Environmental Engineering Reference
In-Depth Information
2.5.1 Forward Osmosis Using Nanocomposites Based on Hydrogels
Forward osmosis is a technique to purify water that uses a semipermeable membrane to
effect separation of water from dissolved solutes. The driving force for this separation is
an osmotic pressure gradient that induces a net low of water through a semipermeable
membrane into the draw solution, thus effectively separating the water in the feed from
its solutes. While a high concentration of a solute will produce such osmotic gradient, the
osmotic solute remains in the inal solution. An alternative is to use a highly hydrophilic
solid (e.g., hydrogel) to create the gradient and retain the pure water. Then, the water can
be extracted from the gel using pressure, temperature, or other stimuli [182]. The large
swelling capacity of nanocomposites based on polyacrylamide hydrogels and conduct-
ing polymers [65] makes them ideal candidates for forward osmosis. Moreover, the water
can be released by triggering the gel collapse using microwaves [183]. Mechanically sta-
ble hydrogels with large swelling degree (Figure 2.10) will be especially useful for this
purpose.
2.5.2 Drug Liberation from Hydrogel Nanoparticles
Like monolithic solids, hydrogel nanoparticles can be used to carry and release drugs for
aquaculture organisms. While this approach will ensure the internalization of the phar-
maceutical drug into the organisms, the possibility of leakage of nanoparticles loaded with
drugs that could harm the environment increases. Therefore, some ways to control the
nanoparticle transport in the aquaculture media should be devised. One way involves
loading bigger (>100 nm) hydrogel nanoparticles with small (<10 nm) magnetite nanopar-
ticles. In that way, as it is shown in Figure 2.18, the gel can be manipulated with a magnet,
avoiding the release of nanoparticles into the environment.
2.5.3 Solid-Phase Extraction for Contaminant Analysis
Contaminants in drinking water are usually present in low concentration [184]. Therefore,
to successfully analyze real samples, preconcentration is necessary. Solid-phase extraction
is a technique widely used to analyze organics in water, using porous hydrophobic solids
[185]. Nanoporous hydrogels can be used to extract less hydrophobic organics from water.
Additionally, hydrogels loaded with chelating agents can be used to selectively extract
metals from water for further analysis. Nanoporous carbon surfaces can be modiied with
functional groups that promote the chemisorption of speciic analytes.
2.5.4 Detection of Harmful Waterborne Microorganisms through Fast DNA Sensing
Water is a source of harmful pathogen microorganisms affecting humans and aquatic
organisms [186]. However, only some strains of bacteria are actually harmful. The classic
methods of detection, involving seeding and cultivation in nutritive media, are quite slow.
An alternative involves the detection of short DNA fragments only present in danger-
ous organisms. We have collaborated with the group of M.-C. Pham (ITODYS, U. Paris
VII, France) in the development of electrochemical oligonucleotide (ODN) sensors using
electroactive polymers functionalized with synthetic ODN [187]. It was also shown that
porous electrodes made of multiwall carbon nanotubes glued with Naion ® could improve
the sensitivity of the sensors through an increase of the effective surface area [188]. HPC
(e.g., HPC-f or 2SPC) electrodes can be used as platforms for DNA sensors, allowing high
Search WWH ::




Custom Search