DIPSLIDES

 

Bacterial testing of systems should take place on a weekly basis and when bunkering. Incubate the dipslides for 24 hrs at 25-3O°C (see instructions in the kit boxes for variations on this dependent what bacteria is being tested for).

Product A - Combination Dipslide for aerobic/coliform (SCT)- NATO STOCK # JO13 6640-993168071

Product B Combination Dipslide for aerobic yeast & fungi (RBS)- NATO STOCK # JO13 6640-992589066

Product C - Culture tube for anaerobic bacteria (SRB)- NATO STOCK # JO13 6640-998771680

Dipslide Incubator - NATO STOCK # JO13 6640-993654664

Bacterial Contamination in Fuel Oil Systems:

Microbe Monitoring. In oil technology, microbes can be defined as comprising bacteria, yeasts and fungus. All these, when present, can attack additives in the oil and change them chemically so that they no longer function in the way intended and simultaneously there is a reduction in the quantity present.

In addition to the chemicals present in the fuel oil, extra food can be provided by the addition of leakages of any fluids waste and water draining into the system. This additional food causes the microbes to multiply more quickly. Quick identification of the presence of bacteria will mean that the problem can be treated before mechanical breakdown occurs. When testing with dipslides in oil dip the slide into the water phase of the fuel oil or preferably the oil/water interphase. When testing ballast water or drinking water it should first be fully agitated or tested at the bottom and top of the tank.

Aerobic:

These exist mostly as small rods. They would almost certainly always be present in the bilges.

They are detected by the Aerobic Yeast & Fungi Dipslide. The colonies are easily seen.

Yeast and Fungi:

These are less common than bacteria, but are one hundred times larger than bacteria and, therefore, only 10,000 yeasts will attack the chemicals and as much as 1,000,000 bacteria.

They are more resistant to biocide attack than bacteria and it is necessary that the biocide used in the oil will kill these as well as bacteria.

Ease of use and a wide range of applications make the Aquamarine Dip Slide range the ideal answer for service engineers and busy laboratories where speed and repeatability are primary requirements.

Anaerobic Bacteria (Culture Tube Test):

These exist when the oil is stagnant. They reduce chemicals in the oil emulsion to give hydrogen sulphide which is the noxious ‘Rotten Egg' smell given off when the oil is disturbed. They also give off acids which reduce the alkalinity of the emulsion and in certain cases promote corrosion.

Coliform Bacteria:

These are bile tolerant bacteria which pass through the body of animals or man and emerge in the faeces. Whilst they are not necessarily pathogenic there are pathogenic bacteria usually associated with them. These are usually shigella and salmonella. It is easier to detect the Coliform bacteria which are present in greater numbers.

If a significant number - say 10/5 colonies/ml - are regularly found, medical advice should be sought.

The majority of bacteria found in oils are non-pathogenic, but there are occasions when "opportunist" pathogenic bacteria may be present. There are at least three ways in which these can enter the body: -

(a) Ingestion of spray. Spray removal equipment should be used.

(b) Entry through cuts in the skin. These should be protected.

(c) Entry through defatted skin pores.

Paraffin or similar solvents should not be used to wash hands. Barrier creams and proper non-abrasive soaps should be provided.

The possibilities for unrestricted growth of bacteria should be minimised and this can be summed up

(a) Good housekeeping to keep oils clean i.e. pipes, storage and stop water leakages into oil systems

(b) Clean the tanks, pipes, with a steriliser/cleaner before introduction of fresh oil (Aquamarine Stericlean)

(c) Use an oil containing a biocide effective against bacteria, yeasts and fungus (Aquamarine Aquabac)

(d) Identify by testing first stages of bacterial contamination so that the problem may be treated.

Bacterial Contamination in Water Systems:

The Coliform slide may be used to check all water systems including cooling water, ballast and boilers. The count is not high enough to give a low enough count for drinking water systems but will identify a potential risk of system fouling or risk of Legionella disease. Aquamarine is approved for testing for Legionnaires disease. A full RBS/SCT/SRB check is recommended.

NB Full user instructions are found in every kit supplied together with date and sample identification labels and all equipment required for the testing. Aquamarine can supply incubators which are recommended for regular dipslide monitoring.

Aqamarine can offer full advice on treatment of all forms of Bacterial contamination.

What are Microbes?

  1. Microbes in fuel are either bacteria, yeasts or moulds. In the marine industry they are normally the hydrocarbon degrading and corrosive species.
  2. They need water, nutrients, warmth and oxygen (or sometimes lack of oxygen) to grow.
  3. Microbes live in the water phase, but feed off nutrients in the fuel phase.
  4. Microbes dislike agitation, preferring a dormant fuel system.

Test kit

Sources of Microbial Contamination

  1. Imported infested hydrocarbons from refineries, tank farms or delivery barges.
  2. Previous onboard delivery barges.
  3. Sea Water.

On board however there will always be a source of contamination to shipboard cargo fuel from one of the following:

  1. Load port contamination of storage tanks
  2. Load part delivery pipes
  3. Cargo tanks of the vessel
  4. Pump room of the vessel
  5. Sea Water ingress

The latest microbe species have spawned new types of bacteria in fuels, which produces sticky polysaccharide polymers similar to cling film, which clogs filters by trapping particles.

Microbial attach over time will degrade the fuel reducing its calorific value. Waste products such as hydrogen sulphide will cloud point and thermal stability of the fuel will be affected and a stable water haze will be created. Eventually the fuel will fail specification tests for water separation.

Prevention

The first point to note is that low numbers of viable microbes will ALWAYS find their way into a system, if they reproduce slowly they will not accumulate if a large infestation occurs the potential for trouble will be established.

Physical Prevention

Water is the key ingredient to tackle.

  1. assess fuel tank water bottom drainage systems.
  2. Implement a water drainage programme
  3. On a regular basis clean and chemically disinfect fuel systems, purifiers, filters and coalescers.
  4. Isolate service tanks against suspect fuel.
  5. Implement a fuel tank inspection schedule for bio film and corrosion damage.
  6. Eradicate microbial levels on a regular basis.
  7. Monitor fuel suppliers' quality.

Test kit

Decontamination

Microbes do not die naturally they must be killed or removed, all of the following are possible approaches;

  1. Settling: microbes are denser than fuel and will settle at the bottom
  2. Centrifugal: microbes subjected to centrifugal forces will separate out.
  3. Heat: Microbes exposed to heat in excess of 70°C will be killed.

Fuel Biocides

They should be chemically compatible with the fuel, the machinery and the system components. Moderately contaminated fuels can be used after dosing providing the biocide has been circulated fully.

Severely contaminated fuels will have sediment after dosing with biocides. This deposit must be removed physical decontamination to prevent blocked fuel systems.

Identifying Microbial Attack

Routine sampling and microbiological testing is the only effective way to detect and identify if microbes are present and viable.

Ready to use and on board cargo fuel should be tested weekly, water phase samples from storage tanks or engine room tanks should be taken and if infected results are discovered action should be taken. The tests that shall be taken are for bacteria, yeasts and moulds and SRB (anaerobic) bacteria should be taken and action taken if moderate infection levels are detected as shown in the dipslide and SRB boxes as provided by Aquamarine.

 

ADDITIONAL INFORMATION RELATING TO BACTERIA ON BOARD SHIP

Test kit

NB dipslides may be ordered by credit card by visiting www.tektrak.co.uk

 

For more information or help in MBC treatment please call 01684 290077