Ballast water is absorbed by seagoing vessels in order to ensure sufficient stability of the vessel during voyages without cargo (ballast travel) or with only a small cargo . The water is taken up in appropriate ballast tanks .
The ballast water always and inevitably contains organisms that get into the ballast tanks with the water. Many die there during the journey (for example from lack of food, changes in water temperature, unsuitable salt content or the like). Some survive and are drained or pumped out of the ship with the ballast water. So they get into a foreign ecosystem . Some organisms survive there, some of them also manage to reproduce there and survive all year round. They have thus immigrated into the ecosystem as neozoa . The Asiatic mussel Limnotherma protonei spread in large numbers on the west coast of South and North America. It has no natural enemies there and migrates up the rivers. Due to their massive reproduction, mussels of this type can also clog flows and power plants. The comb jellyfish , which were introduced into the Caspian Sea , are also invasive species . There, fishing is falling significantly because its high demand for plankton means that it lives in food competition with other marine animals living there. In addition to fishing, this also applies to the entire food chain up to the sturgeon , the producer of caviar . Even single-celled organisms such as the red tide , which produce toxins, can contribute to the death of fish and even to the poisoning of humans by mussels, in which the poison of the single-celled organisms accumulates, if they are carried off into foreign coastal waters.
The largest animal that has been shown to have been carried away by ballast water is the Chinese woolly crab .
Until the beginning of the shipping crisis (mid-2008), many merchant ships were sailing in their upper speed range due to high charter rates and freight prices. The shorter the period of time that living things are in the ballast water of a ship, the greater their chance of survival. Since the beginning of the crisis and because of the relatively high fuel prices ( heavy oil ) for years , many ships have been cruising slowly . The time between taking in and releasing ballast water is then longer than when driving fast.
In order to minimize the risk of organisms being introduced into an aquatic ecosystem, a ballast water agreement was adopted in February 2004 as part of a diplomatic conference of the International Maritime Organization . It stipulates that in ports (which are often located at the mouth of rivers into the sea) ballast water may only be released if certain limit values are observed.
Ballast water management
There are currently two different methods for ballast water management:
- Exchange of ballast water at sea
- Ballast water treatment on board.
Ballast water exchange
The following procedures for ballast water exchange are used and accepted: In the sequential exchange of ballast water, a ballast water tank is first completely emptied and then refilled with fresh seawater. With the flow-through method, a filled ballast water tank is constantly rinsed with fresh seawater. In the dilution process, seawater is filled into the ballast water tank from above and ballast water is simultaneously withdrawn from below so that the fill level remains constant.
Ballast water treatment
A distinction is made between mechanical, physical and chemical processes for the treatment of ballast water according to their operating principle. They can be used individually or in combination. Mechanical separation processes are often combined with physical and chemical processes.
Mechanical separation processes are often used to pretreat ballast water. With filters or cyclones removed organisms and particles from the ballast water. In order to remove bacteria and viruses , membranes, such as those used for. B. used in the production of drinking water ( reverse osmosis ). Microorganisms up to a size of typically 0.2 µm can be separated.
Physical principles of action are z. B. a thermal treatment, UV radiation or ultrasound application.
During thermal treatment, the organisms in the water are exposed to a temperature that is sufficient to kill them. There are essentially three possible methods of thermal ballast water treatment: mixed preheating of ballast water while flushing a ballast water tank, heating of ballast water in the tanks and heating of ballast water when it is received or released. The ballast water is mainly heated using engine cooling water or other heat sources such as B. auxiliary boilers .
The disinfection of ballast water by means of UV radiation is a disinfection process that is also known from drinking water treatment. A UV disinfection unit through which water flows essentially consists of several quartz tubes containing UV lamps.
With ultrasonic disinfection, the water is exposed to a sound field (20 to 400 kHz), so that alternating negative and positive pressure areas form in the fluid. In a negative pressure phase of the sound field, vapor bubbles arise in the water, which collapse like an implosion in the subsequent positive pressure phase ( cavitation ). When the vapor bubbles suddenly collapse, shock waves arise, which tear the cell membranes and thus kill organisms contained in the water.
In the case of chemical ballast water treatment, one or more chemical substances are added to the ballast water, either directly or indirectly through electrolysis, so that a toxic reaction takes place that kills the harmful aquatic organisms and pathogens. For the disinfection of ballast water, substances such as B. ozone , chlorine , chlorine derivatives and biocides in question. Ozone disinfection is also a process known from drinking water treatment and can be used to kill bacteria and viruses in ballast water. Since ozone is unstable, it is generally generated on site from air or oxygen in ozone generators or by irradiating the air with UV lamps. Chlorine and chlorine derivatives are also used on cruise ships to disinfect drinking water and kill vegetative bacteria and many viruses. Various biocides can also be used to kill aquatic organisms, bacteria and viruses.
Operation without ballast water exchange
In the meantime, a ballast water system has been presented for a container ship, which does not require ballast water exchange during operation and can therefore do without the costly ballast water treatment. By means of a suitable tank division and a corresponding pumping and piping system, with a sufficient constant amount of ballast water, sufficient stability for the required loading conditions of the ship is ensured by pumping between the tanks. The ballast water is carried permanently in the ship without coming into contact with the marine environment, and no sediments can be deposited. The comparison with the structurally identical conventional container ship, in which various loading cases were examined, shows that this alternative is well suited. In addition to checking the intact stability, this student thesis also provided evidence of leakage safety in accordance with the current harmonized regulations of SOLAS .
- International Maritime Organization: Ballast Water Management Convention . IMO, London 2005
- Christian Mehrkens .: Analysis of ballast water treatment on seagoing ships . Hamburg-Harburg, Technical University, thesis, 2006
- Karl-Heinz Hochhaus, Christian Mehrkens: Ballast water treatment - an overview . In: Schiff & Hafen , No. 3/2007
- Katja Hartig: Design of a container ship for operation without ballast water exchange . Lecture at the STG conference “Students meet Industry” on October 29, 2010 at the University of Duisburg-Essen
- Katja Hartig: Design of a container ship for operation without ballast water exchange . In: Yearbook of the Shipbuilding Society , 2010
- Overview of the Convention on the IMO website
- Convention on the Monitoring and Treatment of Ballast Water and Sediments from Ships ; Retrieved November 20, 2010
- Ecological facts about ballast water. (English)
- General article on the Ballast Water Convention with a link to the full text (PDF; German)
- International Maritime Organization International Convention for the Control and Management of Ships' Ballast Water and Sediments (see: Conventions / Ballast Water Management; English)
- gollaschconsulting.de (PDF; 43 kB) on the introduction of exotic species in ballast water (German)
- Ecological facts about the ballast water (English)
- Ralf-Norbert Hülsmann: Ballast water - a controversial medium. elfenbeinturm.net
- Folkert Lenz: ballast water system.
- Wolfgang Weitlaner: Researchers warn of ballast water tank contents in ships .
- “Stowaways” threaten the marine ecosystem .