Ballast Water Management Systems for Vessels - Global Maritime Transport and Ballast Water Management: Issues and Solutions - page 113

A minimum salinity is needed for its effi cient use, in freshwater and lower brackish
ballast water uptake zones marine water may be pumped into the line from a previ-
ously fi lled ballast tank to reach the required minimum salinity.
Chemical Dosing
A large number of chemical disinfectants are commercially available. These have
been used successfully for many years in land-based potable and wastewater
treatment applications. For the purpose of ballast water treatment several sub-
stances and formulations were considered, e.g., Chlorine dioxide, PeracleanOcean
and SeaKleen. These systems have in common that an on board storage is needed
and it would be benefi cial that a supply of additional such substances is available
in all ports the vessel is calling which may be logistically challenging. Further,
ozone, generated on board from ambient air, is used in several BWMS. Most
chemicals are usually applied during ballast water uptake with a mixing device
to allow effi cient treatment.
Neutralisation
The vast majority of ballast water treatment systems which make use of active sub-
stances add a neutralization substance. Such a neutralization step may not always be
needed as e.g. on longer voyages the active substance may be (bio-)degraded before
the ballast water discharge occurs. It seems most useful to apply the neutralising
substance during the ballast water discharge. Proper mixing should occur so that the
neutralizer is well circulated in the ballast water and that its neutralizing power is
applied before the ballast water has left the vessel. Our review has shown that
Sodium Thiosulphate is the most frequently used neutralizer today (see Table 2 ).
Application of Ballast Water Management Systems
Technologies on Vessels
Different vendors developed different BWMS combining different technologies.
Different systems (or parts of these) have their application in different stages of the
ballasting process, i.e., at the uptake of ballast water, during holding the ballast
water in tanks during navigation, and/or at discharge.
Among the 104 BWMS identifi ed (see Table 2 ), 100 apply some treatment at
the uptake, of these four apply treatment at the uptake and during the voyage
(Table 2 , nr. 17, 61, 74 and 95), and three are known to apply the treatment only
during the voyage (nr. 12, 38 and 58). 29 BWMS treat the ballast water at uptake
and discharge.