What is the science behind water purification?

Answer 1

Many methods for water purification and seawater desalinization have been used for a number of years starting in ancient times with good old fashion distillation (boil the water and catch the condensate leaving the bad stuff behind). The leading method now is membrane based...reverse osmosis. Expensive to build, expensive to operate and maintain.







Carbon nano-tubes built into membranes and electrically charged to repel salt ions before reaching the membrane, and bio-mimetic membranes utilizing aquaporins in a similar charged fashion hold some promise to improving the efficiency of RO systems but are still in the theory and development stage.

One new process that is actually in commercial development is Capacitive De-ionization which uses a flow-through capacitor designed to eliminate dissolved solids from water using a small electrical charge.

Answer 2

River water is filtered through beds of sand and settling tanks to remove most pollutants.Bacteria are killed by the addition of chlorine or ,more recently, exposure to Ultra Violet Light which generates ozone gas. 'Ozonificatin' has the same effect at killing bacteria but without adding any taste.

A flocculent or haze remover, is added in the form of aluminum sulphate. Any particles suspended in the water clump together and sink thus improving clarity of the final product.It is stored in underground tanks to stop algae growing in sunlight.

Answer 3

Three ways:

1. Evaporation (boiling), when pure clean water rises as steam.
2. Physical and chemical treatment (filtering and chlorinating).
3. Pressure and reverse osmosis. Water is forced through membranes that only allow pure water through.

Answer 4

There are many types, the simplest being the cartridge filter. In this we have a plastic canister about a foot long screwed to a plastic fitting that is threaded to accept common Plumbing couplings. The incoming water pipe is fixed onto one side and water flows down the outside of the removable cartridge that fits into the canister. It must penetrate the filtering material of this cartridge to reach the centre and flow up to the outlet side where it goes to the faucet. - My favorite type has a clear plastic canister and a removable cartridge, 2" x 10" that comes in many filter types. The simplest and most used is a 20 micron 'sediment' cartridge. These are made of fibrous material that will catch tiny solids in the water. The filter density can be as small as 1 micron. These catch almost everything in water, but do impede flow. These cartridges usually cost about $2 - 4 and are thrown away when full of contaminants.They take about 5 minutes to change.

This is very basic water filtering, and 'the tip of the iceberg' of filter technology.

Answer 5

The science is:

• testing can tell you if the raw water is reasonably safe
  
• big lumps settle out
  
• lumps can be filtered out
  
• organics and odours can be oxidized or stripped out
  
• viruses and bacteria can be killed with chlorine
  
• testing can tell you if the treated water is acceptable