Water Filtration

Sea Water Reverse Osmosis, or SWRO, is a reverse osmosis water treatment that has been in use since the early 1970s.  SWRO removes the salt from seawater–a process  called desalination–without need for heating or phase changes.  The typical single-pass SWRO process consists of intake, pre-treatment, a high-pressure pump, a membrane assembly, a pH and remineralization adjustment, and disinfection.  Pre-treatment is essential when working with SWRO due to the spiral wound design of filtration membranes, which only allow for one-way water flow.  Since the water being filtered cannot backpulse or agitate for scouring or solids removal from its surface, any accumulated material cannot be removed from the membrane surface and the water is vulnerable to loss of production capacity.  The pump used in SWRO supplies the pressure needed to push water through the membrane, which is simultaneously allowing and rejecting salt to pass through it.  Once water has been desalinated in this fashion, it is initially extremely corrosive and has to be stabilized by adding lime to protect pipelines and storages downstream.  Liming water will also allow the treated water to meet potable water specifications for effective disinfection.  Water must next be prepared for distribution.   Desalination processes have proven to be effective in blocking pathogenic (disease-causing) organisms, but disinfection is performed to kill any lingering harmful bacteria or virus that may have bypassed the SWRO process to remain in the water.  Disinfection may include UV lamps, the use of chlorine, or the use of chlorine combined with ammonia. 

New research and testing of reverse osmosis water treatment systems is constantly under development for both large- and small-scale operations.   With so many people drinking filtered water these days, and the large population of the planet, we will doubtless need further innovation in the water treatment field to maintain a healthy existence in the future.

There are many functions of reverse osmosis systems that treat water that we use every day and may not know about.  In areas such as Los Angeles that deal with water shortages, rain water collected from storm drains is purified with reverse osmosis water processors so that it can be used for landscape irrigation and industrial cooling.  At power plants, reverse osmosis removes minerals from boiler water, being treated numerous times so that it can made as pure as possible, preventing corrosion on machinery and cleaning groundwater.

Reverse osmosis is an economical solution for concentrating food liquids, such as fruit juices, than more widely used methods that use heat treatment.  Reverse osmosis is also used in the dairy industry to concentrate milk, ultimately reducing its shipping costs.  It is also used to produce whey protein powders that are frequently used by bodybuilders.  Reverse osmosis is now acceptable for use in the wine industry, though it was once considered unfavorable.  It can improve the concentration in wine, remove undesirable components such as acetic acid and smoke taints from wine, and remove unwanted alcohol content from wine as well.  Reverse osmosis is also used in some car wash rinses to prevent water spots on vehicles and in the production of maple syrup.  Salt water fish enthusiasts often choose reverse osmosis systems for purification of their aquariums.
 

Reverse osmosis (RO) water treatment has become a frequently used method for the treatment of household drinking and cooking water.  The overall effectiveness of a reverse osmosis water filtration system depends on the initial levels of contamination in existing household water supply, as well as available water pressure.  RO systems are not generally appropriate for treating a water supply contaminated by coliform bacteria, or a water supply that serves more than one household.

Reverse osmosis systems are usually used to reduce the levels of total dissolved solids.  RO treatment may also be used to reduce naturally occurring substances in a water supply that result in foul smells, tastes, or colors, as well as substances have compromised the water supply and resulted in adverse health effects.  RO units that include a carbon filter may also have the capability to reduce soluble organic compounds such as pesticides, dioxins, and some volatile organic compounds such as chloroform and petrochemicals.  In Minnesota and the Dakotas, the principal use for an RO system is to reduce the high levels of nitrate, sulfate, sodium and total dissolved solids present in the water supply.

Reverse osmosis systems(RO) use a separation process that uses pressure to force a solvent through a membrane that retains the solute on one side and allows the pure solvent to pass to the other side. More formally, it is the process of forcing a solvent from a region of high solute concentration through a membrane to a region of low solute concentration by applying a pressure in excess of the osmotic pressure. This is the reverse of the normal osmosis process, which is the natural movement of solvent from an area of low solute concentration, through a membrane, to an area of high solute concentration when no external pressure is applied. The membrane here is semipermeable, meaning it allows the passage of solvent but not of solute.

The membranes used for reverse osmosis have a dense barrier layer in the polymer matrix where most separation occurs. In most cases the membrane is designed to allow only water to pass through this dense layer while preventing the passage of solutes (such as salt ions). This process requires that a high pressure be exerted on the high concentration side of the membrane, usually 2–17 bar (30–250 psi) for fresh and brackish water, and 40–70 bar (600–1000 psi) for seawater, which has around 24 bar (350 psi) natural osmotic pressure which must be overcome.

This process is best known for its use in desalination (removing the salt from sea water to get fresh water), but it has also been used to purify fresh water for medical, industrial and domestic applications since the early 1970s.