Bubble Washing Biodiesel

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Bubble washing biodiesel is a very popular method of washing this biofuel. This method is gentle enough that it deters emulsions - only mist washing is gentler.

How it Works:

In the wash tank there is a layer of water on the bottom, and the biodiesel floats on top. An aquarium stone sits on the bottom of the tank producing bubbles. These bubbles carry a bit of water with them as they rise through the biodiesel. As the droplets of water rise, the contaminants in the biodiesel cling to them and rise as well. When the bubbles reach the top, they pop, and the water droplets travel back down to the bottom layer of water taking the contaminants with them. After many hours of bubble washing biodiesel, the mixture is allowed to settle, the wastewater drained, and the process begins again until all contaminants are removed.

Supplies Needed:

• Wash tank

• Outlet to drain the wash water

• Aquarium bubbler with at least 3 watts of power (some will melt after a few washes in biodiesel, so try to find a wooden or metal one!)

• 6-inch aquarium air stone (wood or ceramic will hold up well in biodiesel)

• Timer to turn off the bubbler (optional, but very convenient)

• pH strips to test the waste water and determine when to stop washing

How to Bubble Wash:

Fill the wash tank 2/3 full of biodiesel and 1/3 of water. (When adding the water, add it very gently pouring it down the side of the tank to deter emulsions.)

Secure the air pump to the tank above water level, drop the air stone in and bubble for a 6-8 hours.

After 6-8 hours of bubbling, turn the bubbles off, let it sit for one or more hours while the water settles out.

Drain the wash water through the water outlet. If there is an emulsion, drain that into a separate container and visit the emulsion page. Add clean water (still 1/3 to 2/3 biodiesel) and repeat the process a few more times until the exiting wash water is clear.

Now you may use one of these tests while washing biodiesel to make sure the fuel is completely clean. If it doesn't pass the tests, you will need to continue washing.


Bubble washing biodiesel uses less water than some of the other methods, is simple and effective, but it can take several days.

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