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Reverse Osmosis and DeionizationSystems for Aquaria
Thoram Charanda
Sr. ChemistWalt Disney World Co.
Life Support
Lake Buena Vista, FL
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1st AQUALITY Symposium, April 2 - 7, 2004, Oceanario de Lisboa, Portugal
Reverse Osmosis and Desalination
1. Theory of Osmosis
2. Typical Industry Applications of ReverseOsmosis (RO), Desalination
3. Practical Considerations for RO in Aquaria
4. Designing an RO System for a Salt Water
Exhibit
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1st AQUALITY Symposium, April 2 - 7, 2004, Oceanario de Lisboa, Portugal
Theory of Osmosis
Fresh
Water
Sea
Water
H2O
Initial Condition
Fresh
Water
Sea
Water
(diluted)
H2O
Equilibrium
H2O
Semipermeable
Membrane
Fresh
Water
Sea
Water
H2O
Pressure
Reverse Osmosis
The Osmotic Pressure, , is defined as: = MRT
For sea water at 35 ppt, is about 350 psi.
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Key Terms in RO Systems
PermeateThe purified product water exiting the
system.
ConcentrateThe concentrated salt solution exiting the
system. In some system designs this outflow is returnedto the aquarium for salt recovery.
Feed FlowThe total flow rate of the source water
pumped in the system.
Recovery - The percentage of permeate achieved in a
system, % Recovery = permeate flow/feed flow x 100.
RejectionThe percentage of dissolved solids removed
from the source water by the membrane.
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RO Membrane Filter Detail
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Industrial Applications of RO
Systems
Purification of potable or fresh water sources: Purified, very lowTotal Dissolved Solids (TDS) water is produced for various uses. Inthe aquarium industry it can be used for:
- Make up water in fresh and salt water aquariums
- As a pure water base for artificial salt water systems
- As a non-scaling/spotting wash or rinse water for aquarium exhibitwindows.
Desalination of Sea Water:
- Production of potable drinking
- Source water for combustible turbine power plants
- Irrigation and non-potable utility water uses
- It can also be used as a salt recovery system for closed-filtration seawater aquaria
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RO System for Fresh Water
300 to 1,000 gallon per day
RO System
Requires a reservoir tank, high
level shut-off switch and
delivery pump
Pre-Filtration: Requires a 5-micron sediment filter and a
GAC filter to remove any
chlorine residual and organics
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Desalination RO Systems
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Design Considerations for a Salt
Recovery RO System Consider your feed water source: Natural or Artificial Sea Water.
Identify the typical range of the water chemistry parameters.
pH
Temperature Salinity
Silt Density Index (SDI)
Silica
Level of Particulates
Presence of Organics or Residual Oxidizers What is the desired rate of permeate (fresh water) removal from your
system? This will dictate the required feed flow rate for the ROsystem.
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Design Considerations for a Salt
Recovery RO System Consider any future requirements for system upgrade in fresh water
removal capacity, e.g. system can accept an additional membrane,
high pressure pump is slightly oversized.
Identify the best location in the aquarium filtration pathway to connect
the feed source.
Consider connecting the return filtration line post ozonation.
Identify pre-filtration requirements:
GAC filter to removal residual oxidants, e.g. bromine, ozone Additional particulate filters for highly loaded systems
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ROSA 5.4 Reverse Osmosis Design
Software
Specialized software can be used to assist in the initial
design and membrane performance parameters required for a
successful salt recovery system.
A freeware program is offered by DOW Chemical called
ROSA 5.4, that offers the ability to calculate the required
feed, permeate and concentrate rates based on the feed water
chemistry and a given sea water RO membrane type.
The URL for this program is www.filmtec.com.
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5,000 gpd RO System at Shark Reef, Typhoon
Lagoon
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Shark Reef Salinity Recovery: RO System
25
26
27
28
29
30
31
32
0 2 4 6 8 10 12 14 16 18 20
Days
Salinity
400,000
425,000
450,000
475,000
500,000
525,000
System
Volume(gal)
Salinity Volume (gal)
Initial Salinity = 30.4
Recovered Salinity = 30.3
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Deionization Water Filtration Systems
1. Principles of Deionization (DI)
2. Applications for DI Water
3. Water Chemistry Parameters and Considerations
for a DI System
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Ion Exchange Beads
Ion exchange beads are typically
constructed of a polymeric resin or gel
with an average diameter of 0.3 to 1.2
millimeters. The beads can have either
cationic or anionic functional groups
attached to the surface.
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Types of Ionic Exchange Resins
Strong Acid Resins
- contain functional groups of R-SO3H on the
polymeric resin
Weak Acid Resins
- contain functional groups of R-COOH
Strong Base Resins
- contain functional groups of R-OH
Weak Base Resins
- contain functional groups of R-NH3
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Strong Acid Cationic Resin
Polymeric ResinR-SO3-H
Na+
K+
Cu2+
Mg2+
Ca2+
Typical Cations
Metals
Fe2+
Zn2+
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Applications for DI Water
Analytical grade water for laboratory use
Essentially salt and micro nutrient free water that can be
used to make artificial sea water Replenish system water loss due to evaporation
Makeup of specialized water quality environments, ie.
natural waters with very low TDS and specific
concentrations of cations
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Design Engineering of DI Systems
Identify the source water for the DI system
Analyze for the key water chemistry parameters:
pH
Free and Total ChlorineTotal Dissolved Solids (TDS)
Identify the intended volume of DI required per day
A GAC prefilter is required to remove residual chlorine
and dissolved organics-typically sized from 0.0283 to 0.057 m3 (or 1 to 2 ft3)
Plan for a reputable company to provide an exchange
service for the mixed resin beds and GAC filter
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Mixed bed ion exchange capacity = 353,357 grains per m3
10,000 grains per ft3
Design Engineering of DI Systems
Example: Your source water is potable city water and you require up
to 400 liters per day of DI water.
Source water TDS: 200 ppm
Equivalent grains per gallon = 11.7 gpg (divide TDS by 17.1)
Planned DI resin exchange frequency = 30 days
Minimum required amount of mixed bed resin = 0.105 m3
3.71 ft3
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Summary
Reverse osmosis systems are a good design choice where:
- Moderate (2,000 liters) to large (+18 m3) volumes of water arerequired per event and there is sufficient space for the purified waterreservoir
- Desalinated water source for utilities and as a purified water sourcefor DI analytical laboratory grade water
- Desalination system for salt recovery
Deionization systems are a good design choice where:
- A relatively fast flow rate (> 35 Lpm) of pure water is required
- Only cost effective for relatively small exhibits, < 2,000 liters
- Analytical laboratory grade water
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Acknowledgements
Dow Chemical Company
GE Water Technologies
Reverse Osmosis of South Florida
US Filter Corporation
David Cohrs, National Aquarium in Baltimore
Kent Semmen, Brooksville Zoo
Eric Kingsley, Monterey Bay Aquarium