County Fleet Biodiesel Use Grows in Southwest


by Annette Bair, SRDC; Dan Thiede, MN Project - August 2007

A survey was sent to County Highway Departments in Southern & Southwest Minnesota to ask about their fleet biodiesel use. All counties in Minnesota use the minimum 2% biodiesel blend in their fleet, but the percentage of use varies by county. A higher percentage biodiesel fuel is being used in the warmer months, so a couple counties have decided to vary their percentages during the year. Alongside 2004 and 2005 biodiesel mix surveys of the same counties, it can be seen that summer biodiesel mix has grown significantly in a number of counties. On top of rounding up county percentages, this survey was also helpful for identifying a key issue with biofuel use since the Fall of 2006—microbial growth.

Survey Results:

The summer use of biodiesel ranges from 2 to 50 percent, while the winter mixture for the majority of the counties is 2%, with Pipestone and Nicollet Counties using 5%. The chart on the next page shows that counties such as Redwood and Pipestone have made large increases in their use of biofuels, and Lincoln County has a history of using a 10% blend. Winter additives are used by some in the winter. Six of the counties indicated they use a fuel additive(in addition to the mix of #1 diesel), and six counties reported they routinely add biocides to prevent or mitigate microbial growth problems.

Microbial Growth:

Why are some experiencing the growth of microbials(bacteria & fungal)? In the past, there has been a higher content of sulfur in diesel fuel, and sulfur naturally kills microbials. The Clean Air Act called for the reduction of sulfur in highway diesel fuel sold at retail locations nationwide as of October 15, 2006. This fuel is referred to as Ultra-Low Sulfur Diesel(ULSD). The sulfur content in ULSD (15 parts per million) is equivalent to one ounce of sulfur per tanker truck of diesel. Moisture in the fuel tanks can also contribute to the growth of the microbes. Application of Biocide Products may assist in resolving this issue. See below.

Application of Biocide Products (source)

Storage: Biocide product containers should be kept closed at all times and should not be exposed to water at any time. Water contamination will lessen the effectiveness of these products.

Application in Storage and Fuel Tanks:

  1. When preparing a storage system to be treated with biocide, the water in the bottom of the tank should be drained if possible. If applying biocide to a fuel tank and it is possible to drain water out of the tank, do so. Maintaining water bottoms at a minimum level will lessen the chances of microbial contamination, but may not prevent it.
  2. The tank should be as empty as possible, and no more than 50% full, when the biocide product is added.
  3. When selecting the biocide, use one that is “universally soluble.” This will kill microbial organisms in both the water and fuel phases.
  4. Add twice the amount of biocide recommended by the manufacturer’s highest dosage (typically this doubled amount will be about 1 gallon biocide to 2,000 gallons fuel, or 500 ppm).
  5. Fill the tank with the fuel up to maximum capacity. This will promote mixing and help kill any microbial growth on the walls of the entire tank.
  6. For vehicle fuel tanks, all filters in the system, including pre-filters and fuel filters, need to be replaced after the biocide has been added.
  7. Since some initial filter plugging may occur, filters should be monitored after biocide addition.

As a preventative measure, it is important to keep tanks as full of fuel as possible, and to keep the amount of air in the tank minimal.

Source from above: Application of Biocide Products provided by: Hoon Ge, MEG Corp, Wayzata, MN 55391, 952.473.0044; and Mike Youngerberg, MN Soybean Growers Assn, Mankato, 1.888.896.9678

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Minnesota Department of Commerce Division of Energy Resources University of Minnesota Regional Sustainable Development Partnerships and Extension Great Plains Institute Southwest Regional Development Commission