What effect does conductivity have on microporous membrane filtration?

What is conductivity? Conductivity is a measure of the material's ability to conduct current. It is the reciprocal of resistivity. Usually the conductivity of a solution is expressed in units of Siemens per meter (S/m) or millhos per meter (mho/m). In practical applications, it is more It is common to use units of millisiemens per centimeter (mS/cm), with conductivity ranging depending on the nature of the solute and solvent and the concentration of ions or charged particles present in the solution.

General estimates of the conductivity of some liquids can be provided to give us an idea of its approximate range. For example, pure water is about 0.055 µS/cm (microSiemens per centimeter) at 25°C; the conductivity of drinking water is usually about 50-500 µS/cm, depending on its mineral content; some dilute solutions range from hundreds of µS/cm to several mS/cm; some strong electrolyte solutions can exhibit higher conductivity, The range is generally 1-10 S/cm, or even higher. These approximate ranges are for informational purposes only, as they are subject to wide variation and variation depending on specific ingredients, conditions, etc.

So, what effect does conductivity have on membrane filtration? Here are a few key points to consider:

1. The impact of scaling. The scaling involved in microporous membrane filtration refers to the accumulation of particles, solids or other substances on the membrane surface, resulting in a decrease in filtration performance, because conductivity can affect some fouling in various ways, especially In high conductivity solutions, there will be dissolved salts or ions. These salts or ions will promote the formation of scale or precipitates on the membrane surface. Over time, this will lead to scaling on the surface and inside of the membrane. These deposits will reduce Small effective pore size or form a barrier that prevents fluid from passing through the membrane.

2. Conductivity leads to polarization of the filter membrane. The so-called polarization refers to the conductivity. When ions in the solution gather near the membrane surface due to electrostatic interaction, the applied electric field will be redistributed, which will cause Membrane polarization occurs when charges move or accumulate on the membrane surface. Its polarized layer can produce a concentration polarization effect, in which a higher concentration of solute near the membrane will hinder the flow of water or other solvents through the membrane, which will reduce the membrane's filtration efficiency and increase the resistance through the membrane.

3. Conductivity will affect membrane integrity and performance. In some cases, high conductivity solutions can also cause swelling or degradation of part of the filter membrane, because high conductivity solutions usually contain high concentrations of dissolved ions or charged particles. These ions It will cause an osmotic pressure imbalance on the filter membrane, causing water molecules to flow into a solution with a higher concentration, which will cause the filter membrane to swell; similarly, solutions with high conductivity will also have polymers that react with the filter membrane material and destroy the membrane. The structure and its integrity can cause membrane degradation, so it is important to ensure that the membrane material and structure are compatible with the conductivity level of the solution being filtered.

4. Electrically assisted filtration. Although in the above introduction, we have all mentioned the negative impact of conductivity on membrane filtration, in some applications, conductivity can be used to enhance the performance of membrane filtration. This is electrically assisted filtration technology. For example, electrofiltration or electrodialysis applies an electric field to the membrane to drive the transport of ions or particles. Conductivity improves the separation or concentration effect of the membrane by promoting ion migration. It must be said that conductivity plays a role in these processes. Crucial role.

Therefore, the impact of conductivity on membrane filtration largely depends on the relevant system type, membrane type and the nature of the material being filtered. For users, it is important to combine the impact and benefits of conductivity on membrane filtration performance. factors to select membrane materials suitable for specific conductivity levels, and appropriate filtration system configurations, etc.