Reasons for the Decrease of EDI equipment product water resistivity

The reasons for the decrease in resistivity during the operation of EDI equipment are related to the water quality, pressure, flow rate, voltage, and pollution of feed water quality. .

1) Unqualified feed water of EDI equipment

If the salt content of the raw water is high, it is recommended to use double reverse osmosis equipment first for desalination, to ensure the conductivity of feed water be kept at 1-3us/cm. Besides, the pH value shall be adjusted by regulation dosing device to neutral around 7 to ensure the operation performance of EDI equipment.

2) Problem with current control in EDI equipment

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 surplus ions act as carrier ions for conduction. 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) Iron contamination in EDI equipment

Iron contamination in the operation of EDI equipment is one of the main reasons for the progressive decline of its water resistance. If ordinary steel pipes be used in the pretreatment systems without internal anti-corrosion treatment, the iron content in the system will increase. After being corroded, most of the iron dissolved in water exists in the form of Fe(OH)2, and is further oxidized to become Fe(OH)3. 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.

4) Organic contamination in EDI equipment

The feed water of EDI equipment is contaminated by organic colloids, and reverse osmosis can only remove organic colloids with a relative molecular weight greater than 200. The molecular weight below 200 will enter the EDI system. This part of low molecular weight substances are adsorbed on the mesh of the skeleton and the surface of the anion and cation membranes by the anion and cation exchange resins in the module, which hinders the replacement reaction of the anion and the cation and the speed of the penetration of the anion and the cation membrane by the ions in the water. , resulting in a decrease in EDI performance and a decrease in the resistivity of the product water.

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