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Untreated biodiesel waste product is toxic - mostly because it contains methanol.
In a lot of smaller plants biodiesel waste product is not disposed of properly. This is unfortunate as biodiesel producers are typically very environmentally aware.
The glycerin that comes out of the biodiesel process is laden with methanol and caustic chemicals. Glycerin is probably the worst biodiesel waste product. The real problem with glycerin is that it is hard to process without investing a lot of money in expensive equipment.
The glycerin is only really about 40% glycerine and is hard to purify to a pharmaceutical grade. The balance is water, methanol and soaps.
For every 100 liters of biodiesel that you make you will end up with 20-25 liters of glycerin. This 20-25 liters of glycerin can have up to 25% methanol in it and should be considered hazardous waste.
50ml of methanol is a lethal dose so there is a lot of methanol in glycerin. It should be treated in the same way as pure methanol, all the handling precautions that are dealt with in the biodiesel safety section should be followed.
In small scale production three things typically happen to the glycerin.
I have seen producers with small plants who have thousands of liters of glycerin stashed away. Need I say it, this is a bad idea!
There are products that can be made out of the glycerin, most commonly soaps, hand cleaners, floor cleaners etc. Although it is brown and very unattractive the glycerin makes a very good soap . It is important that the methanol is removed before it is converted into another product. Have a look at our biodiesel soap recipe pages for more information.
Manufacturing soap out of a biodiesel waste product like glycerin is very beneficial as it is recycling an already recycled item.
The easiest way to remove the methanol is to distill it out. You do not need a sophisticated still to remove the methanol, a relatively simple column still will do just fine.
Once the methanol has been removed the glycerin is a lot safer to dispose of and this can be done in a number of ways.
The wash water that is used to clean biodiesel will also be contaminated with methanol. As a biodiesel waste product this must be disposed of properly.
The water from the first wash will have a lot of methanol in it. This methanol means that the water is toxic. It will also contain a lot of soaps and caustic chemicalst.
Most home made biodiesel producers dispose of the water down the nearest municipal drain.
You should check with your local water treatment plant as to whether this is acceptable to them or not. Some water treatment plants do not mind some methanol as the bacteria in the plant thrive on it. However it is always a matter of degree and you must consult them before doing anything.
The wash water should never be disposed of down a French Drain or into ground water. Doing so can result in methanol contaminating the water table which could be a major pollution problem.
Alternatively, recover the methanol from your biodiesel before it goes into the wash system and then add some acid into the wash water to neutralize it before disposal. Use ph test strips to check that the PH is around 7. This effectively makes the water harmless and it may safely be disposed of down the drain.
If your municipality cannot process your waste water then buy a biodiesel dry wash system. This will not use water - problem solved.
Of course the dry wash chemicals are also a biodiesel waste product and need to be disposed of properly, but this is a lot easier to do.