Around the world, household drinking water purification systems, including a reverse osmosis step, are commonly used for improving water for drinking and cooking.
Such systems typically include a number of steps:
a sediment filter to trap particles including rust and calcium carbonate
optionally a second sediment filter with smaller pores
an activated carbon filter to trap organic chemicals and chlorine, which will attack and degrade TFC reverse osmosis membranes
a reverse osmosis (RO) filter which is a thin film composite membrane (TFM or TFC)
optionally a second carbon filter to capture those chemicals not removed by the RO membrane
optionally an ultra-violet lamp for disinfecting any microbes that may escape filtering by the reverse osmosis membrane
In some systems, the carbon pre-filter is omitted and cellulose triacetate membrane (CTA) is used. The CTA membrane is prone to rotting unless protected by chlorinated water, while the TFC membrane is prone to breaking down under the influence of chlorine. In CTA systems, a carbon post-filter is needed to remove chlorine from the final product water.
Portable reverse osmosis (RO) water processors are sold for personal water purification in various locations. To work effectively, the water feeding to these units should best be under some pressure (40 psi or greater is the norm). Portable RO water processors can be used by people who live in rural areas without clean water, far away from the city's water pipes. Rural people filter river or ocean water themselves, as the device is easy to use (Saline water may need special membranes). Some travelers on long boating trips, fishing, island camping, or in countries where the local water supply is polluted or substandard, use RO water processors coupled with one or more UV sterilizers. RO systems are also now extensively used by marine aquarium enthusiasts. In the production of bottled mineral water, the water passes through an RO water processor to remove pollutants and microorganisms. In European countries, though, such processing of Natural Mineral Water (as defined by a European Directive) is not allowed under European law. (In practice, a fraction of the living bacteria can and do pass through RO membranes through minor imperfections, or bypass the membrane entirely through tiny leaks in surrounding seals. Thus, complete RO systems may include additional water treatment stages that use ultraviolet light or ozone to prevent microbiological contamination.)
Membrane pore sizes can vary from .1 to 5,000 nanometers (nm) depending on filter type. "Particle filtration" removes particles of 1,000 nm or larger. Microfiltration removes particles of 50 nm or larger. "Ultrafiltration" removes particles of roughly 3 nm or larger. "Nanofiltration" removes particles of 1 nm or larger. Reverse osmosis is in the final category of membrane filtration, "Hyperfiltration", and removes particles larger than .1 nm.
In the United States military, R.O.W.P.U.'s (Reverse Osmosis Water Purification Unit, pronounced "roh-poo") are used on the battlefield and in training. They come ranging from 1500 GPD (gallons per day) to 150,000 GPD and bigger depending on the need. The most common of these are the 600 GPH (gallons per hour) and the 3,000 GPH. Both are able to purify salt water and water contaminated with N.B.C. (Nuclear/Biological/Chemical) agents from the water. During a normal 24 hour period, one unit can produce anywhere from 12,000 to 60,000 gallons of water, with a required 4 hour maintenance window to check systems, pumps, R.O. elements and the engine generator. A single ROWPU can sustain a force of a battalion size element or roughly 1,000 to 6,000 soldiers.(from Wikipedia)
Dec
20
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