Types of reverse osmosis membranes

A RO membrane must be freely permeable to water, highly impermeable to solutes, and able to withstand high operating pressures. It should ideally be tolerant of wide ranges of pH and temperature, and should be resistant to attack by chemicals like free chlorine and by bacteria. Ideally, it should also be resistant to scaling and fouling by contaminants in the feedwater. There are three major types of RO membranes: cellulosic, fully aromatic polyamide, and thin-film composite. A comparison of characteristics of these three membrane types is given in Table 2.

Table 2 Comparison of reverse osmosis membranes

Comparison of reverse osmosis membranes

Feature

Cellulosic

Aromatic polyamide

Thin film compositea

Rejection of organic

L

M

H

Rejection of low-molecular-weight organics

M

H

H

Water flux

M

L

H

pH tolerance

4-8

4-11

2-11

Temperature stability

Maximum 35 oc

Maximum 35 °C

Maximum 45 °C

Oxidant tolerance(e.g., free chlorine

H

L

L

Compaction tendency

H

H

L

Biodegradability

H

L

L

Cost

L

M

H

a Thin film composite type having polyamide surface layer.

a Thin film composite type having polyamide surface layer.

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