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.
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.