Environmental Engineering Reference
In-Depth Information
The following summarizes the various advantages offered by photocatalytic oxidation.
1)
Operation
: Photocatalytic processes have mild operation conditions, i.e., room
temperature and pressure.
2)
Energy friendly
. The photocatalytic process only uses natural, renewable and
sustainable sunlight as energy source. Moreover, with proper configuration, it is
possible to reclaim the electrons generated during the photocatalytic process,
which can be used as electric source in other applications such as hydrogen
generation. This may lead to a positive energy output in overall water
purification process, benefiting the energy balance in a large scale.
3)
Environmental friendly:
Unlike many treatment techniques, such as adsorption or
filtration, the photocatalytic reaction leads to a complete destruction of most
tested organic pollutants and eliminates them from the environmental systems
instead of transferring or concentrating the compounds from one phase to the
other (e.g., water to gas or vice versa). The most widely used photocatalyst TiO
2
systems also exhibit great stability under various environmental conditions.
Furthermore, photocatalytic TiO
2
systems generally have the minimum
environmental impacts.
4)
Cost-effective:
Using natural sunlight as energy, considerable savings can be
achieved. Moreover, as a fully matured commercial product, the cost of TiO
2
is
very low.
5)
Non-selectivity:
TiO
2
is proved to be effective over a variety of organic
compounds, and a large pH range. Also, the photocatalytic process has a very
good efficiency in treating high concentrations of halogenated compounds, which
in most cases are very toxic and untreatable by biological treatment systems.
Non-selectivity:
TiO
2
is proved to be effective over a variety of organic
compounds, and a large pH range. Also, the photocatalytic process has a very
good efficiency in treating high concentrations of halogenated compounds, which
in most cases are very toxic and untreatable by biological treatment systems.
6)
Short treatment time:
The time scale of photocatalytic reaction is generally in
hours, or even minutes when combined with other AOPs, which is a significant
reduction of reaction time comparing to most biological treatments.
However, before wide applications of photocatalytic oxidation on industrial scale
water purification processes can be realized, some challenges and drawbacks need to be
addressed.
1)
Scale-up to industrial size reactors:
Although some creative designs have
showed good removal efficiency in pilot scale tests, engineering design and
operation strategies are lacking for efficient use of reactors at large scale
operations.
2)
Fouling of light fixtures:
Any photocatalytic reactor must have at least one side
that is transparent to light, which is required for light to penetrate through the
solution. However, the light intensity could be significantly reduced over long
operation time due to the fouling of the light fixtures by photocatalyst and other
substrates. This is a severe challenge especially for slurry reactor systems.
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