After biodiessel is produced, there are several impurities present in the raw fuel that must be removed before it can be used safely. Biodiesel washing can be achieved by several methods, such as water washing or dry washing. Washing biodiesel with water is time consuming. After water wash, the biodiesel fuel still needs to be dried to remove any water that may be present and, therefore, this method is limited to small scale biodiesel production.

A more convenient and faster method of washing biodiesel is dry washing system in which biodiesel is run through filtration towers or vessels containing filter media that either adsorb or absorb impurities present in the raw biodiesel.