Technical principle and development process of water purifier

Water purifier overview

This is a machine that purifies tap water. With the improvement of people’s living standards, water pollution is becoming more and more serious. So there is a “water purifier” that can purify tap water, thereby achieving a non-toxic and potable effect. .
As one of the high-tech in the 21st century, due to the serious pollution of water source and secondary pollution, it is difficult to achieve the effect of deep purification of domestic drinking water with ordinary filter media. Ultrafiltration membrane purification technology uses high-precision pure physical filtration principle, the filtration accuracy reaches 0.01 micron, without adding any chemical substances, relying on the dense pores on the surface of the ultrafiltration membrane for sieving, thereby retaining harmful substances, thereby achieving filtration purification, Purification effect. At the same time, the ultrafiltration membrane filtration has the function of flushing and discharging sewage. By flushing the ultrafiltration membrane filaments forward and backward, the trapped pollutants can be flushed out and the service life of the ultrafiltration membrane filaments can be prolonged. In addition, ultrafiltration membrane filtration can be realized only by the pressure of the tap water itself, without electricity and pressurization. It has the characteristics of low voltage and no phase change, low energy consumption, safety and energy saving. With the development of membrane technology and production scale, ultrafiltration membrane performance has become more stable. At present, it is the mainstream technology for purifying drinking water. At the same time, it is widely used in beverages, biology, food, medicine and other fields.

Overview of ultrafiltration membrane technology

● One of the high-tech in the 21st century;
● One of the most promising high-tech in the 21st century;
● Low temperature operation at normal temperature, no phase change, low energy consumption;
● Main trend technologies for drinking water and sewage treatment.
Ultrafiltration membrane separation technology, as one of the six high-tech in the 21st century, has become the standard of the separation process due to its remarkable characteristics such as normal temperature, low pressure operation, no phase change, and low energy consumption. Ultrafiltration membrane performance becomes more stable and membrane cost is greatly reduced. At present, ultrafiltration membranes have been widely used in drinking water purification, industrial water treatment, beverages, biology, food, medicine, environmental protection and many other aspects.

Ultrafiltration membrane filtration principle

Ultrafiltration is a screening process using membrane separation technology. The pressure difference across the membrane is used as the driving force, and the ultrafiltration membrane is used as the filter medium. Under certain pressure, when the original solution flows through the membrane surface, many fine micropores densely distributed on the surface of the ultrafiltration membrane only allow water and small molecular substances to pass through and permeate, while the material in the original solution having a volume larger than the micropores on the membrane surface is trapped in the membrane Into the liquid side and concentrated, so as to achieve the purpose of purification, separation and concentration of the original liquid.
There are about 6 billion 0.01 micron pores per meter of ultrafiltration membrane wire wall. Its pore size allows only water molecules, beneficial minerals and trace elements in the water to pass through, while the smallest bacterial volume exceeds 0.02 microns. Therefore, bacteria and colloids, rust, suspended matter, sediment, macromolecular organic matter, etc., which are much larger than the volume of bacteria, can be retained by the ultrafiltration membrane, thereby realizing the purification process

1. Ultrafiltration membrane water production process

Tap water first enters the ultrafiltration membrane tube. Under the effect of water pressure difference, many 0.01 micron micropores densely distributed on the membrane surface only allow water molecules, beneficial minerals and trace elements to pass through, and become purified water. However, harmful substances such as bacteria, rust, colloid, sediment, suspended matter, macromolecular organic matter, etc. are trapped in the ultrafiltration membrane tube and discharged when the ultrafiltration membrane is cleaned.

2.Ultrafiltration membrane washing process

After using the ultrafiltration membrane for a period of time, harmful substances such as bacteria, rust, colloids, suspended matter, and macromolecular organic matter will adhere to the inner surface of the ultrafiltration membrane, which will gradually reduce the water production of the ultrafiltration membrane, especially when the quality of tap water When it is seriously polluted, the ultrafiltration membrane is more likely to be blocked, and regular washing of the ultrafiltration membrane can effectively restore the membrane’s water production.

3. Ultrafiltration membrane filter

Cast the bundled ultrafiltration membrane wire into the super filter element shown in the figure below. The filter element is composed of an ABS shell, an epoxy resin head at both ends of the shell, and a bundled ultrafiltration membrane wire. The epoxy resin head fills the gap between the membrane filament and the membrane filament to form a separation between the original liquid and the permeate. The raw solution first enters the pores of the ultrafiltration membrane, and becomes the permeate after being filtered by the ultrafiltration membrane, preventing the raw solution from directly entering the permeate without filtering.

4. Calculation of total membrane area of ​​ultrafiltration membrane filter element:

In the case of constant water production per unit membrane wire area, the larger the membrane area filled by the filter element, the larger the total water output of the filter element.
The calculation formula is:
S = πdL × n (inside)
S = πDL × n (outside)
Where S is the total internal surface area of ​​the membrane filaments and D is the inner diameter of the ultrafiltration membrane filaments;
S (outside) is the total external surface area of ​​the membrane filament, and D is the outer diameter of the ultrafiltration membrane filament;
L is the length of the ultrafiltration membrane wire;
N is the number of ultrafiltration membrane filaments.
Internal pressure and external pressure hollow fiber ultrafiltration membrane
Ultrafiltration membranes consist of hundreds to thousands of hollow fiber filaments. Generally, a hollow fiber membrane with an inner diameter of 0.6-6 mm is called a capillary ultrafiltration membrane. The inner diameter of the capillary ultrafiltration membrane is large, and it is not easy to be blocked by large particles.

According to the different water inlet methods, the ultrafiltration membrane is divided into internal pressure type and external pressure type:
1.Internal pressure type:
That is, the raw liquid first enters through the hollow fiber, and is driven by the pressure difference to penetrate through the hollow fiber in the radial direction from the inside to the outside, while the concentrated liquid remains in the hollow fiber and flows out from the other end.
2.External pressure:
The hollow fiber ultrafiltration membrane passes through the hollow fiber to penetrate the raw liquid from the outside to the inside in the radial direction through the pressure difference to become the permeate, and the trapped material is collected outside the hollow fiber.

Characterization of ultrafiltration membranes

Ultrafiltration membrane performance usually refers to the physical and chemical properties of the membrane and its separation and permeability properties. The physical and chemical properties mainly include the mechanical strength, chemical resistance, heat-resistant temperature range and applicable pH range of the film. Separability and permeability mainly refer to the water flux, cleavage molecular weight and retention of the membrane.
Ultrafiltration membrane materials and characteristics
Main raw materials: polyacrylonitrile, polyvinyl chloride, polyvinylidene fluoride, polyethersulfone, etc.
Polyacrylonitrile film:
● Excellent chemical stability, acid resistance, alkali resistance and hydrolysis resistance, can be widely used in various fields.Low film filament has good strength and flexibility;
● After hydrophilic modification, the water production is large and the pollution resistance is strong.
● The film silk has fewer formula materials and the process is easy to control. There will be no problems with the film itself due to excessive PVC raw material formula.Polyvinylidene fluoride film: Excellent UV, pollution and chemical resistance;
● The temperature can reach 140 ℃. Ultra-high temperature steam and ethylene oxide can be used for sterilization.
● It can be used in a wide range of pH (1-13), it can be used under strong acid, strong base and various organic solvents.

Factors affecting water production

1. Effect of temperature on water production: As the temperature increases, the activity of water molecules increases and the viscosity decreases, so the water production increases. On the other hand, water production is reduced, so even the same ultrafiltration system can have very different water production in winter and summer.
2. The effect of operating pressure on water production: The water production of ultrafiltration membrane is proportional to the pressure in the low pressure section, that is, the water production increases with the increase of pressure, but when the pressure value exceeds 0.3 MPa, The increase in water volume is also small, mainly due to the increase in water permeability resistance due to the compression of the ultrafiltration membrane under high pressure.
3. Influence of inlet turbidity on water production: the larger the inlet turbidity, the smaller the water production of the ultrafiltration membrane, and the larger the inlet turbidity, the more easily the ultrafiltration membrane will be blocked.
4. The effect of flow on water production: The effect of flow change on water production is not as obvious as the effect of temperature and pressure. Too slow flow rate can easily cause blockage of ultrafiltration membrane, while too fast flow rate will affect water production.
With the growing global industry, most water bodies are seriously polluted, exacerbating the contradiction of water shortage. Traditional tap water treatment methods can no longer guarantee the provision of high-quality drinking water, and there are two pollution problems in urban water supply. For example, high-rise tank water supply and long tap water pipelines can cause potential pollution problems such as rust, scaling and microorganisms. Therefore, various brands of water purifiers came into being.

Classification of water purifiers

According to water quality treatment technology, it can be divided into the following five categories:
1. Microfiltration membrane filtration technology: the pore size ranges from a few microns to a few microns, and is generally used for pretreatment of drinking water advanced treatment systems.
2. Ultrafiltration membrane ultrafiltration technology: 0.01 micron micropore, requires municipal qualified tap water.
3. Nanofiltration membrane filtration technology: the pore size is between reverse osmosis and ultrafiltration, and the range is about several nanometers.
4. Reverse osmosis membrane pure water technology: 0.0001 micron micropore. The effluent is pure water and requires a relatively large water pressure, which is usually assisted by a pump.
5. Electrolysis technology: The pH of water can be adjusted by decomposing the water in the current.

How to buy a household water purifier?

1. Pure activated carbon filter water purifier: used to purify water quality and remove residual chlorine, sediment, organic matter and other impurities in the water through activated carbon adsorption. Its disadvantage is that it cannot filter out harmful substances in the water, such as bacteria, microorganisms, heavy metals and other harmful substances. In addition, due to the adsorption saturation of activated carbon and other factors, bacteria and organic matter can also grow. Therefore, the filter element needs to be replaced every six months or three months, and the filtered water is not drinkable.
2. Ultrafiltration membrane filter water purifier: used to purify water. Macromolecular substances in the water, including silt, rust, bacteria and some organic substances, are removed by membrane filtration. The disadvantage is that the residual chlorine, heavy metals and other small molecules in the water cannot be removed. The taste of the filtered water outlet is not good.
3. Ion exchange water softener: by reducing the content of calcium and magnesium ions in the water to soften the water quality and reduce the hardness of the water. The disadvantage is that strong chlorine, bacteria, microorganisms, various organic substances, heavy metals and other harmful substances cannot be removed from the water, filtered water cannot be consumed, and long-term drinking of soft water is likely to cause cardiovascular disease. Some data show that among people who drink soft water (calcium and magnesium content below 3.0 mg / L), the age mortality of cardiovascular disease is 15% -20% higher than that of people who drink hard water. Drinking soft water is not good for human health.

What is the difference between a water softener, water purifier and water purifier?

Water Purifier:
Function: It can filter out chlorine, odor, bacteria, heavy metals, colloids and other impurities above 0.02 microns in tap water. This water can meet the standards of raw drinking, and retain useful minerals in tap water.
Features: no motor, no power supply, hydraulic drive filter. There is no water storage tank, there are five levels of filtration and integrated. Five-stage filtration, the first stage is a filter element, the second and third stages are activated carbon, the fourth stage is a hollow fiber membrane or ceramic filtration, and the fifth stage is a refined activated carbon, which is mainly used to improve the taste. The whole is a tank, and all filter materials are contained in the tank.
Pure water machine:
Function: Filter out all substances above 1/10000 microns in tap water. The purity of water is higher than that of a water purifier, which is equivalent to the pure water we buy. Compared with water purifiers, water purifiers can only filter impurities. The water purifier also filters out calcium, magnesium ions and minerals in the water. If you want the water in your water purifier to contain minerals, you can add a type of maifanite. Therefore, mineral water is mineral water rich in minerals. Of course, this kind of mineral water is definitely better than water that the water purifier can drink.
In a word: the water in the pure water machine is equivalent to bottled pure water sold outside. If Maifanite is added, it is roughly equivalent to mineral water sold. As for the water purifier, the discharged water is pure water, and tap water contains minerals and can be drunk raw. The main difference is whether the minerals in the water can be filtered (tap water contains both beneficial and harmful minerals).
Features: Motors, power supplies and water storage tanks are generally five-stage filtration, the first stage is a filter element, the second and third stages are activated carbon, the fourth stage is a reverse osmosis membrane for aerospace technology (this is the core), and the fifth stage Refined activated carbon is mainly used to improve the taste. A sixth stage can be added to place Maifan Stone.
water softener:
Function: It mainly softens the water quality, removes the alkaline water in the water, and cannot be directly consumed. It is household water, such as bathing and beauty. Good beauty salons use water softeners to beautify customers.
Features: Resin filtration and regular placement of large salt particles restore the vitality of the resin.

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