Microbes need a habitable temperature, a food source and water, all of which can be found in many fuel tanks. In heavy residual fuels the temperatures involved in storage, handling and treatment are often enough to kill microbes. However, in marine gas oil and low viscosity fuel oils, the conditions can be much more suitable for growth.
Depending on the type of microbes present, the problems can be different but some can cause corrosive damage to storage tanks if left untreated whilst others may produce a thick slime which could block fuel filters and may have to be manually removed from tanks affected.
Read more: https://www.manifoldtimes.com/news/fobas-microbial-contamination-and-monitoring-in-marine-fuels-and-bunker-storage-tanks/