Recent Advances in Understanding the Role of Wastewater …
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Fig. 3 Nitrogen adsorption through zeolite column
the membrane used in RO is <0.05 µm whereas ultrafiltration is usually used to
separate solutes above a molecular weight of 500–2000, which implies a relatively
small osmotic pressure, reverse osmosis is used to remove material of low molecular
weight, which causes a high osmotic pressure. RO processes are selective for water
and small ions whereas the UF separation is based on the molecular size and shape
of the molecule. Table 1 summarizes the characteristics of the various membrane
separation processes.
Table 1 Membrane separation processes
Membrane process
Working principle
Membrane size range
Function
Reverse osmosis
Pressure gradient
<0.05
Selective transport of
water and ions
Ultrafiltration
Pressure gradient
5 × 10 –3 –10
Selective to molecular
size and shape
Electrodialysis
Electrical potential
gradient
<0.1
Selective to ions
Dialysis
Concentration
gradient
<0.1
Selective to solute
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Fig. 3 Nitrogen adsorption through zeolite column
the membrane used in RO is <0.05 µm whereas ultrafiltration is usually used to
separate solutes above a molecular weight of 500–2000, which implies a relatively
small osmotic pressure, reverse osmosis is used to remove material of low molecular
weight, which causes a high osmotic pressure. RO processes are selective for water
and small ions whereas the UF separation is based on the molecular size and shape
of the molecule. Table 1 summarizes the characteristics of the various membrane
separation processes.
Table 1 Membrane separation processes
Membrane process
Working principle
Membrane size range
Function
Reverse osmosis
Pressure gradient
<0.05
Selective transport of
water and ions
Ultrafiltration
Pressure gradient
5 × 10 –3 –10
Selective to molecular
size and shape
Electrodialysis
Electrical potential
gradient
<0.1
Selective to ions
Dialysis
Concentration
gradient
<0.1
Selective to solute