Microbial Contamination FAQ's

Microorganisms are present whenever sources of food and water come together. In a fuel storage systems or tanks the Hydrocarbon Alkanes in the fuel provide the food source, whilst the water provides the kick start they need. Water can come from the fuel itself, but its external sources such as atmospheric humidity (condensation) and Free Water ingress from the outside i.e. leaking tank and filler seals or breathers that cause most of the problems. The hygroscopic nature of Biofuel is also an attractant for moisture. With considerable amounts of food available and the on-going ingress of moisture/water the microbes (bugs) are free to grow, divide (multiply) and colonise the fuel storage or tank system.

Water is heavier than fuel and so is found at the bottom of tanks, be it the supply company's or your own storage or equipment tanks. Microbes tend to live at the fuel water interface, living in the water and feeding off the Alkanes in the fuel. They also seek out low flow areas of the fuel system and over time are known to actively create these conditions by 'digging in' to tank and fuel line structures, resulting in corrosion and pitting taking place. Heavy contamination can block filters and stop engines as well. Unfortunately you can almost guarantee that will occur at the most inopportune time with possible outcomes being dangerous or even catastrophic.

Governments the world over are taking measures to reduce emissions and eke out the dwindling fossil fuel stocks. There is also an urgency to reduce the economic risk of and politically unacceptable dependence on those fossils fuels and their multi-national suppliers. The emissions drive has led to sulphur, seen as the main culprit in the emissions debate, being targeted for reduction. Most countries that have made the move have bought their sulphur levels down from many thousands of ppm to just 50. Some have even come down to 10 ppm or less. This fuel is commonly called Ultra Low Sulphur Diesel or ULSD. Along with this some countries are regulating the addition of Biofuels to fossil fuels. This is seen as the best current solution to eking out those fuel stocks and spreading the risk. However, as far as microbial contamination goes changes in both ferocity and the profile of microbes are being seen.

Sulphur is a lubricant, so reducing the levels increases fuel system wear and lessens the fuels efficiency. Older engines, particularly the seals in the fuel system suffer from this reduction. Unknown to most though is that sulphur is a bacteria-stat. This means that it interferes with the lifecycle of microbes (the bugs) and slows down their ability to grow and colonise the fuel system.

Biofuel is a term used for fuel derived from organic/plant sources. From purpose grown and professionally processed crops like jatropha to highly variable waste by-products like tallow and spent chip shop oil. The products are developed from a renewable source and are known for emitting lower emissions after going through the combustion process. Biodiesel, also known as FAME (Fatty Acid Methyl Ester) is becoming popular in many countries with a number of them now regulating for its use. However, FAME (Biodiesel) has a tendency to attract higher levels of moisture. This is believed to be the major factor behind the increasing incidence of microbial contamination in blended fuels. They also have a tendency to stick to tank and pipeline structures, which make them very difficult to remove completely from bulk fuel supply ships and pipelines. Thus cross contamination, albeit with very small quantities occurs in all fuels, again resulting in higher levels of microbial activity.

In Europe, the EU is driving changes in this area through a continuous stream of directives. Road transport is at the forefront of these changes, mainly through a variety of Fuel Quality Directives. Non road machinery fuels in the marine, mining, construction, heating and ventilation and power generation industries are next on the hit list. These trends are slowly progressing worldwide. All parties to the Kyoto agreement are moving in a similar direction as are both New Zealand and Australia. Further information can be found in government reference papers and the Fuelstat manufacturer's online library.

The solution involves a multi-stage procedure. The first stage is to establish if there is a microbial problem or not and if so how severe is it. The next step is then to select and apply appropriate remedial treatments i.e. Biocides, conditioners, circulation systems etc. And finally, in order to prevent further problems down the track, fuel users should design and rigorously implement a fuel hygiene/housekeeping regime appropriate to the risk of the individual system at any point in time. Regular testing is the only reliable way to establish and monitor the microbial status of the fuel system. And with a real time option now available monitoring that status has never been easier.

A variety of tests are available based on various technologies with their respective pros and cons. These technologies include the laboratory only IP385, which is the gold standard, Colony Forming Unit counts, ATP (bioluminescence) and pregnancy style immune- assay based methods. The features and benefits of the market leaders, most of which are approved by IATA (International Air Transport Association) are compared in the table at the end of this text.

Treatments include fuel additives (conditioners), biocides and mechanical methods (circulation systems). Remedial actions may also involve draining and physical cleaning out of the tank.

Fuel additives (often called Fuel Conditioners) are designed to remove water and slow down the growth of microbes. Some claim to even eliminate the bugs. They are often a cocktail of ingredients aiming to offer a number of benefits like increased lubricity, fuel efficiency and lower emissions. These fluids act through biological and/or chemical activity. They often include enzymes. 

Biocides are toxic chemicals that kill microbes when administered under the right/correct conditions. These conditions include having a full fuel tank, the right dose rate and appropriate on-going treatment intervals. Personal protection and disposal precautions are essential due to the toxicity of the products.

Under dosing and frequent use can result in development of resistance strains i.e. bugs that become immune to the product. Biocides are contact killers so their use when an infection is heavy should be avoided. Best practice is to drain the fuel then open the tank and physically clean it out before refilling it to the top and Biociding the fuel to kill off any remaining spores.

Fuel Polishing through a circulation system encompasses a variety of mechanical means of reducing the contaminant level in the fuel. Cost and effectiveness vary. Methods include filtering, magnets and UV systems. Most are used as one-off interventions, however there are also in-line and kidney loop systems that can be retro-fitted to provide on-going protection to the fuel system.

In the early stages of responding to either the threat or the reality of microbial contamination in the fuel system most users just need a quick diagnosis before deciding on the next course of action.

The Conidia Bioscience pregnancy style immuno-assay FUELSTAT™ test is ideal in these circumstances. It is a fast accurate on-site test, which needs no special skills or equipment. It is known as the 10 minute test for good reason as it offers real-time results. Alternative tests require hundreds of dollars in capital investment, extensive training and additional equipment plus up to 4 days of elapsed time for the results to develop. Some don't even adequately distinguish between the types of organism and their levels, therefore don't indicate the true nature of the problem. A comparative table showing the different tests available can be found below.

If you have a microbial problem and don't have the internal engineering resources required, then your regular maintenance supplier should be able to design and implement a solution. There are also many specialist tank cleaning and maintenance organisations, consultants, fuel suppliers, fuel treatment, testing and remedial equipment suppliers and trade organisations, all of which have useful resources to offer. Links to some of these organisations can be found on the Fuel Test website. Fuel Test also offers a consultancy service to carry out risk assessments and design of suitable systems to combat microbial contamination.