What is the order of membrane processes from largest to smallest impurity size allowed through?

In membrane separation processes, the order of the membranes from largest to smallest impurity size that can pass through reflects the different filtration mechanisms and the sizes of the particles they are designed to remove.

Microfiltration operates with the largest pore sizes, allowing larger particles such as sediments, bacteria, and some larger organic molecules to pass while retaining larger solids. Following microfiltration, ultrafiltration uses smaller pore sizes to remove smaller molecules, such as viruses and smaller proteins, but still allows some dissolved substances to pass through.

Next in the sequence is nanofiltration, which has even smaller pores and is designed to remove divalent and larger univalent ions and organic molecules from the solution, managing to retain more charged species than ultrafiltration.

Reverse osmosis has the smallest pore size and is capable of removing virtually all impurities, including monovalent ions and most dissolved solids. It effectively filters out salts and other very small molecules by applying pressure to overcome osmotic pressure, making it the tightest filtration process in the series.

Thus, the correct order of membrane processes from the largest to smallest impurity size allowed through is indeed microfiltration, ultrafiltration, nanofiltration, and finally reverse osmosis. This provides a clear progression of filtration capabilities