What are the organic and inorganic substances that foul and clog in membrane applications?

Fouling and clogging are common problems in membrane applications and can significantly reduce the efficiency of membrane processes and increase operating costs. The accumulation and fouling of the filtered liquid are mostly particulates, including some organic and inorganic substances. The following are some of the main organic and inorganic substances that cause membrane fouling and clogging:

1. Particles in the liquid, suspended particles in the feed water during filtration will accumulate on the surface of the membrane, resulting in scaling. Particles can be organic or inorganic and can vary in size from a few nanometers to a few micrometers. The organic matter, including oil, protein, sugar, cholesterol, extracellular polysaccharides, etc. These organic matter are often a source of nutrients for microbial growth and are the main cause of biofouling.

2. Minerals in the filtrate, including calcium, magnesium, iron, copper, zinc and other minerals. These minerals are usually inorganic salts dissolved in water, and when water is filtered by the membrane, they can form deposits on the surface of the membrane, causing membrane clogging and reducing membrane flux.

3. Suspended particles are also the most common in liquids, including sediment, dust, suspended microorganisms, suspended organic matter, etc. These particles are usually solid particles in the water that can deposit on the membrane surface and form a fouling layer that can lead to membrane clogging and reduced membrane flux.

4. The more difficult to deal with is the easily soluble organic matter in the liquid, which includes chemicals, dissolved organic matter, drugs and so on. These organics are usually dissolved organics in water, which can adsorb on the membrane surface and form a fouling layer, leading to membrane clogging and reduced membrane flux. For example, easily soluble organic matter will form colloidal particles in water. The particle size of these particles is usually between a few nanometers and tens of nanometers, which is smaller than typical suspended particles, so it is difficult to be removed by traditional filtration methods (such as microporous filtration) . These colloidal particles may accumulate on the membrane surface, leading to clogging of the membrane and reduced flux.

At the same time, these easily soluble organic substances may combine with other dissolved substances in water to form colloidal particle agglomerates, which are larger in size than individual colloidal particles and thus more difficult to filter. Furthermore, the formation of these clumps may lead to clogging of the membrane and reduced flux. These organic substances may be adsorbed on the membrane surface to form a dense fouling layer, which leads to membrane clogging and flux reduction. These organics are generally more polar species and thus may be more readily adsorbed on the membrane surface. Therefore, for these organic substances, some special membrane filtration technologies can be adopted, such as reverse osmosis, nanofiltration, etc., which can remove smaller particles and larger molecules to improve filtration efficiency. In addition, pretreatment methods, such as adsorption, oxidation, etc., can also be used to convert easily soluble organic matter into a form that is easier to filter, so as to improve the flux and service life of the membrane.

From the above analysis, it can be seen that in order to prevent fouling and clogging, appropriate pretreatment must be carried out on the feed liquid, including filtration, pH adjustment and chemical treatment. Regular cleaning of the membrane is also essential to maintain its performance.

Citation

1.Baker, R. W. (2012). Membrane technology and applications (3rd ed.). John Wiley & Sons.

2.Childress, A. E., & Elimelech, M. (Eds.). (2011). Membrane fouling and scaling. John Wiley & Sons.

3.Van der Bruggen, B., & Vandecasteele, C. (2003). Removal of pollutants from surface water and groundwater by nanofiltration: overview of possible applications in the drinking water industry. Environmental Pollution, 122(3), 435-445.

4.Vrouwenvelder, J. S., van Paassen, J. A., & van der Kooij, D. (2010). Membrane fouling in ultrafiltration and nanofiltration: measurements, mechanisms and control. Desalination, 250(2), 1107-1117.