The term diesel bug refers to the microbial contamination of diesel fuel. It can be considered a type of classic biofouling. This means the general damage to material caused by microorganisms growing on the material surface. More specifically, it is a mucous film or flakes of various organisms such as bacteria and fungi in a solution. Fundamentally, all surfaces and boundaries can develop such biofilms. Almost all industrial applications are affected, in particular the tank and engine system. One of the reasons for this is the increased use of methyl esters in place of petrodiesel and heavy fuel oils.
The topic is relevant for the preparation of fluids by means of fluid filters, in particular fuel filters, as the surface can become clogged by a biofilm. This results in the differential pressure increasing. In fuel filtration, this mainly occurs when water enters the fuel system and growth occurs at the boundary surface between water and fuel. A mucous film forms, varying in thickness. A biofilm of this type is caused by bacteria that populate the fluid boundary layer and feed from nutrients in the fuel. Forming a biofilm allows the organisms to survive in such extreme environmental conditions.
The bacteria living in a biofilm benefit from the film enormously. The film offers a degree of protection from mechanical stress. Apart from this, its irregular formation enables aerobic and anaerobic zones to develop, offering a habitat for a wide range of organisms. Within the biofilm, the individual bacteria engage in a vigorous exchange of genes. This makes it possible for the colonies to adapt to new conditions quickly and is one of the reasons for the increasing resistance to biocides. Generally, it can be said that bacteria in a biofilm are more capable of surviving and more resistant to external stress.