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To resolve issues with unsatisfactory resistivity and conductivity in ultrapure water from a system, the first step is to identify the underlying causes of the low resistivity. For example, is it due to the quality of the raw water, leading to lower resistivity in the produced water? Or is it caused by damaged or expired reverse osmosis membrane elements? Below is a detailed explanation of "How to resolve unsatisfactory resistivity and conductivity in ultrapure water from a system?"
Some users find that the resistivity of the produced water deviates from the set value when using ultrapure water equipment, resulting in water quality that fails to meet usage standards. So, what causes low resistivity in ultrapure water?
1. Low resistivity in ultrapure water may be affected by the quality of the raw water. Changes in the conductivity of the raw water will naturally affect the produced water.
2. The mechanical filters, activated carbon filters, and security filters in the ultrapure water equipment may be clogged and have not been backwashed in a timely manner.
3. The reverse osmosis membrane elements in the ultrapure water equipment may be damaged or expired.
4. The RO desalination rate and permeate flow rate were not cleaned in a timely manner when they increased or decreased.
5. The CO2 content in the EDI system feed water was high. If the CO2 content is greater than 10 ppm, the EDI system cannot produce high-purity water.
6. There was a problem with the current control of the EDI system.
7. The ultrapure water equipment was not operated and maintained in accordance with the user manual.
1. Analyze the following operating conditions: average current of each module; actual current of each module; pressure in the desalination and concentrate chambers; low flow rate; trend of operating conditions over time.
2. Analyze the testing instruments: electrode constant; calibration; temperature compensation; probe wiring; instrument grounding; poor sampling due to insufficient flow rate through the probe.
3. Analyze the following parameters of the influent: conductivity; pH; CO2; silica content; hardness; check the reverse osmosis equipment; perform laboratory analysis of the water quality.
Ultrapure water equipment typically uses EDI devices, which combine traditional electrodialysis and ion exchange technologies. Under the influence of an electric field, the selective permeability of cation and anion membranes and the exchange of ions in the water by ion exchange resins cause ions to migrate directionally, thus achieving deep purification and desalination of water.
Conductivity refers to the electrical conductivity of dissolved salts in water, which are in an ionic state. The more dissolved salts there are, the more ions there are, and the greater the conductivity. Conductivity indirectly indicates the amount of dissolved solids in water, and can provide a preliminary assessment of water quality.
From the above two paragraphs, we can see that solving unstable conductivity should focus on the following aspects:
1. Insufficiently detailed water quality analysis. Due to insufficiently detailed water quality analysis, the understanding of ionic substances in the water is unclear, and the ultrapure water equipment used does not meet the production water standards.
2. Insufficient electric field strength. Insufficient electric field strength causes some ions to migrate in the wrong direction, failing to meet the production water standards.
3. Infrequent cleaning of the anion and cation exchange membrane (also known as anion and cation exchange resin). Over time, microorganisms, fine particles, colloids, and other impurities easily form fouling on the membrane surface, clogging the anion and cation exchange membrane and preventing the anions and cations in the water from migrating in the desired direction, resulting in conductivity problems.
