the IHS Ballast Water Guide - RWO Marine Water Technology

IHS Fairplay Solutions Guide to Ballast Water Treatment Systems Sponsored by
How systems work
The technology used to treat ballast
water has generally been derived from
other industrial applications, in which
forms of solid-liquid separation and
disinfection processes were applied.
The separation process concerns the
removal of solid suspended material from the
ballast water by sedimentation or straining
by means of a filter. This produces a waste
stream that comprises backwash water from
the filtering or a hydrocyclone operation. The
waste stream is discharged during ballasting.
Disinfection may be achieved in a number
of ways. Chemical treatment uses oxidising
biocides that interfere with the microorganism’s
organic structure or non-oxidising
biocides that interact with reproductive
or metabolic functions. Physico-chemical
treatment systems use UV light, heat or
cavitation. Deoxygenation is another method,
in which the organism is asphyxiated.
Solid-liquid separation
The filtration process uses discs or fixed
screens with automatic backwashing and is
generally effective for larger particles and
organisms. The low membrane permeability
means that surface filtration is not practical,
so backwashing is required to maintain flow
because of the pressure drop.
As a means of removing larger particles,
hydrocyclones are a good alternative. These
separate the particles through high-velocity
centrifugal rotation of the water.
So, there are three fundamental ballast
water treatment technologies, which are
generally combined within one system. These
are mechanical, which consists of filtration
or cyclonic separation; physical disinfection,
comprising ultrasound, ultraviolet (UV)
radiation, heat, cavitation, deoxygenation,
and coagulation; and chemical treatment and
biocides, comprising electro-chlorination,
ozonation, chlorination, chlorine dioxide and
advanced oxidation.
Most systems use a two-stage approach
involving mechanical separation at the first
stage, followed by a second-stage physical/
chemical treatment, at which some systems
use a combination of two or more treatments.
Operational implications, extended
ballasting time as a result of pressure drops,
consumables needed and energy requirements
all need to be assessed. Solutions compares the
various technologies, each of which has its
Both filtration and cyclonic separation can
be improved by pre-treatment in the form of
coagulation, but this needs extra tank space
and an ancillary powder to generate the flocs.
Oxidising biocides
When diluted in water, chlorine destroys cell
walls of organisms, while electro-chlorination
creates an electrolytic reaction using a direct
current in the water. Both methods are wellestablished
municipally and industrially, but
are virtually ineffective against cysts unless a
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