What is the Difference Between Microfiltration Ultrafiltration and Nanofiltration

The key difference between microfiltration ultrafiltration and nanofiltration is the size of pores in their membranes. Microfiltration uses membranes with microscale size pores, while ultrafiltration uses membranes with microscale pore size, but the pore size is designed in such a way that a pore is about one-tenth of the particle size. Nanofiltration, on the other hand, uses membranes with nanoscale pores.

All microfiltration, ultrafiltration and nanofiltration are types of membrane filtration analytical techniques that are useful in separation processes. These methods are mainly useful as purifying steps in the process.

CONTENTS

1. Overview and Key Difference
2. What is Microfiltration 
3. What is Ultrafiltration 
4. What is Nanofiltration
5. Microfiltration vs Ultrafiltration vs Nanofiltration in Tabular Form
6. Summary – Microfiltration vs Ultrafiltration vs Nanofiltration 

What is Microfiltration?

Microfiltration is an analytical technique that is useful for filtration. A contaminated fluid can be passed through a membrane having microscale pores in order to separate the microorganisms and suspended particles from this liquid. This analytical technique is commonly used in conjunction with various other separation processes, including ultrafiltration and reverse osmosis. This provides a product stream that does not contain any undesired contaminants.

Usually, microfiltration serves as a pre-treatment method that is important in separation techniques such as ultrafiltration. Moreover, we can use it as a post-treatment step for granular media filtration processes. Typically, the pore size for microfiltration ranges from 0.1 to 10 micrometers. The membranes used for this filtration are specifically designed to prevent the passing of sediments, algae, protozoa, and large bacteria. Furthermore, these filters tend to allow the passing of ionic materials such as water molecules, monovalent species such as sodium and chloride ions, natural organic matter that are dissolved in the fluid, small colloids, and viruses.

In this method of the microfiltration process, we need to pass the fluid through the membrane with a high velocity (about 1-3m/s). Here, we can use a low to moderate pressure that is parallel or tangential to the semi-permeable membrane. The membrane is typically in a sheet form or a tabular form. We can use a pump to allow the fluid to pass through the membrane filter. This pump can be either pressure-driven or vacuum.

There are several applications of microfiltration, including water treatment to remove pathogens such as protozoa, remove turbidity, etc. sterilization, petroleum refining, dairy processing, clarification and purification of cell broth, clarification of dextrose, etc.

What is Ultrafiltration?

Ultrafiltration is an analytical technique in which a force such as pressure or concentration gradient is used for the separation through a semi-permeable membrane. In this method, the suspended solids having a high molecular weight cannot pass through the membrane while water and low molecular solutes can pass through. The residue that cannot pass through the membrane is known as the retentate, whereas the portion that can pass through the filter is known as the permeate or filtrate. This method is useful in purifying and concentrating steps.

Fundamentally, ultrafiltration is similar to microfiltration because both these techniques perform separation according to the size exclusion or particle capture method. However, it is fundamentally different from membrane gas separation because the latter involves separation using absorption techniques and diffusion.

Generally, the pore size of the membrane used in the ultrafiltration has to be one-tenth of the particle size that is to be separated. Therefore, it limits the entering of large particles through the membrane. However, it also limits the entering of small particles through pores and adsorbing them to the pore surface. They can block the entrance, so we need simple adjustments of cross-flow velocity to dislodge the particles.

What is Nanofiltration?

Nanofiltration is an analytical technique that uses membrane filtration mainly to soften and disinfect water. It is a type of membrane filtration method using pore size in nanoscale. The pore size ranges from 1-10nm. This pore size is smaller than pore sizes in microfiltration and ultrafiltration. But the pore size is comparatively larger than the pore size in reverse osmosis.

Typically, the membranes that we can use for the preparation of the membranes used in nanofiltration are polymer thin films. We can use materials such as polyethylene terephthalate or metals such as aluminum to prepare this kind of membrane film. We can also control the pore dimensions of these membranes by controlling the pH, temperature and time needed for pore development.

There are many different uses of nanofiltration techniques, including fine chemistry and pharmaceuticals, oil and petroleum chemistry, bulk chemistry, medicine, production of natural essential oils and similar products, etc.

What is the Difference Between Microfiltration Ultrafiltration and Nanofiltration?

The key difference between microfiltration ultrafiltration and nanofiltration is the size of pores in their membranes. Microfiltration uses membranes with microscale size pores, while ultrafiltration uses membranes with microscale pore size, but the pore size is designed in such a way that a pore is about one-tenth of the particle size. Nanofiltration, on the other hand, uses membranes with nanoscale pores.

The below infographic lists the differences between microfiltration ultrafiltration and nanofiltration in tabular form for side by side comparison.

Summary – Microfiltration vs Ultrafiltration vs Nanofiltration

Microfiltration, ultrafiltration and nanofiltration are types of membrane filtration analytical techniques that are useful in separation processes. Microfiltration uses membranes with microscale size pores, while ultrafiltration uses membranes with microscale pore size, but the pore size is designed in such a way that a pore is about one-tenth of the particle size. Nanofiltration, on the other hand, uses membranes with nanoscale pores.  Thus, this is the key difference between microfiltration ultrafiltration and nanofiltration.

Reference:

1. “Microfiltration“. An overview | ScienceDirect Topics.

Image Courtesy:

1. “Overall setup for the Microfiltration system” By Jeraz Cooper/Enrico Martini – DRAWN ON MICROSOFT VISIO (CC BY-SA 3.0) via Commons Wikimedia
2. “Cross Flow” By CEIC3004 24 – Own work (CC BY-SA 3.0) via Commons Wikimedia
3. “Process diagram nanofiltration-desalination” By Natttyc – Own work (CC BY-SA 3.0) via Commons Wikimedia