29.04.09

Research into biological growth in biodiesel blends

It is a well-known fact that ordinary diesel (petrochemical diesel) refined from oil from, for example, the oil wells in the North Sea, can be contaminated with bacteria if it is stored incorrectly. Bacterial contamination is a living biomass of bacteria, fungi and algae that live on carbon, the substance of which diesel is made. Despite the fact that biomass is a familiar phenomenon in petrochemical diesel, bacterial contamination is seldom discussed, probably due to the fact that everyone knows how to deal with the fuel in order to avoid bacterial contamination.

The introduction of biodiesel in petrochemical diesel changes the fuel’s chemical structure and it is therefore important to consider how this may affect the growth of biomass in the fuel. In cooperation with OK a.m.b.a., Daka Biodiesel a.m.b.a. and Samtank A/S therefore, Danish Technological Institute has investigated blends of petrochemical diesel with second generation animal biodiesel. The aim was to establish whether it is necessary to take special precautions when handling and storing biodiesel (i.e. different precautions than for ordinary diesel), in order to avoid biological growth.

Preliminary results indicate that biomass growth is to a great extent affected by the same factors in fuel blends of biodiesel and petrochemical diesel as in pure petrochemical diesel. This means, for example, that the fuel must be kept separate from water, which facilitates growth, e.g. of bacteria. Yachtsmen are familiar with such problems as they often find a clogged filter due to bacterial contamination in a tank that has accumulated condensation during the winter months. Similarly, temperature is significant for biomass growth in fuel. Access to air or the lack of it is also a factor that determines the kind of biomass that can grow in fuel.

The conclusion is that it is to a great extent the same mechanisms that determine creation of biomass in blends of biodiesel and petrochemical diesel as in pure petrochemical diesel. The research shows that pre-existing knowhow and current material in the distribution chain, ranging from large storage tanks on harbours to the fuel tank in any car, can be used with biodiesel blends too and that the precautions, e.g. that a tank must be free of water, are the same as when handling a pure petrochemical diesel.

Image: Research into biological growth in biodiesel blends. Gitte Sørensen holds a flask with B20 (20 % biodiesel blended with ordinary diesel) which is the upper layer, and water (the bottom layer).

By Consulent Gitte Sørensen, M.Sc.

Centre for Chemical and Water Technology, Danish Technological Institute, Aarhus, Denmark