10+
Gallery 8

Reverse Osmosis

a reverse osmosis device made of perspex, pvc piping, and a metal winding device.
a reverse osmosis device made of perspex, pvc piping, and a metal winding device.

Extracting freshwater from brackish or salt water using reverse osmosis is an energy-intensive technique.

How it works

Turn a handle to generate enough energy to separate a small amount of freshwater from a brackish source of water using reverse osmosis.

Things to try or ask around the exhibit

  • How much 'wastewater' is there compared to 'clean water'?
  • Would reverse osmosis be an efficient process to treat greywater, or to extract freshwater from salt water?

Background

The water to be cleaned ('brackish' water) is pumped against a filter under high pressure. Holes in the filter are large enough to allow water molecules to pass through, but they hold back larger, unwanted molecules, such as dye or salt impurities.

The process of reverse osmosis takes a great deal of energy, as the water (solvent) needs to be pumped from the concentrated brackish solution, to a more dilute solution, whereas under normal osmosis, the water would move from the dilute solution and into the brackish to solution to 'equalise' concentrations.

Finding the science in your world

Extracting freshwater from brackish or salt water using reverse osmosis is an energy-intensive technique, but reverse osmosis is sometimes used for water purification and in medicine and industry.

Reverse osmosis can remove the salt from sea water to make it drinkable, but the process uses a lot of energy and produces waste (brine) which needs to be disposed of carefully to minimise environmental impact.