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Drinking Water

The fine points of methane removal

October 13, 2010
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Methane gas (CH4) is a complex and, unfortunately, often misunderstood water problem that most water professionals tend to avoid. How does this substance enter our water systems? Typically, this occurs through natural decomposition of plant and animal waste, or from industrial processes, such as dewatering that usually accompanies mining processes.

In its natural form, methane is colorless, odorless, tasteless and lighter than air, although well water containing methane can have a musty odor due to other substances such as hydrogen sulfide or sulfate-reducing bacteria.

Although the US Environmental Protection Agency (EPA) does not regulate the methane content of drinking water, it is important that you stress the significance of its removal to your clients. It has the potential for harmful side effects: It may produce suffocation by replacing oxygen in confined air spaces. Although this is a rare phenomenon, it has this capability given the proper environment.

Water hammer or pressure surge is yet another drawback of methane in a water system. These may occur when methane is released into pipes. In some cases, water hammer from a methane buildup can knock a drinking glass out of a person’s hands.

Also, lighter-than-air methane readily will find its way out of a water system, and although methane is non-toxic, it is flammable and potentially explosive when mixed with air. With higher levels of methane, it is possible to turn on the faucet and get a flare-up of flame when you run a match by the faucet. In some instances, you may be able to turn on a tap and light it. In some of the more extreme cases, it will remain lit.

There are some viable tests that can be applied to help diagnose a methane application; as always, proper precautions and safety measures must be correctly in place.

• First, we need to time how long it takes the gas to come out of the water. When you run water from any tap into a glass, you’ll have bubbles adhering to the inside of the glass, but the liquid inside becomes clearer or more transparent. If it clears up quickly (say, within 45 seconds), often that is a good indication of the presence of methane, which is ready to be released with depressurization. Gas staying in the water for two minutes or more is often an indicator of carbon dioxide (CO2), which takes a little more work to pull out.

• Second, fill a plastic beverage bottle about three-quarters full of water and put the cap on it (you can let it sit to the side while you time the water clarity in the previous test). Keeping safety in mind, take the cap off the bottle and run a match by it. A flame will be produced if it is methane. This may be difficult to see because it usually is a small blue flame.

Ventilation, temperature, pressure
Aeration units are not only the most common but also the simplest form of removal.

Remember that in a 5 percent to 15 percent concentration in air, methane can become explosive and present a health hazard. Awareness is needed as you work on any water treatment systems that deal with methane. Again, methane is lighter than air and has the potential of concentrating into pockets within the building — this is why proper ventilation is necessary.

Ventilation options are limited: You can use a power fan to dilute methane in the air and send it to the outdoors according to local building specifications. Another method is point-of-entry air injection, which dilutes the methane as it comes in, significantly reducing any hazards.

When you are diluting air in the system and/or properly evacuating it, you must consider water temperature. Methane is completely dissolved in water at 42 degrees Fahrenheit (5.5 C) but can be completely released (as a gas) at 58 degrees F (14.5 C).

As a rule of thumb, most well water is 54 degrees F (12.2 C). Increasing this temperature will get the best results. Water being pushed through a small apparatus at 54 degrees F by no means has time to warm up, and the methane will not release completely. Similarly, sending the water into an outbuilding where it is only 40 degrees F (4.5 C) will keep the methane in the water. So be mindful of where your treatment equipment is located.

Another factor in methane treatment is depressurization: When you depressurize water, dissolved gases will form small bubbles and release from the water. Bringing the water up to atmospheric pressure significantly helps achieve the best results.

If conditions around or in your treatment apparatus include cold temperature and high pressure, methane removal will be less efficient. Point-of-use equipment should be in a heated basement or a heated shed to help bring water temperature up and make a more efficient piece of equipment.

Oxidation, sanitation
Opening a sealed system with aeration/ventilation introduces the possibility of bacteria, so sanitizing the water must follow aeration. An easy way to sanitize is chlorination, with a storage tank. Primary sanitation immediately will kill any bacteria in the water, and secondary sanitation leaves a chlorine residual inside the tank to prevent further bacterial growth.

If there is any iron or manganese in the water, or anything that can be oxidized, you’ll follow with mechanical filtration.

Other treatment can be applied after filtration if necessary, such as water conditioning followed by treatment for drinking water.

Maintenance
A methane removal system involving sanitation should be checked once a year at a very minimum. Other water issues may require more frequent checks of the system anyway.

Of course, when sourcing drinking water systems, look for those in which all components are of food-grade quality and are NSF-certified.


Tate A. Burckhardt is vice president of Better Water Industries Inc., an OEM of water conditioning equipment headquartered in Tyler, MN. Early in his career, he worked for National Semiconductor as a fabrications operator inside a clean room, becoming a certified hazmat technician. He is now a second-generation water treatment professional and holds a bachelor’s degree in electrical engineering from South Dakota State University. He can be reached at (507) 247-5929 or by e-mail at: tate@betterwaterind.com.
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