MTBE Contamination and Five Examples for Remediation

This Bioremediation Blog describes the basics of the organic chemical compound MTBE (Methyl tert-butyl ether), gives an overview of MTBE contamination and finally provides you five examples of MTBE remediation methods for cleaning a MTBE spill.

What is MTBE?

MTBE stands for Methyl tert-butyl ether, sometimes referred to as tert-butyl methyl ether. MTBE is a simple organic compound created from methanol with a structural formula of (CH3)3COCH3. MTBE is a highly volatile, flammable, and colorless liquid which has a high solubility in water.

What are the Main MTBE Uses?

The largest global application of MTBE is a gasoline additive, but it is also used in the industry as a safer alternative for diethyl ether, as a solvent in academic research, and in contact dissolution therapy, MTBE is injected directly into the gallbladder to dissolve gallstones.

MTBE in Gasoline

Gasoline can contain as much as 10% to 15% of MTBE. As a gasoline additive, MTBE has two purposes:

  • MTBE raises the octane number of the fuel. The higher the octane number, the more compression the fuel can withstand before igniting, and the better it prevents so called engine knocking.
  • MTBE functions as an oxygenate in the fuel, which means that it adds oxygen into the burning reaction and thus reduces the amount of unburned hydrocarbons and harmful carbon monoxide in the exhaust gas and dilute gasoline components such as aromatics including benzene.

MTBE Production

MTBE is produced via the chemical reaction of methanol and isobutylene. Methanol is derived from natural gas, and isobutylene is derived from butane obtained from crude oil or natural gas, thus MTBE is an organic compound derived from fossil fuels.

MTBE was taken into use as s gasoline additive initially in 1970’s. The large scale use of MTBE began in 1990, after the Clean Air Act of 1990 went into effect in the US.

Before MTBE was used to produce unleaded gas, tetraethyl lead (TEL) was used as an octane booster.

The US Energy Policy Act of 2005 prompted gasoline refiners to transition to the use of ethanol as a gasoline additive, in place of MTBE.

MTBE Pollution

MTBE has a minty odor and it gives water an unpleasant taste already at very low concentrations.

MTBE, just like many other oxygenates possess a high solubility in water and tend to partition more strongly from the vapor phase into the aqueous phase than the other components in gasoline such as BTEX (benzene, toluene, ethylbenzene, and xylenes) do.

MTBE usually spread more efficiently in the groundwater than other gasoline components. Sorptive processes do not significantly slow down the spread of MTBE within the groundwater. Therefore, MTBE plume is likely to be longer than a corresponding BTEX plume. Because MTBE may migrate over greater distances, the magnitude of dive it takes within the groundwater moving downwards may be greater. It is critical to characterize MTBE plumes both vertically as well as horizontally.

Consequently, early detection and response to gasoline leaks and MTBE spills is essential.

How MTBE Spills Happen?

MTBE is often introduced into groundwater systems by leaking underground storage tanks (UST) at gasoline stations, above-ground gas storage tanks and pipelines, or by a direct gasoline leak causing a MTBE spill onto the ground. There are several examples of MTBE having polluted groundwater after being spilled or leaked at gas stations.

If MTBE gets in the ground, it can travel faster and farther through groundwater than other gasoline components. This makes it more likely to contaminate public water systems and private drinking water wells if gasoline is spilled on the ground or leaks out of underground storage tanks. MTBE can remain in underground water for a long time.

Even small amounts of MTBE in water can give it an unpleasant taste and odor, making the water undrinkable.

Five Examples for MTBE Remediation

MTBE can be degraded by microbes, but not as well as other components in gasoline and cleaning has turned out to be a problematic at many MTBE spill sites. MTBE can be biologically degraded under both aerobic and anaerobic conditions and both in situ and ex situ. However, anaerobic conditions can result in incomplete degradation of MTBE, and consequently this can lead to formation of tert-Butyl alcohol, or t-butanol (TBA).

Generally, aerobic conditions have been shown to be far more effective in the complete biological MTBE remediation and removal.

When compared with more easily biodegradable compounds such as BTEX, MTBE contamination sites are likely to require corrective action for longer periods of time and may require more extensive monitoring.

Groundwater remediation technologies shown to be effective for the treatment and removal of MTBE include both ex situ technologies such as pump and treat, and in situ technologies air sparging, chemical oxidation, phytoremediation and electro kinetic oxidation.

Here is a list of five commonly used bioremediation techniques for removing MTBE contamination:

MTBE Remediation through Pump-and-Treat

Pump-and-treat processes, which have been shown to have a lower effectiveness for petroleum contaminants, are effective in treating MTBE contamination due to the low affinity MTBE compound has for organics in the soil. Pump-and-treat has the ability to flush MTBE contaminants from the soil.

MTBE Remediation by Air Sparging

Air Sparging is a subsurface MTBE remediation technique that involves the injection of pressurized air into contaminated ground water causing hydrocarbons to change state from dissolved to vapor state. The air is then conducted to a vacuum extraction systems to remove the contaminants. The extracted air is treated to remove the toxic MTBE contaminants.

MTBE Remediation through Chemical Oxidation

In Chemical oxidation, reactive chemical oxidizers, substances that can oxidize other substances and to cause them to lose electrons are injected or otherwise introduced directly into the soil and groundwater volume containing MTBE to destroy the chemical contaminants in place. Commonly used oxidizing agents include: hydrogen peroxide, ozone, persulfates and permanganates. MTBE chemical oxidation is an in situ remediation method.

In Chemical Oxidation, the reactants take away electrons from the organic contaminant compounds, and change them into harmless compounds.

Natural oxidation processes take place in natural waters and serve as an important mechanism in the natural self-purification of surface waters.

MTBE Remediation through Phytoremediation

Phytoremediation technology involves using living plants and the associated micro-organisms to clean up soil and groundwater contaminated with MTBE. Phytoremediation is a cost-effective approach for MTBE remediation that takes advantage of the ability of plants to concentrate elements and compounds from the environment and to metabolize various molecules in their tissues.

Electrokinetic Remediation for MTBE Contamination

Electrokinetic remediation technology with oxidation enhancement produces a controlled low voltage electric field in a polluted area to amplify the remediation power of nature. In electro kinetic oxidation deployments, thin steel rod electrodes are inserted into the MTBE contamination area approximately 5 meters apart in a grid formation. The grid of electrodes is then coupled together in to rows of anodes and cathodes.

Electrokinetic remediation solution layout - EKOGRID

The low voltage electric pulses driven within the grid are controlled by an above-the-ground control unit. The electro kinetic oxidation method has proven to be an ecological, sustainable and cost-efficient way for remediating soil and groundwater affected by a MTBE spill.

Electrokinetic remediation installation by EKOGRID
Electrokinetic remediation is a fast, cost-efficient and unobtrusive in situ remediation method for MTBE contamination.

 

MTBE Contamination Spreads Quickly, but several MTBE Remediation Methods Exist

MTBE is a toxic, organic compound found in high concentrations from groundwater and drinking water as a result of a MTBE spill; which often occur due to gasoline leaks in petrol stations. There are several ways to clean up a MTBE contamination including fast and cost-efficient solutions such as electrokinetic remediation. For more information, don’t hesitate to contact EKOGRID!