Typical Industry Applications of Reverse Osmosis (RO), Desalination
Practical Considerations for RO in Aquaria
Theory of Osmosis Fresh Water Sea Water H 2 O Initial Condition Fresh Water Sea Water (diluted) H 2 O Equilibrium H 2 O π Semipermeable Membrane Fresh Water Sea Water H 2 O Pressure Reverse Osmosis The Osmotic Pressure, π, is defined as: π = MRT For sea water at 35 ppt, π is about 350 psi.
Key Terms in RO Systems
Permeate – The “purified” product water exiting the system.
Concentrate – The concentrated salt solution exiting the system. In some system designs this outflow is returned to the aquarium for salt recovery.
Feed Flow – The 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.
Rejection – The percentage of dissolved solids removed from the source water by the membrane.
Purification of potable or “fresh” water sources: Purified, very low Total Dissolved Solids (TDS) water is produced for various uses. In the 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 exhibit windows.
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 sea water aquaria
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
Desalination RO Systems
Strong Acid Cationic Resin Polymeric Resin R-SO 3 -H R-SO 3 -Na R-SO 3 - R-SO 3 -H R-SO 3 - Na + K + Cu 2+ Mg 2+ Ca 2+ H + Ca 2+ H + H + Typical Cations Metals Fe 2+ Zn 2+
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
Mixed bed ion exchange capacity = 353,357 grains per m 3 10,000 grains per ft 3 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 m 3 3.71 ft 3