If hollow fiber membranes are the three thousand troublesome fibers, reverse osmosis membranes are the core with a thousand knots. The common voice of membrane mages: "Magic mirror, magic mirror, tell me why the reverse osmosis membrane is blocked again?" Reverse osmosis membrane: "Guess!" Reverse osmosis membrane is the "soft girl" in the membrane, very delicate and fragile. When the grille, biochemistry, and ultrafiltration have blocked most pollutants and the water is already clean, whether we can block it or not depends on our mood. The joke ends, let's get back to the point. Below is a summary of the reasons why reverse osmosis membranes are clogged:
In reverse osmosis desalination systems, the selective permeability of the membrane allows water molecules to continuously pass through the membrane from the high-pressure side, while solute molecules remain in the original solution, resulting in a concentration difference between the feed liquid on the membrane surface and the inlet feed liquid. In severe cases, a high concentration gradient can be generated, which is called concentration polarization. Concentration polarization increases the osmotic pressure of the feed solution and reduces the effective driving force, resulting in a decrease in permeability and desalination rate. For example, it's like waiting for a train at a busy subway station during rush hour, and coincidentally, we don't have the habit of queuing up and giving way. When the train arrives, everyone rushes in, and the more people behind, the tighter the crowd gets, making it difficult for those in front to get in.
2. Inorganic salt scaling: Salts with small solubility products such as CaCO3, CaSO4, BaSO4, SrSO4, CaF2, and SiO2 may precipitate during reverse osmosis due to concentration exceeding their solubility products, resulting in sediment staying on the membrane surface or forming scale in the inlet channel. 3. Adsorption pollution belongs to the range of brackish water. Some well water sources generally contain low-priced iron ions and manganese ions, which have certain reducibility. The main reason for membrane fouling and blockage in such water sources is the colloidal particle fouling and blockage caused by iron, aluminum, manganese, etc. on the membrane surface. When O2 enters the influent containing Fe2+, the high alkalinity water source forms iron carbonate and iron silicate. Reducing bacteria are mixed in, and the formation of iron scale becomes faster and faster. The conversion of iron flocculant causes colloidal iron... Emma, it's so lively! The characteristic manifestation after metal pollution is a decrease in water production and an increase in pressure difference. 4. The formation of biological sludge comes from surface water and sewage sources, and most of the problems encountered are biological sludge. When the surface of the membrane is covered with microbial sludge with strong vitality, the salts removed by the membrane will be trapped in the viscous layer, which is not easily washed away by water, providing abundant nutrients for microbial reproduction. At the same time, the scale inhibitors, water softeners, etc. added during the pre-treatment of reverse osmosis inflow can promote microbial growth.
5. Colloidal pollution of groundwater and surface water contains substances such as iron, aluminum, silicon, and organic matter. These substances, along with coagulants, coagulants, and scale inhibitors added during pretreatment, form colloids that deposit on the membrane surface, causing colloidal pollution. Colloidal pollution is difficult to treat because it carries the same charge, is relatively stable, and is not easy to settle. However, when RO membrane filters water, it is trapped on the membrane surface, forming hydrates, which can easily contaminate the membrane and lead to a decrease in water flux. This trend is generally evaluated using the Pollution Index (SDI). Usually, when SDI<3, there is no such fouling on the membrane surface; When SDI>3, fouling will occur. Attention, this is the most difficult type of pollution to deal with!
6. For reverse osmosis systems, due to unreasonable design, there is a large amount of air inside the membrane shell during the initial debugging stage. When the liquid to be treated instantly enters the membrane shell, the air is compressible and cannot be completely discharged in an instant; When the air reaches a certain pressure inside the membrane shell, it will suddenly burst and release, causing the reverse osmosis membrane to collide, squeeze, and move inside the membrane shell, resulting in the phenomenon of "water hammer". In reverse osmosis systems, the hazard of water hammer is the irreversible damage to the reverse osmosis membrane components. Of course, this phenomenon can also be avoided through well-designed solutions.
7. Suspended particulate matter security filters may cause leakage of filter media, corrosion debris, and foreign objects (such as small core yarn) due to "short circuits" or defects, or incomplete flushing of reverse osmosis during initial use, which may contaminate the membrane components, block the inlet channel, and form amorphous precipitates on the membrane surface. But this situation is rarely encountered.
8. Pollution caused by other factors, such as hydrocarbons and silicone based oils and lipids covering the membrane surface, leading to membrane contamination; The hydrolysis of membranes, erosion by organic solvents and oxidizing substances can also cause fundamental changes in membrane materials. If the membrane is dirty, it can be washed. If the membrane is broken, don't mention the past anymore. Everything becomes a fleeting past. If you want reverse osmosis membranes to be less prone to fouling, you need to purchase anti clogging and anti fouling reverse osmosis membranes!
