In the competitive field of reverse osmosis (RO), purity is expected and water treatment or desalination plants are required to operate around the clock to produce clean drinking water or industrial process water.
In the water processing RO units, the main RO element is the membrane. In presence of chlorine, the membrane may be damaged beyond the point that chemical cleaning can restore the system back to its original operating efficiency.
The use of raw water without chlorine is highly desirable to extend the RO membrane’s life. Proper process monitoring of the chlorine presence can provide advanced warning and protection with the help of online sensors showing no-drift in the said chlorine absence.
Depending what the membrane material is, several parameters can affect its properties and as such the RO performance.
Lately, aromatic polyamide has emerged as the most prominent material for thin film composite (TFC) reverse osmosis and nanofiltration membranes.
However, these membranes are susceptible to chemical attacks from free chlorine and other strong oxidising agents, creating points of leakage for dissolved salts to pass through which results in significantly lower water quality.
A membrane loses its performance after about 1,000ppm•h upon “chlorine” exposure and is considered degraded when salt rejection drops below 90 per cent.
This necessitates the removal of this “chlorine” from the feedwater before desalination. Removing the chlorine residuals can be done by injection of chemicals, by carbon bed adsorption, or by 254nm ultraviolet irradiation.
Each of these methods comes with its weaknesses. Unregulated chemical injections imply unnecessary consumption of chemicals, and charge on the RO membrane. Chlorine is widely used as a disinfectant for drinking water all over the world.
Confirming the “dechlorination” efficiency in the use of raw water with zero chlorine content has the desired effect of extending the RO membrane’s life and bringing down costs in desalination plants.
Protect and monitor
Monitoring the absence of chlorine content in water after pre-filtration is one way to extend the life of the RO membrane.
Several methods exist to measure chlorine residuals; the most well-known and used are: DPD colorimetric detection, oxidation reduction potential (ORP) and amperometric methods.
Protection of the RO membrane against chlorine attacks enhances process efficiency and increases the durability of process technology.
Feed-forward/feedback control techniques, integrating multiple chlorine monitoring, optimise the raw water’s dechlorination.
With its technology advantages in chlorine absence, such as the long measurement stability and its low detection limit, an amperometric sensor with immobilised membrane – Type MS02 Chlorine (Cl2)/chlorine dioxide (ClO2) Sensor Cube – is an innovative option from Bürkert to control and protect the RO unit in real time.
But how do you find the fault if your water quality drops by way of membrane damage? Parameters such as water conductivity shed light on this; if pollutants pass through the diaphragm, the conductivity increases.
At Bürkert, we have developed an automated system that allows you to monitor your permeate at any time and to detect membrane defects in the individual pressure pipe at an early stage.
It automatically monitors the permeate of the individual pressure pipes in reverse osmosis or nanofiltration plants, enabling you to locate errors early on and rectify them quickly and preemptively.
Be it water treatment or seawater desalination, once installed, the solution provides you with a quick and easy overview of large plants.
As a result, downtime is reduced, while performance is increased and the permeate quality is in the desired range.
Each system is customised to meet the requirements of our customers with software adapted to their needs.
From zero-chlorine monitoring solutions through to automated permeate monitoring solutions, our decades of experience supporting industrial water and water treatment industries should provide peace of mind. At Bürkert, we make ideas flow.
This partner content is brought to you by Bürkert Fluid Control Systems. For more information, visit www.burkert.com.au.
