Introduction of RO water treatment process and RO membrane working principle
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Introduction of RO water treatment process and RO membrane working principle

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Introduction of RO water treatment process and RO membrane working principle

Introduction of basic RO water treatment process: raw water → raw water tank → raw water pump → multi-media filter (quartz sand filter) → activated carbon filter → precision filter → high pressure pump → primary reverse osmosis (RO) device → pure water tank → water point

The desalination rate is high, and bacteria, toxins and other organic substances can be removed at the same time, and the effluent quality meets the national standard GBI7323-1998;

The main components of reverse osmosis pure water equipment adopt imported composite membrane elements and imported high-pressure stainless steel pumps, which have unique advantages compared with other reverse osmosis components in terms of water inflow adaptability, desalination rate and service life;

·Design pressure: 1.05~1.6Mpa, desalination rate: 96~99%;

·High degree of automation, stable operation, low failure rate and low operating cost;

·Low energy consumption and low operating cost.

·Reasonable structure and less floor space.

·Advanced membrane protection system, when the equipment is shut down, the desalinated water can automatically wash away the pollutants on the membrane surface and prolong the life of the membrane.

·The system has no vulnerable parts, does not need a lot of maintenance, and has long-term effective operation.

Reverse osmosis equipment can not only be used in the food and beverage industry, but also in the electronics industry for cleaning water, reclaimed water treatment and recycling, brackish water, seawater desalination, etc.

The working principle of the RO membrane is the reverse osmosis membrane - the membrane that is selective for the permeable substances is called a semi-permeable membrane, and the membrane that can only permeate the solvent but not the solute is generally called an ideal semi-permeable membrane. When the same volume of dilute solution (such as fresh water) and concentrated solution (such as salt water) are placed on both sides of the semipermeable membrane, the solvent in the dilute solution will naturally pass through the semipermeable membrane and flow to the concentrated solution side spontaneously, This phenomenon is called penetration. When the osmosis reaches equilibrium, the liquid level on the concentrated solution side will be higher than that of the dilute solution by a certain height, that is, a pressure difference is formed, and this pressure difference is the osmotic pressure. The size of the osmotic pressure depends on the inherent properties of the solution, that is, it is related to the type, concentration and temperature of the concentrated solution and has nothing to do with the properties of the semipermeable membrane. If a pressure greater than the osmotic pressure is applied to the concentrated solution side, the flow direction of the solvent will be opposite to the original permeation direction, and it will begin to flow from the concentrated solution to the dilute solution side. This process is called reverse osmosis. Reverse osmosis is a reverse migration movement of osmosis. It is a separation method that separates solutes and solvents in solution by means of selective interception of semipermeable membranes under pressure driving. It has been widely used in various liquids. The most common application example of purification and concentration is in the water treatment process, using reverse osmosis technology to remove impurities such as inorganic ions, bacteria, viruses, organic matter and colloids in raw water to obtain high-quality pure water.

The working principle of RO reverse osmosis is: under the action of external force, the solute in the solution is forced to separate from the solvent by means of the interception effect of the semi-permeable membrane, so as to achieve the purpose of concentration, purification or separation, and can remove more than 90% of the solubility from water. Salts and more than 99% of colloidal microorganisms and organic matter, etc.

At present, the following three theories are popular in the academic circle to explain the mechanism of reverse osmosis separation:

1. Dissolution-diffusion modelhome RO water purifier - qinhuangwater

Lonsdale et al. proposed a dissolution-diffusion model to explain the phenomenon of reverse osmosis. He treats the active surface skin of reverse osmosis as a dense, non-porous membrane, and assumes that both solutes and solvents are soluble in a homogeneous non-porous membrane surface layer, each diffusing through the membrane driven by chemical potentials caused by concentration or pressure. Differences in solubility and diffusivity of solutes and solvents in the membrane phase affect the amount of energy they pass through the membrane. The specific process is divided into: the first step, the solute and the solvent are adsorbed and dissolved outside the surface of the feed liquid side of the membrane; the second step, there is no interaction between the solute and the solvent, they are driven by their respective chemical potential differences. way through the active layer of the reverse osmosis membrane; in the third step, the solute and solvent are desorbed on the surface of the permeate side of the membrane.

In the process of the above solute and solvent permeating the membrane, it is generally assumed that the first and third steps are carried out very quickly. At this time, the permeation rate depends on the second step, that is, the solute and solvent are driven by the chemical potential difference. Diffusion through the membrane. because

The selectivity of the membrane allows the separation of gaseous or liquid mixtures. The permeability of substances depends not only on the diffusion coefficient, but also on their solubility in the membrane.

2. Preferential adsorption-capillary flow theory

When different kinds of substances are dissolved in the liquid, its surface tension will change differently. For example, organic substances such as alcohols, acids, aldehydes, and fats are dissolved in water, which can reduce the surface tension. However, when some inorganic salts are dissolved, the surface tension is slightly increased. This is because the dispersion of the solute is not uniform. That is, the concentration of the solute in the surface layer of the solution is different from that in the solution, which is the surface adsorption phenomenon of the solution. When the aqueous solution is in contact with the polymer porous membrane, if the chemical properties of the membrane make the membrane negatively adsorb the solute and preferentially adsorb water, a layer of pure water with a certain thickness adsorbed by the membrane will be formed on the interface between the membrane and the solution. . Under the action of external pressure, it will pass through the capillary pores on the surface of the membrane, so that pure water can be obtained.

3. Hydrogen Bond Theory

In cellulose acetate, due to the action of hydrogen bonds and van der Waals forces, there are two parts of the crystalline phase region and the amorphous phase region in the film. There is a crystalline phase region that is firmly bonded and arranged in parallel between macromolecules, while an amorphous phase region is completely disordered between macromolecules, and water and solutes cannot enter the crystalline phase region. In close proximity to the cellulose acetate molecule, water forms hydrogen bonds with the oxygen atoms on the carbonyl group of cellulose acetate and forms so-called bound water. When cellulose acetate adsorbs the first layer of water molecules, it will cause a great drop in the entropy of water molecules, forming a structure similar to ice. In the larger pore space in the amorphous region, the occupancy rate of bound water is very low, and there is water of ordinary structure in the center of the pore. It migrates in an ordered diffusion fashion, passing through the membrane by continuously changing the position of hydrogen bonds with cellulose acetate. Under the action of pressure, the water molecules in the solution and the oxygen atoms on the carbonyl group, the activation point of cellulose acetate, form hydrogen bonds, and the hydrogen bonds formed by the original water molecules are broken, and the water molecules dissociate and move to the The next activation point and new hydrogen bonds are formed, and then through a series of hydrogen bond formation and breaking, water molecules leave the dense active layer on the membrane surface and enter the porous layer of the membrane. Since the porous layer contains a large amount of capillary water, water molecules can flow out of the membrane smoothly.