Growth of microorganisms in petroleum products has been recorded since 1895, causing fouling, malfunction and corrosion in storage tanks, equipment, pipelines, filters and engines.

The microbes feed on the fuel which enables them to multiply and form colonies. Microbial contamination is most commonly seen as sludge that forms in the bottom of storage tanks and accumulates on filters.

This sludge affects engine operations in several ways:
• it blocks filters
• causes poor fuel combustion leading to fuel inefficiencies
• contributes to poor emissions (seen as black exhaust smoke)
• causes incorrect fuel gauge storage readings

The life cycles of bacteria of a variety of types, both aerobic and anaerobic, produce corrosive acids and sticky sugars that further impinge on engine and system functions:
• organic sulphurous and sulphuric acids corrode fuel tanks,
pipelines, rubber seals, ‘O’ rings and hoses
• sugars caramelise in and on fuel injectors which adversely
affects the fuel spray pattern and can ‘glue’ together injector
parts to cause failure of the injectors

Microbes
The presence of microbial contamination has generally been accepted and accounted for in component design and service schedules with sufficient success for the problems to be of little consequence to fuel distributors and users.



However, it is worth revisiting fundamental properties of petroleum diesel: it is inherently unstable, deteriorates over time and it is hygroscopic. It is the presence of water (along with the darkness and warmth of a fuel tank) that provides microbes with the conditions they need to live and proliferate - and it is the microbes that drive the fuel’s deterioration