Ocean waters run clean

A system designed by Alfa Laval to decontaminate water used as ships' ballast could prevent a major threat to the world's oceans.

A new product, PureBallast, developed by Alfa Laval in partnership with global shipping firm Wallenius, aims to combat the spread of invasive species in ballast water, eliminating potentially dangerous introduction to new ocean environments.

An essential part of any sea vessel, ballast is a weight that increases the stability of a ship, stopping tipping, heeling or capsizing. Water ballasts are conventionally used in cargo ships in preference to solid forms of ballast because water can readily be dumped through a valve at the bottom of the ballast chamber, reducing the weight of the boat when taking it out of the water, and then added back in after the boat is launched.

However, a disadvantage of water ballast in cargo vessels is the dispersal of marine organisms, picked up with the water in one area and dumped with the ballast in another area. Oceanic contamination can cause huge environmental and ecological problems. The movement of organisms when water is transported from one ecosystem to another poses one of the four greatest threats to the world's oceans, according to some specialists and can lead to serious health and financial consequences.

These species include anything small enough to pass through the ship's intakes and pumps - bacteria and other microbes, as well as small invertebrates, eggs, cysts and larvae. Fortunately, most of the species carried in ballast water are not likely to survive the voyage. The ballasting and deballasting processes are often fatal to the organisms, and the environment within the ballast tanks can be hostile. In a few cases, however, organisms are able to beat the odds and establish a reproductive population in the host environment. This may be the start of a troublesome invasion, in which native species are out-competed and populations of the new species become unmanageable.

One such invasion is that of the North American Mnemiopsis leidyi, a filter-feeding jellyfish, which has reached biomass densities of up to 1 kg/m³ in the Black Sea. The jellyfish has caused the depletion of native plankton stocks, contributing to the collapse of entire commercial fisheries.

The proposed solution from Alfa Laval is a chemical-free system with a compact design that can be installed into the engine room of any large vessel. PureBallast is based on advanced oxidation technology (AOT), a non-chemical process similar to smart products such as self-cleaning windows of cars and skyscrapers - preventing the growth of organisms through an AOT reaction that occurs when sunlight strikes titanium dioxide.

Depending on a ship's ballast water volume, PureBallast involves one or more AOT units, which treat the water during ballasting and deballasting. The units contain titanium dioxide catalysts that generate radicals when hit by light, which in turn break down the cell membrane of potentially dangerous microorganisms. With the cell membrane disrupted, the organism's chlorophyll disappears and it cannot reproduce.

During ballasting, water passes through a pre-filter to remove any larger particles and organisms. The water then continues to the AOT unit. Sediment build-up in the ballasting tanks is avoided thanks to the pre-filter stage, and any backflushing water is returned to the ocean directly at the ballasting site. During deballasting, water passes through the AOT unit again, in order to destroy any organisms that might have regrown in the tanks during the voyage. The filter is bypassed, avoiding any filter backflushing. This eliminates the risk of contamination via the filter at the deballasting site.

The whole chain is fully automated, with monitoring of alarms and possibilities for both local and remote operation. The system can be started and stopped at the push of a button, and involves no preparation, chemical dosing or waste streams. To ensure that the performance of the AOT unit is not affected by scaling from seawater contaminants, an automatic cleaning unit has been integrated into the system.

Alfa Laval has begun the complicated International Marine Organisation (IMO) approval process, with an application for Active Substance Basic Approval submitted alongside the full-scale land-based tests of PureBallast that began in October 2005.

The IMO convention adopted in 2004 will require ships constructed in 2009 or later to meet ballast water treatment standards. Existing ships will have to start meeting the IMO standards by 2014. The new standards are stringent, with separate limits set for different sizes and types of organisms. Organisms larger than 50 microns, for example, must be reduced by more than 99.99%, which means a decrease from at least 100 000 organisms to less than 10 organisms per cubic metre. Even bacteria such as cholera must be treated effectively.

In general, the IMO approval process takes over a year. PureBallast was officially made commercially available in December 2006 and Alfa Laval's goal is to have the first fully approved ballast water treatment system, with certification completed in mid-2007.