The main difference between ultrafiltration and reverse osmosis is that ultrafiltration can separate tiny particles up to 0.01 to 0.1 microns, whereas reverse osmosis can separate more tiny materials up to 0.0001 microns. Furthermore, ultrafiltration can separate milk proteins, gelatin, endotoxin pyrogens, colloidal silica, and viruses from a solution while reverse osmosis can separate metal ions, aqueous salt, synthetic dyes, and lactose from a solution. 

Ultrafiltration and reverse osmosis are two filtration methods used to remove particulate matter from water by forcing water through porous media or membranes. 

Key Areas Covered 

1. What is Ultrafiltration
     – Definition, Process, Importance
2. What is Reverse Osmosis
     – Definition, Process, Importance
3. What are the Similarities Between Ultrafiltration and Reverse Osmosis
     – Outline of Common Features
4. What is the Difference Between Ultrafiltration and Reverse Osmosis
     – Comparison of Key Differences

Key Terms 

Membrane Filtration, Osmosis, Reverse Osmosis, Ultrafiltration, Water Purification

What is Ultrafiltration 

Ultrafiltration is a filtration method that uses either osmosis or reverse osmosis principles to filter a solution. Generally, it operates through a concentration gradient or hydrostatic pressure, respectively. On the other hand, it uses either a semipermeable membrane or porous material for the filtration. 

Figure 1: Ultrafiltration – Drinking Water Treatment

Moreover, it is an important process in water purification. However, it allows water and low molecular weight solutes to pass through the membrane or the porous material. Therefore, sometimes, it is used as the pre-filtration method of reverse osmosis.  

What is Reverse Osmosis 

Reverse osmosis is a method of water purification, removing ions and other unwanted molecules from drinking water. Moreover, it works in opposition to the osmosis in which water molecules move through a gradient of water potential across a semipermeable membrane. Therefore, to operate, the applied pressure should be higher than the osmotic pressure.

Figure 2: Reverse Osmosis Production Train

On the other hand, reverse osmosis can produce pure water without any particulate or biological matter, including bacteria and viruses. Therefore, it is important for the production of pharmaceutical-grade water. 

Similarities Between Ultrafiltration and Reverse Osmosis 

• Ultrafiltration and reverse osmosis are two types of filtration methods used to separate particulate matter from water. 
• Therefore, they are important for water purification. 
• Water runs either through a semipermeable membrane or a porous medium. 
• Moreover, the forces for the water movement can be either pressure or concentration gradient. 
• Additionally, the size of the pores determines the size of particles to be separated. 

Difference Between Ultrafiltration and Reverse Osmosis 

Definition 

Ultrafiltration refers to a filtration method that uses a medium fine enough to retain colloidal particles, viruses or large molecule. On the other hand, the reverse osmosis refers to a process by which a solvent passes through a porous membrane in the direction opposite to that for natural osmosis when subjected to a hydrostatic pressure greater than the osmotic pressure.  

Filtration Mechanism 

Filtration mechanism of ultrafiltration can be either osmosis or reverse osmosis, while reverse osmosis occurs in the opposite direction to the natural osmosis. 

Pore Size 

Moreover, the pore size in ultrafiltration is 0.01 micrometres or larger, while the pore size in reverse osmosis is much smaller. 

Size of the Separated Particles 

Range of filtration is the main difference between ultrafiltration and osmosis. Ultrafiltration can separate tiny particles up to 0.01 to 0.1 microns while reverse osmosis can separate more tiny materials up to 0.0001 microns. 

Molecular Weight 

Moreover, ultrafiltration can remove molecules up to 1 kDa while reverse osmosis can remove all element from water.  

Type of Molecules 

Ultrafiltration can separate milk proteins, gelatin, endotoxin pyrogens, colloidal silica, and viruses from a solution, but reverse osmosis can separate metal ions, aqueous salt, synthetic dyes, and lactose from a solution. 

Significance 

Generally, ultrafiltration is used as the pre-filtration method in reverse osmosis while reverse osmosis produces pure water, removing all elements. 

Conclusion 

Basically, ultrafiltration is a method of filtration which separates particulate matter from a solution. Here, the solution runs through a membrane or a porous medium with pores of 0.01 micrometre or larger. Therefore, this method can remove particles such as milk proteins, gelatin, colloidal silica, viruses, etc. from the solution. On the other hand, reverse osmosis is a method which separates particulate matter from a solution. Generally, it works opposite to osmosis with the addition of hydrostatic pressure higher than osmotic pressure. Furthermore, it can remove all the particulate matter from the solution, resulting in pure water. Therefore, the main difference between ultrafiltration and osmosis is the range of filtration. 

 References:

1. Woodard, J. “What Is Ultrafiltration? How an Ultrafiltration Membrane Works.” Fresh Water Systems, 30 Jan. 2019, Available Here.
2. “Reverse Osmosis and Ultra Filtration Class Lecture.” Scribd, Scribd, Available Here.

Image Courtesy:

1. “Ultrafiltration Grundmühle” By W.E.T. GmbH – W.E.T. GmbH (Attribution) via Commons Wikimedia   
2. “Northcapecoral-RO” By Twhair – Own work (CC BY-SA 4.0) via Commons Wikimedia   

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