After the transesterification (the process of mixing vegetable oil with the catalyst) and the resultant separation of glycerol, the resultant biodiesel must be 'washed'.

The traditional Water Wash system works.  However, producing perfectly good biodiesel prior to the water wash is negated by adding water to eliminate the remaining glycerol, methanol and potassium hydroxide from the product.

This method needs a source of water (which has its own unknown chemical additives) to run through the biodiesel until the separated water is clear.  This process is often time consuming; with the added danger of producing soap in the process.  As if this is not enough, the resultant contaminated water must be treated before being disposed of; and the final product filtered before being regarded as safe to use in your vehicle.  It is recommended that the Water Wash system is used in conjunction with an excellent filter/water separator and on small batches only.

The Dry Wash system eliminates the need for water.  Most importantly this sytem produces close-to-spec biodiesel with the minimum risk of a batch turning to soap.  The ion exchange resin used (a Rohm & Haas product called Amberlite BD10DRY) absorbs impurities, water, glycerol and KOH from the biodiesel after the transesterification process.  However, it does not remove methanol. 

Bioman Energy has devised a simple methanol recovery system for this purpose.  The running cost of using the Amberlite resin is around 26-30 cents per litre.  Well worth the money to produce the resultant high-grade biodiesel.