Causes and treatment methods of ultrafiltration membrane fouling

Cause analysis of ultrafiltration membrane pollution

The pollution of the ultrafiltration membrane is mainly caused by the chemical properties of the inner membrane material and the solute in the solution, and the result of the interaction between the membrane and the solute. Regardless of the application, the objects separated by ultrafiltration are mostly dissolved or colloidal high molecular weight organic substances. When these substances come into contact with the ultrafiltration membrane made of synthetic organic polymer materials, There will be a strong tendency of adhesion, adsorption and even bonding between the solute and the membrane material, thereby forming an adsorbed dirt layer on the membrane surface, causing membrane fouling. In addition, membrane pollution also includes the deposition of suspended solids in the feed solution on the membrane surface.

Once the ultrafiltration membrane is contaminated, it will cause the membrane permeable flux to decrease, and the attenuation of this flux is usually irreversible, which will cause the ultrafiltration process to be unable to perform stable operation for a long time, and affect the full efficiency of the ultrafiltration.

Membrane pollution control measures include

1) The water permeability of the membrane can be restored through effective cleaning

2) Design filtration, coagulation and sedimentation measures as pre-treatment

3) Increase the tangential velocity of the membrane surface, reduce the thickness of the boundary layer and increase the mass transfer coefficient

4) Select the appropriate operating pressure to avoid increasing the density and thickness of the sedimentation layer

5) Research and develop membrane materials with good anti-pollution performance

How to clean ultrafiltration membrane

The service life of the ultrafiltration membrane is usually 12 to 18 months. Due to the interaction between the solute and the ultrafiltration membrane in the ultrafiltration process, the membrane surface will form an adsorption deposition layer and cause membrane fouling. Therefore, the membrane must be cleaned regularly to restore and maintain the membrane's permeable flux and extend the life of the membrane. Membrane cleaning methods include hydraulic cleaning, chemical cleaning and mechanical cleaning, etc., which should usually be determined according to the nature of the membrane and the treatment liquid and the form of the membrane module.

Since most of the processing objects in the ultrafiltration process are macromolecules and colloidal solutions, the membrane is easily contaminated, and the ultrafiltration membrane needs to be cleaned regularly. The formulation of the cleaning solution is generally determined according to the nature of the membrane and the type of contaminants. For example, detergents have a good cleaning effect on protein, polysaccharide and colloidal pollution; emulsified oil wastewater, such as the coolant of machining enterprises, mostly use surfactants and alkaline aqueous solutions to clean the membrane surface; sodium hypochlorite solution is often used when the membrane process is used to treat domestic sewage. If there are ready-made information, the cleaning formula and cleaning cycle must be determined through experiments.

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