What is the order of membrane technology pore sizes from large to small?

The correct sequence of membrane technologies by pore size from large to small is Microfiltration, Ultrafiltration, Nanofiltration, and then Reverse Osmosis.

Microfiltration has the largest pore size, typically allowing particles larger than 0.1 micrometers to pass through while retaining larger particles like bacteria and suspended solids. Ultrafiltration offers smaller pores than microfiltration, typically in the range of 0.01 to 0.1 micrometers, effectively filtering out larger organic molecules and some viruses. Nanofiltration has even smaller pore sizes, around 0.001 to 0.01 micrometers; it can remove divalent ions and larger monovalent ions, as well as smaller organic molecules. Finally, Reverse Osmosis employs extremely small pores, usually less than 0.001 micrometers, allowing only water and very small solutes to pass through, effectively removing almost all contaminants.

This order highlights the increasing level of filtration effectiveness and decreasing pore size, which is crucial for understanding how these technologies can be applied in water treatment processes, especially in managing different types of contaminants.