 |
| 1. Controller |
13. Flush solenoid |
| 2. Transformer / relay |
14. Conductivity probe |
| 3. Inlet 3/4" BSPM |
15. Permeate flow meter |
| 4. Drain Outlet 3/4" BSPM |
16. Concentrate flow meter |
| 5. GAC filter |
17. Permeate outlet 1/2" |
| 6. Pressure control |
18. Membrane |
| 7. Low pressure gauge |
19. Low pressure switch |
| 8. Pump pressure gauge |
20. Membrane connections |
| 9. Back pressure gauge |
21. Pump motor |
| 10. Inlet solenoid |
22. Pump |
| 11. Recirculation flow control |
23. High pressure switch |
| 12. Flush flow control |
24. Recirculation flow meter |
Reverse Osmosis is the process that is used to
remove a wide range of salts to give water of
a high purity - Osmosis is a natural process involving
fluid flow across a semi permeable membrane barrier.
It is the process by which nutrients feed the
cells in our bodies and how water gets to the
leaves at the top of trees.
If you separate a solution of salts from pure
water using a basic thin semi-permiable membrane
like a sausage skin, the pure water passes through
the membrane and tries to dilute the salt solution.
If the salt solution is connected to a vertical
pipe then the progressively diluted solution will
fill the pipe until the 'osmotic pressure' drawing
the pure water through the membrane is the same
as the head pressure of the diluted solution.
This process can be reversed - hence 'reverse
osmosis' - by applying a higher pressure to the
salt solution. Pure water will then pass the other
way through the membrane in a process that is
easy to visualise as 'filtration' where the filter
will only let through the small water molecules.
This means that water containing a high level
of natural salts can be purified without the need
for chemical regenerants such as the acid and
caustic used in demin plants.
Reverse osmosis is therefore considered a much
safer route of producing pure water for many commercial
and industrial applications, and additionally
the plant does not need to be taken out of service
for regeneration as a demin plant does.
Rejection rates of salts from water is generally
in the region of 95-99.5% dependant upon membrane
type used and the raw water feed quality. RO systems
can be designed to utilise the wide range of membranes
available, which will give different permeate
water qualities. Standard designed RO's are manufactured
using the low energy membranes which will give
a permeate water quality of approx. 10 microsiemens
from an input water of between 500 - 700 microsiemens.
RO System Management
Reverse Osmosis systems in their basic form consist
of a pressure pump, housing and the membrane.
Water is forced into the housing under pressure
and the pure water (or permeate) is collected
and passed to service.
Reject water (or concentrate) is collected form
another outlet and routed to drain, with a portion
of the concentrated water recycled back to the
inlet pump. This means that the portion of water
sent to drain is kept to a minimum allowing a
recovery ratio of approx 75% to be achieved without
significant fouling of the membrane. The re circulation
allows a higher flow of water through the pump
reducing the load on its bearings and keeping
the pump running cooler. The re circulation on
all units is adjustable.
The controller used on the RO system constantly
monitors the quality of the permeate water and
is also linked with safety controls on the system,
to ensure the unit cuts out on low and high pressure,
high & low conductivity and full permeate
tank signal. It will also run various pre and
post flush cycles to maximise the lifetime of
the membrane. The constant monitoring is automatic
and the programming is all preset to ensure protection
of the system at all times and to maximise the
quality of the pure water.
RO plants must be supplied with softened, de-clorinated
or de-chlorinated anti scalent dosed water. A
duplex softener is recommended for continuous
operation. Utilising softened water for the feed
to the RO will reduce the scaling potential on
the membrane and therefore lengthen its working
life. De-chlorination of the feed will reduce
oxidation damage to the surface of the membrane.
High output reverse osmosis plant offers considerable
advantages over traditional deionisation systems,
with no acid/caustic consumables nor problems
with COSHH compliance. If softened service water
is needed elsewhere on the same installation site,
concentrate water can be returned to a softened
water holding tank, eliminating water wastage.
Specifying and sizing
| RO Dimensions |
Width mm |
Depth mm |
Height mm |
| RO B Series |
400 |
575 |
1300 |
| RO Compact 1000-8000 |
600 |
625 |
1450 |
The size of the RO and choice of membrane will
be determined by the permeate quantity required,
feed water salinity and permeate quality expected.
Low energy membranes allow the units to run at
pressures around 150 - 200 psi, and as such the
pressure booster pumps required to generate the
pure water are smaller, and the power consumption
is reduced significantly.
These membranes will produce water quality of
approx. 10 microsiemens form an input water of
between 500-700 microsiemens. If higher permeate
quality is required a different range of membranes
with higher pressure pumps can be used.
RO units are normally built and used as single
units producing the quantity required during the
working day. If circumstance demand, the RO units
can be duplexed with a central control panel being
used to allow manual or automatic switching of
the RO plant in service, and will also allow the
units to run in parallel when the demand for water
is higher, this doubling the permeate production.
Also for very high purity waters the RO can be
manufactured in "Double pass mode" -
This means the permeate water from the first unit
is fed as raw water into the second pass of the
RO - This already high quality water will then
be improved and a very pure water is produced,
typically less than 1 microsiemen.
When sizing the pre-treatment system the quantity
of water available on the raw water feed side
needs to be checked carefully as the RO system
needs a higher feed flow than it's permeate output,
as the recovery of the units is approx . 75% of
the pure water. The 25% concentrate that is rejected
by the RO can be used for any application where
soft water is required such as wash water, gray
water for toilet flushing or in some cases cooling
tower make-up. The use of this water minimises
any waste from the feed supply.
RO Plant size & technical specification
| B SERIES / COMPACT |
B/C1000 |
B/C2000 |
B/C4000 |
C6000 |
C8000 |
| Output litres/hour |
150 |
300 |
600 |
900 |
1,200 |
Input litres/hour
75% recovery |
200 |
400 |
800 |
1,200 |
1,600 |
| Membrane (ESPA-1) |
4021 |
4040 |
2x4040 |
3x4040 |
4x4040 |
| Pump power KW |
0.75 |
0.75 |
1.1 |
1.1 |
2.2 (3phase) |