by Lisa M. Williams, Corrective Action Coordinator, QA/QC at Predictive Maintenance Services Inc.
Microbes are found at the fuel-water interface. They use fuel as food, converting additives into new chemicals and water as the oxygen source, thus ruining your fuel. Some of their food becomes new bugs or biomass, and the rest become byproducts or metabolites. These metabolite molecules range from carbon dioxide to slime. Some of the metabolites contribute to sludge formation or make organic acids, which make fuel and associated water bottoms corrosive. If you take a look at a slime sample at the fuel and water interface, you will find the proportion of the mass that is actual bugs is astonishingly small.
Think of these microbes as minuscule machines that convert fuel into non-fuel products. If left unchecked and under the proper conditions, your tank will contain more byproducts than pure fuel. These bugs can produce so much slime because they contain enzymes. The enzymes cut, reshape and join molecules. Each enzyme performs a very specific step in converting a hydrocarbon molecule into either new cell components or metabolites. Another interesting concept is that these bugs use mechanisms similar to those we use in a factory. Not just one person can build a car; it takes a group of people working together to get it accomplished. These bugs work in the same fashion because several bugs together do things that an individual cannot. Dr. Frederick Passman offers the best analogy, “Bugs are the workers; enzymes are their machines.”
Since there are really no microbial standards for fuels, microbial contamination remain undetected unless slime starts to plug fuel filters. If you reach this point, it will be very expensive to fix. Drastic changes in the fuel industry are forcing us to monitor and control microbial contamination. The use of diesel additives, ethoxylated gasoline additives, vapor recovery systems and cardlock pumps are more prevalent. These items are being used at retail and wholesale outlets. The increase in use is the cause of increased awareness and rate of occurrence of microbial contamination in all fuel grades.
I am a microbiologist so I know what to look for. You, however, do not have to be a microbiologist to detect microbes in your fuel system once they reach excessive levels. Here are a few methods you can use to determine if you have microbes. Check the filters and filter housings first because the microbes that are flushed by the fuel tanks will be trapped here. Once they are trapped, they multiply and form the slime that plugs the filter. If this slime smells yeasty or like rotten eggs, you have extremely heavy microbial contamination. It is really crucial to get the fuel tested before it reaches this point so you can save money and avoid damage to injectors and other fuel system components. Now, when you pull the filter, drain the fluid from the housing into a glass jar or clear sample bottle. If you see water, invert-emulsion, large suspended particles, or it just looks suspicious, get the sample tested immediately. If your results come back positive for microbes, it is advised that you take a sample from the bottom of the tank at about mid-depth. You also should treat the tank with a biocide.
The key to discovering and regulating microbial contamination is establishing a baseline of information. When we run oil samples, we always suggest to customers that they send a series of samples so we can establish a trend. These fuel tests are viewed in much the same way. If you do not know how to determine if your filters are clean or if there is the slightest hint of contamination, you will not be able to catch the contaminations until your system is overloaded with microbes. Here is the suggested plan. Check your system to establish a baseline. If you have microbes, treat it and sample again in a few weeks. If you do not find contamination, monitor the system and when you change the filters check them. If your routine check is constantly changing, send a sample to a laboratory. Send another sample in a week and if the contamination is worse, take corrective action. As the cliché goes, early detection is the key. Tank cleaning and biocide treatment cost only a fraction of draining the entire tank and wasting fuel.
Remember, consistent quality is important to customers. If you are the customer and your supplier has bugs, you will get them also. Smaller retailers depend on the reputation of their suppliers. Refiners tend to believe that if the fuel passes spec at the time of sale and failed later, it is not their problem anymore. Since the Clean Air Act is being pushed more and more lately, there is increased consumer awareness and increased fuel reformulation. Market participants are going to have to cooperate to ensure that the customer is getting consistently good fuel. If you think about it, contamination at any stage of the distribution process is bad. Each stage contributes more problems because the fuel is divided and sent to more places. It would be easier to treat the problem at the larger tanks before all of the splitting makes it impossible to trace.
The best treatment for contaminated fuel tanks is a biocide. The biocides kill or inhibit the organisms. Any product used for fuel treatment needs to be approved as a fuel additive. There are three classes of biocides: fuel soluble, water soluble and universally soluble. Fuel soluble biocides are unstable or insoluble in water. The major advantage is that they reside in the fuel phase, thus can be transported throughout the fuel system. The disadvantage is they are inactivated by water, where the microbes tend to grow. They are primarily used in treating systems with little free water. Water-soluble biocides are insoluble in fuel. They are best for shock treating bottom water contamination in tanks that are not drained on a regular bases. They are inexpensive, but they do not stay in the fuel long enough to come into contact with the microbes in the tank-wall slime. However, the microbes found in the bottom water can contribute to the wastewater treatment process. Universally soluble biocides are stable in both fuel and water. They are mostly fuel soluble with sufficient water solubility to perform in both phases. They can be conveyed throughout the fuel system. They also are effective against the biofilm and bottom water microbes since they are also water-soluble; however, they are high cost. Biocides may be expensive, but nothing compares to “bugs” found in every tank and diesel engine your company owns.
In order to keep your equipment running smoothly, you must get your fuel tested. Make sure to drain all of the free water, and when you change the filters, cut them open and check them. You may even want to consider a hydrophobic vent filter on your storage tank to remove moisture from the air as the tank “breathes.” Again, microbes are becoming a major concern and a reoccurring problem. Do not let your equipment or your wallet suffer. This may be something that you will not see until it is too late, so do not hesitate and test your fuel.