Sampling and Analysis of Ballast Water in the Context of PSC

The underlying principle of Port State Control procedures is that sampling and analysis of ballast water treated onboard a vessel will not be more stringent than what is currently required for the scope of type approval. Port State Control procedures will be globally implemented when the International Convention on Ballast Water Management becomes effective. Sampling and analysis of ballast water is a complex issue while ships’ inspections are also a matter of concern. Thus IMO recently issued revised guidelines on ballast water sampling for trial use as BWM.2/Circ.42.

2013.09.25 - Sampling and Analysis of Ballast Water in the Context of PSC

The Guidelines attempt to provide answers to a number of sensible questions:

  • What would happen to a vessel boarded by Port State Control Officers, if the initial indicative analysis reveals that the number of living organisms in discharged ballast water is well above the D2 standard limits?
  • Is the measurement of salinity sufficient enough to demonstrate that exchange of ballast water in the open sea has taken place, as D1 standard requires?
  • Does a careful visual analysis underestimate the number of organisms greater than 50 μm, when used as an immediate inspection method?
  • How much time does a culture of bacteria requires for testing purposes and what volume of treated ballast water must be sampled?
  • How practical is to sample a very large volume of ballast water and analyze it for very low concentrations of organisms?

To verify compliance with the D2 discharge standard, two tiers of analysis are to be used: an Indicative and a Detailed Analysis. This reminds us the two stages of a routine inspection of ships. First, the examination of the documents and certificates combined with a deck or engine room walk of Port State Control Officers. Secondly, an expanded inspection in case that clear grounds exist that the vessel does not comply with the international standards and regulations.

The Indicative Analysis is a compliance test that is relatively a quick, indirect or direct measurement of a representative sample of ballast water. It might use a naked eye counting, stereo microscopy, photometry or measurement of certain chemical substances depending on the size of targeted organisms.

The absence of an international standard for ballast water analysis perplexes the things, but a very careful approach will safeguard the credibility of the vessel inspected and the performance of the ballast water treatment system.  Visual analysis might be worth applying in counting viable organisms bigger than 1,000 μm while, stereoscopy requires the transfer of samples to laboratory manned by experienced personnel.

The Detailed Analysis is a compliance test that is likely to be more complex than the indicative analysis involving a direct measurement of a representative sample aimed at determining the population of viable organisms in ballast water. Not only the measurement should be directly comparable with the limits of the D2 standard, but it must be also of adequate quality and quantity to provide a precise measurement of the concentration of organisms with an equally sufficient detection limit.

As for organisms bigger than 50 μm, simple microscopic examination is recommended for compliance monitoring due to the simplicity, the relative accuracy and the low cost of the method. Other modern methods such as flow cytometry are considered to be complex, expensive, requiring very small sample sizes to be formed following better concentration of ballast water collected.

As recommended in the IMO G2 Guidelines for Sampling of Ballast Water, the samples must be taken from the discharge line, as near to the point of discharge as practicable, during the actual discharge of ballast water.  Grab sampling from a ballast water tank is limited only for the purpose of an indicative analysis due to the high sample error.

The existing sampling protocols can be divided into two distinct categories: a) taking a specific number of equal volumes of samples over a period and b) continuous sampling based on flow integration over a period that can be achieved by either taking a small amount of sample throughout the entire duration of the discharge or taking multiple samples over certain periods (i.e. every 10 minutes, etc) repeatedly throughout the discharge.

It is obvious that in the case of detailed analysis, the time between sampling and the end of analysis, might be considerable. Port State Control must be expeditious, should not interfere with the safe operation of the vessel and must be conducted in a responsible manner against the seafarers working onboard.

The abovementioned guidelines will go through a trial period that will allow the assessment of the proposed approach and methods. As it happens with all IMO Conventions, the operational requirements of the Ballast Water Convention would constitute a new field of ships’ inspections. Port State Control is a right but also an obligation of coastal states to exercise upon foreign-flagged vessels. The best way for a ship operator to ensure that his vessels will keep performing well during inspections without being charged with deficiencies or detained, is to have a reliable treatment system fitted onboard.

Source: Safety4SeaERMA FIRST

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