305
infrastructure and high power needed to pump the wastewater through the system.
However, the results from the impact categories cannot be compared directly to each
other as they were expressed in different measurement units. From the engineering
point of view, these constraints mainly arise from the low photoactivity of the catalyst
used under solar irradiation. Further materials engineering solutions and studies
should be carried out to resolve such technical issues to permit the scaleup of the
technology to a commercially viable process.
Future Challenges and Prospects
Semiconductor photocatalytic technology using either UV light or solar has become
more prominent owing to its advantages of the use of vast additive chemicals or
disinfectants and its mineralization aspects. These are particularly important, as
recalcitrant organics are mineralized rather than being transformed to another phase.
Coupled with the ambient operation of the process, all these make photocatalytic
water treatment technology a viable alternative for commercialization in the near
future. Different water contaminants, ranging from hazardous contaminants of pesticides, herbicides, and detergents to pathogens, viruses, coliforms, and spores, are
effectively removed by this photocatalytic process.
The applicability of the heterogeneous photocatalytic technology for water treatment is constrained by several key technical issues that need to be further investigated. The first consideration would be whether the photocatalytic process is a
pretreatment step or a stand-alone system. The nonselective reactivity on the nonbiodegradable water-soluble pollutants means that the photocatalytic process can be
used effectively as a pretreatment step to enhance biodegradation of recalcitrant
organic pollutants prior to biological water treatment. In such a way, the residence
time and reaction volume for the biological treatment could be significantly reduced.
If the photocatalytic process is used as a stand-alone treatment system, the residence
time required might be prolonged for total bacterial inactivation or mineralization. As
discussed, this is hindered by the slow kinetics, low photo-efficiency, and a need for
continuous (without interruption) illumination to achieve the required total organic
carbon removal or microbial inactivation. For the stand-alone system, the site area
requirement might be proportionally from any increased reaction volume required.
In order to promote the feasibility of photocatalytic water treatment technology
in the near future, several key technical constraints ranging from catalyst development to reactor design and process optimization have to be addressed. These include
(1) catalyst improvement for a high photo-efficiency that can utilize wider solar
spectra; (2) catalyst immobilization strategy to provide a cost-effective solid–liquid
separation; (3) improvement in the photocatalytic operation for wider pH range and
to minimize the addition of oxidant additives; (4) new integrated or coupling system
for enhanced photomineralization or photo-disinfection kinetics; and (5) effective
design of photocatalytic reactor system or parabolic solar collector for higher utilization of solar energy to reduce the electricity costs. Currently, the utilization of
Recent Developments in Photocatalytic Water Treatment Technology
infrastructure and high power needed to pump the wastewater through the system.
However, the results from the impact categories cannot be compared directly to each
other as they were expressed in different measurement units. From the engineering
point of view, these constraints mainly arise from the low photoactivity of the catalyst
used under solar irradiation. Further materials engineering solutions and studies
should be carried out to resolve such technical issues to permit the scaleup of the
technology to a commercially viable process.
Future Challenges and Prospects
Semiconductor photocatalytic technology using either UV light or solar has become
more prominent owing to its advantages of the use of vast additive chemicals or
disinfectants and its mineralization aspects. These are particularly important, as
recalcitrant organics are mineralized rather than being transformed to another phase.
Coupled with the ambient operation of the process, all these make photocatalytic
water treatment technology a viable alternative for commercialization in the near
future. Different water contaminants, ranging from hazardous contaminants of pesticides, herbicides, and detergents to pathogens, viruses, coliforms, and spores, are
effectively removed by this photocatalytic process.
The applicability of the heterogeneous photocatalytic technology for water treatment is constrained by several key technical issues that need to be further investigated. The first consideration would be whether the photocatalytic process is a
pretreatment step or a stand-alone system. The nonselective reactivity on the nonbiodegradable water-soluble pollutants means that the photocatalytic process can be
used effectively as a pretreatment step to enhance biodegradation of recalcitrant
organic pollutants prior to biological water treatment. In such a way, the residence
time and reaction volume for the biological treatment could be significantly reduced.
If the photocatalytic process is used as a stand-alone treatment system, the residence
time required might be prolonged for total bacterial inactivation or mineralization. As
discussed, this is hindered by the slow kinetics, low photo-efficiency, and a need for
continuous (without interruption) illumination to achieve the required total organic
carbon removal or microbial inactivation. For the stand-alone system, the site area
requirement might be proportionally from any increased reaction volume required.
In order to promote the feasibility of photocatalytic water treatment technology
in the near future, several key technical constraints ranging from catalyst development to reactor design and process optimization have to be addressed. These include
(1) catalyst improvement for a high photo-efficiency that can utilize wider solar
spectra; (2) catalyst immobilization strategy to provide a cost-effective solid–liquid
separation; (3) improvement in the photocatalytic operation for wider pH range and
to minimize the addition of oxidant additives; (4) new integrated or coupling system
for enhanced photomineralization or photo-disinfection kinetics; and (5) effective
design of photocatalytic reactor system or parabolic solar collector for higher utilization of solar energy to reduce the electricity costs. Currently, the utilization of
Recent Developments in Photocatalytic Water Treatment Technology