Liquid fuel tanks and other storage systems are susceptible to microbial contamination. As FuelStat explains, when the conditions are right, bacteria (aerobic and anaerobic) will thrive in these places, leading to microbiological contamination of fuels. Middle distillate fuels such as jet fuel, diesel, gas oil, and heating oils are the most susceptible to microbial contamination.

This article will help you know about microbial contamination, where it comes from, the effects, how to test and how to rid fuel from contamination.

The Main Causes of Microbial Contamination in Fuel

Generally, when fuel leaves the refinery process, it is sterile. However, during storage, distribution and supply chain, the fuel becomes contaminated with particulates, microbial growth and water.

The main causes of fuel contamination are:

Water

Accumulation of water in fuel storage tanks and systems is inevitable. Even though fuel has low water content when leaving the refinery, multiple opportunities can lead to water finding its way into the fuel. Water can find its way into the fuel through rainwater penetration, condensation of moist air that enters the tanks and storage systems through the vents or adsorption from the air.

The presence of water in fuel is a cause of concern because it encourages microbial growth, thereby increasing the chances of microbial contamination. Water also accelerates the oxidation and breakdown of fuel, providing the microbes with the food they need to multiply. Water in fuel also accelerates the corrosion of tanks.

Diesel Bug and Microbes

Bacteria, yeasts and fungi are naturally found in soil from where they are carried by air. During storage, these microbes find their way into fuel storage systems. Even though they are harmless in their natural state, if the conditions in the fuel storage systems are perfect, they start to germinate, leading to microbial contamination of the fuel.

The fungal and bacterial microbes need both water and diesel to thrive. Fuel acts as a primary food source for bacteria and fungi, while the water provides the perfect environment for microbial growth. According to IATA (International Air Transport Association), the predominant microbiological species that cause microbial contamination of jet fuel and is also very common in diesel fuel is Hormoconis resinae (H.res).

Fatty Acid Methyl Esters (FAME)

Even though FAME, mainly found in biodiesel, offers several benefits over fossil fuels, its presence in jet fuel and diesel increases the chances of microbial contamination. FAME is hygroscopic – the methyl esters absorb moisture from the air. FAME absorbs significantly more water from the air than petroleum-derived diesel.

The introduction of FAME into diesel and jet fuel and reducing Sulphur content in fuels increases the risks of microbial contamination.

Effects of Microbial Contamination of Fuel

The primary consequence of microbial contamination of fuel is fuel degradation. Contaminated fuel has reduced combustion efficiency, elevated pour point and poor detergency.

Microbial contamination also leads to operational issues by running assets out of operation. The contamination leads to blocked injectors and filters, fuel probe malfunctions and contaminated water scavenge systems.

Metal structures used to store fuel get corroded from microbial infections – Microbially Influenced Corrosion (MIC). Corrosion and blockage of fuel systems can lead to a complete fuel system failure which can have profound safety implications.

How to Test Fuel for Microbial Contamination

To test fuel for microbial contamination, draw fuel samples from various points into clear and clean containers. Head to a well-lit room and look out for dirt floating in the fuel or at the bottom of the container. The presence of dirt means the fuel is contaminated with rust, dirt or algae. A murky appearance is an indication that the fuel is contaminated with water. Also, look out for separation. The layers in the fuel sample can be due to mixed fuel or water.

How to Get Rid of Fuel Contamination

Prevention is the best and most effective way to ensure fuel is free from contamination. The prevention methods essentially involve keeping fuel tanks clean. Here are the steps to follow to avoid the inconvenience and expensive costs of fuel contamination:

• Conduct regular fuel tests at least twice a year. This helps minimise microbial fuel contamination problems by detecting microbial growth early on.
• Buy fuel from a reputable supplier. Poor quality fuel has high levels of FAME and is poorly refined and thus has high water content.
• Fuel System Maintenance. Regularly clean fuel storage tanks with diesel fuel biocides to kill microbes, insulate fuel tanks to stabilise temperatures, regularly remove sludge at the bottom of the tanks and routinely discharge water bottoms.
• Rotate your fuel usage to avoid keeping fuel in one tank for long periods.
• Top up your fuel tanks to minimise air spaces, thus reducing chances of water condensation forming.