252
Potential Applications in Water Treatment
The overall efficiency of a photocatalytic water treatment process strongly depends
on the configuration and operation parameters of the photoreactor. Two configurations are commonly used: slurry reactors and reactors using immobilized TiO 2 .
Various dispersion/recovery or catalyst immobilization techniques are being pursued to maximize its efficiency. Extensive investigation on operating parameters has
been carried out with these lab- or pilot-scale systems. A recent critical review outlines the effects of water quality and a wide range of operating parameters including
TiO 2 loading, pH, temperature, dissolved oxygen, contaminant type and concentration, light wavelength, and intensity [59]. Readers are referred to this review for
details regarding process optimization. A commercial product, Purifics Photo-Cat™
system, has a treatment capacity as high as two million gallons per day with a small
footprint of 678 ft
2
. Pilot tests showed that the Photo-Cat™ system is highly efficient for removing organics without producing waste streams and it operates with
relatively low specific power consumption of about 4 kWh/m
3
[3, 25, 324]. NanoTiO 2 - facilitated solar disinfection (SODIS) has been extensively tested and appears
to be a feasible option to produce safe drinking water in remote areas of developing
countries. The SODIS system can be small scale for one person or scaled up to
medium-size solar compound parabolic collectors.
Photocatalysis has shown great potential as a low-cost, environmental friendly,
and sustainable water treatment technology. However, there are several technical
challenges for its large-scale application, including (1) catalyst optimization to
improve quantum yield or to utilize visible light; (2) efficient photocatalytic reactor
design and catalyst recovery/immobilization techniques; and (3) better reaction
selectivity.
Metal oxide nanomaterials such as TiO 2 and CeO 2 as well as carbon nanotubes
have been studied as catalysts in heterogeneous catalytic ozonation processes that
provide fast and comparatively complete degradation of organic pollutants. Both
radical-mediated and non-radical-mediated reaction pathways have been proposed
[241]. The adsorption of ozone and/or pollutants on the catalyst surface plays a critical role in both mechanisms. Nanomaterials have large specific surface area and an
easily accessible surface, leading to high catalytic activity. Some nanomaterials
were also reported to promote decomposition of ozone into hydroxyl radicals, facilitating degradation process through radical-mediated routes [250]. For future industrial scale applications, a better understanding of the mechanism of
nanomaterial-enabled catalytic ozonation is in critical need.
Disinfection and Microbial Control
The dilemma between effective disinfection and formation of toxic disinfection byproducts (DBPs) poses a great challenge for the water industry. It is now well recognized that conventional disinfectants, such as chlorine disinfectants and ozone,
13 Wastewater
Potential Applications in Water Treatment
The overall efficiency of a photocatalytic water treatment process strongly depends
on the configuration and operation parameters of the photoreactor. Two configurations are commonly used: slurry reactors and reactors using immobilized TiO 2 .
Various dispersion/recovery or catalyst immobilization techniques are being pursued to maximize its efficiency. Extensive investigation on operating parameters has
been carried out with these lab- or pilot-scale systems. A recent critical review outlines the effects of water quality and a wide range of operating parameters including
TiO 2 loading, pH, temperature, dissolved oxygen, contaminant type and concentration, light wavelength, and intensity [59]. Readers are referred to this review for
details regarding process optimization. A commercial product, Purifics Photo-Cat™
system, has a treatment capacity as high as two million gallons per day with a small
footprint of 678 ft
2
. Pilot tests showed that the Photo-Cat™ system is highly efficient for removing organics without producing waste streams and it operates with
relatively low specific power consumption of about 4 kWh/m
3
[3, 25, 324]. NanoTiO 2 - facilitated solar disinfection (SODIS) has been extensively tested and appears
to be a feasible option to produce safe drinking water in remote areas of developing
countries. The SODIS system can be small scale for one person or scaled up to
medium-size solar compound parabolic collectors.
Photocatalysis has shown great potential as a low-cost, environmental friendly,
and sustainable water treatment technology. However, there are several technical
challenges for its large-scale application, including (1) catalyst optimization to
improve quantum yield or to utilize visible light; (2) efficient photocatalytic reactor
design and catalyst recovery/immobilization techniques; and (3) better reaction
selectivity.
Metal oxide nanomaterials such as TiO 2 and CeO 2 as well as carbon nanotubes
have been studied as catalysts in heterogeneous catalytic ozonation processes that
provide fast and comparatively complete degradation of organic pollutants. Both
radical-mediated and non-radical-mediated reaction pathways have been proposed
[241]. The adsorption of ozone and/or pollutants on the catalyst surface plays a critical role in both mechanisms. Nanomaterials have large specific surface area and an
easily accessible surface, leading to high catalytic activity. Some nanomaterials
were also reported to promote decomposition of ozone into hydroxyl radicals, facilitating degradation process through radical-mediated routes [250]. For future industrial scale applications, a better understanding of the mechanism of
nanomaterial-enabled catalytic ozonation is in critical need.
Disinfection and Microbial Control
The dilemma between effective disinfection and formation of toxic disinfection byproducts (DBPs) poses a great challenge for the water industry. It is now well recognized that conventional disinfectants, such as chlorine disinfectants and ozone,
13 Wastewater