Isolated aft-peak tanks on tankers and bulkers, limited ballasting requirements on semi-submersibles and infrequently ballasting workboats can be addressed by a compact, low-cost BWTS
The implementation of the Ballast Water Management Convention initially focused on ballast water treatment systems (BWTS) capable of treating an entire ship’s ballast water. In cases of very large crude carriers, tankers, and bulkers this means BWTS capable of very high capacity rates and volumes to keep pace with cargo operations. Such systems are complex by necessity, requiring significant power and support systems.
More recently, attention has turned to special, smaller capacity situations; often-ignored, aft-peak ballast tanks on tankers and bulkers, limited ballasting requirements on semi-submersibles and infrequently ballasting workboats.
Most of the ballast water on tankers is in the gas hazardous cargo body ballast water tanks. This requires a high-capacity BWTS approved for those hazardous gases. In addition, tankers have a relatively small volume aft-peak ballast water tank that is in a safe area. By regulation, the aft-peak ballast water cannot mix with the gas hazardous cargo body ballast water.
In the case of bulkers, since the aft-peak tank is located far away from the cargo body, it is usually serviced by a separate piping system, requiring a flow rate that is typically one-tenth of the cargo body.
The result for tankers and bulkers is typically the installation of a second BWTS that is a smaller version of the same ballast treatment technology as the cargo body. While highly capable, these systems have features that are overly complex and not needed when treating only the aft-peak tank.
Kevin Reynolds, managing director of specialty BWTS manufacturer oneTank, LLC, says another option is to treat the vessel’s aft-peak tank with a significantly smaller, simpler, and lower-cost solution as an add-on with the cargo body treatment plant. For such ‘corner cases’, oneTank has developed a low-cost, compact, easy-to-install system that is IMO BWMS certified and US Coast Guard type approved and that treats aft-peak tanks that are not easily accessible to the ship’s primary BWTS.
“oneTank treats tanks up to 4,000 m3 in volume,” explains Mr Reynolds. “Treatment is achieved by applying and mixing bulk chemicals in-tank, with in-tank neutralisation prior to discharge. It has no filters to clog or clean, no ultra-violet bulbs and no electrolytic generators.”
Adds Mr Reynolds: “Focusing on treating just one tank at a time resulted in a greatly simplified, extremely small, and low-cost system. oneTank was specifically designed to treat aft-peak tanks on tankers and bulkers. It continues to find similar corner cases where it can be effectively applied.”
BWTS for semi-submersibles and workboats
Such cases include semi-submersibles that spend months to years in a same location, where ballasting operations are critical to mission and safety. However, same-location ballasting does not require treatment. It is only when these vessels transit to other locations that ballast water treatment is required. Importantly, transit draught requires filling only a few ballast water tanks and it is only that transit ballast water that needs to be treated. “oneTank can address this corner case by being fitted in only those transit draught tanks,” says Mr Reynolds, “avoiding multiple large complex treatment plants. As a bulk chemical system, there are no complex components to corrode and fail during extended idle periods.”
Many workboats have been successful in eliminating ballast water operations all together through locked-in ballast or operational measures. However, others can be caught in-between – they have eliminated most ballast operations, but on occasion they need to treat their ballast water.
“oneTank has introduced the ‘treatment tank’ approach for these cases,” says Mr Reynolds. “The vessel outfits one pair of ballast water tanks with oneTank’s in-tank treatment system. The workboat maintains normal operations, even taking up ballast water as needed. On the occasion it needs to discharge, that ballast water is transferred to the treatment tanks for treatment and discharge. This is a compliance approach that is low cost and takes up very little space in crowded machinery spaces.”