Environmental Engineering Reference
In-Depth Information
23.7
Porous mEdia and cEramics
Porous ceramics are another good candidate for the development of water filters because of their increased surface area during
nanoparticle growth [31]. Some ceramics like maganese oxide can effectively change the valence state of metal ion in water,
which can easily removed by reaction with iron oxide to form a stable material [32]. Very often these reactions can be enhanced
by adding other nanomaterials such as copper and copper oxide and this combination can effectively remove phosphate, heavy
metals, lead, arsenic, and other pollutants. According to established norms, the permissible arsenic level in safe drinking water
is about 50-10 µg/l; however, many regions of the world have very high arsenic levels in available groundwater. It has been
shown that a combination of nano manganese oxide fibers combined with nano iron oxide is effective in removing arsenic from
groundwater [33]. The nano Mno
2
and Fe
2
o
3
base medium has higher breakthrough bed volume than other media; additionally,
it is equally effective for As (III) and As (V). As we know, As (III) is more toxic than As (V). This medium is also effective for
high Pb (II) adsorption. Porous ceramics activated with iron oxide nanoparticles can also provide effective remediation of
pollutants like trichloroethylene (TCE) and tetrachloroethylene.
23.8
nanofiltration
Nanofiltration can remove dissolved solids, but is often used to soften water by removing dissolved organic carbon. The nano-
filtration membrane works in a similar manner to Ro, except that a relatively low pressure is required because of the large pore
size (0.05-0.005 µm). Membrane technologies including ultrafiltration, nanofiltration, and Ro are now emerging as key com-
ponents in the domain of advanced water purification and desalination systems (Fig. 23.4). Some recent reviews in the litera-
ture have focused on the importance of nanofiltration for removing cations, natural organic matter, biological contaminants,
organic pollutants, nitrate, and arsenic from ground- and surface water [34]. It was also reported that nanofiltration can effi-
ciently remove traces of uranium from seawater. Nanofiltration has also been evaluated for desalination of seawater, and it was
observed that in combination with Ro it could effectively convert saline water to potable water [35]. Nanofiltration can be a
good solution for improving water quality even in large water distribution systems by substantially reducing organic and
biological contaminants [36, 37].
Engineered nanoparticles nowadays provide unprecedented opportunities for efficient water purification catalysts and redox
active media by their optical electronic and catalytic virtues. It is important to understand that chemical groups are key biological
constituents that make these nanomaterials functionalize. Recently it has been reported that CNTs can be successfully used to
fabricate carbon nanofilters. These CNT nanofilters are hollow cylinders with radially aligned CNT walls. It was observed that
these nanofilters can efficiently reduce bacterial contaminations (Fig. 23.5) such as
Salmonella typhi
,
Escherichia coli
, and
Staphylococcus aureus
, as well as polio virus sabin 1 from contaminated water [38].
Pressure (bar)
100
Reverse osmosis
10
Nanoltration
Ultraltration
1
Microltration
Pore size
(μm)
1nm
0.1
10
-4
0.001
0.01
0.1
1
10
Ions
Hormones
Macromolecules
Viruses
Microorganism
Emulsions
Colloids
figurE 23.4
Ranges for nanofiltration, ultrafiltration, Ro, and microfiltration, and indicative molecules passing through these membranes.
