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Dow Kathon FP 1.5 Biocide
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Dow Kathon FP 1.5 Biocide


Microbial contamination is not specific to any one fuel type – diesel, petrol, ULSD, biodiesel, kerosene, gasoline, and other fuels used in marine, aviation, automotive and home heating applications are all susceptible. Similarly there is no single specific organism that can be identified as being responsible for degradation and spoilage. As a general rule, wherever fuel and water come into contact in a storage or distribution system microbial contamination is likely to occur.

  • No matter how well maintained a storage system is, a water bottom is almost invariably present. This results from a number of sources:
  • Freshly refined fuel contains some water. This separates out as the fuel cools down
  • Atmospheric condensation: humidity in the air in the storage tank condenses out and adds to the water bottom
  • Rain or snow may enter the tank via sampling ports, breather vents or ill -fitting seals on floating roofs
  • Transport or storage in tankers or barges can result in contamination from ballast Water

In addition certain end use applications – notably marine fuel – naturally lend themselves to allow water ingress into a storage system. Water from all of these sources accumulates in the storage tank to form the water bottom.

Microorganisms can be air or waterborne. Consequently as the water bottom develops a microbial population builds up in it. For many of the species present in the water bottom, liquid hydrocarbon fuels represent an excellent nutrient source. As a result there is a population explosion: the microorganisms proliferate at the fuel/water interface, surviving in the water phase whilst feeding on the fuel. In so doing, they secrete detrimental waste into the fuel and can push the fuel out of specification.

Consequences of Microbial Growth

In the initial stages of contamination the organisms present are predominantly aerobic, using the dissolved oxygen in the water for respiration. As this supply of oxygen is depleted, anaerobic organisms, known as sulphate reducing bacteria, develop. These organisms do not require oxygen for respiration and form corrosive waste products such as hydrogen sulphide.

Once a microbial population becomes established fuel quality rapidly deteriorates. As outlined below problems such as haziness, failure to meet specifications, corrosion, filter plugging and additive degradation can occur. All of these problems are related directly to the presence of microorganisms or their associated by-products.

Fuel Haziness: This is a clear indication that fuel is out of specification. The primary cause of haziness is an increase in the water content of the fuel resulting from the production of biosurfactants. These are by-products of microbial growth and alter the surface tension at the fuel/water interface. As a consequence the solubility of water in the fuel is increased.

Degradation of Additives: Certain additives, especially those rich in nitrogen and/or phosphorous, encourage microbial growth. In the process the additives are degraded and consequently their effect is lost.

Microbially Induced Corrosion: MIC is associated with biofilm growth on surfaces within fuel tanks and pipe lines. In particular, Sulphate Reducing Bacteria can produce H2S. This is easily soluble, highly corrosive, and will contribute to increased localized corrosion (pitting).

Sludge Formation: Microbial debris is deposited on the tank bottom where it forms a layer of sludge. This sludge creates an environment which favours microbially induced corrosion. It may also become contaminated with viable microorganisms and unless removed will act as a reservoir of infection every time the tank is used.

Filter Plugging: Biopolymers are formed during microbial growth. These are viscous, adhesive substances which, along with microbial and other debris, are deposited on filters and pipes leading to reduced flow rates and blockages. At end user level this can have serious consequences causing engine damage and in extreme cases complete failure.

Odor: A problem commonly associated with microbially contaminated fuel is that of foul odor. This is principally as a result of hydrogen sulphide production by sulphate reducing bacteria.

Kathon FP 1.5 Fuel Biocide has wide ranging approvals in aviation, marine, automotive, home heating and military fuels. Approvals have been obtained from:

  • Specialist fuel companies
  • Customs accredited laboratories
  • Global militaries
  • Industrial gas turbine manufacturers
  • Diesel engine manufacturers
  • Commercial airlines
  • Filtration equipment manufacturers
  • Airframe manufacturers
  • Aviation engine manufacturers
  • Aviation auxiliary power unit manufacturers
Inhibition of Contaminants
Organism TypeOrganismATCC #MIC (ppm AI)
Mold (a)Hormoconis resinae(c)227123
Yeast (b)Candida albicans166511.5
 Candida lipolytica(c)166171.5
Bacteria (b)Citrobacter freundii67501.5
 Enterobacter aerogenes130480.375
 Escherichia coli112291.5
 Proteus mirabilis46751.5
 Pseudomonas aeruginosa(c)339880.375
 Pseudomonas oleoverans80620.375

Key to above: (a) MIC at 7 days, (b) MIC at 48 hours, (c) Hydrocarbon Utilising Microorganism.

The data in the table above was achieved under laboratory testing, and under controlled conditions. These data are intended as an indication of the broad spectrum of activity of KATHON FP 1.5, and should not be interpreted as having relevance to the effectiveness or dosing against specific bacteria in formulated products or in process systems. The data cannot be used to predict performance in fuels. Dow Microbial Control always recommends that a microbial study of the fuel is carried out before a treatment strategy is decided.

Treatment Guidelines:

Aviation Fuels
Water and sludge should be removed from fuel tanks before application of the biocide.
100ppm v/v of KATHONTM FP 1.5 as supplied should be used to achieve microbial control, as described by EU BPD and US EPA regulations. To achieve this, the user should treat every 10,000 litres of aviation fuel with 1 litre of KATHON FP 1.5. The biocide should be added in such a manner so as to allow good mixing and distribution across the fuel. Ideally, this should be into a fuel supply line to ensure agitation. A contact time of up to 24 hours is recommended, depending on the severity of infection.

All Other Fuels
Water and sludge should be removed from fuel tanks before application of biocide and again after the retention period.
KATHON FP 1.5 has been tested and found effective in a wide range of fuels, including diesel, petrol, ULSD, biodiesel, kerosene, gasoline, and other fuels used in marine, aviation, automotive and home heating applications.

KATHON FP 1.5 is typically dosed at 200 to 300 ppm (200mL to 300mL per 1000L fuel) for curative treatment (i.e. when there is evidence of bacterial contamination). A minimum residence time of 12 hours should be allowed, before the fuel is used, though 24 hours is recommended. The biocide should be added in such a manner so as to allow good mixing uniform distribution of the biocide across the fuel.

KATHON FP 1.5 can also be used as a preventative/maintenance measure (to guard against bacterial contamination) in fuels that lack microbial contamination. For such a use, the recommended dosage is 100 to 150 ppm (100-150mL per 1000L fuel). The biocide should be added in such a manner so as to allow good mixing and uniform distribution of the biocide across the fuel. In such a case the residence time should still be at least 12 hours. Extreme care must be taken to avoid the addition of a preventative/maintenance level dosage of KATHON FP 1.5 to a heavily contaminated fuel system.

KATHON FP 1.5 can also be used as a shock biocide, for fuels that are heavily contaminated. If this is the case, doses up to 1000 ppm can be administered (1L biocide per 1000L fuel) according to the BPD. The US EPA allows the use of up to 400 ppm KATHON FP 1.5 in heavily contaminated fuel systems (400mL biocide per 1000L fuel). In this case, the residence time is recommended to be a full 24 hours.


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