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Deposition Designation Station

A Look Back

Between 1994 and 1999, I had the opportunity to write a series of articles for National Petroleum News (NPN). Each article focused on one aspect of the connection between microbial contamination and operational problems in fuel retail systems. In the 13-years that have lapsed since the publication of Knowing When You Have Contamination, our basic understanding of the issue hasn't changes, but some of the tools available to petroleum marketers have.

Beginning with Uncontrolled Microbes Eat Earnings last month, and continuing with each of the other articles in the following months, Total Fuel Quality is pleased to present reprints of each of my NPN articles with my comments about what has changed since their original publication.

Knowing When You Have Contamination provided a few very simple techniques that enabled non-technical people to check for microbial contamination. Most of the information in the original article is still valid today, however there are few items that need updating.

My comments about inspecting the fuel-water residue in filter housings need updating. Although I still inspect filters and filter housings that I remove from gasoline dispensers, I no longer expect to find a fuel-water emulsion in the housings. These days, I look for corrosion on the retainer spring and filter-canister base plate. I also cut out portions of the filter medium and run microbiological tests on them.

I still follow the technique that I described for inspecting fuel-tank bottom samples. As the market for ethanolblended gasoline, ultra low sulfur diesel and biodiesel has mushroomed over the past decade, bottom-sample gross observations have become an even more useful tool for detecting microbial contamination. All of these newer fuels have a greater water-holding capacity and greater risk of microbial attack. Except for long-term storage systems the major issue isn't damage to the fuel; it's damage to the system. Component failure events are strong indicators of serious microbial contamination in the fuel system.

The comments that I made about bottom-water pH are no longer valid for systems holding the newer fuels. Acid production by microbes is masked by additives that move from the fuel-phase into the bottom-water. Even bottomwaters with heavy microbial growth can have alkaline pH values

In my 1994 article I mentioned rapid detection methods in Knowing When You Have Contamination. Over the past five years, the ATP test has become a valuable field test for microbes in fuels. ASTM is currently balloting a standard method for testing fuels for ATP content. Increasingly, fuel retailers are using this simple, 5-minute test to monitor their tanks for microbial contamination. Companies that have made ATP testing part of their quality assurance monitoring program have reported substantial reductions in their corrective maintenance costs.

For people who are used to seeing colonies form in or on a growth medium, there are great new kits available now that weren't on the market in 1994. However, it still takes several days for visible colonies to form. This is why I still have a strong preference for rapid methods like the ATP test.

In the years since Knowing When You Have Contamination was published, ASTM has created two documents that help non-technical people in the fuel industry to better understand fuel microbiology and its impact on fuel systems. ASTM D6469 Standard Guide for Microbial Contamination in Fuels and Fuel Systems provides a brief overview of the problem and simple steps for diagnosing problems caused or made worse by microbial contamination. ASTM Manual 47 - Fuel and Fuel System Microbiology: fundamentals, diagnostics, and contamination control provides industry stakeholders with the background information and tools they need to get a good understanding of the problem and its prevention. Both of these documents are available from ASTM at

Knowing When You Have Contamination

Since there are no microbial standard for the fuels, microbial contamination remained undetected unless slime started to plug the filters. Dramatic changes in the fuel industry are driving a need to revise the way we monitor and control microbial contaminations. Ethoxylated gasoline additives, diesel additives, vapor recovery systems and increased use of cardlock pumps at both whole-sale 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

. . .Continue to read rest of article (PDF).

Dr. Frederick Passman, PhD is a Certified Metalworking Fluids Specialist with over 35 years experience in Environmental & Industrial Microbiology. His company, Biodeterioration Control Associates, Inc. (BCA) provides clients with unparalleled expertise in Microbial Contamination Control.

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