Biocides: Best practice & use when tank cleaning

Readers will be well aware of microbial growth in fuel tanks; the sludges and slimes found on tank bottoms and walls that often block filters or corrode tanks, but awareness of treatment options is often less well known. The subject is complicated by differing advice from different bodies as well as procedures, fuel test methods and specifications changing regularly.

New PEIMF member, Fuelcare, have vast experience in this field and share their knowledge with us here.

Fuel microbiology sits at the intersection of engineering, chemistry and biology. Industry knowledge varies, and specialists such as ourselves have been providing advice for over thirty years. The issue affects any hydrocarbon in storage where, under optimal conditions, microbes can replicate exponentially, leading to rapid growth of sludges and slimes on tank bottoms and walls which lead to filter blinding, fuel starvation as well as microbial induced corrosion (M.I.C.).

Snake oil?

Whilst sampling & testing are straightforward, the use of biocides can be unclear. Over many years, we have heard industry professionals decry their use completely; often described as ‘snake oil’. Others believe they cure a huge range of issues and are used too frequently, but most industry leaders maintain biocide procedures.

The simple equation for microbial growth is;

‘No Water’ = ‘No Bug’

If water can be completely removed from the fuel supply chain storage, microbes have no medium on which to live and breed. However, even the best fuel housekeeping procedures and storage systems cannot completely prevent the buildup of water.

If supply chain partners cannot prevent the growth of microbes in their fuel, how can end users maintain their fuel storage if it is potentially being contaminated every fuel delivery? This is where fuel biocides come in; as a curative or preventative
maintenance solution.

What are fuel biocides?

Fuel biocides are chemical fuel additives that are designed with chemical mechanisms to partition between the fuel and water phases of a fuel tank (and microbes may reside in both parts of the tank). Good biocides are often described as ‘broad spectrum’ i.e. they eradicate as many species of microbes as possible and neutralise a tank of live, microbial growth in 6-7 hours.

Where end users have discovered microbial growth, biocides can be used in less severe cases as a complete solution. However, their use must not replace tank cleaning, because other contaminants may continue to reside in fuel storage that requires physical removal. Conversely, in some instances, microbial growth is so severe that biocides may not penetrate a large buildup of sludges without physical agitation.

On-going maintenance

In all cases, biocides should be used as part of an ongoing maintenance regime: with bottom sampling, testing and tank cleaning. However, where microbial growth has been detected and biocides then used, it is important to remember that the biocide does not remove the dead matter, the microbial biomass, even though ‘dead’, will continue to reside in the tank without some form of physical interaction. In less severe or moderate cases, a biocide can be employed quickly and cost effectively to solve the contamination issue and, in most cases, can be caught by bulk filtration after being broken up.

Finally, when tank cleaning has been employed, biocides can help break up the contaminants prior to man entry, reducing the time spent within a dangerous environment, but also used when tank cleaning has been completed. Tank storage systems are only as clean as the fuel delivered. If your tanks have been cleaned at great expense, using a biocide with the first refill, or thereafter on a preventative basis, can prevent the reoccurrence of microbial issues.

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