RO purification system is one of the best purification systems to get good source of drinking water. Of course RO will produce pure drinking water which contains much less minerals. (TDS lies between 10 and 30 mg/L.) In such case it is necessary to re-mineralise the water after purification by adding controlled quantity of good salts to bring TDS at least above 80 mg/L. Such water is the best drinking water which can keep us free from contamination of many impurities such as heavy metals, chemical waste, bacteria, radioactivity contamination etc. But traditional RO purifier generates about 75% waste water. How to reduce this by modifying the design of RO purifier?
1. There is a method to limit the amount of water discharged by an osmosis unit. It is a question of making it turn in a semi-closed circuit.
How to do it? Simply reinject the concentrated water at the source of your osmosis unit to filter it again and several times. Thus, you can drastically reduce the amount of water discharged.
Caution: With each passage through the osmosis unit, the concentration of undesirable elements in the water increases. However, there is a concentration limit that should not be exceeded. It all depends on your equipment; this limit can be extremely high on a specific industrial installation, but on a domestic or professional osmosis unit, it is around 1000 ppm (i.e. 1 g of residue per litre of water).
2. On the other hand, it is very easy to create your system without rejection with just a few accessories:
- a pressurized tank to store the temporarily discharged water
- a quick T-connector to connect the tank to your drain outlet
- a metal valve to connect the drainpipe to the network
- a chrome T-fitting to connect the valve to your cold water supply
- a non-return valve to prevent mains water from filling the tank unnecessarily
INSTALLATION STEPS:
1 - cut the drain pipe into 4 parts:
- small piece to connect the plastic T to the tank
- small piece to connect the non-return valve to the plastic T
- large piece to connect the plastic T to the drain outlet of the osmosis unit
- large piece to connect the non-return valve to the metal valve
2 - cut off the water supply and unscrew the cold water hose from the supply T of your osmosis unit
3 - screw the chrome T above the one already installed
4 - screw the metal valve into the chrome T and connect one of the long pieces of pipe to it
5 - connect the non-return valve in the right direction (arrow towards the drain)
6 - connect the non-return valve to the plastic tee itself connected to the pressurized tank
7 - connect the plastic T to the drain outlet of the tank
8 - turn on the water supply and enjoy reverse osmosis water without rejection!
Regards
Now a day’s No need for addition of external mineral it can control TDS by its internals.
It is also interesting to note that this same feature is sometimes marketed as ‘TDS Modulator’ by some water purifier brands. However, TDS Controller and TDS Modulator are one and the same thing and there is no functional difference between the two.Turn the screw clockwise to reduce the TDS level or anti-clockwise to increase the TDS level. Please note, in most RO purifiers, TDS Controller is located inside the assembly along with all other RO parts. So for adjusting the TDS level, you will have to first open the outer cover. Generally TDS Controller are a screw based devices that are adjusted and left alone to keep doing their work. But when the TDS level of your water supply changes from the source, you must make the adjustments again to ensure you get the perfect TDS level for Consumption.
TDS Controller is basically a manual device that consists of two water inputs, one water output, and a TDS Control screw.
Water Input 1: Purified water output from the RO membrane
Water Input 2: a) Purified Water from Activated Carbon Filter in case of RO+UV+TDS Controller Water Purifiers
Purified Water from UF Membrane in case of RO+UF+UV+TDS Controller or RO+UF+TDS Controller Water Purifiers
Water Output: Mix of two water inputs in the required ratio.
TDS Control Screw: TDS Control screw controls the TDS value in output water by manually adjusting the flow of water from the two water inputs.
I) If TDS needs to be reduced then the flow of input water from the RO membrane is increased and the flow of input water from Activated Carbon Filter or UF membrane is reduced.
If TDS needs to be increased then the flow of input water from the RO membrane is reduced and the flow of input water from Activated Carbon Filter or UF membrane is increased.
Thank you Dr Bachir Achour for your nice explanation on minimising waste water from RO unit during water purification. As you have mentioned for domestic application the concentrated waste water TDS will raise upto 1000mg/L TDS after a few cycles. I fully agree with you. Is there any provision to know that TDS of concentrated water is exceeding to a threshold limit so that once the limiting value reaches, it will not further allow to cycle in the system?
Moreover should I request you to give a small schematic diagram of modification in RO unit to minimise loss of waste concentrated water.
Best regards.
There are many ways to minimize wastewater production for RO or for whatever treatment process you may be using. "Traditional" is a subjective term; RO waste for me is not 75% but typically far less than 25%. It depends on your water, what pretreatment you may do, what recycle you may do, membrane type and pressure used, temperature, etc. You might want to read a book or two or hire a consultant. You could also consult the RO membrane manufacturers (eg: Dow/Dupont) manuals and simulation software (online for free) and start doing some design work; then, with a little work, things will come into focus.
Good luck.
Cheers//
A pretreatment before using RO is appropriate to reduce the volume of reject or waste. It is marked under dual treatment options.
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