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i want to know about Reverse Osmosis plants, how to reduce the TDS value and what is the difference between treated water, reject water and raw water,

Dear Sir, i want to know about Reverse Osmosis water quality and what is the difference values between the reject water, raw water and treated water.

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"Raw water" is untreated water. It enters a Reverse Osmosis (RO) plant where (after pre-treatment) it is pumped through RO membranes. Some water passes through the membranes this is the "treated water" and, because the membranes hold back salt, this water has reduced levels of "TDS" (total dissolved solids - or salt). Those dissolved solids don't disappear, they need to go somewhere. They mainly remain before the membrane, where the water gets increasingly salty. This water is therefore rejected hence called "reject water" or brine.

This whole process requires massive pressure, hence is very expensive in terms of energy requirements. It also leaves you with a much more saline (higher TDS) reject stream which you need to somehow deal with. As such RO and other desalination processes are normally only used where there is no other sustainable alternative.

If you would like a more detailed explanation, I have written one here:

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You may like to have a look at the following link to the International Desalination Website. The site provides several fact sheets on membrane technology and desalination.

I would like to repeat the first piece of advice that was ever given to me with regards to RO plants. It was along the lines of "Remember that RO membranes are only for reducing the level of dissolved salts in the water. They are not for filtering out particles, so ensure that before the water reaches the RO membranes it has been cleaned to a high degree. If not, you will degrade the very expensive membranes rather quickly." Unfortunately a lot of water engineers have learnt that lesson the hard way.

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