Reverse Osmosis

This page is offered to give people a little more insight into reverse osmosis, its functions as a filtration technique and how it can be utilised within water treatment applications.

Many years ago when reverse osmosis made its first steps into the water treatment industry it was expensive, reverse osmosis membranes were nowhere near as efficient or as cost effective as they are today,  also industries that used age old demineralisation filter units for decades were reluctant to change. Gradually, over time as uptake increased, RO technology improved and the benefits gradually negated industries initial reluctance.

The main beauty of reverse osmosis when it comes to industrial water filtration over demineralisation (which could generally be considered its counterpart) is the fact that unlike demin systems reverse osmosis doesn’t require the use of chemicals, therefore its a much cleaner and less time consuming process.

To this day our on site engineers still maintain and service demin systems, however the tide has definitely turned as more and more people see the benefits of switching their own plant from demineralisation over to reverse osmosis. Obviously the initial cost is a genuine concern for most businesses, however when you take into account the chemical usage and the man hours required for the maintenance of demineralisation systems then reverse osmosis can often pay for itself in as little as a year of operation.

How does a typical Demineralisation plant operate?

A typical demin plant functions by using a process called ion-exchange. As raw water is fed into the plant it undergoes an exchange process whereby minerals and salts within the water column are exchanged with acids, this treated solution is then sent onto the next vessel where the newly exchanged acids are absorbed by anion resins.

Over time due to the Anion to Cation exchange process taking place the resins become exhausted and have to be regenerated. Its this regeneration process that requires the use of chemicals, namely hydrochloric acid and caustic soda. This chemical regeneration process cleans the resin beads making the ion-exchange process effective once again.

It is this very process that sets reverse osmosis filtration apart from demineralisation. Hazardous chemicals are not only costly but are also an obvious health and safely concern not only for the plant operators but also for anyone working at or visiting site. All manual handling and safety concerns will need to be addressed and adhered to in order to provide and maintain a safe working environment when working with hazardous chemicals.

Unlike demineralisation reverse osmosis requires no such chemicals so is therefore a much cleaner water treatment process.

How does a typical Reverse Osmosis plant operate?

Reverse osmosis works by forcing pressurised water through either single or multiple membrane elements, the quantity of elements typically equates to the amount of water required, usually referred to in litres per hour (l/ph). The membranes themselves are semi-permeable so as water is forced through the membrane housing(s) at pressure, only water molecules are able to pass through the ro membrane(s) therefore stripping the water of any contaminants including viruses and bacteria (something which demineralisation is unable to achieve).

In a nutshell this is how reverse osmosis works, its beauty is in its simplicity!

However there are some issues that need to be addressed when considering reverse osmosis over other filtration techniques. The most important one being that RO membranes are highly sensitive to certain elements which could be contained within your incoming water feed, the most important of which are chlorine and hardness, both of these elements need to be considered and treated separately when planning for a reverse osmosis plant.

Hard water as we are all probably well aware can cause issues not only in industry but also domestically. The results of scaling caused by hard water can be extremely costly especially on an industrial scale.

As hard water causes scale to build up within pipework, on elements and causes devastating damage to sensitive equipment its these very same effects that are also inflicted upon your reverse osmosis plant, the end result being a reduced output and often times irreparable damage to the sensitive ro membrane elements themselves. As scale damage is often a gradual process the degenerative effects typically take time to be noticed, however once the negative effects from limescale start to be noticed the damage is often already beyond simple repair and costly to resolve.

The simplest way to negate any possible damage to your reverse osmosis equipment is with the installation of a water softener. As the name suggests a water softener softens water by removing calcium and magnesium ions (the main two elements that cause limescale) through an ion exchange process, the end result being softened water free to be passed onto your reverse osmosis filter without causing issues. A correctly sized and properly maintained water softener will eliminate all the harmful scaling effects caused by limescale meaning your equipment will operate more efficiently and your RO membranes will last much much longer.

The second element that will need to be reduced from your incoming water supply is Chlorine. Widely used in mains feed water to prevent the contamination of bacteria and viruses such as Salmonella and Norovirus Chlorine unfortunately has a negative impact on reverse osmosis membranes resulting in a severe performance loss and eventual irreparable damage. Because the RO process is able to remove any pathogens, viruses and bacteria from water the Chlorine within the mains feed can be simply removed with the use of a carbon filter which is a very effective method of Chlorine removal.

As a reputable producer, supplier and installer of industrial reverse osmosis filtration equipment at the very least we would always recommend a pre filtration stage consisting of a water softener and carbon filter, ideally though a water analysis would be initiated in order to determine the exact elements that currently reside within your incoming supply. This will give us the ability to not only correctly size the filtration equipment to your requirements but also to accurately determine  the quality of water you will have once passed though the filtration process.

If you have any questions regarding reverse osmosis, correctly sizing equipment or general water treatment techniques then please contact us. We have a team of experienced water treatment professionals who are always on hand to provide advice and offer help if required.