Environmental Engineering Reference
In-Depth Information
worldwide population will face fresh water shortage by 2075.
2
Given the threat to all
living organisms, there is an urgent need to address this issue and to develop new
technology and devices for water puriication. Many technologies such as distillation,
sand iltration, treatment with chemical disinfectants, reverse osmosis (RO), and
membrane-based iltrations have been employed to purify water.
3,4
Among these,
membrane-based iltration is a relatively new technique with certain advantages like
low power consumption, scalability, nonuse of chemicals, and relatively low operational
temperature.
5,6
In general, a membrane can be deined as a semipermeable membrane that allows only
certain molecules and compounds to pass through and restrict the passage of others. This
is illustrated in Figure 23.1, where the luid particles are allowed to pass through the mem-
brane, whereas the contaminant molecules are blocked.
The separation across the membrane takes place either by a sieving mechanism or
by diffusion. Larger particles are blocked on the surface due to a sieve effect, and par-
ticles smaller than the surface pores are collected by the membranes by interception or
by static electrical attraction. Although advanced membranes are developed, several
problems still persist such as membrane fouling and chemical stability.
7
These prob-
lems lower their operational lifetime and increase the energy demands. The iltration
eficiency is highly dependent on membrane thickness, surface electronic properties,
and the surface chemical functionalities. Besides the eficiency, properties like pres-
sure drop and lux resistance are also very important to be evaluated for the iltering
media.
Membrane-based iltration systems can be improved with the use of nanoibrous media.
Nanoibers, due to their higher porosities and well-connected pore structures, offer higher
permeability to water iltration over the conventional materials being used. Among all,
electrospinning is a most successful technique to fabricate nanoibers. Electrospun nano-
ibers provide high iltration eficiency with a small decrease in permeability. Small
pore size, high permeability, and low cost of production make them suitable to remove
unwanted microsized or nanosized impurities from water.
8
Contaminants
Fluid molecules
FIGURE 23.1
Schematic of a membrane iltration system.
