Ships have carried ballast since the beginning of maritime trade - up to the turn of the 20th century as rock, sand and even low value manufactured goods (such as iron lace) sold in the new colonies to make space for the valuable wool and grain cargoes back to the European motherlands.
The development of world trade on an industrial scale in the 20th century lead to some undesirable environmental consequences. As ships sizes grew they needed to carry sea water ballast to make them controllable and which in turn gave invasive species the opportunity to 'emigrate'.
Vonks Plankton
Well known examples have been the Zebra Mussels in the US/Canadian Great Lakes and Asian dinoflagellate algae into Tasmania from wood chip carriers. Interim controls have focused on either quarantining ballast water (hard on a cargo ship which has to deballast in order to load cargo) or mid-ocean ballast water exchange. Ballast water exchange is done to flush out the highly populated coastal water with lowly populated oceanic water, especially around the equator.
Ballast water exchange has its own dangers and impacts. Flushing the tanks (flow through) method requires 300% of the tanks' volume to be overflowed and can put pressure stress on the hull structure. Discharging and reloading the ballast can have intended consequence on the vessel's stability, as the crew of the PCTC 'Cougar Ace' discovered when she became unstable and took an 'angle of loll' when the double bottom tanks were being 'exchanged'. The salvage cost the life of one of the Salvors and the 'writing off' of a complete cargo of Mazda cars. The cars were undamaged but Mazda couldn't take the chance of subsequent warranty claims and so the whole cargo of 5,214 vehicles went through the crusher!
Cougar Ace adopting an angle of loll of Alaska
Recognising the limitations, risks and cost (in time and fuel) to exchange ballast, the IMO requires new vessels to treat ballast water - shorthand for kill the little wriggling zoo plankton, dinoflagellates and organisms before they are discharged into an unsuspecting environment.
The three basic treatments rely on an additive bio-cide (small ships), ultra-violet light (medium sized) or, for large scale industrial carnage, electro-chlorination.
The AM's fleet will use electro-chlorination - the reduction of chlorine gas from sea water (sodium chloride, or salt in solution) and then the re-injection of the chlorine gas back into the ballast water stream. When you need to treat ballast water at up to 6,000 tonnes an hour, bio-cide or U/V just don't cut it. A big bulkie will carry between 90,000 and 110,000 of sea water ballast on a her return leg.
In-line Electro-Chlorination Unit
One emerging problem, which appears to be getting traction with Manufacturers and Class, is that the electro-chlorination process may also be chemically liberating hydrogen, which is in turn being detected in the under-deck structure of ballast tanks. If you watched the massive explosion lifting the top off the Fukushima Nuclear Reactor on TV, that was hydrogen! The AM's site team will be testing for hydrogen gas in the upcoming sea trials for PN65, as accumulation represents an unacceptable in-service risk which if proven will require additional ballast tank ventilators.
The Antipodean Mariner
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