A ballast water system allows a ship to pump water in and
out of very large tanks to compensate for a change in cargo load, shallow draft
conditions, or weather.
The capacity of ballast water tanks might be millions of
gallons on a large vessel. This allows vessels to carry a light or heavy load
while maintaining ideal buoyancy and handling conditions in all situations.
A ship might discharge all ballast water tanks to pass a
shallow area or forward tanks only to raise the bow in rough open seas.
Physical components of the system include; raw water
intakes, large and small strainers, pumps, distribution pipes, ballast water
tanks, treatment system, discharge system, and all the valves, sensors, and
controls to run the equipment.
Invasive Species in
Ballast Water
Invasive species are a significant threat to ecosystems and
the economies of the affected areas. Researchers think that about one-third of
all documented invasive plants and animals are able to travel in the ballast
water tanks of ships.
Zebra Mussels were introduced into Lake Saint Clair in 1988
when a ship emptied ballast water into the Great Lakes System. The Great Lakes
hold nearly twenty percent of the earth’s fresh surface water in a watershed
system. The non-native mussels eliminated native varieties once used by
industry and have caused an estimated 7 billion dollars (US) in damage by
encrusting or clogging underwater equipment essential to industrial and
recreational activities.
Sea Lamprey and Spiny Water Fleas are organisms which feed
off of host fish or compete with young fish for food. Many species of fish
impacted by these invasive species have significant commercial or sporting
value. These animals, and others, can live in fresh or salt water and may
spread into inland waterways from saline ports and harbors.
Plants can also travel long distances in ballast water.
Eurasian Milfoil is a surface plant which can clog equipment and deter
recreation where it forms thick mats. Eurasian Milfoil was introduced to the
United States in the 1940s. Because the plant can produce large colonies from
only one small fragment it is likely the plant was introduced in the ballast
water of a ship.
Resolving Ballast
Water Issues
For years amateurs and professional researchers have
experimented with a huge array of weapons to combat invasive species in a
ship’s ballast water. Most of the difficulty is due to the fact that huge
volumes of water must be treated in a reasonably short period of time. Many
land-based systems for treating public supplies takes many hours or days to
pass water through their treatment systems.
A ship, on the other hand, must be able to discharge ballast
water as quickly as cargo is loaded. In emergency situations, ballast tanks
need to empty as quickly as possible. A quick pass through most ballast water
treatment systems is not enough to kill all the organisms that may be present.
Ballast Water
Treatment Solutions and Shortcomings
No Discharge or
Ballast Exchange Rules - International, National, and Local law governs
ballast water discharge. Some areas require ballast tanks to be sealed while
others allow ballast to be exchanged. Ballast exchange allows tanks to be
filled with local waters. Sealed ballast tanks may need to be emptied in an
emergency situation and exchange is hindered by the fact that foreign waters
must be discharged in close proximity to sensitive area for vessels to operate
safely.
Mechanical Filters
– Filters which are fine enough to remove the small immature young and eggs of
invasive species clog quickly and require constant maintenance.
Thermal Treatment
– The idea is to heat ballast water to kill any unwanted organisms.
Unfortunately heating such a huge volume of water is impractical due to time
and energy constraints.
Other Energy
Treatments – Ultraviolet, sonic, and other radiation have all been tried
but have similar problems to thermal treatment; limits on time and energy.
Chemical Treatments
– One of the earliest and most dangerous of all the methods used to control
invasive species in ballast water. Chlorine bleach and other toxic chemicals
will kill existing organisms but the release of these chemicals on the scale
necessary to treat every ship would reach toxic levels for all aquatic life
near the discharge points.
The Future of Ballast
Water Treatment
Researchers are pursuing this difficult and financially
lucrative goal at institutions around the world. In 2011, a team announced
their successful small-scale test of a two-phase ballast treatment system which
eliminates unwanted organisms and produces sodium bicarbonate as a byproduct.
The system is undergoing full-size tests in the Great Lakes.
The test for a scalable system is expected to perform well. It is not clear how
regulatory agencies around the world will respond to the potential discharge of
industrial amounts of sodium bicarbonate into their waters. Sodium bicarbonate
is a common and safe chemical in small amounts, but studies must be conducted
to assure this method is safe for long term use.
