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.

Our Reverse Osmosis systems are some of the best on the market and operate at a reliable 70% efficiency with low energy membranes. So in other words, for every 100ml of impure water you put through the system, you get 70ml of pure water to service.

This is a pretty good ratio. You may find some companies promising you 80% efficiency, but you should be careful of these, as it simply means that their systems force the membranes to work harder. The result is that the membranes do not last as long and need to be replaced more frequently, thus reducing the overall cost effectiveness of the system. You should also be very careful of cheaply marketed Reverse Osmosis systems, as not all RO processes are created equal. We have come across bargain basement systems that have an efficiency of 25% or less. These are simply not worth your money and time.

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.

    Pre-treatment

    However, Reverse Osmosis does not work on its own. The purification process is only as good as the pre-treatment to the water that is feeding it. There are certain contaminants that will damage Reverse Osmosis, including free chlorine, calcium and magnesium.

    So you have to pretreat the freed water with activated carbon to remove the free chlorine and then a water softener to strip out the calcium and magnesium, before it can be put through the RO system.

    If you fail to do this, then the free chlorine in the water will degrade the membrane and let organic contaminants through, and the calcium and magnesium will scale the membrane up, reducing its efficiency and working life.

    This is the reason many industries consider Reverse Osmosis to be wasteful, time consuming and expensive. The conventional alternative is deionisation.

    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.

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    Vulnerabilities

    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).

    Common Mistakes Made With Reverse Osmosis Systems

    Why do mistakes happen?

    A Reverse Osmosis plant only works properly if three factors are taken into consideration:

    1. Correct professional installation

    2. Thorough pre-treatment of water to remove inorganic and chemical contaminants

    3. Regular maintenance of the plant, including cleaning of membranes and replacement where necessary.

    It goes without saying, therefore, that mistakes arise to the extent that these three factors are neglected or ignored. Problems arise in reverse osmosis systems in cases where:

  • The plant has been poorly designed or installed incorrectly
  • Input water has been insufficiently treated to remove chlorine, calcium and magnesium
  • Membranes are not regularly cleaned or replaced, or the plant pumps are not sufficiently maintained
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    Signs there are problems with your Reverse osmosis system

    The following should be seen as an early warning sign that something is not completely right with your RO plant. If you notice anything like this through routine monitoring or inspection, get on the phone to one of our engineers right away, before a serious issue occurs.

    Reverse osmosis recovery rate is less than 70%:

    For any well-designed RO system, 70% recovery of permeate should be the golden standard you should look for. Should it drop below this figure, it should be treated as a ‘Canary in the cage’ that some maintenance is required. It may be that your membranes need cleaning or replacing, or that you need to get someone in to have a look at the workings of your system.

    Membranes are becoming clogged and/or scaled up:

    Membranes should be regularly cleaned in order to prevent buildup of organic material or calcium deposits. However, they do also need to be periodically replaced. With a well-designed and operated unit you can realistically expect a three-year life span for your membranes before they should be monitored closely for signs they need replacing. A common (and costly) mistake some businesses make is to replace membranes when a simple cleaning would suffice to improve performance. The inclusion of a CIP rig in your reverse osmosis installation will help extend the active life of your membranes and save money in operating costs.

    Ways to maintain peak performance

    There are a number of best practices you can adopt to help sustain your RO plant at peak efficiency.

  • Granular Activated Carbon (GAC) can be installed in an automatic backwashing unit such as the FILTERMAT unit for the removal of free chlorine and organic matter
  • Install a generously sized duplex meter pair of controlled release of water softeners, sized at <30 BVH, (bed volumes per hour flow to resin media volume ratio).
  • Install 5-micron absolute rated depth filters for particle and fouling index reduction.
  • Ensure you have adequately sized feed pumps and pipework installation.
  • Install a CIP (clean in place) and disinfection rig for periodic maintenance of the RO membranes.
  • XLE thin film composite RO membranes will provide high flow and low energy consumption
  • A constant softened feed water of < 4ppm hardness will help prevent RO membrane scaling
  • 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.

    Labstar Reverse Osmosis System

    Are you in need of a good reverse osmosis system?

    The Labstar is a compact reverse osmosis system which provides 98 to 99% total solids rejection. It is suitable for a wide range of manufacturing businesses.

    Reverse osmosis is an ideal water purification solution for many facilities, able to produce water that’s nearly 100% pure with dramatically reduced TDS levels.

    Features include:

  • Cost effective
  • Compact
  • Chemical free
  • 35 litres/hour
  • Integral system pump
  • And much more!

    Enquire about our Labstar reverse osmosis system using the form below…


    FREQUENTLY ASKED QUESTIONS ABOUT REVERSE OSMOSIS

    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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