After a contaminated fuel system has been treated with an effective biocide, the microbes present will die. The microbes dead bodies will persist in the fuel system and fall off any surfaces where they have been growing into free suspension in the fuel. Therefore it is important that post biocide treatment , settling sludge should be removed from the system. For ships it is therefore very important to carry sufficient filters to enable filter changes should it be necessary until all the sludge is removed from the system.
Where a large amount of sludge is known to be present in systems, it is advisable to remove this before treatment as biocides are unlikely to penetrate sludge layers.