▸ Biologicals (from microbial decomposition). Micro-organisms
are usually present in the bilge. Nutritional limiting factors and
ecological competition usually prevent problematic septic conditions.
Development of problematic biological conditions can usually be traced
to one of the following conditions: Introduction of anaerobic bacteria
as exists in sewage and sometimes oily sludge/sludge water or an introduction
of an excess of nutrients such as soaps and detergents can alter the
biological balance leading to a dominance of anaerobic bacteria. This
sort of bacteria is often characterized by a filamentous deposition
on filters and other surfaces and has a sulphurous or malodorous smell.
Filamentous bacteria will preferentially accumulate in the high flow/sheening
areas and will cause development of higher pressures or reduction
of flow. These particles can be detected by oil content meters.
▸ Rouge (Iron Oxide Compounds). A major source of rouge
is from microbial decomposition; bacteria need iron to grow. If bacteria
growth is unchecked, large quantities of iron oxide compounds can
be produced. A major source of iron and iron oxide compounds on ship
is from ageing machinery, the hull and fittings. These particles can
also be detected by older 60(33) oil content meters and, when in large
quantities, some newer 107(49) oil content meters.
▸
Soot. Carbon-based soot particles accumulate in engine-rooms from
normal operations. These carbon particles are highly absorbent. Exhaust
leaks and cleaning of engine-room machinery are the largest source
of soot. Bilge treatment system failure often follows heavy engine-room
cleaning when soot particles are allowed to enter the bilge. (Also,
see annex 3 – Emulsions.) Soot particles can contribute to the
creation of oily emulsions and can be detected by an OCM.