How to reduce concentrate discharge?

How to reduce concentrate discharge?

The amount of concentrate discharged into the sewer during cleaning is provided by a flow restrictor. For correct operation of the system, the flow limiter must correspond to the size of the installed membrane. From this, it would seem, it follows that the discharge of concentrate into the sewer during operation of the reverse osmosis system or industrial Ro plant  is a constant. However, the amount of water purified by the reverse osmosis membrane depends on the pressure at the inlet of the membrane element – the higher the pressure, the more permeate penetrates the membrane barrier. On the other hand, the amount of water accumulated in the tank before the auto regulator shuts down the system depends on the air pressure in the corresponding section of the membrane tank – the lower the pressure, the more water is collected in the tank – and the pressure of the source water in the water supply. For reference: the recommended air pressure in the storage tank is 0.6–0.8 atm. Therefore, it is impossible to talk about some fixed value of discharge into the sewer per liter of purified water – too many parameters affect this value. In order to evaluate the effect of the above parameters on the permeate-concentrate ratio in household reverse osmosis, it is useful to consider the data obtained from the operation of a reverse osmosis system with a Dow Filmtec TW30-1812-50 membrane element with a nominal capacity of 50 gallons, or 189 liters, in day, at various values ​​of the pressure of tap water and air pressure in the tank. From the above data shows that at low values ​​of the water pressure in the water supply system, the reverse osmosis system discharges significant amounts of concentrate, reaching almost 15 liters per 1 liter of purified water. It is unlikely that such a system can be considered rational. With increasing water pressure, the discharge of concentrate per unit volume of purified water decreases, reaching a minimum value of 7 liters at an inlet pressure of 5 bar. Are there solutions to reduce the amount of concentrate discharged? Yes, such solutions exist, and one of them is the use of a reverse osmosis system with a pump. Since the flow restriction of the concentrate provides a constant discharge into the sewage system, which is practically independent of pressure, the use of a pump allows you to “push” through the membrane more water. On the one hand, the use of a pump will reduce discharge into the sewers. On the other hand, such intensification of purification will lead to faster contamination of the membrane element and pre filters. Even the minimum received value of the discharge into the sewer may seem quite large. However, it should be remembered that household reverse osmosis is a way of post-treatment of drinking water used by humans in limited quantities – up to 3-5 liters per day. Therefore, the total discharge into the sewer will be relatively small, commensurate with the overspending of water for several extra flushing of the toilet per day. Compensation for this cost overrun will be the high quality and safety of drinking water in the house.

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