Influent quality and pretreatment of RO membrane process

RO Membrane fouling refers to the irreversible changes that occur when particles, colloidal substances, or macromolecules in a material interact physically, chemically, or mechanically with a membrane. This interaction leads to adsorption or deposition on the membrane surface or within its pores, causing pore narrowing or blockage, which in turn reduces permeate flux and impairs separation characteristics. 

Based on the type of foulants, membrane fouling can be categorized into four types:

1. Inorganic fouling: Caused by sparingly soluble inorganic salts that easily form scale, such as carbonates and sulfates. 

2. Organic fouling: Primarily due to dissolved organic substances like humic substances, polysaccharides, and proteins present in the feed water. 

3. Colloidal fouling: Involves the accumulation of colloidal particles on the membrane surface.

4. Biological fouling: Results from the growth and metabolic activities of microorganisms, leading to the formation of biofilms on the membrane. 

Recent studies have shown that the properties of the membrane surface directly influence the extent of fouling in the following aspects:

1. Hydrophilicity of the membrane surface: Most foulants are hydrophobic. A hydrophilic membrane surface can bind with water molecules, forming a "free water" hydration layer that inhibits direct contact and adsorption of foulants on the membrane surface. 

2. Surface roughness of the membrane: The closer the size of the foulants is to the roughness of the membrane surface, the more likely adsorption and deposition will occur on the membrane surface. 

3. Charge of the membrane surface: Charged foulants can experience electrostatic attraction or repulsion with the membrane surface. When the charges of the foulants and the membrane surface are opposite, electrostatic attraction accelerates foulant adsorption. 

4. Pore size of the membrane: When the membrane pore size is larger than the particle size of the foulants, the foulants can directly enter the membrane pores, leading to pore blockage. 

Understanding these factors is crucial for developing strategies to mitigate membrane fouling and enhance membrane performance in various applications.