Reverse Osmosis (RO)

Industrial Reverse Osmosis (RO) Systems

Reverse osmosis is an increasingly popular solution in water purification. In many cases it has replaced conventional chemical deionisers. RO is popular because it removes the requirement to hold aggressive regeneration chemicals at the clients premises. It also does not produce a chemical effluent discharge. To many industries the security of an RO membrane is attractive as is the ability to readily validate the performance of the membrane.

Some popular uses of RO are as follows:


  • TDS (total dissolved solids) reduction for high pressure steam boilers.
  • HTM20-30 compliance for hospital purified water systems.
  • Renal Dialysis for kidney patients
  • Instrument sterilisation for hospitals and Dentists
  • TDS reduction and pre treatment to purified water systems
  • Alcohol removal
  • Endoscope sterilisation
  • Pharmaceutical production
  • Potable water production from high saturation bore hole supplies

How Reverse Osmosis Works

The osmosis process is a naturally-occurring phenomenon where less concentrated saline solution tends to migrate to a more concentrated solution. Osmosis occurs everywhere in nature, from our kidneys absorbing water from our blood, to plant roots absorbing water.

A semi-permeable membrane, usually made of thin film polyamide is used to clean water which is pumped past its input side under pressure of up to 15 bar and up to 220 psi in a cross-flow direction. From 15 to 70% of the water that passes through the membrane will do so as permeate, while the remainder leaves the membrane as a concentrate containing 99% + of the feed water TDS.

Reverse osmosis is the same process, but in reverse. This type of system will remove 99% of organic and inorganic contamination.

Applications for Reverse Osmosis

Reverse osmosis systems are typically used to treat surface, ground and brackish water from small to large flows. Many industries use the reverse osmosis system to treat their water. These industries include metal finishing, boiler feed water, semiconductor manufacturing and pharmaceutical.


All RO systems depend on good pre treatment to the feed water. This is achieved by the use of Organic Scavengers, Activated carbon media and base exchange Water Softeners. It is true to say that excellent pre treatment is a requirement for long, reliable and efficient Reverse Osmosis operation.

Reverse Osmosis membranes will not tolerate any form of hydraulic shock. It is important that RO is installed in a carefully designed purified water system with all of the necessary safeguards and monitoring.

This is where an ongoing partnership with the experts at Wychwood Water Systems will pay dividends.

Chemical attack happens when a membrane comes into contact with an oxidiser like chlorine, which will burn the membrane and effect performance. Activated carbon is a pre requisite for this purpose.

Benefits and Disadvantages

A reverse osmosis system effectively removes contaminants like pyrogens and colloids, and is easy to monitor and confirm performance.

The waste stream, (concentrate) is flushed to drain during plant operation. Because of this 70% of the feed water is recovered as purified water, (permeate).

Is Reverse Osmosis Right for you?

If you are unsure about the benefits of reverse osmosis for your application, our team members can help. They can not only recommend the right system for you, but can also answer your questions about any type of water purification system and technology available. Click here to see our reverse osmosis systems, or visit our contact page to get in touch with us via email or phone.


1. What is reverse osmosis?

Reverse osmosis, often referred to as RO, is an advanced water purification method that was initially developed to produce drinking water from sea water for submarine crews. It is a membrane filtration technology that works by forcing water under pressure through the very tiny pores of a semi-permeable membrane. Modern reverse osmosis systems can be fed on mains, river or borehole water, following suitable pretreatment, to produce water with very low conductivity for all applications that require pure water.

2. How does reverse osmosis work?

After softening and filtration down to 5 micron, water enters the reverse osmosis membrane, a very tight, sheet-like filter, that allows water to pass but rejects typically 98-99% of all the dissolved solids. The rejected dissolved solids are concentrated in a waste stream (concentrate) which is used to cleanse the membrane surface and then flows to drain or a recovery system. The purified water then flow to the process, either directly or via a storage tank until it is needed. The conductivity of the purified water leaving the RO unit (permeate) is constantly monitored and displayed so that the quality of the purified water can be seen at all times during the plant operation.

3. I need deionised water, can I use a reverse osmosis system or do I have to buy a deionisation plant?

Reverse osmosis systems and deionisers or demin plants, can both achieve the same result and effectively remove most dissolved solids from raw water, but the processes are quite different. RO filters water through a semi-permeable membrane. A deioniser uses ion exchange resin to capture ions from the water, leaving only water molecules behind. Deionisers have a lower capital cost but need acid and caustic soda for their regeneration with associated HSE issues. RO plant only uses salt for softening in the pre-treatment stage. So to answer the question, yes, RO can be used as an alternative to conventional deionisation. The final design of the plant will however depend on the required conductivity of the water.

4. I was told that reverse osmosis units waste a lot of water. Is that true?

RO units have to get rid of the dissolved solids that they remove and also flush the surfaces of the membranes to prevent fouling, this is achieved by discharging between 25 and 30% of the feed to the unit as a waste stream. However, the effluent, or concentrate, from the RO need not be wasted. It can be collected and used for any domestic, but non-potable use, or process wash-down, or it could be fed to a cooling tower, subject to further examination.

5. What are the operating costs?

The main costs are for:-

a. Energy, to power the high pressure pump, which will typically vary in size from 1 to 10 kW, depending on the plant capacity.

b. 5 micron cartridge filters which are replaced on a quarterly basis.

c. Salt for softening the feed water.

We will be pleased to give projected costs for specific systems.

6. How long do RO membranes last?

Typical membrane life is about 3 to 5 years, depending on the nature of the water that is processed and the quality of the pre-treatment. Feed to an RO should be free of chlorine, hardness and suspended solids.

7. What regular attention to RO systems need?

Little or no physical attention is required, apart from a daily visual examination with logging of flows, pressure and conductivity values, all of which can be easily obtained from our plant. The pre-treatment, particularly the softening, also needs daily inspection to ensure that salt levels are maintained in the brine tank and a simple test on the softened feed to the RO to ensure that no hardness is fed to the RO.




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