with the UV/H 2 O 2 process. As energy consumption generates the big part of the
process costs up to 30–50%, cost savings can be expected (Sichel et al. 2011).
7.3.10 UV/Periodate
Periodic acid, H 5 IO 6 , and periodate, IO 4
– , are strong oxidants (see Table 7.1).
Irradiation of periodate solutions under short-UV light generates several radicals
(IO 3
• , HO
•
, IO 4
• ) and other oxidative species (IO 3
– , HOI, I 2 , H 2 O 2 , O 3 ). The
oxidation of a system containing this reagent under UV light is less selective but
more efficient than other AOTs. The proposed mechanism can be very complex
(Weavers et al. 1997).
With this technology, a wide variety of compounds at low concentrations can be
destroyed. It can be used for discoloration of dye-containing waters and for treatment
of other wastewaters. For a better effectiveness, waters should have a low absorbance. So far, there are no legislated discharge requirements for iodine compounds,
from which I 2 and I
– are the more toxic (but still of low toxicity). Iodine can be
recovered by ionic exchange, and periodate can be electrochemically regenerated.
The technology is faster than other photochemical AOTs and seems very promising.
Recently p-nitrophenol was treated with UV-activated potassium periodate leading
to 79.5% degradation after 60 min at the optimum conditions: 30 mg/L of the
substrate, potassium periodate concentration 386.3 mg/L, pH 6.2 (Saien and
Bazkiaei 2018).
7.3.11 UV/Persulfate
The absorption spectrum of PDS is very similar to that of H 2 O 2 , characterized by a
gradual increase in absorption without a noticeable maximum in the accessible wavelength region. At 254 nm, ε ¼ 20 L/(mol cm), and a dissociative transition is reached,
leading to the scission of the –O–O– linkage. ϕ SO4•– is lower than 2, corresponding to a
quantum yield of PDS consumption of below unity (0.58–0.79) (Mark et al. 1990). As
said before (Sect. 7.2.10), since the reactions of PDS are generally slow at normal
temperature, the photochemical activation of PDS to SO 4
•–
, working at ambient
temperature, has been proposed (Eq. 7.126), followed by reactions in Eqs. 7.70, 7.71
and 7.72 (Lau et al. 2007; Anipsitakis and Dionysiou 2004b):
S 2 O 8
2À
þ hν ! 2SO 4
• À
ð7:126Þ
Due to the adverse effects of some metal catalysts such as Co(II) on human
health, PMS activated by UV irradiation was considered as a better, environmentally
friendly and applicable technology (Guan et al. 2011). PMS presents absorption
7 Introduction to Oxidative Technologies for Water Treatment
157
process costs up to 30–50%, cost savings can be expected (Sichel et al. 2011).
7.3.10 UV/Periodate
Periodic acid, H 5 IO 6 , and periodate, IO 4
– , are strong oxidants (see Table 7.1).
Irradiation of periodate solutions under short-UV light generates several radicals
(IO 3
• , HO
•
, IO 4
• ) and other oxidative species (IO 3
– , HOI, I 2 , H 2 O 2 , O 3 ). The
oxidation of a system containing this reagent under UV light is less selective but
more efficient than other AOTs. The proposed mechanism can be very complex
(Weavers et al. 1997).
With this technology, a wide variety of compounds at low concentrations can be
destroyed. It can be used for discoloration of dye-containing waters and for treatment
of other wastewaters. For a better effectiveness, waters should have a low absorbance. So far, there are no legislated discharge requirements for iodine compounds,
from which I 2 and I
– are the more toxic (but still of low toxicity). Iodine can be
recovered by ionic exchange, and periodate can be electrochemically regenerated.
The technology is faster than other photochemical AOTs and seems very promising.
Recently p-nitrophenol was treated with UV-activated potassium periodate leading
to 79.5% degradation after 60 min at the optimum conditions: 30 mg/L of the
substrate, potassium periodate concentration 386.3 mg/L, pH 6.2 (Saien and
Bazkiaei 2018).
7.3.11 UV/Persulfate
The absorption spectrum of PDS is very similar to that of H 2 O 2 , characterized by a
gradual increase in absorption without a noticeable maximum in the accessible wavelength region. At 254 nm, ε ¼ 20 L/(mol cm), and a dissociative transition is reached,
leading to the scission of the –O–O– linkage. ϕ SO4•– is lower than 2, corresponding to a
quantum yield of PDS consumption of below unity (0.58–0.79) (Mark et al. 1990). As
said before (Sect. 7.2.10), since the reactions of PDS are generally slow at normal
temperature, the photochemical activation of PDS to SO 4
•–
, working at ambient
temperature, has been proposed (Eq. 7.126), followed by reactions in Eqs. 7.70, 7.71
and 7.72 (Lau et al. 2007; Anipsitakis and Dionysiou 2004b):
S 2 O 8
2À
þ hν ! 2SO 4
• À
ð7:126Þ
Due to the adverse effects of some metal catalysts such as Co(II) on human
health, PMS activated by UV irradiation was considered as a better, environmentally
friendly and applicable technology (Guan et al. 2011). PMS presents absorption
7 Introduction to Oxidative Technologies for Water Treatment
157