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Reverse osmosis system includes three parts: raw water pretreatment, reverse osmosis plant and post treatment. Reverse osmosis system has its specific requirements for the pretreatment of raw water.
Due to the various kinds of raw water, its composition is very complex. According to the requirements of the main process design parameters, such as the water quality of the raw water and the recovery rate of RO system, the appropriate pretreatment process system is selected to reduce the fouling and scaling of the RO film, and to prevent the reduction of the desalination rate and the water yield of the RO membrane, especially for the shortage of water source. With the deterioration of water quality, selecting a correct pretreatment system will directly affect the function of the whole water treatment system. As everyone knows. The failure of the RO system is mostly due to the imperfect function of the preprocessing system. In order to ensure the normal operation of the reverse osmosis process, the raw water must be treated strictly.
The purpose of preprocessing of reverse osmosis system
1. Remove suspended solids and reduce turbidity
2, Control the growth of microbes
3, Inhibition and control of the deposition of micro dissolved salts
4, The adjustment of inlet temperature and PH
5. Removal of organic matter
6, Precipitation control of metal oxide and silicon
Preprocessing method of reverse osmosis system
1、chemical oxidation
Chemical oxidation treatment is usually a chemical treatment method for the decomposition of organic pollutants in water by strong oxidizing agents. At the same time, some oxidants can go out in water, smell, odor, iron, enzyme bath and so on. Some oxidants are also good fungicides.
Chemical oxidant treatment process can be combined with coagulation, filtration, adsorption and other unit processing technology to achieve good treatment effect. The main oxidants commonly used in industrial water treatment are chlorine, sodium hypochlorite, chlorine dioxide, Potassium Permanganate, ozone, hydrogen peroxide and so on.
2、Drug softening
Chemical softening is a project using the principle of chemical precipitation, which is based on the principle of solubility product to make the hardness of water and so on under the action of appropriate chemicals to form an insoluble compound. The longest shadow in water treatment is the chemical precipitation of calcium and magnesium ions, followed by the determination of the chlorides of metal ions. Pharmaceutical softening is usually carried out in conjunction with flocculation, settling or clarification.
The softening agents used in water treatment plants are mainly lime, soda ash, toxic sodium, sodium phosphate three and sodium hydrogen phosphate two. According to the different types of raw water, different chemicals can be used to treat them. The lime softening method is used for water with high hardness and high alkalinity. The water with high hardness and low alkalinity uses lime soda method, and the lime - gypsum method is used for the water with high alkalinity and negative hardness (that is, total alkalinity is greater than the total hardness).
3、Coagulation flocculation
Coagulation is a chemical agent that points to a certain dose of agentia in water. These chemicals are hydrolyzed in water, collide with the particles of the particles in the water, produce electricity neutralization, produce adsorption, bridge and net capture, thus forming large floc particles and settling from the water to reduce particle suspension and colloids. Effect.
Sometimes when coagulant alone fails to achieve the desired effect, auxiliary drugs can be added to enhance coagulation. This auxiliary agent is called as a coagulant, and the coagulant itself can not produce the same effect as coagulant. It can only improve the structure of the floc and make the floc particles increase, toughen and heavy. Therefore, the use of coagulant alone can not achieve good results.
4、Media filtration
Medium filtration is a bed with quartz sand, garnet or anthracite, which makes water through these media under gravity or pressure, and the particulate matter in the water is intercepted by the medium, so that the process of separating water from water is achieved.
5、activated carbon adsorption
Activated carbon adsorption is a method to remove one or more harmful substances from the solid surface by using the porous nature of activated carbon. Activated carbon adsorption has good effect on removing organic matter, colloid, microorganism, residual chlorine, smell and so on. At the same time, activated carbon has a certain reduction effect, so it also has good removal effect on oxidants in water.
6、Disc filtration
Disc filters are made up of filter units and their filtering units are made up of a group of annular reinforced plastic filters with grooves or edges. When the sewage is filtered, the sewage enters from the outside, and the edge formed by the edge edge of the groove on the adjacent filter plate leaves the solid in the water. The water flows from the inside of the annular filter plate to the outside when backwashing, and the pollutants are washed down on the aluminum plate and discharged through the sewage outlet.
The disc filter has the characteristics of large processing function, stable operation and easy control. At present, most of the domestic use is used for ultrafiltration preprocessing, which plays a security role in ultrafiltration.
Disc filters can be divided into two types, semi-automatic washing and full automatic control, and the latter is easier to operate modular control.
7、Security filter
In order to prevent the failure to completely remove or newly produced suspended particles into the reverse osmosis system and protect the high pressure pump and reverse osmosis membrane, a filter core filter is usually set before the reverse osmosis influent.
Filter material mainly includes sintered filter tube, melt blown fiber filter element and honeycomb filter element.
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