Knowing When You Have Bad Fuel Tank Contamination
and Where It Came From

Since there are no microbial standards for fuels, microbial contamination remains undetected unless slime started to plug fuel filters. Dramatic changes in the fuel industry are driving a need to revise the way we monitor and control microbial contamination. Ethoxylated gasoline additives, diesel additives, vapor recovery systems and increased use of cardlock pumps at both wholesale and retail outlets contribute to both increased awareness and incidence of microbial contamination in all fuel grades. Here are a few easy tests to determine if microbes are attacking your profitability.

Fisheyes and Rotten Eggs

The first place to check for contamination is the filters and filter housings. Microbes flushed from fuel tanks are trapped by filters. There they multiply, forming the slime most often responsible for filter plugging. A slime-coated filter that feels slimy to touch or smells yeasty or like rotten eggs reflects microbial contamination in the fuel tank.

“You don’t have to be a microbiologist to detect and control fuel system microbial contamination.”

When pulling a filter for inspection, drain or decant the fluid from the filter-housing into a glass jar. Look for water and invert-emulsion (cloudy fuel) layers and flocs (fisheyes). M Fisheyes are the soft, spherical colonies the fungi forms in fluids. Again, smell the fluid for the odors described above.

Any indication of microbial contamination of the filter and filter housing requires the drawing of two samples from the fuel tank, one from mid-depth, the other from the tank bottom. There are various sampling devices available. Of primary consideration is the need to get samples from known tank-depths.

Decant the fuel sample into a clean glass jar. Compare the mid-column and bottom samples visually. Are there differences in color, clarity or concentration of suspended particles? These differences may be caused by nonbiological, chemical reactions, but, in concert with positive indications from filter inspection, they are most likely to be caused by microbial activity.

Is there a membrane-like layer between the water and fuel phases of the bottom sample? This is a typical biofilm layer in which a community of microbes works to degrade fuel.

With a bench-top centrifuge, spin a sample from each tank depth and check for free water and suspended solids. Use pH paper to test the pH of any free water. Any pH below 5.5 strongly suggests that microbes are producing corrosive, organic acids.

Since microbes grow in the water phase, not the fuel phase, use water samples for microbiological tests. There are several dipstick and broth kits for determining the presence of viable microbes. Alternative rapid detection tests are gaining popularity for onsite microbial contamination testing. Positive microbiological test results, combined with the other symptoms described above, mean that the fuel system must be treated.

Baseline is Crucial

The key to detecting and controlling microbial contamination is establishing a baseline of information. If you don’t know what contamination-free filters, mid- and bottom fuels or bottom water look and smell like, you won’t be able to catch microbial contamination until your system is seriously fouled.

Most systems should be checked monthly. Establish a baseline. If the fuel system is contaminated, treat it. If you know your system is contamination free, monitor all parameters for two to three months. After that, check filters at each change; bottom sample monthly.

If your routine check indicates that the system is changing, run the complete series confirming microbial contamination. Draw a confirmation sample about a week after the first one showing signs of microbial contamination. If the symptoms are worse, initiate corrective action. If the results seem confusing, contact an expert to help interpret the observations.

Compare the relative costs of tank-cleaning and biocide treatment. Including the expense of routine monitoring, early detection and treatment costs a fraction of the expense of tank clearing. Moreover, preventative treatment ensures that the system operates unfouled and that customers get consistent quality.

Remember, you don’t have to be a microbiologist to detect and control fuel system microbial contamination. You don’t need to be an economist to recognize that contamination prevention can help you retain more earnings dollars.

Dr. Frederick J. Passman, PhD, is president of Biodeterioration Control Associates, Inc., and an editorial board member for the International Journal of Bioremediation & Biodeterioration and associate editor for Lubrication Engineering.