Before talking about the role of reverse osmosis scale inhibitor, the water treatment equipment briefly describes the reverse osmosis system: the reverse osmosis water treatment equipment passes the raw water through precision filter, granular activated carbon filter, compressed activated carbon filter, etc., and then pressurizes it through a pump with an aperture of 1 / 10000 μ M (equivalent to 1 / 6000 of the size of E. coli and 1 / 300 of the size of virus), the reverse osmosis membrane (RO membrane) changes the high concentration water into low concentration water, and isolates all the impurities mixed into the water, such as industrial pollutants, heavy metals, bacteria, viruses, etc., so that the water treatment equipment can meet the physical and chemical indexes and health standards specified for drinking, and produce clear to pure water, It is the best choice for human body to supplement high-quality water in time. Because the water purity produced by RO reverse osmosis technology is the highest among all water making technologies mastered by human beings, and the cleanliness is almost 100%.

Reverse osmosis membrane is the key equipment of reverse osmosis system. When the system runs continuously for a long time, calcium and magnesium plasma in water will continuously precipitate and adhere to the surface of reverse osmosis membrane, forming scaling and blocking membrane holes, which will affect the water outlet efficiency of reverse osmosis system and damage the reverse osmosis membrane. Since the reverse osmosis membrane is relatively expensive, a dosing system shall be added during the system operation. The water treatment equipment shall add reverse osmosis scale inhibitor in the water to delay the precipitation of calcium and magnesium ions and the scaling on the membrane surface.

AIter reverse osmosis scale inhibitor is a scale inhibitor specially used for reverse osmosis (RO) system, nanofiltration (NF) and ultrafiltration (UF) system. It can prevent membrane surface scaling, improve water production and water quality, and reduce operation cost.

characteristic

① Effectively control inorganic scaling in a large concentration range

② It does not agglomerate with iron aluminum oxide and silicon compound to form insoluble matter

③ It can effectively inhibit the polymerization and deposition of silicon, and the SiO2 concentration on the concentrated water side can reach 290ppm

④ It can be used for reverse osmosis Ca and TFC membrane, nanofiltration membrane and ultrafiltration membrane

⑤ Excellent solubility and stability

⑥ The pH value of feed water is valid in the range of 5-10

Basic functions of reverse osmosis scale inhibitor:

① Complexation and solubilization: the reverse osmosis scale inhibitor is ionized after dissolving in water to form a negatively charged molecular chain. It forms a water-soluble complex or chelate with Ca2, so as to increase the solubility of inorganic salts and play the role of scale inhibition.

② Lattice distortion: some functional groups in the reverse osmosis scale inhibitor molecule occupy a certain position on the inorganic salt crystal nucleus or microcrystalline, which hinders and destroys the normal growth of inorganic salt crystal and slows down the growth rate of crystal, thus reducing the formation of salt scale;

③ Electrostatic repulsion: the reverse osmosis scale inhibitor is dissolved in water and adsorbed on the microcrystals of inorganic salts to increase the repulsion between particles, hinder their coalescence and make them in a good dispersion state, so as to prevent or reduce the formation of scale.

④ Reverse osmosis scale inhibitors are used to improve the performance of reverse osmosis and nanofiltration systems

⑤ Scale inhibitors and dispersants are a series of chemicals used to prevent the precipitation and scaling of crystalline mineral salts.

Function of scale inhibitor

a. Inhibition of precipitation function in the system with scale inhibitor, the ion product value of cation, anion and anion of easy structural components at the beginning of precipitation is much larger than the critical precipitation ion product value without scale inhibitor.

b. Dispersion function: when there is scale inhibitor, the precipitated particles are difficult to agglomerate because of their small size, which is more difficult to settle than when there is no scale inhibitor.

c. The crystal precipitated by lattice deformation effect in the system with scale inhibitor has spherical, polyhedral, snowflake and other amorphous states. It is generally considered that amorphous crystal is a crystal whose surface growth rate decreases sharply due to the adsorption of scale inhibitor on the crystal growth point in the process of crystal growth.

d. The dosage of scale inhibitor with low limit effect is equivalent to that of scaling composition in water, which can also show scale inhibition effect.

Application of RO scale inhibitor

a. When polyacrylic acid scale inhibitor is used, special care shall be taken. When the iron content is high, it may cause membrane pollution, which will increase the operating pressure of the membrane. Acid pickling shall be carried out to effectively remove this kind of pollution.

b. If cationic coagulant or filter aid is used in pretreatment, special attention shall be paid to the use of anionic scale inhibitor. It will produce a viscous pollutant, which will increase the operating pressure, and this pollutant is very difficult to clean.

Picture C. The scale inhibitor hinders the growth of RO influent and salt crystal in concentrated water, so it can allow the insoluble salt to exceed the saturated solubility in concentrated water. The use of scale inhibitor can replace or cooperate with acid addition. There are many factors that affect the formation of mineral scaling. The decrease of temperature will reduce the solubility of scaling minerals, except calcium carbonate. On the contrary, its solubility decreases with the increase of temperature, and the increase of TDS will increase the solubility of insoluble salts, because high ionic strength interferes with the formation of crystal seeds.

d. The ideal addition amount and the maximum saturation of scaling substances and pollutants are best determined by the special software package provided by the reagent supplier. Excessive addition of scale inhibitor / dispersant will lead to deposition on the membrane surface, resulting in new pollution problems. When the equipment is shut down, the scale inhibitor and dispersant must be completely washed out, otherwise it will stay on the membrane and cause pollution. When RO water is used for low-pressure flushing, stop injecting scale inhibitor and dispersant into the system.

e. The design of the scale inhibitor / dispersant injection system should ensure that the reverse osmosis elements can be fully mixed before. The static mixer is a very effective mixing method. The injection point of most systems is set before the RO inlet security filter to promote mixing through the buffer time in the filter and the mixing effect of RO inlet pump. If the pH of the system is adjusted by adding acid, it is recommended that the acid adding point be far enough upstream and have been fully mixed before reaching the scale inhibitor / dispersant injection point.

f. The dosing pump for injecting scale inhibitor / dispersant shall be adjusted to the maximum injection rate, and the recommended injection rate is at least once every 5 seconds. The typical addition amount of scale inhibitor / dispersant is 2-5ppm. In order to make the dosing pump work at the highest frequency, the reagent needs to be diluted. Scale inhibitors / dispersants are available in concentrate or solid powder. The diluted scale inhibitor / dispersant will be biologically contaminated in the storage tank. The degree of contamination depends on the room temperature and dilution multiple. The retention time of diluent is recommended to be about 7-10 days. Under normal circumstances, undiluted scale inhibitor / dispersant will not be biologically contaminated. Another major problem in selecting scale inhibitor / dispersant is to ensure full compatibility with reverse osmosis membrane. Incompatible agents can cause irreversible damage to the membrane.