206
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a process and apparatus for the purification of water contaminated with methyl tert-butyl ether (MTBE) with air and/or a gas containing ozone. Optionally, there is provided a pressurized container and gas stripping means. The contaminated water may come available from lake water, ground water and underground water supplies.
BACKGROUND OF THE INVENTION
MTBE is a chemical compound that is manufactured for primary use in gasoline. MTBE, a colorless, flammable liquid with a turpentine-like odor, is highly water soluble, highly flammable, and extremely volatile. It is resistant to biodegradability in either aerobic or anaerobic conditions. MTBE is a common component in reformulated fuels developed to reduce smog and meet Clean Air Act goals and has been used in gasoline since 1979. The characteristics of MTBE are unlike those of other gasoline constituents and solvents. MTBE is highly soluble and migrates quickly with groundwater. Groundwater in equilibrium with gasoline containing 15 percent MTBE could contain as much as 9,600 ppm MTBE. It does not significantly adhere onto soil particles, and it does not appear to readily biodegrade in the environment.
MTBE is more difficult and more expensive to remove from water than other chemicals found in gasoline. Also, MTBE plumes can appear as discontinuous slugs. It moves more quickly through soil than most gasoline components, and its plumes tend to expand more rapidly. MTBE has been used in cold climates in the United States since 1979 as a de-icer. The Environmental Protection Agency (EPA) has tentatively classified MTBE as a possible human carcinogen, and in February 1991 the California EPA office of Environmental Health Hazard Assessment (OEHHA) established an interim action level of 35 ppb for MTBE. Depending on the state, regulatory requirements for MTBE range from 20 to 200 ppb.
MTBE is thought to get into surface waters such as lakes and reservoirs from the use of motorized watercraft. It may also travel into these waters in polluted runoff, or it may be deposited from the atmosphere by rainwater or other means. MTBE can get into groundwater from leaking underground fuel storage tank systems and leaking petroleum pipelines.
Available literature suggests that the treatment alternatives for removing MTBE from groundwater include pump and treat, air stripping, GAC absorption, and advanced oxidation processes.
Ethers under normal conditions are non-reactive and, in the case of MTBE, remain unchanged in soil and groundwater environments. However, oxidation by hydroxyl radical occurs readily with ethers. As long as the hydroxyl radical is in excess, this reaction will go to completion for all ethers, hydrocarbons or chlorinated solvents under controlled conditions.
It has long been known to ozonate water in order to oxidize pathogens and any other oxidizable organic or inorganic material that might be present in contaminated water. Ozone is a semistable gas formed of three oxygen atoms, instead of the two atoms that form oxygen gas. Ozone is most typically produced by an electrical arc discharged through air causing oxygen atoms to combine with an oxygen free radical that is formed. Ozone rapidly undergoes reaction to revert to more stable oxygen, releasing an oxygen free radical in the process. Two such free radicals can combine to form an oxygen molecule or the free radicals can oxidize an oxidizable substrate.
Ozone is fast emerging as the most efficient and ecologically sound oxidant to treat both organic and inorganic substances. Ozone has been used for water treatment for over 100 years, and is a preferred means of disinfecting potable waters. Many new applications of ozone are being evaluated.
A natural ingredient of the Earth's upper atmosphere, ozone (O
3
) is a three-atom allotrope of oxygen (O
2
) and exists in a gaseous form at ambient conditions. Ozone is such an aggressive oxidant, it is second only to fluorine in electronegative oxidation potential. However, unreacted ozone decomposes in a matter of hours to simple molecular oxygen and therefore cannot be stored. It must be produced on-site and destroyed by burning.
DESCRIPTION OF THE PRIOR ART
It is well known in the art to use ozone to treat contaminated substances. Land et al, in U.S. Pat. No. 5,615,974, which is incorporated herein by reference, teaches the use of ozone to treat subsurface contamination. Specifically, according to Land et al, chemical oxidation is a process in which the oxidation state of a substance is increased. Oxidizing agents usually supply oxygen as the electron acceptor in oxidation reactions. In the process of Land et al, any oxidant is suitable but the preferred oxidant is hydrogen peroxide.
In an embodiment of Land et al, ozone, with or without Fenton's reagent, may be the oxidant. Fenton's reagent is a broad term used to describe that compound which results from the combination of an acidic solution, such as hydrogen peroxide, with a ferrous salt. The oxidization reaction with ozone generates the “hydroxyl radical” (OH.) and this hydroxyl radical is believed to degrade and volatilize contaminants, such as petroleum hydrocarbons and volatile, semi-volatile and nonvolatile organic compounds. Fenton's reaction generates heat and the heat generated helps to volatilize contaminants which might not initially react.
It is also known in the art to use ozone to clean water. Typical systems using ozone can be found in U.S. patents to Teller et al., U.S. Pat. No. 4,021,347, Laraus, Nos. 4,104,166 and 4,250,040, Tamir No. 4,804,478 and Brown, No. 5,004,537. The referenced patents to Teller et al., Laraus, Tamir and Brown are incorporated herein by reference. Ozone is 600 to 3000 times more active against bacteria than chlorine in similar concentrations. In addition to being more effective than chlorine, ozone does not exhibit the drawbacks of chlorine, such as odor and/or skin irritation.
It is also known in the art to use both ozone and ultraviolet radiation to purify water, as taught in U.S. patents to Engelhard, U.S. Pat. No. 5,709,799, Gastman et al., No. 5,711,887, Dadd, No. 4,230,571, and Campen et al., No. 4,230,571. The reference patents to Engelhard, Gastman et al., Dadd, and Campen et al. are incorporated herein by reference.
The use of carbon as a filter or a catalyst is also known in the art. Specifically, MTBE contaminated water has been passed through carbon beds. Good results can be obtained using activated carbon (surface area 400-800 m
2
/g). Alumina and silica can also be used. In general, solid components and mixtures thereof can be used which have an absorption capability or affinity to the toxic component to be treated. In practice, the solid filter preferably has a surface area of at least 50 m
2
/g and a pore volume greater than 0.1 cm
3
/g. However, carbon beds alone are not effective.
The prior art, however, does not teach an efficient and effective use of ozone in a pressurized environment to purify water that is becoming increasingly more contaminated with potentially dangerous MTBE.
SUMMARY OF THE INVENTION
The current invention teaches an efficient and effective apparatus and method for purifying MTBE contaminated water by subjecting the water to an oxidant such as ozone or ozone enriched fluid and then stripping off the oxidized products.
Advantageously, the ozone or an ozone enriched gas is delivered as a stream of microbubbles to provide a greater surface area of ozone contact. Placing the contaminated water and ozone in a pressurized environment increases the oxidation reaction.
REFERENCES:
patent: 3445001 (1969-05-01), La Raus
patent: 5399267 (1995-03-01), Wang et al.
patent: 5505856 (1996-04-01), Campen et al.
patent: 5545330 (1996-08-01), Ehrlich
patent: 5562822 (1996-10-01), Furness, Jr. et al.
patent: 5707528 (1998-01-01), Berry
Hoey Betsey Morrison
John Lezdey & Assoc
Simmons David A.
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