Selection and Maintenance of Filters in Pure Water Equipment

Faced with a wide variety of pure water equipment on the market, how should we choose and maintain pure water equipment? Here, the relevant professionals of our company will provide you with some suggestions.


The coarse filter is different according to the amount of filtered water. The most common ones are sand filter, wedge wire filter element, and PP fiber filter element. The most commonly used lengths of the non-woven filter element and PP fiber filter element are 10 inches and 20 inches. There are two kinds of filter elements, and the pore size of the filter element used as a coarse filter should generally be about 25u.  
The function of the coarse filter is to remove the suspended impurities with large particle size in the water, to prevent these impurities from entering the activated carbon filter and cover the surface of the activated carbon so that the capillary structure of the activated carbon loses the ability to absorb impurities in the water.   
With the increase of retained solid impurities, the resistance of the strainer rises sharply, and the water flow gradually decreases. If it is not treated in time, the water flow requirements of the subsequent treatment process cannot be met. For sand filters, backwash should be done in time after the pressure rises to a certain level. Part of the fine sand is washed out of the filter during backwashing, so sand should be added to the sand filter regularly. After multiple backwashing, the degree of fragmentation of the sand will increase. The remaining silt in the sand gradually increases, and the sand layer will appear “hardening” phenomenon, and the sand layer should be replaced at this time. For non-woven or PP fiber filter elements, it is generally difficult to rinse with water after the filter holes are blocked, and the filter element must be replaced regularly. 

Activated carbon filter

The function of an activated carbon filter is mainly to remove macromolecular organic matter, iron oxide, and residual chlorine. Organic matter, residual chlorine, and iron oxides can easily poison the ion exchange resin, while residual chlorine and cationic surfactants will not only poison the resin but also damage the membrane structure and make the reverse osmosis membrane ineffective.  
An activated carbon filter uses the abundant capillary pores of activated carbon to adsorb and filter macromolecular organic matter, residual chlorine, iron oxides, and other colloids in water. This adsorption is irreversible, that is, activated carbon has a certain saturated adsorption capacity. After the adsorption is saturated, the activated carbon loses its adsorption performance, and the pollutants cannot be washed away by backwashing. In addition, after the activated carbon adsorbs organic matter, it provides abundant nutrients for bacteria, causing the bacteria to multiply in the activated carbon filter, and the microbial content in the water increases after being filtered by the activated carbon.  
Before the activated carbon is saturated with adsorption, backwash is carried out regularly to flush out a large number of bacterial clusters and suspended solids on the surface of the activated carbon. After the activated carbon is saturated with adsorption, it should be replaced with a new activated carbon immediately, otherwise, it will cause irreparable damage to the reverse osmosis membrane.   

water softener

The function of the water softener is to remove the calcium and magnesium ions in the water and soften the water. If there is no water softener or the water softener fails, calcium and magnesium salts will form insoluble precipitates on the surface of the reverse osmosis membrane due to the sharp increase in concentration, which will block the pores of the reverse osmosis membrane and shorten the service life of the reverse osmosis membrane.  
The water softener used for making pure water generally uses sodium cation exchange resin, which is regenerated with salt after the resin is saturated. After a few years of use, the resin is more and more broken and gradually loses its softening ability. Especially when the activated carbon filter is saturated and the activated carbon is not replaced in time, the iron, organic matter, and residual chlorine in the raw water will directly enter the water softener and poison the resin. Once the resin is poisoned, it cannot be regenerated by regeneration. When the working exchange capacity of the resin decreases significantly, the resin should be replaced.  

Doing a good job in the maintenance of reverse osmosis is the key to ensuring the quality of pure water. During the working process of the reverse osmosis membrane, the salt concentration on the membrane surface is higher than that in the main fluid, a phenomenon called concentration polarization. The consequence of concentration polarization is to make some salts precipitate on the membrane surface, block the water production channel of the reverse osmosis membrane, and reduce the water production capacity of the membrane. The organic matter in the feed water will deposit on the membrane surface when it is not flushed out continuously or periodically, especially some surface-charged reverse osmosis membranes, attract the charged organic matter and stick it on the membrane surface. The deposition of organics on the membrane surface causes more serious damage to the membrane than the precipitation of salts on the membrane surface, and sometimes this damage is irreversible. The concentration of organic matter and various salts on the membrane surface is much higher than that of the main water flow, which provides abundant nutrients for the reproduction of bacteria. A large number of microbial flora not only block the water production channel, but also because the reverse osmosis membrane itself is also an organic matter, it will be decomposed by microorganisms, causing irreversible damage. Oxidative substances in water, such as residual chlorine, are enriched on the membrane surface. After the enrichment reaches a certain level, the concentration exceeds the concentration that the membrane itself can bear, and the reverse osmosis membrane will be oxidized and decomposed by the sub. The above factors all cause the water production of the reverse osmosis membrane to gradually decrease, the salt permeability rate to increase gradually, and the quality of pure water to decline. Under normal circumstances, the service life of the reverse osmosis membrane is three years. If the reverse osmosis membrane is damaged, it should be replaced in time, otherwise it will not only affect the water production, but also deteriorate the water quality.   
A membrane that is selective for the permeable substances is called a semi-permeable membrane, and a membrane that can only permeate a solvent but cannot permeate a solute is generally called an ideal semi-permeable membrane. When the same volume of dilute solution (such as fresh water) and concentrated solution (such as salt water) are placed on both sides of the semipermeable membrane, the solvent in the dilute solution will naturally pass through the semipermeable membrane and flow to the concentrated solution side spontaneously, This phenomenon is called penetration. When the osmosis reaches equilibrium, the liquid level on the concentrated solution side will be higher than that of the dilute solution by a certain height, that is, a pressure difference is formed, and this pressure difference is the osmotic pressure. The size of the osmotic pressure depends on the inherent properties of the solution, that is, it is related to the type, concentration and temperature of the concentrated solution and has nothing to do with the properties of the semipermeable membrane. If a pressure greater than the osmotic pressure is applied to the concentrated solution side, the flow direction of the solvent will be opposite to the original permeation direction, and it will begin to flow from the concentrated solution to the dilute solution side. This process is called reverse osmosis.  
Reverse osmosis is a reverse migration movement of osmosis, which is a separation method that separates solutes and solvents in solution by means of selective retention of semipermeable membranes driven by pressure. It has been widely used in the purification and concentration of various liquids. The most common application example is in the water treatment process, using reverse osmosis technology to remove impurities such as inorganic ions, bacteria, viruses, organics and colloids in raw water. Get high-quality purified water.  

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