Environmental Engineering Reference
In-Depth Information
3.5.3 Bacteria, Virus and Fungus
The well-known solar disinfection process can be enhanced with the presence of
TiO 2 as illustrated by many researchers. It is certain that photocatalytic reaction can
enhance the disinfection rate against a wide range of microorganisms in laboratory
studies. The ROS generated either on or near the nano-TiO 2 surface is believed to be
able to cause oxidative damages to the cell membrane and lead to the death of
microorganisms. One major advantage of the photocatalytic disinfection over
conventional chlorination is that the later process generates carcinogenic disinfection by-
products (DBPs), such as trihalomethane. On the contrary, the photocatalytic
disinfection process using ROS as oxidant which will self-degrade in nanosecond and
millisecond scale in the presence of water, leaving no unwanted chemical residuals.
(Hoffmann et al., 1995, Mills and Hunte, 1997)
One of the earliest studies of photocatalytic disinfection was reported by
Matsunaga et al. (1985). Significant enhancement in bacterial deactivation, including
Lactovacillu acidophilus , Saccharomyces cerevisiae and Escherichia coli , was observed
comparing to UV treatment alone. It was found that the intracellular CoA of
Saccharomyces cerevisiae could be oxidized by the presence of TiO 2 , leading to
inhibition of cell respiration and cell death. However, green algae, Chlorella vulgaris ,
was the least affected by TiO 2 , due to the thick cell wall of polysaccharides and pectin.
Similar to other photocatalytic research, the photocatalytic disinfection
experiments are carried out in suspension form most likely. McLoughlin et al.,
(McLoughlin et al., 2004) have reported that 44% enhancement compared to solar
irradiation alone is achieved with the presence of 3 ppm of TiO 2 in suspension using the
CPC system. However, post-reaction treatment, namely particle separation appears to
be the major drawback when applying the process to small-scale water purification
systems. Moreover, substantial reduction of bacterial killings is observed if a fixed bed
reactor system is used. Thus, there are many challenges, such as performance against
more resistant bacteria, pro-longed reaction rate, no residual disinfection capability and
activity under direct sunlight, that need to be addressed before the use of TiO 2 as
publicly acceptable water disinfection technique. Some current and past photocatalytic
disinfection works are summarized in Table 3.4.
3.6
Conclusions
Photocatalytic purification of water and wastewater appears to be a promising
technology that has many advantages over conventional treatments. It has great
potential in becoming a major water and wastewater treatment process for the removal
and detoxification of organic or toxic compounds and water disinfection.
 
 
 
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