According to a survey carried out by VTT, ship wastewater discharges have a
minor impact on the state of the Baltic Sea. However, the impact is not
insignificant as the nutrients entering the sea with unprocessed wastewater
from ships accelerate algae growth. A much more prominent source of nitrogen
is ship exhaust gases. The largest nutrient inputs into the Baltic Sea are
caused by agriculture in the watershed and by municipal wastewater.
The aim of the survey conducted by VTT was to investigate the scope of ship
wastewater nutrient inputs in the Baltic Sea. The results indicated that ship
wastewater only makes up a small part of the total loading, being 0.04 % for
nitrogen and 0.3 % for phosphorus. Compared with wastewater discharges, the
amount of eutrophicating nitrogen entering the Baltic Sea with ship exhaust
gases each year is substantially higher. At the turn of the millennium, 6 % of
the nitrogen fallout in the Baltic Sea was caused by exhaust emissions from
However, the environmental impact of ship wastewater is much more severe than
suggested by mere percentages in that most of its nutrients are in a form
biologically exploitable by algae. In addition, most wastewater nutrients
enter the Baltic Sea in summer, at which point algae have already depleted
most of the nitrogen and phosphorus having dissolved into run-off water in
spring. Wastewater discharges also have local harmful effects on heavily
trafficked shipping routes. The wastewater released into the sea also contains
pathogens, heavy metals and organic compounds harmful to aquatic organisms.
The largest sources of nitrogen and phosphorus in the Baltic Sea are
agriculture in the watershed and insufficiently disinfected municipal
wastewater. Approximately one-quarter of the nitrogen load takes the form of
aerial fallout. Based on point-type sources in rivers and the coast, a total
of 744,900 tons of nitrogen (approximately 74 % of the total amount) entered
the Baltic Sea each year at the beginning of the millennium. The nitrogen
fallout was 264,100 tons (approximately 26 %). Almost all (99 %) of the 34,500
tons of phosphorus in the Baltic Sea is caused by run-off water. It has been
estimated that the nutrient loading caused by ship wastewater each year is 356
tons for nitrogen (0.04 %) and 119 tons for phosphorus (0.3 %).
Current situation with processing ship wastewater
In Helsinki, Stockholm or Tallinn, most of the wastewater from vessels in
regular traffic is pumped into the sewerage system in ports and from there to
wastewater purification plants. According to the Port of Helsinki, all
passenger ships in regular traffic pumped wastewater into the sewerage system
in the port in 2008. The environmental awareness of shipping companies has
increased as the amount of wastewater pumped out of ships in ports is much
higher than 10 years ago. Furthermore, port reception facilities have been
According to international maritime regulations, the discharge of sewage into
the sea is prohibited, except when the ship is discharging comminuted and
disinfected sewage using a approved system at a distance of more than 3
nautical miles from the nearest land, or sewage which is not comminuted or
disinfected at a distance of more than 12 nautical miles from the nearest
land, provided that in any case, the sewage that has been stored in holding
tanks shall not be discharged instantaneously but at a moderate rate when the
ship is en route and proceeding at not less than 4 knots.
If restrictions are placed on the nutrient content of ship wastewater in
future, this will also impose requirements on the manufacturers of waste water
purification equipment, shipping companies and port reception facilities.
Purifying wastewater on board or transporting it to the port may be a
competitive advantage to shipping companies as passengers are concerned about
the poor condition of the Baltic Sea.
Considering the impaired state of the Baltic Sea, it is absolutely essential
that the amount of all types of nutrients is reduced. It would be easier to
control ship wastewater than the nutrient inputs caused by agriculture. It is
already technically possible to purify wastewater on board. However, this
calls for investments in expensive purification technology, so on-board
purification is not in widespread use. The possibility to leave wastewater in
the port should also be provided as an alternative to on-board purification.
Shipping companies currently have a reserved stand towards ship wastewater
intake services as their amount, quality and reliability vary considerably
according to the port.
Collecting wastewater in ship tanks and pumping it into port reception
facilities is also problematic as large, heavy tanks limit the space available
to other functions and affect ship ballast and thereby safety. According to
VTT’s survey, it seems that there could be need for further development in
onboard wastewater purification technology and thus also business potential.
The results are being utilised in the work of the Maritime Group of the
Helsinki Commission, HELCOM Maritime (http://www.helcom.fi/groups/maritime/).
HELCOM Maritime works to prevent any pollution from ships including deliberate
operational discharges as well as accidental pollution. The working group also
aims to assign the status of a special area to the Baltic Sea through the
IMO’s agreement. The status involves the requirement that the nutrient loading
caused by ship wastewater discharges must be limited in the area.
VTT’s survey is based on information obtained from port facilities, shipping
companies and reference literature. It was concerned with passenger ships,
cruise ships and cargo vessels, but not recreational vessels. The share of
ship traffic wastewater discharges causing eutrophication in the Baltic Sea
was investigated by VTT for the first time in 2007 and an update was published
this year. The investigation was financed by the Finnish Maritime
Baltic Sea Portal http://www.fimr.fi/
Research publication on the Internet: /Documents/2009_VTT_R_07396_08.pdf