What are the reasons for the decrease in resistivity during the operation of reverse osmosis EDI pure water equipment?

      Reverse Osmosis EDI During the operation of the pure water equipment, the resistivity decreases. Resistivity is another indicator that characterizes the water's ability to conduct electricity, with units of MΩ·cm ，which refers to the resistance value of water between two planar electrodes with a cross-sectional area of 1cm2的两个平板电极在相距1cm when separated by a distance of 1μS/cm when the conductivity is above 1μS/cm it can be characterized by conductivity; when the conductivity is below

1 The reasons for the decrease in resistivity are related to the influent water quality, pressure, flow rate, voltage, influent water quality pollution, etc. Reverse osmosis equipment effluent is unqualified (including conductivity, hardness, and variable valence metals).

      If the raw water salinity is high, it is recommended to use bipolar RO reverse osmosis equipment for pre-desalination, and its conductivity should be maintained at 1 ～ 3μS/cm is optimal. ; Influent CO2 content is high, it is recommended to use a degassing membrane or degassing tower to remove CO2去除。 pH deviates too much from neutral, use pH adjustment to make the EDI Influent pH value at 7 ～ 8 During contact with air, the carbon dioxide gas dissolved in high-purity water causes the conductivity to rise. Therefore, the conductivity of high-purity water should be tested under online closed conditions.

2、 EDI Problems in system current control

      The operating current increases, and the water quality continuously improves. However, if the current is increased after reaching the highest point, due to the water ionization-produced H+ and OH- ions are excessive. In addition to being used for resin regeneration, a large number of excess ions act as charge-carrying ions for conduction. At the same time, due to the accumulation and blockage during the movement of a large number of charge-carrying ions, and even back-diffusion, the resulting water quality decreases.

3、 pH Value change

EDI System influent CO2 content is high, if CO2 content is greater than 10ppm， EDI the system cannot prepare high-purity water.

4 Iron contamination

EDI Iron contamination during system operation is one of the main reasons for the progressive decrease in the resistivity of the produced water. If ordinary steel pipes are used in the raw water and pretreatment system without internal anti-corrosion treatment, the iron content in the system will increase. After iron is corroded, it mostly exists in the water in the form of Fe(OH)2 and further oxidizes into Fe(OH)3 。 Fe(OH)2 is a colloidal substance, Fe(OH)3 is in 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 anion and cation exchange water treatment, the anion and cation beds will undergo regeneration or cleaning, and most of the iron in the resin can be removed. However, in EDI equipment operation, 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 membranes. Iron has strong conductivity, and before it has time to react with the cation resin, it is EDI component near the anion membrane in the water, and under the action of a large current, it migrates to the cation membrane. Pure iron ions are easy to penetrate, while colloidal iron compounds are not easy to penetrate the cation membrane, and are adsorbed on the surface of the cation membrane, polluting the anion and cation membranes, ultimately leading to EDI component performance degradation, poor water quality, and a progressive decrease in resistivity.

5 Organic matter pollution

      Reverse Osmosis edi If there is organic colloid contamination in the influent water of the pure water equipment, reverse osmosis can only remove organic colloids with a relative molecular weight greater than 200的有机物胶体。低于200 Those with a molecular weight below EDI system. This part of the low-molecular-weight substance is adsorbed by the anion and cation exchange resins in the component on the pores of the skeleton and the surface of the anion and cation membranes, hindering the exchange reaction of anions and cations and the speed at which ions in the water penetrate the anion and cation membranes, thus causing EDI performance degradation and a decrease in the resistivity of the produced water.