Technical Articles
Reverse osmosis (RO) membrane elements are an essential component in residential and commercial membrane systems. They are designed to effectively remove impurities and provide clean, purified water. However, the presence of residual chlorine in the water can have a significant impact on the performance and lifespan of these membrane elements. It is important to understand the effects of residual chlorine and take appropriate measures to mitigate its impact.
Overview of reverse osmosis membrane elements
These are thin film composite membranes that consist of multiple layers. These layers allow water to pass through while rejecting impurities such as dissolved solids, bacteria, and viruses. They are highly efficient in removing contaminants and are widely used in water purification applications.Importance of understanding the impact of residual chlorine
Residual chlorine is commonly used as a disinfectant to prevent membrane contamination from biofouling. However, if not properly controlled, residual chlorine can have adverse effects on the RO membrane elements. The oxidation caused by residual chlorine can lead to a decline in the salt rejection rate of the membrane, compromising its effectiveness.The concentration of residual chlorine in the water plays a crucial role in determining the rate of membrane degradation. Even a low concentration of 1PPM (parts per million) of chlorine can cause degradation within 200 to 1000 operating hours, depending on the water quality.
It is therefore essential to monitor and control the levels of residual chlorine in the water to ensure the longevity and performance of the reverse osmosis membrane elements. This can be achieved through proper disinfection techniques, such as using chlorine dioxide or UV sterilization, which are less detrimental to the membrane.
Understanding the impact of residual chlorine on reverse osmosis membrane elements is vital for maintaining the efficiency and lifespan of these components. By effectively managing residual chlorine levels, water treatment systems can ensure consistent water quality and prolong the service life of the membrane elements.
Forming of Residual Chlorine
To prevent membrane contamination of biofouling, chemical substances such as chlorine, sodium hypochlorite, calcium hypochlorite are usually used for disinfection. They rapidly hydrolyzed into hypochlorous in water.Cl2 + H2O ← → HOCl + HCl NaOCl + H2O ← → HOCl + NaOH Ca (OCl) 2+ 2H2O ← → 2HOCl + Ca (OH) 2 in the water as hypochlorous acid, and hypochlorous acid is decomposed into hydrogen ions with the ions. These substances sum of HOCl ← → H ++ OCl- Cl2 NaOCl Ca (OCl) 2 HOCl OCl- is called free chlorine (FAC), after disinfection, they are called Free Residual Chlorine (FRC mg/l CL2). Partial Chlorine and Ammonia in water forms the chloramines after disinfection.
Reverse osmosis (RO) membrane elements are crucial components in residential and commercial membrane systems. These thin film composite membranes effectively remove impurities, ensuring clean and purified water. However, the presence of residual chlorine in the water can significantly impact the performance and lifespan of these membrane elements. Understanding the effects of residual chlorine and taking appropriate measures to mitigate its impact is essential.
Chemical substances used for disinfection
To prevent membrane contamination from biofouling, chemical substances such as chlorine, sodium hypochlorite, and calcium hypochlorite are commonly used for disinfection. These substances help in sterilizing the water and preventing the growth of harmful bacteria and viruses.Formation of chloramines with partial chlorine and ammonia
After disinfection, partial chlorine and ammonia in the water combine to form chloramines. These chloramines, along with residual chlorine, can cause oxidation and lead to a decline in the salt rejection rate of the reverse osmosis membrane. Even a low concentration of 1PPM of chlorine can result in membrane degradation within 200 to 1000 operating hours, depending on the quality of the water.Monitoring and controlling the levels of residual chlorine in the water are crucial for maintaining the efficiency and longevity of reverse osmosis membrane elements. By employing proper disinfection techniques, such as chlorine dioxide or UV sterilization, which are less harmful to the membrane, water treatment systems can ensure consistent water quality and prolong the service life of the membrane elements.
Influence of Residual Chlorine on Membrane Degradation
The residual chlorine and reverse osmosis membrane will form oxidation, its salt rejection rate will decline. Approximately 1PPM of Chlorine will lead to membrane element degradation within 200 - 1000 hours and the speed of this occurring depends on the quality of water. When the membrane is under alkaline conditions, the speed of degradation will be faster than membrane that is slower and medium under acidic conditions. To prevent residual chlorine damage to the membrane film, dichlorination should be implemented. Activated carbon dechlorination has been a standard way of reducing residual chlorine in feed waters, but it may also be done by using Sodium Bisulfite (SBS): NaHSO3+ HOCl→HCl+ NaHSO4.Oxidation and salt rejection rate decline
Residual chlorine in water can have a significant impact on the performance and lifespan of reverse osmosis (RO) membrane elements. When residual chlorine comes into contact with the membrane, it can cause oxidation, leading to a decline in the membrane's salt rejection rate. This decline in performance can result in reduced efficiency and compromised water quality.Effects of chlorine concentration on membrane degradation speed
The concentration of residual chlorine also plays a role in the speed of membrane degradation. Even a low concentration of 1PPM of chlorine can lead to membrane element degradation within 200 to 1000 hours of operation. However, the exact time frame depends on the quality of the water being treated. Higher chlorine concentrations can accelerate membrane degradation, shortening the lifespan of the membrane elements. It is crucial to closely monitor and control the levels of residual chlorine in water treatment systems to ensure the efficiency and longevity of reverse osmosis membrane elements. By employing proper disinfection techniques that are less harmful to the membrane, such as chlorine dioxide or UV sterilization, water treatment systems can maintain consistent water quality and prolong the service life of the membrane elements.Caution with Chemicals Application
- When both the acid and SBS are added to the system, the acid should be added first because the SBS will form Sodium Sulfite in acid conditions.
- Among pretreatment systems, must make sure no residual chlorine flows into the Reverse osmosis or nanofiltration system. If excessive chlorine is found, the SBS should be applied. The amount of is typically 1.8 to 3.0 times of residual chlorine (food grade).