RO vs NF vs UF vs MF: 4 Filtration Types Compared

Membrane filtration is the backbone of modern water treatment, but choosing the right technology — Reverse Osmosis (RO), Nanofiltration (NF), Ultrafiltration (UF), or Microfiltration (MF) — can be complex. Each technology operates at a different pore size range and pressure, making them suited for distinct applications. This comprehensive comparison will help engineers and procurement teams select the optimal membrane technology for their specific needs.

Understanding the Four Membrane Types

Microfiltration (MF) uses the largest pore sizes (0.1–10 µm) and operates at the lowest pressures. It effectively removes suspended solids, bacteria, and large colloids while allowing dissolved salts and smaller molecules to pass through. MF is commonly used as a pretreatment step before RO or NF systems.

Ultrafiltration (UF) bridges the gap between MF and NF with pore sizes of 0.01–0.1 µm. UF membranes reject viruses, proteins, and endotoxins while passing dissolved salts. They are widely used in drinking water treatment, wastewater reclamation, and as pretreatment for RO systems.

Nanofiltration (NF) operates between UF and RO with pore sizes of 0.001–0.01 µm. NF selectively removes divalent ions (calcium, magnesium) while allowing monovalent ions (sodium, chloride) to partially pass. This makes NF ideal for water softening and selective separation processes.

Reverse Osmosis (RO) has the tightest membranes (less than 0.001 µm) and the highest rejection rates. RO removes virtually all dissolved solids, including monovalent ions, making it the standard for desalination and ultrapure water production.