Environmental Engineering Reference
In-Depth Information
Photoadsorption
Photocatalytic
reduction
Photolysis
Photocatalytic
oxidation
Photodisinfection
Photochemical
Advanced
oxidation
Oxidize
�ermal
disinfection
Catalytic
oxidation
Chemical
�ermal
Disinfect
Ion
exchange
Distillation
Separate
Filter
Sand
Deionization
Adsorbants
Membranes
Activated carbon
Microfiltration
Ultrafiltration
Nanofiltration
FIGURE 24.5
New photochemical puriication technologies address emerging contaminants.
24.6 Puralytics Process
Puralytics has developed a unique and innovative “puriication engine” for water, which
is scalable and can be packaged to meet the needs of the target markets. The core technol-
ogy uses light energy supplied by either semiconductor light-emitting diodes (LEDs) or
sunlight to activate a nanotechnology coated ibrous mesh and thereby to enable the ive
simultaneous and synergistic puriication processes described below.
24.6.1 Photocatalytic Oxidation
Illumination of the photocatalyst with precise wavelength photons produces highly reactive
hydroxyl radicals. These break the carbon bonds in organic compounds in the water, pro-
viding destruction of the emerging contaminants, including pesticides, petrochemicals, and
pharmaceuticals. Photocatalytic oxidation by a photo-activated semiconductor photocatalyst
has been actively studied [7-10] as an advanced oxidation process applicable to water puri-
ication. This process offers nonselective degradation of organic contaminants in water
into simpler and less toxic compounds, and ultimately into inorganic ions, CO
2
, and water.
Photocatalytic oxidation involves the absorption of energetic photons by the semiconductor
and the subsequent production of hydroxyl radicals at the semiconductor surface. While
many nanotechnology catalysts have been studied, anatase TiO
2
is a particularly effective
semiconductor photocatalyst in converting light into hydroxyl radicals—a more powerful
oxidizing agent than ozone and twice as powerful as chlorine—with suficient energy to
completely mineralize organic contaminants. The critical reaction pathway is
(TiO
2
) +
h
ν → e
−
+ h
+
[electron/hole production]
(H
2
O ⇆ H
+
+ OH
−
)
ads
+ h
+
→ H
+
+ OH°
[hydroxyl radical production]
Reactant + OH° → Intermediates → CO
2
+ H
2
O + minerals
