The Application of Electrodialysis for Drinking Water Treatment
325
5 Application of Electrodialysis in Surface Water
Treatment
Amsterdam Water Supply studied several alternatives for the extension of their
production plant Leiduin from 70 to 83 million m 3 year· 1 • The existing plant uses
coagulation, sedimentation and filtration as a pretreatment, followed by surface
infiltration, rapid sand filtration, ozonation, pellet softening, biologically activated
carbon filtration and slow sand filtration. For the extension, an integrated
membrane system is foreseen so that surface infiltration and pellet softening can
be cancelled.
At first, reverse osmosis (RO) was chosen as the most applicable membrane
technology to fulfill the functions of desalination, hardness removal, removal of
organics (pesticides and micropollutants) and disinfection (van den Berkmortel
and Graveland 1994). Nevertheless, the pilot operation showed that the
requirements for organic removal and disinfection were well fulfilled by the other
treatment steps, so that desalination, hardness removal and bromate control
remained as the tasks for the membrane step. Therefore, electrodialysis became a
realistic alternative.
From 1996 until 1998 VA TECH W ABAG, together with Amsterdam Water
Supply and Eurodia company, carried out pilot tests for the application of
electrodialysis as an alternative to reverse osmosis in the integrated membrane
system for surface-water treatment The scale of the pilot plant was 5 m 3 h· 1 • The
task of the electrodialysis unit was desalination and the removal of hardness and
bromidelbromate from surface water. The electrodialysis system was integrated
into the whole treatment train of pretreatment, ozonation, biologically activated
carbon filtration and slow sand filtration. Electrodialysis was applied as a final
treatment step after slow sand filtration as well as an intermediate step after
pretreatment Parameters to be investigated were temperature dependency, scaling
and fouling effects, bromate control and energy and chemical consumption.
In principle, the Eurodia system utilised by VA TECH W ABAG showed results
similar to a second electrodialysis system tested by Amsterdam Water Supply (van
der Hoek et al. 1998). Nevertheless, by optimisation of several features the
performance of the Eurodia system could be markedly improved.
The temperature of the raw water varied in the range of +5 to +25 DC.
Compared with reverse osmosis, the influence of the temperature fluctuations was
slightly higher for electrodialysis. Scaling and fouling effects can be easily
controlled. However, when electrodialysis was operated as an intermediate step,
directly after pretreatment, a regular cleaning was necessary. As an interesting
side effect, it could be observed that a fouling layer made the membranes selective
for monovalent ions. Regarding bromate control, electrodialysis could not comply
with the required bromate standard of 5 )lgr 1 when operated as a final treatment
step. For this reason, electrodialysis was applicable only as an intermediate step.
In this case, bromide is sufficiently removed so that bromate formation during
ozonation is low.
325
5 Application of Electrodialysis in Surface Water
Treatment
Amsterdam Water Supply studied several alternatives for the extension of their
production plant Leiduin from 70 to 83 million m 3 year· 1 • The existing plant uses
coagulation, sedimentation and filtration as a pretreatment, followed by surface
infiltration, rapid sand filtration, ozonation, pellet softening, biologically activated
carbon filtration and slow sand filtration. For the extension, an integrated
membrane system is foreseen so that surface infiltration and pellet softening can
be cancelled.
At first, reverse osmosis (RO) was chosen as the most applicable membrane
technology to fulfill the functions of desalination, hardness removal, removal of
organics (pesticides and micropollutants) and disinfection (van den Berkmortel
and Graveland 1994). Nevertheless, the pilot operation showed that the
requirements for organic removal and disinfection were well fulfilled by the other
treatment steps, so that desalination, hardness removal and bromate control
remained as the tasks for the membrane step. Therefore, electrodialysis became a
realistic alternative.
From 1996 until 1998 VA TECH W ABAG, together with Amsterdam Water
Supply and Eurodia company, carried out pilot tests for the application of
electrodialysis as an alternative to reverse osmosis in the integrated membrane
system for surface-water treatment The scale of the pilot plant was 5 m 3 h· 1 • The
task of the electrodialysis unit was desalination and the removal of hardness and
bromidelbromate from surface water. The electrodialysis system was integrated
into the whole treatment train of pretreatment, ozonation, biologically activated
carbon filtration and slow sand filtration. Electrodialysis was applied as a final
treatment step after slow sand filtration as well as an intermediate step after
pretreatment Parameters to be investigated were temperature dependency, scaling
and fouling effects, bromate control and energy and chemical consumption.
In principle, the Eurodia system utilised by VA TECH W ABAG showed results
similar to a second electrodialysis system tested by Amsterdam Water Supply (van
der Hoek et al. 1998). Nevertheless, by optimisation of several features the
performance of the Eurodia system could be markedly improved.
The temperature of the raw water varied in the range of +5 to +25 DC.
Compared with reverse osmosis, the influence of the temperature fluctuations was
slightly higher for electrodialysis. Scaling and fouling effects can be easily
controlled. However, when electrodialysis was operated as an intermediate step,
directly after pretreatment, a regular cleaning was necessary. As an interesting
side effect, it could be observed that a fouling layer made the membranes selective
for monovalent ions. Regarding bromate control, electrodialysis could not comply
with the required bromate standard of 5 )lgr 1 when operated as a final treatment
step. For this reason, electrodialysis was applicable only as an intermediate step.
In this case, bromide is sufficiently removed so that bromate formation during
ozonation is low.