Como Hacer Biodiesel > Biocides:

Microbial growth has been known to be a problem when storing biodiesel fuel, particularly in larger tanks and for longer periods. Microbes can feed on both biodiesel and petroleum based diesel.

These microbes form a slimy colony that lives at the fuel/water interface. They grow quite rapidly in warmer temperatures. They can even grow in cold weather when fuel tank heaters are installed. Parts of the colony can break off and clog the fuel lines and fuel filters.

Typical measures to eliminate these problems are to to either kill the microbes with a biocide treatment, or eliminate the water, a necessary component of microbial life. Biocides are chemicals that kill bacteria and molds growing in fuel tanks without interfering with the combustion of the fuel or the operation of the engine. If a biocide is used, it must be added every time a tank is refilled until the problem is fully resolved. Biocides kill the microbes in the tank, but these dead orgamisms can then form sediments which can move through your fuel system. The risk of filter clogging may continue for a short period after biocide treatment until the problem has been completely resolved, so expect to replace fuel filters as the debris is drawn from the tank.

Biocides are available on-line or at marine stores to treat petroleum diesel fuels. These same biocides can be used as an additive for biodiesel. They are typically added to the fuel tank in your vehicle (or in a storage tank used for dispensing biodiesel)in small amounts. Used properly, the can eliminate or inhibit the growth of the problem causing microbes. Biocides are toxic and should be used only as directed by the manufacturers. Precautions should be taken to avoid any contact with the products (wear gloves and eye protection) and to prevent any spills or drips.

References:

Wikipedia Diesel Fuel Article, accessed July 10, 2006

Cytoculture.com - Biodiesel Handbook, accessed July 10, 2006