Ballast water treatment systems available in the market today are based on a range of diverse technologies. Often, they are designed to maximise treatment efficiency by combining two systems such as filtration as pre-treatment and ultraviolet irradiation or electro-chlorination to kill or sterilise smaller organisms.
However, as Coldharbour Marine CEO Andrew Marshall points out, no single technology is 100% effective leaving bulk carriers, for example, open to the risk of marine organism re-growth during lengthy ballast hauls. Neither the IMO nor the US Coast Guard type approval test procedures address this issue effectively, Marshall says. The IMO tests ballast water samples after only five days, and the US Coast Guard after just one. Meanwhile, a ballast haul between China and Brazil typically takes about 42 days.
Marshall believes the operators of bulk carriers, particularly large vessels deployed on long routes, therefore face formidable challenges, which makes choosing the best system a complex matter. Treating ballast water on intake is unlikely to prove a comprehensive process because surviving marine organisms can thrive and multiply on a lengthy ballast haul. In-voyage treatment, such as that offered by Coldharbour for large bulk carriers, tankers and gas carriers is a more effective way of ensuring ballast water discharge standard compliance, he says.
Other systems have various drawbacks, Marshall explains. Bulk carriers often handle cargo at estuarial or coastal terminals where waters contain high levels of total suspended solids (TSS). The ships are designed to load and discharge as quickly as possible, requiring large volumes of ballast water to be handled during cargo-handling operations.
This means that as bulkers discharge cargo, they take on large volumes of ballast water in a short time. In waters with high levels of TSS, this places a huge load on filters which, even with frequent back-flushing, may block and cause delay. Even if the filtration system is not actually blocked, it may work at reduced efficiency, thereby failing to keep up with required pumping rates. Delays are highly likely.
If the treatment system is based on filtration followed by ultraviolet irradiation, the filtered ballast water is then treated to kill smaller organisms that have not been trapped by the typically 40-micron filters. But ultraviolet treatment is only partially effective in waters with high TSS levels, so it is quite possible that ballast water treated by such systems still contains large numbers of marine organisms which then thrive on a ballast haul.
Electro-chlorination systems are also used with filters providing pre-treatment. The filtration issues are the same but electro-chlorination technology is typically based on very weak dilutions of sodium hypochlorite (NaOCl), commonly known as bleach and recommended in ballast water treatment at concentrations not greater than ten parts per million (ppm) to ensure no damage to coatings.
Classification society Lloyd’s Register recommends an even lower content not exceeding five ppm. By way of comparison, Unilever’s Domestos, a brand of household bleach, contains 100,000 parts per million.
Electro-chlorination is not effective in waters of low salinity. This is because treatment systems based on this technology require the salt present in sea water as a key component to produce the biocide sodium hypochlorite. In waters of low salinity, it may be necessary to use large volumes of sea water to procure sufficient volumes of salt for the biocide. This can require high levels of power which may or may not be available on board a bulk carrier during cargo operations.
Once again, the treatment technology is unlikely to have captured or sterilised all of the marine organisms present in the ballast water. Those that remain may well multiply during the ballast haul, once again risking that the ballast water fails to meet the required discharge standard at the next load port.
Coldharbour Marine has come up with its own bespoke system, designed specifically for bulk carriers, particularly large ones. It is a version of the Coldharbour inert-gas based GLDTM treatment plant, and it was unveiled recently at Kormarine. The system allows for the unique operating requirements of bulkers, including treating the wing tanks and heavy weather cargo hold ballast, plus the current practice of discharging wing tank ballast directly overboard. Marshall says: “our aim was to create a system that allowed ship owners to operate their vessels after BWTS fitment in the same way that they did before.”
In the Coldharbour system, ballast water is treated during part of the ballast voyage, ensuring that the risks relating to a failure to meet discharge standards at the next load port disappear. These risks, Marshall points out, may not have been full appreciated as yet. They include delays on the berth, financial penalties, possible deviation, additional fuel bills, off-hire and worst of all, possible long-term reputational damage.