During the operation of reverse osmosis edi pure water equipment, the resistivity decreases. The resistivity is another indicator to characterize the conductivity of the water body. Resistivity and conductivity are inversely related. In order to improve the accuracy of the characterization of the electrical conductivity of water, when the conductivity is higher than 1 μS/cm, it can be characterized by conductivity, and when the conductivity is less than 1 μS/cm, it can be characterized by resistivity. The reasons for the decrease in resistivity are related to the water quality, pressure, flow rate, voltage, pollution of the influent water quality, etc.
Here are the reasons of the problem
1. The effluent of the reverse osmosis equipment is unqualified (including conductivity, hardness, variable price metals, etc.)
If the salt content of the raw water is high, it is recommended to use a bipolar RO reverse osmosis equipment as a pre-salt removal device, and its conductivity should be kept at 1-3 μS/cm. CO2 removal. The pH deviates too much from neutral, and pH adjustment is adopted to make the pH value of the EDI influent at 7-8. In the process of contact with air, the carbon dioxide gas dissolved in the high-purity water causes the conductivity to rise. Therefore, the conductivity of high-purity water should be tested under the condition of online airtightness.
2. There is a problem with the current control of the EDI system
The working current increases, and the water quality continues to improve. However, if the current is increased after increasing to the highest point, the amount of H+ and OH- ions generated by water ionization is too large. Except for the regeneration of resin, a large number of excess ions act as carrier ions to conduct electricity. At the same time, due to the movement process of a large number of carrier ions Accumulation and blockage occur in the process, and even reverse diffusion occurs, resulting in a decline in the quality of the produced water.
3. Changes in pH
The influent CO2 content of the EDI system is high. If the CO2 content is greater than 10ppm, the EDI system cannot prepare high-purity water.
4. Iron pollution
Iron pollution in the operation of EDI system is one of the main reasons for the progressive decline of its water resistance. If ordinary steel pipes are used in the raw water and pretreatment systems without internal anti-corrosion treatment, the iron content in the system will increase. Become Fe(OH)3. Fe(OH)2 is a colloidal substance, and Fe(OH)3 is a suspended state. The resin has a strong affinity for iron, and after being adsorbed by the resin, it will cause an irreversible reaction. In the treatment of anion and cation exchange water, the anion and cation beds will be regenerated or cleaned to remove most of the iron in the resin. However, in the operation of EDI equipment, there is no regeneration and cleaning, and trace iron elements in the water will adhere to the anion and cation resins and anion and cation films. Iron has strong electrical conductivity, and before it can react with the cationic resin, it is moved to the cationic membrane by the EDI component near the anion membrane water under the action of a large current. Pure iron ions are easy to penetrate, while colloidal iron compounds are not easy to penetrate the cationic membrane, so they are adsorbed on the surface of the cationic membrane, polluting the cationic and cationic membranes, and ultimately lead to the decline of the working performance of the EDI module and the poor quality of the water produced. The resistance value showed a progressive decrease.
5. Organic pollution
The influent of reverse osmosis edi pure water equipment is polluted by organic colloids, and reverse osmosis can only remove organic colloids with a relative molecular weight greater than 200. Those with a molecular weight below 200 enter the EDI system. This part of low molecular weight substances are adsorbed on the meshes of the skeleton and the surfaces of the anion and cation membranes by the anion and cation exchange resins in the module, hindering the replacement reaction of anion and cation and the speed of water ions penetrating the anion and cation membranes. , resulting in a decrease in EDI performance and a decrease in the resistivity of the produced water.
