Reverse Osmosis Plant: Process, Pretreatment & Maintenance

The scarcity of clean drinking water has made reverse osmosis technology one of those terms that we all use without understating what it means! Most of us, though, think of the little RO machines we have fixed up in our kitchens. Indeed the RO technology is actually one of the most commonly used water purification techniques.

However, its utilisation goes far beyond our little kitchen units. From industrial to military applications, RO technology actually has a wide application. It is not just used to clean waters, the RO technology is equally effective in filtering any liquid. This is why it is even used in fruit juice manufacturing units. In short, reverse osmosis plant manufacturers work with a range of different fields and industries.

What is reverse osmosis?

To understand reverse osmosis we first need to understand osmosis. This is a phenomenon that occurs very frequently in nature. This is a processes where the molecules of a less concentrated solution will pass a semipermeable membrane to join a more concentrated solution. We can see this taking place all around us. Osmosis is why water from soil moves towards the roots of a plant. So, a less saline solution will move towards a more saline solution.

Now reverse this process and you get reverse osmosis. Here, the semi-permeable membrane will allow the movement of water while barring dissolved salts, bacteria, pathogens and other organic matter. However, where osmosis occurs naturally, reverse osmosis needs an extra ‘push’, an energy applied from an outside source. This energy has to counter and exceed the natural osmosis process. In other words, reverse osmosis needs an extra boost of energy to push water against its natural osmotic flow.

How does it work?

The extra force for the RO process comes from a pump that puts high pressure on the saline or contaminated side to push it through the semi-permeable membrane. Almost all the dissolved matter is left on the other side. This is the reject steam. Sometimes the reject water is again taken through the RO unit for maximum utilisation.

The water we get is, hence, free of most organic matter or completely deionised. This is also known as permeate water. It is free of almost 95% to 99% of its original dissolved salts. The reject water is simply discarded.

So how does the RO differ from simple filtration? Reverse osmosis plant manufacturers use cross filtration instead of standard filtration. Unlike the standard filtration here the water passes the filter, creating two different outlets. The cleaned water goes to one side, while the contaminated water flows to the other side. There is accumulation of contaminants as in standard filtration. Instead the turbulence generated by cross flow filtration ensures that the membrane stays clean and contaminants are wiped clean.

Pretreatment in RO plants

While our small kitchen units rarely require any pre-treatment, in bigger plants set up by reverse osmosis plant manufacturers this is a necessary requirement. Pretreatment reduces the chances of scaling or fouling that can badly damage the RO membrane. Since the feed water contains less contaminants, the unit also needs less frequent clean-ups than otherwise.

Pretreatments solutions include:

  • Multi-media filter
  • Microfiltration
  • Scale inhibitors and antiscalants and
  • Softening
  • Sodium bisulfite injection
  • Granular activated carbon

Maintenance of RO plants

Many of the RO plants become dysfunctional because of the lack of any maintenance. Ignoring regular maintenance can have disastrous consequences. Not only can it seriously compromise the quality of water purification, it can slowly damage the entire plant. As anyone in manufacturing will tell you, it is less expensive to invest in regular maintenance than rebuilding an entire damaged plant. Not only will that mean a major expense, the stalling of operations and consequent slow-down can be even more damaging.

How do we ensure regular maintenance?

RO maintenance is a specialist job. So, ideally your plant manufacturer should have a maintenance team. It could also prove cheaper to get a maintenance package from the people who are setting up the plant. They will also have specialist knowledge of the plant and be best equipped to carry out regular cleaning and maintenance work. However, there are also plenty of third-party maintenance specialists that you can hire.


Today reverse osmosis plant manufacturers are partnering with a range of industries and institutions. This simple process is one of the most effective means of purifying water. However, the plants need both pretreatment and regular maintenance for proper functioning and long life.

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