Designing Novel Photocatalysts for Disinfection of Multidrug-Resistant …
447
But the dosage at which it is performed results in the creation of unsolicited disinfection by-products like bromates from bromide which has been proven a potential
human carcinogen (Agus et al. 2009). Lower dosage may not efficiently inactivate
cysts, spores, and viruses (Cho et al. 2003), other factors like contact time, the target
microorganisms and characteristics of the wastewater matrix also play an important part. Interesting observations were reported by Selma et al. (2007), where 1.6
and 2.2 mg L
−1 of initial ozone doses result 3.7 and 5.6 log reduction of 10
8 CFU
mL
−1 of S. sonnei, respectively. Consequences of ozonation on MDR bacteria have
been scarcely addressed Oncu et al. (2011) did a comparative investigation on chlorination, ozonation, and feebly applied heterogeneous photocatalytic process for
disinfection of MDR microorganisms. Chlorination had no impact on the plasmid
DNA structure, whereas ozonation at concentrations 1–4.42 mg L
−1 and treatment
time 1 min and photocatalysis lead to conformational changes in them, which showed
direct correlation with oxidant doses. Investigations by Lee et al. (2013) stated 3-log
reduction in chlortetracycline-resistant bacteria from livestock wastewater within
10 min (Öncü et al. 2011).
1.3.3 UV Irradiation
UV radiation is the most globally used disinfection treatment as far as surface, water
and food-based sterilization are concerned. UV-C (250–280 nm) radiation has the
most detrimental effect on the genetic material (DNA and RNA) of microorganisms.
It results in the inhibition of the replication machinery and reproducibility if the
doses applied are lethal. The UV dose is the main factor to specify by what means it
will be used for decontamination of wastewater. It is described as the product of the
average UV intensity in mW cm
−2 and the average exposure time in seconds(s).
UV irradiation might fail in the inactivation of MDR and ARG lessening in
wastewater under commonly applied doses of 30 mJ cm
−2 . However, UV dosages
somewhat near or equal to 50 mJ cm
−2 , inactivation of the MDR could be achieved.
But according to them, UV radiation increased the MDR selectivity and ARG lessening (Guo et al. 2013); in particular, this treatment could reduce the percentage
of erythromycin-resistant bacteria, augmented that of tetracycline-resistant bacteria,
and ARG concentrations. Thus as per the references in literature, damaging of ARGs
requires substantially high UV doses of 200–400 mJ cm
−2 in contrast to that required
for 4–5 log reduction of MDR (McKinney and Pruden 2012).
UV disinfection effect had been assessed at large-scale setups for effluents to
observe in-significant reduction of MDR and ARGs [tet(G) or tet(Q)] (McKinney
and Pruden 2012) and found almost equivalent to chlorination process as per the
statistical student t-test (p > 0.05). The investigators highlight that even though it was
indecisive to reach an apparent conclusion, UV irradiation mediated disinfection to
decrease loads of some tetR gene and their respective diversity is still under question.
In a further large-scale study report by Francy et al. (2012) adenovirus was detected in
the UV-treated effluent in between 25 and 36%. Though these detection percentages
447
But the dosage at which it is performed results in the creation of unsolicited disinfection by-products like bromates from bromide which has been proven a potential
human carcinogen (Agus et al. 2009). Lower dosage may not efficiently inactivate
cysts, spores, and viruses (Cho et al. 2003), other factors like contact time, the target
microorganisms and characteristics of the wastewater matrix also play an important part. Interesting observations were reported by Selma et al. (2007), where 1.6
and 2.2 mg L
−1 of initial ozone doses result 3.7 and 5.6 log reduction of 10
8 CFU
mL
−1 of S. sonnei, respectively. Consequences of ozonation on MDR bacteria have
been scarcely addressed Oncu et al. (2011) did a comparative investigation on chlorination, ozonation, and feebly applied heterogeneous photocatalytic process for
disinfection of MDR microorganisms. Chlorination had no impact on the plasmid
DNA structure, whereas ozonation at concentrations 1–4.42 mg L
−1 and treatment
time 1 min and photocatalysis lead to conformational changes in them, which showed
direct correlation with oxidant doses. Investigations by Lee et al. (2013) stated 3-log
reduction in chlortetracycline-resistant bacteria from livestock wastewater within
10 min (Öncü et al. 2011).
1.3.3 UV Irradiation
UV radiation is the most globally used disinfection treatment as far as surface, water
and food-based sterilization are concerned. UV-C (250–280 nm) radiation has the
most detrimental effect on the genetic material (DNA and RNA) of microorganisms.
It results in the inhibition of the replication machinery and reproducibility if the
doses applied are lethal. The UV dose is the main factor to specify by what means it
will be used for decontamination of wastewater. It is described as the product of the
average UV intensity in mW cm
−2 and the average exposure time in seconds(s).
UV irradiation might fail in the inactivation of MDR and ARG lessening in
wastewater under commonly applied doses of 30 mJ cm
−2 . However, UV dosages
somewhat near or equal to 50 mJ cm
−2 , inactivation of the MDR could be achieved.
But according to them, UV radiation increased the MDR selectivity and ARG lessening (Guo et al. 2013); in particular, this treatment could reduce the percentage
of erythromycin-resistant bacteria, augmented that of tetracycline-resistant bacteria,
and ARG concentrations. Thus as per the references in literature, damaging of ARGs
requires substantially high UV doses of 200–400 mJ cm
−2 in contrast to that required
for 4–5 log reduction of MDR (McKinney and Pruden 2012).
UV disinfection effect had been assessed at large-scale setups for effluents to
observe in-significant reduction of MDR and ARGs [tet(G) or tet(Q)] (McKinney
and Pruden 2012) and found almost equivalent to chlorination process as per the
statistical student t-test (p > 0.05). The investigators highlight that even though it was
indecisive to reach an apparent conclusion, UV irradiation mediated disinfection to
decrease loads of some tetR gene and their respective diversity is still under question.
In a further large-scale study report by Francy et al. (2012) adenovirus was detected in
the UV-treated effluent in between 25 and 36%. Though these detection percentages