PRECAUTIONS AND REMEDIES OF MICROBIOLOGICAL GROWTH IN FUELS

Microbiological growth in fuels is a well-known, well understood phenomenon that has also been thoroughly documented and communicated. Yet, reports of microbial attack and costly consequences persist.

Recently, an alert from a classification society fuel analysis service warned of contaminated marine diesel fuels which have caused rapid and serious fuel system corrosion, in some cases destroying components within days. In almost two dozen reports of damage, some vessels lost generator power with at least one requiring a tow into port. Although the alert was not definitive as to the nature of the 'organic acids' found to be present, the prime suspect for wreaking such havoc would be sulphate-reducing, anaerobic bacteria that can thrive in fuel systems and on tank bottoms under the right conditions.

When high temperatures and water team up, beware! Diesel fuels are most at risk because they contain easily digested carbon and hydrogen microbial food sources. Bacteria, fungi and certain types of yeasts can be present; but even small amounts of water in the fuel are sufficient to trigger rapid growth. Microbes usually thrive in a temperature range of 20 - 35°C, and their growth rate increases in direct proportion to increases in the temperature. Warm temperatures in the system or storage facilities provide the optimal environment for exponential growth and hot summertime weather intensifies the effect.

As suggested by the examples cited, the consequences can be dramatic and extremely expensive. Severe fouling and plugging of tanks, fuel lines, filters and injectors can cause blockages and flow restrictions resulting in equipment malfunctions, energy loss and, occasionally, complete system shutdowns. And the corrosion caused by microbial growth can drastically shorten the life of fuel system equipment. The potential for major damage from any active infestation is significant and basic preventative measures should be standard procedure.

The first line of defence against contamination is to keep the systems as dry and clean as possible by limiting the water ingress and stopping the spread of microbes within the system; alternating tank usage, if possible, is also recommended. Sources of water entry - from condensation, humidity or seawater entry during marine transportation - may be impossible to eliminate. However, when water is detected, centrifuging and/or drain-off from tank bottoms is recommended. Periodic cleaning of the fuel tanks is essential, and filters should be cleaned or replaced frequently, depending on their type. Maintenance doses of selective biocides are also essential for keeping fuel systems clean, and are especially important when conditions are ripe for contamination.

The most meticulous maintenance, however, cannot completely eliminate the potential for microbial problems. Contamination of fuel commonly occurs during storage at the refinery and during transportation to shoreside distribution facilities. It takes several days to confirm the presence of microbes using chemical tests, more than enough time for a contaminated tank to infect the entire system.

For these reasons operators need to be vigilant at all times for indications of microbial contamination, including: objectionable odours, such as hydrogen sulphide smell; discolouration or blackening of copper-bearing metals; the need for unscheduled filter changes or cleanings; presence of green, black or brown slimes or fibrous sludges in the fuel tanks, in lines or on filters; evidence of corrosion, especially under deposits on tank bottoms.

In addition, emulsions that are impossible to remove by filtration or centrifuging separation processes are usually signs of bacterial and fungal action. Of course, all of these symptoms are indicative of well-established, thriving microbial colonies. Damage is minimised and treatment facilitated by early detection through use of inexpensive evaluation kits to test new fuel supplies as well as monitor fuel in storage. These tests provide qualitative or semi-quantitative measures for determining approximate microbial levels and should be supplemented with detailed follow-up laboratory analysis of fuel samples to refine the recommendations for treatment.

Shock dosing with a biocide is essential as soon as biological fouling is observed or suspected, followed by extensive mechanical cleaning and use of a disinfectant if the contamination is heavy. After chemical treatment, filters will require frequent cleaning until the "rag" of microbial remains has been removed from the system.

Because of the variety available, selection of a biocide for a specific system requires consideration of key characteristics. This is an area of special expertise for Fuel Technology Pty Ltd, which takes an active role in the research and development of specialised treatments for fuel systems, and has assisted in evaluating and treating innumerable cases of microbial infestation.

There are obvious prerequisites for effective biocides. While killing the organisms and suppressing reinoculation, the treatment must not affect the quality of the fuel, degrade lubricating oils or be corrosive to metals in the system. Suitable biocides in almost all cases will be soluble in water; solubility in fuel is undesirable because of the dilution effect and reduced effectiveness at the critical fuel-water interface.

The most effective biocide is normally a blend of toxicants which destroys a broad spectrum of microbiological species, acting efficiently on the tank bottom area as well as at the water interface. It should also contain dispersing or sludge-solubilising agents which will gradually remove deposit accumulations and enhance the fuel flow characteristics throughout the system. Standards for personal and environmental safety must be considered as well. Biocidal treatment is typically very cost-effective, especially when compared with the potential damage costs of undetected and untreated problems: Typically a treatment can be used for both routine and emergency dosing of tanks for less than 0.005% of fuel cost at current prices.

Fuel Technology's catalyst, FTC has over the past fourteen (14) years been tested in the laboratory and the field in the control of cladosporium resinae fungal growth in fuel and proven to be a cost-effective biocide, in addition to its cost effectiveness in reducing fuel consumption.

Where a severe fungal growth is identified Fuel Technology will supply an effective biocide providing a broad spectrum control against a variety of bacteria, fungi and yeast contamination found in fuel systems.