Page 478 - Industrial Wastewater Treatment, Recycling and Reuse

448 Industrial Wastewater Treatment, Recycling, and Reuse

11.3 3D TRASAR TECHNOLOGY FOR MEMBRANES
11.3.1 Current Needs of RO Membrane Systems
The most popular membrane technologies practiced currently include MF,
UF, NF, and RO. Figure 11.8 shows how these technologies compare in
terms of the removal capabilities. MF membranes are suited for suspended
particle removal and find applications in the clarification of water and
other fluids. The pore size of these membranes ranges from 0.1 to 1 mm.
UF membranes have a pore size in the general range of 0.01–0.1 mm.
The UF membrane specification is often expressed in terms of molecular
weight cut-off (MWCO), which refers to the lowest molecular weight sol-
ute (of known molecular weight), which has a 90% rejection by the mem-
brane. The MWCO of UF membranes generally ranges between 1000 and
300,000 Da. These membranes are commonly used for concentrating pro-
cess streams, removing bacteria and viruses, and removing organics from
water. Both MF and UF membranes work on the principle of size exclusion,
which means that the species larger than the pore size of the membrane are
rejected while the smaller species are allowed to pass through. NF mem-
branes could have a pore size between 1 and 10 nm. In terms of MWCO,

Figure 11.8 Comparison of membrane technologies in terms of removal capability and
average pore size.