Dave Friday, PE, ThermoRetec Austin
Jonathan Greene, PE, ThermoRetec Houston
Tim Barnhill, ThermoRetec Houston

Overview:

Today many MTBE remediation technologies are available to effectively and efficiently remove MTBE from groundwater for municipal use at flows of 500-1000 gpm. These include: Air Stripping with Off-Gas Treatment, Granular Activated Carbon (GAC), Advanced Oxidation Processes (AOPs), and Synthetic Resin Sorbents. Since treatment cost depends on existing system conditions, water quality, systems flow rates, MTBE influent concentrations, and required effluent goals, individual cost analysis may result in different conclusions and recommendations for different individual applications.

Background:

Methyl tertiary-butyl ether (MTBE) is the most widely used oxygenate, with nearly 90 percent of the nation’s cleaner-burning gasoline using MTBE as the primary pollution fighting oxygenate. MTBE has been used since the late 1970’s to maintain vehicle performance and octane levels in most gasoline sold throughout the United States. With the Clean Air Act Amendments of 1990, MTBE concentrations were increased to levels up to 15% (by volume) in gasoline in areas with poor air quality. Exceeding expectations of the US Environmental Protection Agency and state air officials, MTBE gasoline blends have proven to be effective at reducing toxic air pollutants, ozone, and carbon monoxide. Public risk of exposure to cancer-causing constituents such as benzene and other toxic compounds found in conventional gasoline have been reduced due to MTBE gasoline blends. However, the same properties that makes MTBE an ideal fuel oxygenate tend to make it more difficult to remove once in water. These are: high water solubility, low adsorption to granulated activated carbon, low Henry’s constant, and slow biodegradability.

Treatment Levels:

Aesthetic properties such as taste and odor are generally the basis for MTBE treatment standards. Although there are no federal maximum contaminant levels (MCLs) for MTBE, the U.S. EPA Office of Water has adopted a preliminary Consumer Advisory Level for MTBE to be kept within the range of 20 to 40 parts per billion (ppb) or below, based on taste and odor. However, some states have regulated concentrations ranging from 5 ppb (California), 40 ppb (Rhode Island, Vermont, Missouri), 70 ppb (Massachusetts, New Jersey), to 200 ppb (Wyoming, North Carolina).

Proven Technologies:

• Air Stripping with Off-Gas Treatment
    
• Granular Activated Carbon (GAC)
    
• Advanced Oxidation Processes (AOPs)
    
• Synthetic Resin Sorbents

1. Air stripping is a technology that has proven to productively remove MTBE from drinking water. An air stripper consist of contaminated water flowing down a column filled with packed material while a stream of air flowing upward strips the MTBE from the water. Air stripping specific system technologies include spray towers, bubble diffusion strippers, aspirated air strippers, low profile air strippers, and packed towers. In Rockaway Township, New Jersey and La Crosse, Kansas, drinking water is effectively being remediated by packed towers. By using packed tower aeration, flow rates from 600 gpm and greater (at removal efficiencies 95% and greater), have shown to be not only the best air stripping technology but, the most cost-effective for MTBE removal. If the air stream leaving the treatment system contains 1 lb/day or more of MTBE, then off-gas treatment is usually required. Depending on the level of MTBE, thermal oxidation and vapor-phase carbon adsorption prove to be the most cost-effective way to treat the off-gas emissions.

2. Granular activated carbon (GAC) is a technology widely being used to remove different types of organic compounds such as MTBE from water. This involves pumping water through a bed of activated carbon, which will cause the MTBE to be adsorbed. Once the carbons removal capacity is used up, it can then be returned for reactivation by the manufacturer or disposed of appropriately. Compared to the more innovative technologies, the installation and capital cost are reasonably low for GAC do to the simplicity of the materials and equipment. Compared to other gasoline components, the main difference caused by MTBE is the use of more carbon vessels to ensure that the carbon is completely saturated before reactivation. The type and source of the carbon (coconut shell GAC or coal-based GAC) as well as the occurrence of other contaminants in the water will influence the cost-effectiveness and efficiency for most MTBE applications.

3. Advanced oxidation processes (AOPs) are based on oxidation of contaminants using suitable combinations of hydrogen peroxide, ozone, ultraviolet light, ultrasonic vibration, high-energy electron beams, and/or chemical reactions. After the oxidation treatment, the resultant compounds may be more amenable to treatment by other means, have a lower level of hazard, or even be totally neutralized. Although AOPs are generally considered an up-and-coming technology, this technology has demonstrated to oxidize not only MTBE but also a wide array of organic chemicals to meet drinking water standards at bench and field-scale sites. Hydrogen Peroxide/Ozone and Hydrogen Peroxide/Continuous Wave Medium-Pressure Mercury Vapor Lamps have shown to be the two best AOPs for removing MTBE out of water.

4. Synthetic resin sorbents have shown to have a much higher adsorbent capacity for MTBE when compared to GAC. Resin sorbents continue to show resistance to competitive non-organic matter sorption and they can be regenerated on-site through microwave irradiation or steam stripping. Rohm and Haas (Philadelphia, PA) manufacture a carbonaceous resin called Ambersorb 563. This resin is the leading contender for removing MTBE from drinking water. Data is limited on the overall effectiveness and efficiency of removing MTBE from water with synthetic resin sorbents.

Conclusion:

The problem of MTBE in drinking water is not going away any time soon. Research on the up and coming technologies of MTBE removal from municipal drinking water has shown much progress. Lack of published data, the need to collect more operational data, and more detailed cost analysis reports are improvements that could help in the realm of MTBE remediation. However, with the uses of air stripping, granular activated carbon, advanced oxidation processes, and synthetic resin sorbents MTBE can and will be removed from drinking water effectively and efficiently. Finally, one must realize that stronger measures should be taken to avoid releases of gasoline into drinking water supplies. This would practically eliminate the need for MTBE remediation.

Reference:

Buratovich-Collins, Jacquelin. and Reid H. Bowman. HiPOx: Advanced Oxidation Technology for the Destructive Removal of MTBE from Groundwater. Applied Process Technology, Inc. San Francisco, CA 94104.
webpage

Castle AFB Ground Water Clean-Up website: click here

Clean Air & Clean Water, The Facts on Managing MTBE-Blended Gasoline Releases to Water Supplies.
webpage

CPL Carbon Link: The ACTIVE force in CARBON.
webpage

Environmental Fact Sheet WD-WSEB-3-19, 2000. MTBE in Drinking Water, New Hampshire Department of Environmental Services.

Hydroxyl Industrial Systems- Groundwater Treatment. http://www.hydroxyl.com.

MTBE Water Contamination: About MTBE, Lewis Saul & Associates, P.C.
webpage

National Ground Water Association: Press Release, 2000. NGWA Supports Phaseout of MTBE. Westerville, OH.

Oxygenated Fuels Association, 1999. MTBE: Treatability and Remediation. Arlington, Virginia. April.

Schrader Environmental Systems
webpage

The California MTBE Research Partnership, 2000. Executive Summary- Treatment Technologies for Removal of Methyl Tertiary Butyl Ether (MTBE) from Drinking Water: Air Stripping, Advanced Oxidation Processes, Granular Activated Carbon, Synthetic Resin Sorbents, 2nd ed. National Water Research Institute, Fountain Valley, CA.

The California MTBE Research Partnership, 1999. Evaluation of the Applicability of Synthetic Resin Sorbents for MTBE Removal from Water. National Water Research Institute, Fountain Valley, CA. Dec. Fig.4-1, pg.41. webpage

United States Environmental Protection Agency. MTBE Groundwater Clean-up Levels for Lust Sites: Current & Proposed. Courtesy of Micheal Martinson, Delta Environmental Consultants, Inc. webpage

Water Quality with Laura E. Loverde, Solving the MTBE Problem. webpage

 

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