Liquid purification or separation – Processes – Treatment by living organism
Reexamination Certificate
2002-07-31
2004-08-10
Upton, Christopher (Department: 1724)
Liquid purification or separation
Processes
Treatment by living organism
C210S617000, C210S631000, C210S694000, C210S759000, C210S150000, C210S220000, C210S908000, C435S262500, C435S309200
Reexamination Certificate
active
06773598
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method and apparatus for treating groundwater or other water streams contaminated with oxygenates.
BACKGROUND OF THE INVENTION
In response to the 1990 Clean Air Act Amendments gasoline suppliers began to blend fuels with oxygenates, such as alkyl ethers, particularly methyl-t-butyl ether (MTBE). Unleaded gasoline often comprises as much as 10 to 15% by volume of MTBE. Alcohol oxygenates such as ethanol and t-butyl alcohol (TBA) have also been used for the same purpose.
After using oxygenated fuels for over a decade, it has become apparent that these cleaner burning fuels pose distinct threats to groundwater resources. In particular, many oxygenates are very soluble in water and are slow to degrade in the environment; hence they tend to accumulate in water resources including surface waters and groundwater once released into the environment.
Due to leaks in underground storage tanks or spills, the groundwater at many gasoline retail, distribution, and manufacturing sites is contaminated with benzene, toluene, ethyl benzene, and xylene (BTEX), as well as MTBE and other ethers. For example, MTBE has been detected in groundwater with high frequency in many sites and there are well documented cases of impacts to municipal water supply wells. Due to the fact that MTBE and other ethers are characterized by the properties of high solubility in water, relatively low volatility compared to BTEX, relatively low carbon sorption coefficient, and poor biodegradability, the ethers are more easily transported in groundwater aquifers than BTEX and do not degrade through natural attenuation. In addition oxygenate alcohols such as TBA are also found as contaminants in groundwater since they are often present as impurities in the oxygenate ether feedstocks and/or are breakdown products of the ethers.
The presence of oxygenate contaminants in groundwater and in particular public water supplies poses serious problems since the ether oxygenates have very low odour and taste threshold concentrations. Typically regulators and local authorities require that potable water supplies should not contain more than 20 &mgr;g/L (ppb), and in some cases as low as 5 &mgr;g/L (ppb) of MTBE.
Granular activated carbon (hereafter GAC) has been used for treatment of wastewater and contaminated groundwater at the surface. In “A Review of Potential Technologies for the Treatment of Methyl tertiary Butyl Ether (MTBE) in Drinking Water”, discussing a study by Anthony Brown et al., University of Southern California Department of Civil and Environmental Engineering of the Metropolitan Water District of Southern California, City of Santa Monica, the authors mention the use of GAC, along with polymeric resins and chemically modified clays, but state at page 136 that adsorbability is low on GAC, adsorption capacity for MTBE is low, and frequent GAC regeneration is required. (API-National Ground Water Association “Petroleum Hydrocarbons and Organic Chemicals in Ground Water: Prevention, Detection and Remediation Conference, Houston Nov. 12-14, 1997).
Thus, while MTBE can be removed from recovered groundwater by treatment with granular activated carbon beds (GAC), it is relatively expensive compared to the treatment of BTEX because the GAC beds are subject to frequent exhaustion. Equally important, GAC is not effective at all on tertiary butyl alcohol (TBA) that is found along with MTBE in contaminated groundwater and is the primary metabolite in the biodegradation of MTBE, and is equally poorly biodegradable.
Where groundwater contaminated with BTEX, MTBE, and other ethers is treated using activated carbon there is a need in the art for a method which reduces the need for frequent changing of the carbon bed and which also addresses the problem of degrading alcohol oxygenates such as tertiary butyl alcohol (TBA).
The use of bacteria or naturally occurring microbes for biodegradation of a wide range of organic contaminants is known. However, attempts to degrade MTBE and/or TBA using bacterial cultures have generally met with little success.
For example, K. Mo, et al.
Appl. Microbiol. Biotechnol
. (1997) 47:69-72 proposes isolating from activated sludge and fruit of the gingko tree three pure cultures, belonging to the genera Methylobacterium, Rhodococcus, and Arthrobacter, that are capable of degrading MTBE. However, the data presented by Mo proposes that only a minor portion of the MTBE was degraded by the cultures and very little if any, of MTBE degraded to carbon dioxide within the time frame of the experiment.
An exception to the difficulties encountered in degrading MTBE and/or TBA with bacterial cultures is described in U.S. Pat. Nos. 5,750,364 and 5,902,734, which disclose mixed bacterial cultures capable of biodegrading MTBE and TBA to carbon dioxide and water, and U.S. Pat. No. 5,811,010, which describes aerobic degradation of t-butyl alcohol using activated sludge.
A sample of a mixed bacterial culture prepared according to U.S. Pat. No. 5,750,364 has been deposited with the American Type Culture Collection (ATCC), Patent Depository, 12301 Parklawn Drive, Rockville, Md. 20852, USA, with ATCC number 202057, under the Budapest Treaty (see also Column 2, line 64 to Column 3, line 4 of U.S. Pat. No. 5,902,734). Samples of this culture can be obtained from the permanent collection of the ATCC, Patent Depository (and Column 3, lines 1 to 4 of U.S. Pat. No. 5,902,734 indicate that all restrictions imposed by the depositor on the availability to the public were to be irrevocably removed upon granting of U.S. Pat. No. 5,750,364 (issued May 12, 1998) or of U.S. Pat. No. 5,902,734 itself.
WO 00/63343 describes a pure bacterial culture isolable from mixed bacterial culture ATCC No. 202057, and capable of degrading methyl t-butyl ether (MTBE) to carbon dioxide.
It is apparent from the art that it is more difficult to degrade MTBE and other ethers than BTEX due to the properties of the ethers. The ethers have high solubility in water, relatively low volatility compared to BTEX, relatively low carbon sorption coefficient, poor biodegradability, and are more easily transported in groundwater aquifers than BTEX. MTBE can be removed from recovered groundwater by physical adsorption with a GAC bed, but due to the fact it is not very hydrophobic and the capacity for sorption is not as high as BTEX, it is relatively expensive to remove MTBE by this method compared to BTEX due to frequent exhaustion of the activated carbon beds. In addition, activated carbon is not effective at all on TBA which is often found along with MTBE contaminated groundwater, and is even less hydrophobic.
The use of immobilized biological reactors, in which a biomass of bacteria and/or other microorganisms is retained on the surface of activated carbon particles is a known option for the treatment of contaminated waters. For example, “Experiences with GAC-Fluid Bed for Bioremediation of BTEX-Contaminated Groundwaters”, G. Mazewski, J. Tiffany & Hansen, Biotechnol. Ind. Waste Treat. Biorem., (Pub. 1996)333-344(1992) describes a demonstration project and a full scale remediation project wherein groundwater from an operating recovery well at a bulk storage terminal was treated using a bioreactor of fluidised granular activated carbon particles. In this work the removal of BTEX was more satisfactory than the removal of other compounds such as MTBE.
Further, “Bioreactor Treatment of MTBE and TCE In Contaminated Ground Water”, by Miller, Michael E., et al, from
In Situ and On
-
Site Bioremediation
, Pap. Int. In Situ On-Site Biorem. Symp., 4
th
(1997), Vol. 5, 89-94, describes a study at the Sparks Solvent/Fuel Site (Sparks, Nev.) wherein ground water containing MTBE, BTEX and various chlorinated solvents was treated in two granular activated carbon-fluidised bed bioreactors operating in parallel. For the first few weeks after reactor startup, 85% of the influent MTBE was removed, however effluent MTBE concentrations soon increased, and MTBE removal efficiencies dropped to 10-15% indicating that the initial rem
Byers Dallas Lea
Meyer Charles Lee
Salanitro Joseph Patrick
Sun Paul Ta-chin
Shell Oil Company
Upton Christopher
LandOfFree
Method and apparatus for biodegradation of oxygenates does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for biodegradation of oxygenates, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for biodegradation of oxygenates will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3324592