Available data suggest that heating water to the acute upper lethal temperature of zebra mussels (typically in the range 38°C to 43°C depending on the acclimation temperature), followed by a rapid return to normal temperatures, is a promising mitigation technique for zebra mussel fouling.
Heat treatment of ballast water is potentially attractive because (1) waste heat from the ship's engine is a possible energy source for heating ballast water, and (2) no chemical byproducts or residuals are discharged. Shipboard implementation of thermal treatment would only require additional pipework and possibly an additional pump, starter, and electrical wiring to allow the hot water to be pumped through the ballast tanks using the flow-through method. As discussed in Chapter 4, a number of critical factors will probably limit the use of thermal treatment to certain vessels on specific trade routes. These factors include voyage time, the volume of ballast water to be treated, the ambient water temperature, and specificity to target organisms.
There would be no special safety requirements since the equipment needed is standard shipboard kit.
Higher organisms such as fish are more easily killed by thermal treatment than microbes. Current work focuses on destroying toxic dinoflagellates, and studies will be needed to determine the effectiveness of heat treatment in killing other specific target organisms. An advantage of the proposed flushing method is that the proportion of original sediment in the ballast tanks is reduced, thereby enhancing the overall effectiveness of the treatment.
Heat treatment is a well-known technology for land-based applications, but its use on board ship is at a research stage with the aforementioned Ondo Maru trials. Shipboard implementation will require the installation of a suitable marine system and definition of treatment parameters (temperature and time) to establish the success of thermal treatment in sea-going conditions.
The possibility of using various shipboard waste heat sources has been considered for the case of the bulk ore carrier, Iron Whyalla.1 There are a number of
Other ships operate under different conditions that would need to be evaluated in a broader assessment thermal treatment. Key factors are the availability of waste heat and options for water heating (heating during ballasting or deballasting, heating by circulation during the voyage, or flushing hot sea water through the ballast tanks).