Bubblewashing Wash Biodiesel

Bubble washing

Bubble-washing was developed at the University of Idaho and is popular among home-brewers. It uses a small air-pump, usually an aquarium aerator pump with a bubble-stone. Water is added to the biodiesel in the wash tank (usually a quarter to a half as much water as biodiesel); the water sinks to the bottom; throw in the bubble-stone, which also sinks to the bottom, and switch on the pump. Air-bubbles (lots of little bubbles is best) rise through the water and into the biodiesel, carrying a film of water around them, which washes the biodiesel around the bubble. When it reaches the surface the bubble bursts, leaving the water to sink back down again, washing the fuel again.

Usually three or four washes are used, each of six to eight hours, often less for the first wash, with a settling period of at least 1 hour between washes (some people settle it for much longer). After it’s settled the water is removed via a bottom-drain and replaced with fresh water.

Washing is completed when the water is clear after settling, with a pH of 7 (or the same as your tap-water).

Some of the cheap air-bubble stones aren’t biodiesel proof and can crumble away any time from immediately to soon, especially the blue ones, for some reason.

Get ceramic stones, they’ll last indefinitely. A rough-grade carborundum stone will also work, or a pumice stone, though you’ll have to weight it. Or try experimenting with wood, and weight that too.

Here’s Aleks Kac’s method: Washing.

Mike Pelly’s method: Bubble washing.

Advantages of bubble-washing: It’s easy, it works, it doesn’t take much effort — add the water, switch on the aerator, come back later, do it again. For added convenience add a timer to switch off the air-pump after eight hours so you don’t have to come back until a couple hours later (or a week later if you like) when it’s settled and you can just change the water.

Disadvantages of bubble-washing: It might not take much effort but it takes a lot of time — there are quicker (and better) ways

Bubble-washing is gentle and can mask an incomplete reaction, which agitation will reveal immediately. (It’s always wise to do a wash-test first by shaking up a quarter or half a litre of the fuel with some water in a sealed jar or a PET bottle.)


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