Table 5.

Membrane separation characters for water purification [52,63,64,65,66].

Characters	MF	UF	NF	RO (Low-Pressure)
Separation mechanism	Sieve	Sieve	Sieve, solution/diffusion, Exclusion, electric repulsion	Solution/diffusion, Exclusion
Membrane	Porous isotropic	Porous asymmetric	Finely porous asymmetric/composite	Nonporous asymmetric/composite
Molecular weight cutoff	>1000 kDa	1–300 kDa	200–1000 Da	–
Retained compounds	Colloids, TSS turbidity, some protozoan oocysts, cysts, some bacteria and viruses	Macromolecules, proteins, colloids, bacteria, viruses	LMWC, mono-, di- and oligo-, saccharides; polyvalent anions, some hardness, viruses	LMWC, sodium, chloride, glucose, amino acids, hardness, ions
Transmembrane pressure (TMP)	<5 bar	<10 bar	<20 bar	<100 bar
Flow modes	Crossflow, Dead-end	Crossflow, Dead-end	Crossflow	Crossflow
Geometry	Hollow fiber, spiral wound, plate and frame, tubular	Hollow fiber, spiral wound, plate and frame, tubular	Hollow fiber, spiral wound, tubular	Hollow fiber, spiral wound

HMWC: high molecular weight compounds; LMWC: low molecular weight compounds.