Sylvie Willis
Diesel fuel contamination by microbes, also known as the 'diesel bug', is a serious issue that can clog fuel filters and decrease efficiency. The presence of water encourages microbial growth, which can occur at the interface between oil and water or on tank walls, depending on the microbes' oxygen requirements. Species that may grow in this environment include bacteria such as Clostridium and Pseudomonas, as well as fungi like Aspergillus and Candida keroseneae. Additionally, diesel oil contamination can negatively impact plant growth, with certain plant species exhibiting varying levels of tolerance to diesel oil contamination.
| Characteristics | Values |
|---|---|
| Type of contamination | Water, microbial, solid particulate |
| Microbes | Bacteria, fungi, algae, mould, yeast |
| Bacteria species | Clostridium, Desulfotomaculum, Desulfovibrio, Flavobacterium, Acidovorax facilis, Pseudomonas, Sarcina |
| Fungi species | Aspergillus, Candida keroseneae, Fusarium, Hormoconis resinae |
| Algae | Requires light to grow, rarely found in diesel tanks |
| Mould | A type of fungi with long multi-cellular filaments |
| Yeast | Relatively slow-growing fungi, 3-4µm in size |
| Biofilm | A complex structure of microbes adhering to fuel tank walls and each other |
| Biodiesel | Modern biodiesel is especially hygroscopic |
| ULSD | Ultra-low-sulfur diesel with higher biodiesel content |
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What You'll Learn
Microbial contamination
Diesel bug, or microbial contamination, is a common issue with diesel fuel. It occurs when microbes such as bacteria and fungi contaminate the fuel, often as a result of water ingress. Modern biodiesel is particularly susceptible to water contamination due to its hygroscopic nature, which can lead to condensation and rainwater penetration. This provides an ideal environment for microbial growth, which occurs at the interface between the oil and water or on the tank walls, depending on the microbes' oxygen requirements.
The presence of microbes in diesel fuel can have several detrimental effects. They can form biofilms, which are complex structures of microbes that adhere to the walls of the fuel tank and to each other. These biofilms can produce a protective slime and excrete acids that can corrode and erode metal fuel tanks. Additionally, chunks of biofilm can break off and clog fuel lines and filters, leading to operational issues and increased fuel consumption.
The specific types of bacteria and fungi that may grow in diesel fuel include Clostridium, Desulfotomaculum, Desulfovibrio, Flavobacterium, Acidovorax facilis, Pseudomonas, and Sarcina. Fungal species include Aspergillus, Candida keroseneae, Fusarium, and Hormoconis resinae. These microbes can produce acidic byproducts that increase corrosion and contribute to the premature wearing of engine components.
To prevent microbial contamination, it is crucial to control water buildup in fuel tanks. Regular microbial testing of fuel samples is also recommended, especially for critical systems. While some testing methods may lead to false positives, immunoassay antibody tests are quick, easy to use, and reliable in detecting fuel-threatening microbes.
Once microbial contamination is detected, it can be challenging to eradicate. Biocides can be used to kill the microbes, but mechanical intervention and thorough cleaning of the tank and fuel system may be necessary in severe cases. Therefore, prevention through water control and regular testing are the best strategies to maintain fuel quality and avoid the costly issues associated with diesel bug.
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Bacteria
The growth of bacteria and other microbes in diesel fuel is influenced by various factors. Ultra-low-sulfur diesel (ULSD), which has become the standard in many regions, has a higher biodiesel content, creating an environment that microbes favour. Additionally, the presence of water, even in small amounts, can provide sufficient conditions for microbial growth.
To prevent and manage diesel bug contamination, regular fuel conditioning and maintenance are essential. This includes implementing fuel polishing techniques and utilising services that specialise in tank cleaning and the removal of microbial contamination.
While diesel fuel contamination by bacteria and other microbes can pose challenges, ongoing research and the development of fuel conditioning programmes aim to address these issues and ensure the reliable operation of diesel-powered equipment.
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Fungi
Diesel bug is a consortium of microorganisms that grow on fuels, including bacteria, filamentous moulds, and yeasts. These microbes feed on the hydrocarbons in the fuel and create biomass, biofilms, and damaging by-products. They can enter the fuel through the air or water and can survive in very small amounts of water. The presence of water encourages microbial growth, which can occur at the interface between the oil and water or on the tank walls, depending on the microbes' oxygen requirements.
The best way to prevent microbial diesel fuel contamination is to control tank water buildup. However, even with proper housekeeping, microbial contamination may still occur. Testing is an important part of fuel care, and there are tests available to rapidly screen fuel samples for microbial contamination.
Interestingly, certain fungi may also hold the key to future biofuel production. Researchers are studying fungi such as Gliocladium roseum, which can produce hydrocarbons that are components of diesel fuel. By understanding and harnessing these fungi or their genetic material, it may be possible to manufacture hydrocarbons for fuel in the future.
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Algae
While algae require light to live and grow, making their presence in closed fuel tanks unlikely, certain microbes can survive and feed on diesel fuel. These microbes form colonies that thrive at the interface of fuel and water, growing faster in warmer temperatures. Parts of the colony can break off and clog fuel lines and filters.
To identify a potential algae or microbe problem in a fuel tank, one should look out for warning signs such as a significant depth of water at the bottom of the tank or an increased rate of filter consumption.
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Bioremediation
The process of bioremediation involves the use of microorganisms to break down and remove contaminants from the environment. In the case of diesel fuel contamination, specific microorganisms are introduced to the contaminated area to break down the diesel fuel. These microorganisms are often obtained from rich sources of microbes, such as sludges, composts, or manure, and are chosen for their ability to degrade diesel fuel.
One study found that the addition of activated sludge from a domestic wastewater plant significantly increased the degradation rate of diesel fuel in polluted soil and water. Samples taken from the site revealed that bacteria from the genus Acinetobacter were predominant in the degradation process.
Another investigation developed a simple laboratory methodology for the in situ bioremediation of diesel-enriched soil. The study found that biostimulation with inorganic nitrogen and phosphorus produced the best results, with biodegradation extents higher than 90% after 45 days.
It is important to note that the effectiveness of bioremediation can be limited by the lack of indigenous microflora with the required substrate specificity. In such cases, soil inoculation with cultures possessing the desired catabolic capabilities becomes essential for successful remediation.
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Frequently asked questions
The diesel bug is contamination of diesel fuel by microbes such as bacteria, mould, yeast and fungi.
Water can get into diesel fuel through condensation, rainwater penetration or adsorption from the air. The presence of water encourages microbial growth.
Microbes can clog fuel filters and decrease efficiency. They can also produce a protective slime that can erode metal fuel tanks.
Warning signs include finding a significant depth of water at the bottom of the fuel tank and going through filters at a faster rate than normal.
You can prevent the diesel bug by following a comprehensive fuel conditioning programme and maintaining good fuel housekeeping.
