2020 Water Purifier Filter Knowledge -2

Reverse osmosis membrane (RO) filter element

Naturally, the flow direction of water is from the low concentration direction to the high concentration direction, and the reverse osmosis membrane exerts sufficient pressure on the high concentration side to make the water flow back to the other side of the membrane. The reverse osmosis membrane can retain substances larger than 0.0001μm (ie 0.1nm) (including bacteria and viruses and organic substances with a molecular weight greater than 100) and is currently the most refined membrane separation product on the market. Compared with other filter elements, the water flowing through the reverse osmosis membrane is purer. In addition, reverse osmosis membranes also produce wastewater. The membrane that does not produce wastewater must not be a reverse osmosis membrane.

Nanofiltration membrane (NF) filter element

Nanofiltration membranes are mostly charged membranes, with negative charges on the surface, which can intercept cations with more than two valences in water and retain monovalent ions (such as sodium ions and potassium ions). Therefore, nanofiltration membranes retain some minerals in the water. Material element.

Among the common heavy metal pollutants, arsenic mainly exists in the water as trivalent arsenic ions and pentavalent arsenic ions; chromium mainly exists in the form of trivalent and hexavalent ions in nature. So the nanofiltration membrane can also filter out most of the heavy metals. It can also remove part of calcium and magnesium, so it has a certain effect in softening hard water.

At the same time, nanofiltration membranes can reduce organic matter in water and carcinogens such as trihalomethanes produced during chlorination and disinfection of drinking water.
The smallest known virus has a diameter of 18nm-22nm (data from Wikipedia). Compared with the pore size of nanofiltration membranes of 1-2nm, bacteria and viruses are relatively large, so nanofiltration membranes can be effective Removal of bacteria and viruses does not seem so difficult to imagine.

The working principle of the nanofiltration membrane is partially similar to that of the reverse osmosis membrane. The pressure it bears is lower than that of reverse osmosis membrane, so it produces less wastewater than reverse osmosis membrane.

Ultrafiltration membrane (UF) filter element

The pore size of the ultrafiltration membrane is 0.01μm (10nm). Many water purifiers will emphasize that water purifiers that only use ultrafiltration membranes retain minerals in the water and do not produce wastewater. Well, that's right. But ultrafiltration membranes cannot filter out heavy metals. It can effectively filter out bacteria (the smallest known bacteria is 0.2μm (200nm) long) and some larger viruses.
In some areas, the water is hard water, that is, water with relatively high calcium and magnesium content. This kind of water tastes bad. If you want to convert it into soft water, a water purifier using only this membrane cannot meet the demand.

Ceramic filter
The ceramic filter element can filter out sediment, debris, and bacteria by the small pore size of the ceramic material. It is a kind of microfiltration membrane (MF). The silver ions attached to the ceramic have a sterilizing effect. Regarding the filtration accuracy of the ceramic filter element, the dual-control membrane ceramic filter element with the highest filtration accuracy in the world has an average pore size of 0.1μm. According to this standard, although the ceramic filter element can filter out any bacteria, it cannot filter out many viruses.

Ceramic itself cannot remove chemical pollutants, but the ceramic filter element integrated with high-performance activated carbon can reduce organic pollutants and metal pollutants, and has the function of removing residual chlorine and decoloring. However, this kind of composite ceramic filter element must be replaced regularly, because although the ceramic surface is easy to clean, the activated carbon filled in the ceramic will be blocked after a period of use. If you think about it, you will know that the adsorption effect is minimal or no Up.

Resin filter element
Exchange resin filter elements are commonly used to soften hard water. Cannot filter heavy metals.