Reverse Osmosis

From RTAW Reefpedia

Reverse osmosis filters are devices in which water under pressure is forced through a semi-permeable membrane and in doing so are capable of removing disolved salts.

RO systems take a single water feed from the tap and produce a purified stream that has had contaminents removed, as well as a wastewater stream in which the contaminants have been concentrated. Typical household units produce around 2-4 litres of wastewater for every litre of purified water. The waste water can be used for washing clothes or watering plants, but can be quite wasteful if it is discarded to the drain in areas where water restrictions apply.

There are various membranes available, although TFC or Thin Film Composite membranes appear to be the most appropriate for aquarium applications, and are capable of reducing contaminants to very low levels of Total Dissolved Solids (TDS).

RO filters will normally utilise pre-filters to remove fine particulate solids, and carbon filters to remove chlorine prior to entering the RO stage in order to extend the life of the membrane. They can also be used with a final deionisation column, with such a system referred to as an RO/DI. This allows much lower levels of contaminants to be reached.