Environmental Engineering Reference
In-Depth Information
solution using nanostructure (thin-film) TiO
2
can be reduced at a maximum reduction of
62% total organic carbon (TOC) (Carneiro et al., 2004).
14.3.3 Nano-Photocatalysts for Waste Disposal
Although the treatment of industrial and agricultural wastes through the
incineration process has many advantages (e.g., a high degree of destruction, the reduced
land usage, the potential for energy recovery), waste incineration can cause serious
environmental problems such as toxic dioxin emission from inadequate equipment or
inappropriate incineration. Therefore, photocatalytic degradation of industrial and
agricultural wastes by using nanomaterials as photocatalysts has been studied as an eco-
friendly alternative disposal method (Hidaka et al., 1996; Mills and Le Hunte, 1997).
As a conventional plastic material, a large amount of polystyrene (PS) and
poly(vinyl chloride) (PVC) is used in food service and retail industry. In addition, PS
and PVC foam packaging is widely used to protect electronic instruments, household
appliances, auto parts, and other fragile goods from damage. Due to its inertness, PS,
PVC and related plastic products are non-biodegradable in the natural environment and
landfills, causing a serious environmental problem, the so-called “white pollution”.
Researchers have proposed to utilize a eco-friendly alternative strategy to treat the
current waste landfill and toxic byproduct-emitting incineration of PVC/PS wastes. It is
well known that nano-TiO
2
will produce electron-hole pairs under illumination of UV-
light. Therefore, photodegradable polymer-TiO
2
nanocomposite was developed. Many
studies on nano-TiO
2
photocatalytic degradation of polymers mainly dealt with liquid-
phase reactions, such as photocatalytic degradation of PVC particles in nano-TiO
2
suspension aqueous solution. Usually, TiO
2
particles will aggregate significantly in the
low polar medium if there is not enough steric hindrance (Yukio et al., 1999). If the TiO
2
nanoparticles get a good dispersion in the polymer, the efficiency of photocatalytic
degradation is expected to improve. In order to resolve this problem, Zan et al. (2004)
synthesized a new kind of photodegradable PS-TiO
2
nanocomposite film; the weight-
loss of the PS-TiO
2
film reached 29%. Sung et al. (2006) prepared photo-degradable
PVC/TiO
2
nanohybrid and studied their photocatalytic degradation as an eco-friendly
alternative to the current waste landfill and dioxin-emitting incineration of post-use
PVC.
14.3.4 Nanomembranes for Treatment of Water and Wastes
Currently, considerable studies have been conducted using membranes made
with nanomaterials for treatment of water and industrial/agricultural wastes.
Ultrafiltration (UF), nanofiltration (NF) and Reverse osmosis (RO) are a pressure driven
membrane process. UF and NF are mainly applied for wastewater treatment, drinking
water production, and removal of small organic compounds (Braeken et al., 2006) and
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