The pretreatment is based on the characteristics of the impurities in the raw water, and is processed by a reasonable process to achieve the water inflow requirement of the reverse osmosis membrane element. Straight Water Soluble Fertilizers Straight Water Soluble Fertilizers,High Quality Straight Water Soluble Fertilizers,Straight Water Soluble Fertilizers Details, CN Hebei Monband Water Soluble Fertilizer Co., Ltd. , https://www.wsfertilizer.com
Common methods for reverse osmosis equipment pretreatment process
For reverse osmosis membrane elements, raw water is not directly accessible in most cases, because the impurities contained in it can contaminate the membrane components, affecting the stable operation of the system and the service life of the membrane components. The pretreatment is based on the characteristics of the impurities in the raw water, and is processed by a reasonable process to achieve the water inflow requirement of the reverse osmosis membrane element. Because its position in the entire water treatment process is before reverse osmosis, it is called pretreatment. (Shaanxi Kaipuwei provides you)
Reasonable pre-processing should meet the following requirements:
1. The reverse osmosis pretreatment must be able to remove the substances contaminated by the membrane in the raw water to meet the water inlet requirements of the membrane elements;
2. Reverse osmosis pretreatment must take into account changes in water quality (such as seasonal water volume, water temperature, etc.) to prevent instability of the entire system caused by fluctuations in raw water quality.
3. The reverse osmosis pretreatment system must be able to operate stably and efficiently, while being simple and easy to operate, reducing investment and operating costs.
The pretreatment process in reverse osmosis equipment is:
Flocculation filtration, multi-media filtration, activated carbon adsorption, precision filter (security filtration), oxidation treatment, sterilization, softening, scale inhibitor dosing
Flocculation and flocculation filtration
The object of flocculation treatment is small particle suspensions and colloids in raw water. The principle of flocculation is to add these chemicals (iron or aluminum salts) to form large particles of floc in the water, then precipitate under gravity and separate from water. Flocculation filtration refers to the addition of a flocculant in water. The water and the flocculant repeatedly contact the flocculation reaction during the process of flowing through the sand carbon filter. When the generated floc reaches a certain volume, it is trapped between the sand column gaps. The trapped floc further adsorbs the fine sassafras in the water, thereby making the water clear. Flocculation filtration also has a certain effect on the colloid.
Adsorption, activated carbon adsorption
The adsorption method utilizes a porous solid substance to adsorb some pollutants in the water on the surface thereof, thereby achieving a method of purifying the water body. The pollutants that can be removed by the adsorption method include: organic matter, colloid, residual chlorine, and also remove color and smell. Commonly used adsorbents are activated carbon, large pore adsorbents, etc., and their forms are divided into powders and solid particles. Currently the most commonly used is granular activated carbon.
Activated carbon is a black porous particle made by carbonization and activation treatment using various raw materials such as bituminous coal, anthracite, husk and wood chips. The design of the activated carbon column is in various forms such as pressure type and gravity type. A pressure activated carbon column commonly used in reverse osmosis pretreatment is similar in form and structure to a mechanical filter. The activated carbon filter can be made into a simple activated carbon column, or it can be combined with quartz sand to form a multi-media filter, which can adsorb residual chlorine, organic matter, and also remove suspended matter.
Precision filter (security filter)
Precision filter, also known as microfiltration, security filtration, it uses processed filter materials, such as filter cloth, filter paper, filter, filter, etc., to remove very small particles.
Ordinary sand can remove most of the solid particles, but the effluent still contains a large number of particles with a particle size of about 1-5 microns. Although the particles are small, after entering the reverse osmosis system, under the concentration of the membrane elements, It can cause irreversible contamination of the membrane element.
The precision filter is often placed behind the pressure filter, and sometimes at the end of the entire pretreatment process to prevent the broken filter material, activated carbon, resin, etc. from entering the reverse osmosis system, so as not to bring the particles generated in the previous process into the lower part. In one process. The inlet and outlet of the precision filter should be equipped with a pressure gauge. The difference can be used to determine the degree of contamination of the filter element in the precision filter. When the pressure difference is greater than 15 psi (0.1 KPa), the filter element needs to be replaced.
Oxidation treatment
Oxidation is a chemical method that uses a strong oxidant to oxidize and decompose pollutants in water. For a reverse osmosis system, oxidation mainly removes organic matter and ferrous iron ions in water. Currently used oxidants are chlorine and oxygen, such as: chlorine dioxide, chlorine, sodium hypochlorite, ozone, hydrogen peroxide, and the like. In reverse osmosis pretreatment, only a strong oxidant is added to interrupt the organic chain, which is converted into a small molecule organic matter, and then removed by adsorption.
Sterilization
Natural waters contain microorganisms, including bacteria, fungi, algae, viruses, protozoa, and the like. If the raw water containing microorganisms enters the reverse osmosis membrane element without sterilization, the microorganisms will be concentrated on the surface of the membrane element under the action of reverse osmosis concentration, forming a microbial membrane, which seriously affects the water production and desalination rate of the membrane element, resulting in pressure drop. Increased, there is a telescope phenomenon. Moreover, after the membrane element is contaminated by microorganisms, the cleaning effect is not good, so it is necessary to carry out sterilization treatment, especially sea water, surface water, and waste water.
Sterilization currently has physical sterilization and chemical sterilization. The physical sterilization uses ultraviolet light with a wavelength of 254 nm. After the ultraviolet light is irradiated, the ultraviolet spectrum energy is absorbed by the bacteria, and the vitality changes, and the synthesis of proteins and enzymes in the bacteria is hindered, resulting in mutation or death of the microorganism. Chemical sterilization mainly adopts a method of adding a bactericide, and an oxidizing sterilizing agent such as chlorine gas, chlorine dioxide, ozone, etc. may be added, and a non-oxidizing bactericide such as DBNPA (dibromo- cyanoacetamide) or isothiazoline may also be added. Ketone, formaldehyde, etc. When using oxidizing bactericides, it must be noted that ordinary reverse osmosis membranes have poor oxidation resistance. Therefore, in the pretreatment of adding oxidizing bactericide, a corresponding process must be provided to remove residual oxidants, which can usually be directly adsorbed by activated carbon.
soften
Softening refers to the treatment of chemical methods to remove hardness in water. Divided into two types: ion exchange softening and drug softening.
The softening of the drug is based on the principle of solubility product, and the hardness contained in the water is converted into a poorly soluble compound under appropriate conditions, and then precipitated and removed. The softening of the drug usually adopts the lime softening process, which can effectively reduce the concentration of calcium, magnesium and barium. However, due to the use of a dedicated reactor, the pH of the produced water will increase accordingly, and the operating cost is high. Currently, reverse osmosis pretreatment is often used. The method is softening by ion exchange.
Ion exchange softening refers to the use of an ion exchanger to react a calcium-magnesium plasma in a water body with an effective exchange group (usually sodium ion) of an ion exchanger to soften the water. Since ion exchange softening requires resin regeneration, it takes regeneration liquid (usually industrial salt), and also has high concentration of salty wastewater. For high hardness water economy, it is only used in small systems, and large and medium-sized systems are generally used. Scale inhibitors are added to prevent inorganic salt scale contamination.
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