In-depth | OPINION THEME FEATURE On the vapour trail
JOWA AB’s sister company warns shipowners of the potential dangers from chemicals used in Ballast Water Treatment Systems (BWTS) and the need for better tank level gauging, write captain Michael Lloyd, MNM, Mines Rescue Marine and Michael Haraldsson, JOWA USA
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any methods of BWT now exist to choose from and more are likely to emerge
in the coming years. The common thread in most of these systems is their requirement of expensive equipment and fitting as well as the space for the equipment. Moreover, questions still remain regarding their effectiveness and impact on operations. Today’s
treatment methods use a
variety of substances such as chemical/ ozone, UV and magnetic solutions and inert gas and nitrogen. It is important to note that the reactions between biocides and sea water that could produce harmful by-products have not been extensively studied. More importantly, there is definite concern now being expressed regarding the release of gases in enclosed and confined spaces, by these agents, especially the oxidising agents of ozone and chlorine. One of the dangers of using chemical
solutions is that many ship operators today flood ballast tanks when filling and consider the tank “full” when the ballast water is coming out if the vent pipe. If BWT solutions require or produce
chemicals you can’t flood the ballast tank or floodable cargo hold as this water is classified as poisonous. What will Port Authorities say if a vessel using one of these systems overflows the ballast tanks with the water draining into the port and it has not been neutralised? This then raises the supplementary
question; should owners or shipyards installing this type of ballast water management technology consider not only a standard level gauging system, but also an overfill alarm in ballast tanks as required in cargo tanks today? As all bulk carriers are required by IMO
to have a water ingress alarm in the holds, if a level gauging system was fitted this would
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show the water level in the coaming area and thus would prevent the overflow of potentially poisonous water. If the water ingress alarm system had a
continuous level sensor that measured up to the coaming area, it would be easy to add an additional high level alarm. Ideally a fixed level gauging system that can be maintained from the tank top should be selected, as this would eliminate the need to enter the tank. Chlorine for ballast water treatment is
generated on the ship, from seawater. It is commonly used to treat drinking water and has been used for such treatment for many years at sea, but recent studies suggest that it may not be as safe to humans as once thought. There is also a possibility that chlorine may react with seawater to form toxic chemicals. Te gas combines with nearly all elements
and it is a respiratory irritant to the mucous membranes and lungs and causes cancer. Chlorinated liquids burn the skin and many fabrics. As little as 3.5ppm can be detected as an odour and 1000ppm is likely to be fatal aſter a few breaths. Chlorine can be detected by its odour
below the permissible limit; however, because of olfactory fatigue odour may not always provide adequate warning of the harmful concentrations of this substance. Most chlorination systems apply a dose in
the region of 2mg/l residual chlorine, which has proven to be effective. Unfortunately, some ballast water
solutions use sodium hypochlorite with a concentration of up to 10ppm, which can leave a potentially dangerous gas residue in the tanks aſter the water is pumped out. Not only that, but the water pumped out with this level of chemical can be harmful to sea life in the local area. Tis contamination can also occur when a ballast tank or ballast hold is overflowed. Using a ballast pump that can pump 2,000tonnes per hour, the overflow rate will be over 33,000litres per minute.
Chlorine exposure rates:
The recommended exposure rates for chlorine gas are: TIME-WEIGHTED AVERAGE (TLV- TWA): 0.5ppm - Carcinogenicity Designation A4 SHORT-TERM EXPOSURE LIMIT (TLV- STEL): 1ppm - Carcinogenicity Designation A4
The Naval Architect September 2012 According to the International
Convention for the Control and Management of Ships’ Ballast Water and Sediments,
regulation D2, vessels are
prohibited from pumping out ballast water still containing an active substance and in November 2011, the US Environmental Protection Agency proposed a vessel general permit for discharges incidental to the normal operation of vessels permit that, for the first time would include numeric discharge limits of active ingredients for most vessels. Tese limits are as follows: Ozone is an oxidizing biocide that has
been used to disinfect water supplies ashore for over one hundred years. It is the major component of smog and is a harmful pollutant. It is also oſten used as a biocide in water. Ozone is inherently unstable and dangerous to produce, but it is a very powerful oxidizing agent. The system works by passing water
through machinery that releases ozone bubbles into the water. Te gas then dissolves in the water and reacts with other chemicals in the water to kill the organisms. As not all the gas dissolves in the water this must be destroyed before it enters the atmosphere, as it is toxic to humans. Further, reaction between the ozone and the components of sea water may also result in toxic chemicals.
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