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Reverse osmosis (sometimes abbreviated as RO) is a water purification technology involving pumping water through a membrane under high pressure.
- desalination, where the only other common method, distillation is even more energy intensive,
- water recycling, where the membrane provides an added layer of safety against pathogen breakthrough.
Recycling of storm water is the less energy-intensive option, and has less safety concerns than recycling sewage, but storm water is not available in a steady supply. Large storage units can be built, but these are somewhat expensive, and most significantly, will not help in an extended drought when water is needed most.
Small RO units sometimes operate as vending machines, or are used in water refill stations, especially in parts of SE Asia, such as Bangkok, and supply water at a much lower price than bottled water. If there is reason to suspect that the machines are not properly operated or maintained, extra caution should be taken, perhaps adding a disinfection step such as chlorine or bleach.
Perforations in the membrane will lead to unsafe water output in the case of sewage or storm water treatment, or slightly saline, in the case of saline input.
- capital cost
- operating cost
- applicability to small scale settings
- applicability to large scale settings
- safety, i.e. effectiveness in removing pathogens. Both the microfiltration and the RO methods would presumably need to be supplemented with disinfection, as free-floating smaller pathogens (viruses and small bacteria - note however that usually most pathogens are not free-floating) could pass through microfiltration, and imperfections are likely in the RO system.[Suggested project]