Water Purification

Water Purification

Anyone know the 9 steps of water purification through municipal treatment?

I'd like to know how it happens and how it helps clean the water too...any help is great..thanks!

I don't know about 9 stages, I guess it depends on your local authority which is governed by the feed water source and quality. In most cases it would start with collection in a dam where some settling of suspended solids would occur, if it was ground water it would go through a degasser before that to remove offensive odours such as hydrogen sulphide. At this stage there are a number of different options depending on what undesirables are in the water and how the authorities have chosen to address it. Sometimes it is aerated to oxidise some impurities and this will make them precipitate out of solution in another settling tank. After that it may be traeted with a flocculant such as PAC , this works by changing the electrical charge of the particulate matter so they bond together to form larger particals and become heavier and settle out better. The effectiveness of flocculants is very dependent on the pH of the water so there is usually some pH adjustment for this by adding caustic soda to raise pH or acid to lower it.
After that the water would go through various filters usually first a sand filter which is just a bed of sand that the water migrates through from the top to the bottom and removes any particals bigger than about 20 microns. After that the water will probably pass through a UV disinfection unit, this is not the final disinfection of the water but is used to control bacterial growth in the filters further down the process. Then it may go through a softener, or ion exchange bed. This is a vessel filled with beeds of resin which reduce water hardness. As the water makes contact with the resin it will exchange calcium and magnesium ions for sodium ions and the water is said to be softened. The water would then pass through another filter called a mixed bed multi-media filter. In this vessel the water will come into contact with a variety of mineral sands such as zeolite and birm, this will reduce nitrogen and any residual iron or manganese. Then the water would pass through another filter which contains Activated Carbon, this will remove any chloramines and ensure the water tastes good. After that the water will go through some very fine filters, usually 5 microns and then through a 1micron filter. If your water authority has the money it may even go through another stage which is called microfiltration, where the water is filtered down further to 0.1 microns, which will take out almost all the bacteria. If your really lucky the water may treated by Reverse Osmosis instead, this will filter the water down to a staggering 0.001 microns. After this the water is ready for final disinfection, usually with chlorine or bromine. The water is pretty clean but the chlorine is there so the water doesn't pick up bacteria as it travels through the pipes. At this stage the water may be too soft and may need to pass through a carbonate filter to rebalance the water.
There are many more water treatment options and the ones I have described are not necessarily always used and may be used in a different order. I do know that water treatment officers are usually very proud of what they do and love to talk about what they do, so you should get in touch with your local authority. I'm sure they would be happy to tell you exactly what processes they use.