Users occasionally encounter problems when using pure water equipment, such as scaling of the reverse osmosis membrane and water leakage from the pure water equipment joints. Initially, this may not be a major concern, but the problem will worsen over time. Let's look at the causes of reverse osmosis membrane scaling.

First, during the operation of the pure water equipment, freshwater is produced during the low-pressure flushing process, which naturally increases the concentration of water on both sides and leads to an increase in salt concentration. The salt contains a large amount of precipitable substances, which will eventually lead to scaling.

Second, uneven chemical addition is also an important reason for reverse osmosis membrane scaling. If the antiscalant device leaks severely, it may affect the dosage of the antiscalant. If the operators do not pay enough attention during operation and do not flush the system in time during shutdown, it will also lead to reverse osmosis membrane scaling.

Oxidation of the reverse osmosis membrane is also a phenomenon that easily occurs during the use of the reverse osmosis membrane. Oxidation will inevitably affect its performance. Several common oxidation phenomena of reverse osmosis membranes:

Chlorine attack: Chlorine disinfectants added to the reverse osmosis system's feed water are not completely consumed during pretreatment and enter the reverse osmosis system, resulting in oxidation. Trace amounts of residual chlorine react with heavy metal ions in the feed water to cause catalytic oxidation in the desalination layer. The use of oxidizing disinfectants other than chlorine, such as chlorine dioxide, potassium permanganate, ozone, and hydrogen peroxide, in water treatment will also cause oxidation.

During use, we should take some measures to prevent the oxidation of the reverse osmosis membrane. First, ensure that the feed water of the reverse osmosis membrane does not contain residual chlorine: Generally, tests are conducted before the feed water enters the system using instruments to ensure that no residual chlorine is present. When taking sterilization measures, appropriate disinfectants should be selected, and the reverse osmosis membrane system should be cleaned separately from other systems.

After running for a period of time, pollutants in the water will pollute the filtration equipment. The RO membrane is the core technology of reverse osmosis. To quickly determine whether the reverse osmosis equipment is polluted, it is necessary to understand the pollution phenomena and states of reverse osmosis.

Membrane degradation: Hydrolysis of Hydranautics reverse osmosis membrane elements is caused by excessively low or high pH values, oxidation (e.g., various oxidants), and mechanical damage, such as water hammer, membrane wrinkling, overheating, and abrasion caused by fine carbon or sand particles, can all cause degradation of reverse osmosis membrane elements.

Sediment deposition: If insufficient measures are taken or inappropriate measures are taken, sediment deposition can occur. Common sediments include carbonate scale, sulfate scale, and silica scale.

Colloid deposition: Colloid deposition is generally caused by metal oxides and various other colloids.

Organic matter deposition: Natural organic matter, oils, excessive antiscalants and iron precipitation, and excessive cationic polymers (from pretreatment filters) are all sources of organic matter.

Biological fouling: Microorganisms can form biofilms on the surface of Hydranautics reverse osmosis membrane elements, and bacteria can erode cellulose acetate membranes. These microorganisms include algae and fungi.

So, at this point, many people may ask, how does the reverse osmosis membrane become a "telescope"? In fact, the "telescope" phenomenon of the reverse osmosis membrane is a type of mechanical damage, where the outer casing of the membrane element is misaligned with the membrane element and shifts downstream, sometimes even overlapping the next membrane element. A slight "telescope" phenomenon may not damage the membrane element, but severe cases may cause cracks in the bonding lines and membranes.

The so-called "telescope phenomenon" refers to the situation where the pressure difference between the feed water side and the concentrate side of the reverse osmosis exceeds the limit, causing the membrane sheets and membrane sheets within the reverse osmosis membrane element, and the membrane sheets and the central tube to slip, resulting in one end of the membrane element's membrane sheet being concave inward and the other end protruding outward, resembling a telescope.

8-inch membrane elements are more prone to this phenomenon due to their larger membrane cross-sectional area. It is necessary to ensure that stress rings are installed in the membrane pressure vessel to support the outer casing of the 8-inch membrane elements. Smaller diameter membrane elements are supported by their permeate tubes and stress rings to prevent the outer casing from sliding. If a telescope phenomenon occurs, the damaged membrane element should be replaced with a new one, and the cause should be eliminated.

Every effect has a cause. What causes this "telescope" phenomenon?

First, during installation or removal, the reverse osmosis membranes are misaligned;

Second, the membrane shell does not have sufficient rigidity, and the membrane shell deforms during pressurized operation;

Another important reason is that the system inlet pressure increases too quickly when the high-pressure pump starts.

After membrane compaction, the water production rate usually decreases, and the desalination rate increases. During normal operation, membrane compaction is rare. However, significant compaction tendencies may occur under the following conditions: excessively high inlet pressure, high temperature, water hammer, starting the high-pressure pump when air is present in the reverse osmosis system, and the high-pressure pump pressure increasing too rapidly. This strong impact force on the RO membrane can cause water hammer, easily damaging the reverse osmosis membrane. After membrane element compaction, the damaged membrane elements must be replaced promptly, or additional membrane elements need to be added to the system's rear.

In the reverse osmosis process, due to the continuous passage of water through the membrane, there is a concentration difference between the saltwater near the membrane surface and the inlet saltwater. The concentration of the solution on the membrane surface is higher, which is concentration polarization. As a large amount of water passes through the membrane surface, the concentration increases significantly to become a supersaturated solution. Some salts with low solubility, such as CaSO4 and MgSO4, will slowly precipitate crystals. Initially, these salts are only a few single crystals without crystal nuclei, so they cannot grow. They can only deposit on the membrane surface or form a dissolution equilibrium in the solution. As the concentration of the solution on the membrane surface continues to increase, and the water flow reaches a certain equilibrium, crystal nuclei appear, and the nuclei begin to grow, gradually forming a planar or spiral state. If the external temperature is suitable and there are not many corrosive substances, the crystals will gradually grow, forming a solid scale on the membrane surface, blocking the membrane and greatly reducing water production efficiency.