Environmental Engineering Reference
In-Depth Information
The world health Organization classifies lindane as “moderately hazardous,” and its international trade is restricted and
regulated under the Rotterdam Convention on Prior Informed Consent. In 2009, the production and agricultural use of lindane
was banned under the Stockholm Convention on Persistent Organic Pollutants. Lindane is currently permitted only for applica-
tion as a second-line pharmaceutical treatment for lice and scabies skin conditions. Lindane is a persistent organic pollutant: it
has a relatively long life in the environment, it can be transported for a long distance by natural processes like global distillation,
and it can be bioaccumulated in food chains, though it is rapidly eliminated when exposure is discontinued. Lindane is stable
to light, air, heat, carbon dioxide, and strong acids. Trichlorobenzenes and hydrochloric acid are formed during dechlorination
processes in the presence of alkali or after prolonged exposure to heat.
PCBs were often used as a dielectric fluid in transformers and capacitors. PCBs are very stable compounds, and they do not
decompose promptly. This is due to their chemical inability to oxidize and reduce in the natural environment. furthermore,
PCBs have a long half-life (8-10 years) and are insoluble in water, which contributes to their stability. Their destruction by
chemical, thermal, and biochemical processes is extremely difficult and presents the risk of generating extremely toxic diben-
zodioxins and dibenzofurans through partial oxidation. Intentional degradation as a treatment of unwanted PCBs generally
requires high heat or catalysis. In the atmosphere, PCBs can be degraded by hydroxyl radicals. Starting in the early 1970s,
production and new uses of PCBs have been banned due to concerns about the accumulation of PCBs and toxicity of their
by-products. Today PCBs can still be released into the environment from poorly maintained hazardous waste sites that contain
PCBs, illegal or improper dumping of PCB wastes, leaks or releases from electrical transformers containing PCBs, and disposal
of PCB-containing consumer products into municipal or other landfills not designed to handle hazardous waste. PCBs may also
be released into the environment by the burning of some wastes in municipal and industrial incinerators. At present, most
concentrations of PCBs are detected (up to 280 µg/kg) in bottom sediments.
11.2
principle of the methoD
The principle of the method is based on the destruction of organic substances and bacteria by NPC dispersed on polluted open
land or water. The NPC under natural UV radiation form Oh radicals in the presence of water molecules, and the radicals
destroy organic substances and bacteria. In brief, photocatalytic reactions of an aqueous NPC suspension system can be
described as follows [2]:
−
+
(11.1)
NPCh NPCe h
CB
+→ ++
ν
VB
(
)
→
•
h H urface
+
+
−
OH
(11.2)
VB
+
•
+
hHOOHH
VB
+ →+
2
(11.3)
2
(11.4)
e OO
CB
−
+→
2
−
e h heat
CB
−
+
+→
(11.5)
VB
where hν is the UV irradiation, h
VB
+
is the valence band holes, and e
C
−
is the conduction band electrons. It is known that active
oxygen and radical species existing in the presence of oxygen and water take part in the oxidation-reduction reaction and
destroy organic molecules and bacteria.
The NPC must be harmless and their concentration in water must be lower than the permissible level. Moreover, nanopar-
ticles must form agglomerates within the stipulated time with further coagulation and precipitation; that is, they must form safe
ordinary particles. Many semiconductive metal compounds are used as photocatalysts and the most well known among them is
TiO
2
. Usually photocatalysts are applied on a carrier [3-9], have sizes greater than 1 µm, and cannot be used for dispersion on
a large area. That is why it is necessary to develop a new type of NPC that can meet all the requirements described earlier.
As is well known, nanocomposites combine the properties of two or more different materials with the possibility of novel
mechanical, physical, or chemical behavior arising [10]. Nanocomposites of conjugated materials and metal nanoparticles are
prepared from different metals, different types of conjugated polymers, and oligomer linkers [11-18].
Another type of nanoscale materials are nanocomposites of carbon nanoparticles and polymers. Indeed, for example, elec-
trolytically generated nanocarbon colloids (NCC) have functional groups such as carbonyl, hydroxyl, and carboxyl groups
formed on the surface of carbon nanoparticles [19-22]. These nanocomposites can be modified by attaching different cations.
On the other hand, most polymers can react with different ions and molecules and also participate in the modification of
