Understanding Microbial Contamination
Diesel fuel held in long term storage is susceptible to microbial contamination. This contamination is caused by a consortium of bacteria, yeast and fungi that can grow in your diesel fuel storage tanks.
Microbial contamination, often commonly called “the Diesel Bug” can damage tanks, fuel lines, pumps and injectors as well as result in poor fuel economy and excessive emissions. However, the greatest potential for damage to businesses that rely on fuel storage for Standby and Emergency Generators is blocked fuel filters and unexpected engine shutdowns, particularly following a mains power outage.
What causes the onset of microbial contamination?
There are three elements needed to complete the eternal triangle and enable microbial activity to occur and contamination to build.
Most, if not all microorganisms arrive in a tank as a result of travelling down the fuel supply chain from tank to tank. The microorganisms (bugs) in the fuel use the fuel itself along with the fuels additives as a food source. The water, once present in the tank provides life. In any tank once the eternal triangle is complete microbial growth (biomass) is inevitable.
Gensets are typically only test run for 30 minutes a month, which means that the amount of contamination drawn through into the primary filter sight bowl can be so small that the contamination often remains unseen. The problems arise when the engine is called upon to run in earnest for many hours. It is during this extended run that you will be drawing through much more contamination along with the fuel. It’s at this critical stage that filters can become blocked and may result in a shutdown
H20 and the problems it causes:
When water is allowed to build up in fuel storage tanks it provides an ideal environment for microbial growth to occur. Sample on the right contains rusty water with a small amount of fuel sitting on top.
While water ingress and heavy microbial infections are not uncommon they only usually occur as a result of inaction or lack of preventative measures. If any contamination, however slight, can be seen in primary filter sight glasses or water collection bowls then it is usually too late as the infection will have already taken hold in the bottom of the tank. It only takes very small amounts of water (droplets in fact) to kick-start microbial activity. It is imperative that any water is kept at bay. In Standby fuel storage applications water can ingress into a tank in a number of ways – these being condensation, leaking seals or from a contaminated fuel supply source.
Condensation is caused by tanks breathing in moist air and allowing it to condense on the walls. It can also occur when there is a temperature differential between the inside and outside of a tank e.g. at night or after an engine has been running for long periods of time and pushing back hot fuel via the fuel return line into the tank. The more vacant wall space available, the more water can and will condense and build up in the tank.
Rain water, flooding and/or wash down water can enter tanks via leaking fuel fill points, broken pipework, old seals or even poorly located tank breathers. Underground tanks are particularly vulnerable for this type of water ingress.
Water can also come with the fuel supplied. While it is hard to imagine your fuel supplier is also susceptible to exactly the same problems. While their procedures and maintenance are usually of a very high standard from time to time issues do occur and contamination can be transferred unknowingly along with the fuel.
Water that enters or builds up in the fuel can drop out of phase, run down the walls and eventually build up in the bottom of the tank as ‘Free Water’. While some Free Water may get picked up and separated out in the primary fuel filter (if there is one) it is not normally the case as fuel pickups are generally well above the tank floor. This unfortunately means the water can sit in the bottom of a tank for a very long time undetected, and thus provide the perfect environment for microbes to grow and build biomass/sludge.
Aside from aiding microbes water also causes corrosive (rust) damage to tank surfaces and fuel systems. Heavy rust scaling can often be found in flat bottom tanks in particular.
Best Practice Procedures:
There are a number of Best Practice Procedures that should be utilised in a good Fuel Management Programme to reduce the risk of water ingress and microbial growth.
Where possible all tanks should be kept above 80% full at all times. Top up’s should be done regularly. This prevents condensation building up on the tank walls.
Utilising drain valves where possible to regularly drain off small amounts of fuel and any water from the bottom of tank or from dedicated low points if the tank has them.
Inspect seals, pipework, man-ways (inspection hatches) and breathers regularly for any signs of damage or deterioration. Replace or repair if required.
Only take fuel from reputable sources or suppliers. When large volumes of fuel are being supplied ask for a sample before accepting the fuel.
Fit moisture traps to the breathers on the tank. These filter the movement of air and prevent moisture from being drawn down into the tank.
Sample and test the fuel from the bottom of the tank on a regular schedule basis.
Look at installing an automated fuel polishing system.
Instigate a Fuel Management Programme as a part of your PPM.