Biodiesel Waste Products (Part 2 – Wash Water)

Eleanor Hanson

The second biodiesel waste product that we are going to look at is the wash water that results from water washing biodiesel. Of course if you have a dry wash biodiesel system then you will not have this waste product.

Once biodiesel has been manufactured, it contained significant amounts of waste products which are detrimental to an engine. Some of these are residual methanol, free glycerin, soaps and catalyst. Removing these products is very important to the well-being of a fuel injection system as they cause corrosion, coking of the fuel injectors and damage to the fuel injection pump. Both of these fuel system parts are expensive to replace or repair.

The most common way of removing these waste products is by water washing them.

Water which has been used for washing biodiesel will contain significant amounts of methanol. This methanol means that the water must be disposed of carefully and in an environmentally friendly fashion.

Probably the simplest way of removing the methanol from the wash water is to remove the methanol from the biodiesel before washing. Once the methanol is in the wash water it is very difficult to remove it efficiency. The methanol may be removed from the biodiesel by heating the biodiesel above the boiling point of the methanol (64 deg C) and using a simple still to recover it.

Improper disposal of wash water contaminated with methanol can contaminate groundwater supplies effectively poisoning them and is a really bad idea.

Additionally, on the first wash, the water will be very caustic as it will contain a very high percentage of soaps and residual catalyst. This wash water needs to be neutralized before it is disposed off. This can be done by adding an acid into the water such as vinegar, hydrochloric acid or sulfuric acid. Once the water is Ph neutral it can be disposed of safely.

A number of methods of disposing of the wash water responsibly are available. Visit for a some ideas on disposal options.

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