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Reverse Osmosis: One Of the Most Important Desalination and Water Recycling Technologies of the 20th/21st Century

 

Introduction

Reverse Osmosis is one of the water treatment technologies that I am most passionate about. And who wouldn’t be interested in a polymer membrane which when seawater is pushed hard enough through it, potable water comes out the other end? I mean Jesus turned water into wine but RO technology can turn seawater into drinking water !

My Experience with RO Technology

I started working with RO systems in 2007 in Bulgaria at a coal fired power station. Surface water was treated in a 3 stage RO to create desalinated water which was then completely demineralized using a Mixed Bed Ion Exchange system (MBX) to create ultra-pure water for the boilers. It had an excellent classical pre-treatment system and with regular CIP’s (Clean In Place), the membranes lasted 10 years.

 

 

Problems That RO Technology is Prone To

RO’s are awesome but they are prone to fouling (silt, colloids or organic fouling), scale, and biofouling. So a carefully designed water-pretreatment system is needed to minimise these phenomena and sometimes you just have to live with them and manage them through good operations practices. Good O&M practices are also vital.

When an RO system starts to show signs of increasing normalized pressure or decreasing flow, conduct a troubleshooting and then decide if a cleaning is in order. Have a look at our RO Cleaning Chemicals document. We also have a presentation on performing autopsies on RO membranes.

Manufacturers of RO Membranes

The most reputable RO membrane manufacturers are DOW/DuPont’s Filmtech, Hydranautics and TORAY. The Koreans are also starting to make good RO membranes with their LG brand. The Chinese are catching up fast with their Vontron brand.

Not only can they treat Brackish and Seawater, RO’s are starting to be used to treat tertiary Sewage effluent as well as industrial effluent such as mining waste water which can sometimes contain heavy metals. Many cooling towers can recycle some of their blowdown using RO technology.

RO System Design

RO system design uses RO Projection software which is normally free to download from the RO membrane supplier and this software creates a projection based on the water chemistry which calculates the needed feed pressure as well as things like the need for pH correction or dosing an anti-scalant. Download our presentation on RO Software Projections.

RO’s produce a reject stream also called brine and for sea water RO, it is pretty salty and people worry about its environmental impact when discharged to the environment. However, the technology is constantly evolving and Ultra High Pressure RO can now squeeze more water out of the brine. It works with pressures up to 120 bar !

RO Operations and Maintenance

RO Operations requires careful monitoring of RO system parameters on a daily and weekly basis. When the RO systems shows signs of decline in performance, proper maintenance needs to be performed which normally includes a CIP.

Download our detailed presentation on RO DOM: Design, Operations and Maintenance. Our presentation on Software Projections might also be useful.

RO Technolgy Training

All these interesting topics I teach in my Complete Water Treatment Course or if you choose you can sign up for CIWEM’s Introduction to Reverse Osmosis course which I developed and also tutor. Also make sure you have a look at my free RO presentations on the homepage.

 

Conclusion

If you are replacing RO membranes too often, say once every 6 months, know that it is highly likely that something is wrong with the pre-treatment system. Sometimes an RO Autopsy is needed which will tell you what is causing the failure. Sometimes just looking at the water chemistry is enough to predict what is causing the problem.

Many countries that have access to seawater with arid climates and low rainfall rely on RO technology to desalinate seawater and produce drinking water. For example, Saudi Arabia and Israel. Spain and Greece too. In fact, Israel is home to IDE, one of the most innovative companies when it comes to RO technology. I met the CTO in 2023, Dr Boris Lieberman, who was the engineer that designed the first RO system for the Kremlin in Moscow.

I hope I have piqued your interest in RO Technology. Any one with questions/RO issues feel free to ask, or for clients seeking consultations, send an RFI/RFQ.

 

Kind regards,

Rami Elias Kremesti M.Sc., CSci, CEnv, CWEM

 

Your RO Technolgy Expert Consultant

 

Biography of the Author:

 

Rami Elias Kremesti is a chartered water and wastewater treatment specialist with a background in chemistry. He has worked on a myriad of water treatment and power station projects internationally. He is a British Citizen based out of High Wycombe, UK. He has published three books on philosophical topics which he loves to ponder in  his spare time.