Chemistry Reference
In-Depth Information
Desalted water
from Raw
Water tank
MF
NF
RO
reject
Lime/soda
MC
Heat
exchanger
Lime/soda
CaCO
3
MC
Heat
exchanger
CaCO
3
Salts+Brine
Figure 12.4 Schematic representation of the integrated system developed in the MEDINA
project (after [94]).
capacity in Europe is largely distributed between Spain and Italy. In Spain, more than 69%of
desalination plants use reverse osmosis, while in Italy the figure is about 20%.
In Asia the market for desalination plants is growing fast, due to the enormous populations
and economic growth. Thewide use of reverse osmosis in desalination processes is guided by
the fast development of reverse osmosis membranes. In this process, a suitable pre-treatment
is indispensable for efficient plant operation. Ultrafiltration, microfiltration and nanofiltration
are frequently used to pre-treat a solution before reverse osmosis as they provide many
advantages over conventional processes. Another membrane process that uses reverse
osmosis pre-treatment is the membrane bioreactor, most frequently used for waste water
treatment. An advanced integration of different membrane technologies for desalination,
which can also be used for the valorization of brine, is illustrated in Figure 12.4. In particular,
this introduces the use of a membrane contactor to crystallize salts at different steps in the
purification (retentate of nanofiltration and reverse osmosis). This strategy has been devel-
oped in the MEDINA project, funded by the European Commission within the 6th
Framework Program.
One of the main problems with sea water desalination is brine disposal. An interesting
solution is offered by membrane contactors, such as membrane distillation and membrane
crystallization [98-100]. Both of these are thermally driven, and they are not limited by
concentration polarization phenomena. Therefore, nanofiltration and/or reverse osmosis
retentate streams can be treated with these techniques to recover water and salts contained
within them.
12.4.2 Integrated Membrane Processes for the Fruit Juice Industry
The use of integrated systems is very attractive for the production of high-quality
concentrated juices fruit. The high percentage of pectins and solids creates a very viscous
flow, which gives low permeate flux when processed by reverse osmosis and osmotic
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