UV Ballast Water Treatment

Ballast water is specially injected into the ship to maintain the ship’s balance, adjust the position of the ship’s center of gravity and the distribution of weight. Ballast water is stored in the ballast tank of a ship. For a ship without cargo, the right amount of ballast water is conducive to keeping the ship at a proper depth of immersion to ensure the normal operation of the propeller. In addition, the fuel consumption of the ship during the voyage will bring weight reduction and the rise of its center of gravity. Ballast water can ensure the safety in this respect. Therefore, ballast water plays an important role in keeping a ship safe, upright and stable in the voyage.

Problems with Ballast Water

On the one hand, ballast water solves the safety problem of ships. But at the same time, the use of ballast water also brings harm to the marine environment. When ballast water is introduced into a ship, microorganisms and sediments contained in the water are also loaded into the ballast tanks. They include small invertebrates, bacteria, microorganisms, algae, as well as the larvae, eggs of various marine animals. Some of them will survive the voyage. When a ship sails elsewhere and the ballast water is discharged, many of these organisms are transported to new environments. If they can find the right conditions in the new environment, they will survive and develop, and then become invasive species.

It is estimated that the United States and Australia generate about 80 million tons and 120 million tons of ballast water discharge every year respectively. The International Maritime Organization (IMO) estimates that up to 10 billion tons of ballast water are transferred globally each year. That’s enough to fill about four million swimming pools in Olympic Games. It is estimated that more than 7,000 exotic species may hide in the ballast water at most. They move from one place to another as ships move around the world. A hundred years ago, it was suspected that ballast water was one of the mechanisms responsible for the migration of many exotic creatures. In 1973, researchers first demonstrated that ballast water could act as a transfer vehicle for living marine lives. According to statistics, about 30% of Australia’s 170 or so exotic marine species are imported through ballast water. Examples of species invasions include venomous dinoflagellates in Tasmania, Australia, starfishes in the North Pacific, mussels in the Great Lakes, jellyfishes in the Black Sea and the cholera pandemic from 1960s to early 1990s.

In order to protect biological and ecological balance, ship operators are required by law to ensure that the content of microorganisms such as bacteria and pathogens in ballast water is controlled within a certain range. The ballast water standard developed by the International Maritime Organization (IMO) can help prevent the invasion of exotic aquatic lives. Under the International Convention for the Control and Management of Ships’ Ballast Water and Sediments (BWM) which came into force in 2009, used ballast water from ships must be treated before it can be discharged into the sea. And there should be no more than 10 living microbes of 50 micrometers or larger per cubic meter of water.

In the treatment of ballast water, the traditional treatment methods are emptying, overflow, dilution, electrolysis and the use of biological insecticides. However, these methods are either hazardous in their operation or with the problem of incomplete replacement of the ballast water. In recent years, new treatment methods include ultraviolet, ozone and flocculation. Among these treatment methods, ultraviolet is relatively the most environmental one with the most advantages and the least disadvantages.

Principle of UV Ballast Water Treatment

Chemical dimers are formed when base pairs of DNA or RNA in biological cells are photochemically exposed to UV radiation. These chemical dimers will prevent the reproduction of DNA or RNA during cell division. Therefore, the purpose of inactivation and sterilization of aquatic organisms can be achieved by UV irradiation.

Basic Structure of a UV Ballast Water Treatment Equipment

The basic structure of a UV ballast water treatment equipment is not complicated. The basic components of a set of equipment usually include a stainless-steel chamber, a flow inlet, a flow outlet, one or more UV lamps, end caps for the easy replacement of UV lamps, several automatic wipers for UV lamp cleaning, etc.

Advantages of UV Ballast Water Treatment

Compared with other treatment methods, the advantage of using UV for water treatment is that it is technically mature and it has been widely used. In terms of operation, the operation of UV water treatment equipment is relatively simple. Since no chemicals are used and no toxic byproducts are produced to pollute the marine ecology, the UV ballast water treatment process is environmentally safe. UV method is also less corrosive to ballast tanks and piping than using chemical products. And in terms of cost, compared to chemical treatment methods, the use and maintenance of UV treatment equipment will be much lower.

Other UV Water Treatment Applications

Being environment-friendly and highly efficient, UV water treatment has been widely applied in household and commercial aquariums, swimming pools, beverage production and other industries which are sensitive to water quality. In addition, domestic wastewater treatment is another area where UV can make a big difference with its advantages.