This Appendix provides the basic theory of and describes
the physical and chemical analytical techniques used to diagnose the
presence of contaminants in the annexes.
A. Visual inspection – Detection of
non-emulsified oil
- Visual inspection can be very informative and is one of the best
ways to evaluate the presence of oil (when there is reason to believe
that there is a problem with the OCM). Unlike most of the other constituents
of bilge water, there are no easy, cut-and-dry chemical or direct
instrumental methods for this purpose. Oil residues are very characteristic
and will leave a film on glass surfaces. Inspection of a sample often
times is adequate to determine the presence of oil, as it will generally
be floating on the water and will leave an oily residue which can
be detected by rubbing a finger against the glass. This method is
very dependable for the detection of non-emulsified oil.
- The standard chemical analysis for the presence of oil and grease
is United States Environmental Protection Agency PA method 1664, hexane-extraction.
This is a very dependable method but would be difficult and possibly
dangerous to do on board ship. Samples can be taken and analysed at
a shoreside facility using this method for purposes of confirming
OCM readings. This is a useful test when there is reason to believe
that there is a problem with the OCM. (The United States Coast Guard
uses gas chromatography.)
B. Acid split test – Detection of
emulsified oil
If there is no visible layer of oil on top of the sample and
the sample is turbid (cloudy), it is possible that the turbidity is
caused by emulsified oil. The addition of three drops of concentrated
sulphuric acid to a 50 ml bilge water sample in a tall glass container
will cause any emulsified oil to break out of emulsion and form a
clearly visible layer of oil on top of the sample after approximately
15 minutes.
C. Evaporative residue pH test (ERT pH test) (also
known as non-volatile residue (NVR) test) – Detection
of detergents and non-volatile (i.e. high-boiling temperature) alkaline
solvents
If the acid split fails to clear the turbidity, the presence
of detergents and/or some solvents and/or oils may be the cause of
the turbidity or cloudiness. Note that most detergents and solvents
used in the engine-room are alkaline solvents. (Some acidic solvents
are used in electronics and metal cleaning.) Detergents and some solvents
are alkaline and non-volatile. To determine the presence of detergents,
take a 50 ml bilge water sample in a beaker or evaporating dish and
evaporate until all the water is gone. If the water is not clean,
a non-volatile residue will remain. Moisten a piece of pH paper with
water and swipe the residue. If the pH paper turns blue, indicating
alkalinity, then this residue is most likely detergent or other non-volatile
alkaline materials such as caustics. Note that the presence of some
solvents and detergents in the absence of oil, alone and together,
form micro- and mini- emulsions in water. These contaminants, alone
or together, may or may not cause turbidity, depending on the exact
composition and temperature of the processed bilge water. These non-oil
emulsions can be detected by the OCM even when no visible turbidity
exists. (Visible to the naked eye; visible is a relative term when
instrumentation is involved.) There are limitations of the ERT pH
test in detecting volatile solvents and solvent/detergent mixtures. Detection of volatile and non-alkaline solvents is perhaps the most
difficult to address with quick and easy analysis. Volatile
solvents will NOT be detected by the evaporative reside test. The
most reliable method is the process of elimination and a basic understanding
of why the solvents are so hard to detect. These solvents are either
soluble (e.g., alcohol used for cleaning) or insoluble (e.g., diesel
oil used for cleaning) in water. In the absence of oil, water-soluble
solvents will not cause turbidity in water and will not be detected
by typical oil content meters. (Ultraviolet (UV) and infra-red (IR)
type oil content meters will detect the presence of solvents.) Water
insoluble solvents can sometimes cause turbidity, especially in the
presence of detergents. These can be detected by oil content meters
and read as oil. When mixed with oil both soluble and insoluble solvents
will cause oils to emulsify, causing turbidity and an indication of
oil at the oil content meter. Additionally, other contaminants and
physical processes can also cause emulsions and turbidity. Consulting
with the crew to determine if the bilge system is contaminated with
alkaline solvents is the best next step if solvent contamination is
suspected. If solvent contamination is highly suspected, samples should
be taken and sent for laboratory analysis. (Note that sometimes a
coffee filter can be used to detect soot, but the soot particles are
often so small that they tend to clog these filters.)
D. Combined evaporative residue test (ERT) and
particle filtration – Detection of soot
In general, if soot is present in the bilge, its presence and
cause are usually known by the crew. Soot presence is usually the
result of machinery space equipment cleaning. In order to physically
identify the presence of soot, one can inspect the residue from an
ERT. Soot residues are very characteristic and are easy to detect
and recognize. When dry-soot residues can be detected by visual inspection
and physical examination; soot residue is black. It is also possible
to filter a sample using 5-micron filter paper and inspect the residue
on the paper. Again, soot is very characteristic; black residue on
the filter paper, which has been confirmed not to be iron oxide per
a citric acid test, can safely be assumed to be soot. Because of the
difficulty in passing bilge water through a 5-micron filter under
shipboard conditions, this should be done in a shoreside laboratory.
E. Citric acid test – Detection of
turbidity-causing iron compounds (rouge or rust) particles
Add a pinch of citric acid (approximately 0.2 to 0.5 grams)
to a 50 ml bilge water sample. If the discolouration or turbidity-causing
agent is reddish there will be an outgassing (effervescence) and a
reduction or elimination of the colour within 5 minutes. Outgassing
and colour elimination are a positive indication of iron oxide compounds.
High-iron oxide compound concentrations are usually indicative of
unusual discharges to or in the bilge from cleaning operations or
from intermittent operation of the OWS. These iron-oxide compounds
are from inorganic sources and are often found in older and/or poorly
maintained machinery spaces. These particles can be detected by an
oil content meter and read as oil.
F. Citric acid test – detection of
products of bacterial and microbial decomposition (from sewage and
growth of life forms in the bilge and piping)
Addition of citric acid to a sample will result in turbidity-causing
microbial products of bacterial and microbial decomposition to precipitate
(come out of solution and sink to the bottom) without outgassing and
an improvement in clarity of the sample. Addition of citric acid in
rouge samples will result in no visible precipitation and only outgassing.
Cases of high rouge loading are usually indicative of biological contamination,
unusual discharges to or in the bilge from cleaning operations or
from intermittent operation of an OWS. (Life forms can grow in piping
and tanks that are not operated regularly.) These particles can be
detected by an oil content meter and read as oil.
G. Colour
Colour is usually due to one of the above factors. If colour
remains after citric acid and acid split analyses, then the cause
of the colour is most likely a dissolved compound as opposed to a
suspended material. Colour, in and of itself, resulting from a dissolved
compound, should not be detected by light-scattering/turbidity-type
oil content meters. The identity of the compound is usually most easily
determined by backtracking, but may require laboratory analysis.