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Pretreatment Process Selection Of Membrane Fouling Caused By Colloid In Sewage
- Jul 24, 2018 -

Pretreatment process selection of membrane fouling caused by colloid in sewage


Colloidal pollution mainly occurs on ultrafiltration membrane components. If the content of iron, manganese, silicon, etc. in the reverse osmosis water exceeds a certain value, fouling will also occur in the reverse osmosis membrane element. Therefore, it is necessary to control the iron and manganese in the influent water. , silicon and other content.


Colloids range in size from 1 nm to 1 μm and are usually charged in water. Due to the electrostatic repulsion between the colloidal particles, polymerization does not occur and it is difficult to settle naturally. Therefore, it is necessary to add a specific chemical to water or to precipitate it according to the characteristics of the colloidal substance.


The methods for removing the colloid before the ultrafiltration membrane mainly include agglomeration, flocculation (including electroflocculation), coagulation or air flotation. Coagulation is the addition of a coagulating agent with positive ions in the wastewater. The presence of a large amount of positive ions between the colloidal particles can eliminate the electrostatic repulsion between the colloidal particles, thereby agglomerating the particles. Commonly used coagulants are aluminum sulfate, ferrous sulfate, alum, ferric chloride, and the like. Flocculation is the addition of a polymer coagulating agent to the wastewater. After the polymer coagulating agent is dissolved, a high molecular polymer is formed. The structure of the polymer is a linear structure, one end of the wire is pulled with a tiny particle, and the other end is pulled. Pulling another tiny particle plays a role of bonding bridge between the two distant particles, which makes the particle gradually become larger, eventually forming large particle flocs and accelerating particle sedimentation. Commonly used flocculants are polyacrylamide (PAM), polyferric iron (PE) and the like. The process of combining coacervation with flocculation is a coagulation process. Coagulation has the effect of removing impurities such as suspended solids, organic matter and colloidal substances in raw water, simple operation and low processing cost, and is the most common water treatment method at home and abroad. According to the literature, generally coagulation + filtration can remove 60% of colloidal silicon, and coagulation + clarification filtration can remove 90% of colloidal silicon.