A broad range of wavelengths in the UV region is discharged by medium- and
high-pressure lights and as they possess high light intensity, they have the ability to
penetrate deeper. Therefore, the completion of reaction is done in a short span
of time.
The prime reason behind the combination of UV and H 2 O 2 for formation of
hydroxyl radicals is the cleavage of H 2 O 2 with UV light. This produces a quantum
yield of two hydroxyl radicals per unit of radiation absorbed (Glaze et al. 1987) as
shown in Eq. 10.4.
H 2 O 2 þ hγ ! 2
• OH
ð10:4Þ
Legrini et al. (1993) reported the sequence of the chemical reaction between
hydroxyl radicals and organic matter present in drinking matter. Hydroxyl radicals
react with organic compounds to produce organic radicals, which then further react
with the dissolved oxygen to produce hydroperoxyl radicals. Then, these formed
radicals initiate the oxidation reaction to form innocuous smaller weight fragments.
This technique can be compatibly used for the removal of hazardous waste from
groundwater, chemical process water, drinking water and industrial wastewater.
Various organic pollutants are efficiently degraded by the UV/H 2 O 2 process. In
literature, several successful applications of UV/H 2 O 2 have been reported. For
instance, Rivas et al. (1998) used this process for phenol oxidation while Zhang
et al. (2008) investigated the treatment of contaminated waters.
Furthermore, this UV/H 2 O 2 technology has also been employed for the remediation of ground water containing mixtures of hazardous aliphatic compound trichloroethylene (TCE) present in the concentration range of about 2000–10,000 (μg/L).
The contaminated water was irradiated with medium pressure Hg arc of 3000 W of
electric power followed by the addition of 50 mg/L of hydrogen peroxide. Under
these conditions, significant elimination of TCE was achieved from 3700–4000 (μg/
L) to 0.7 (μg/L) within 50 s of the irradiation (Sharma and Celin 2005). In order to
investigate the effectiveness of this process, water samples were collected from
paper pulp bleaching industries, distillery, and tomato processing plants. The extent
of waste removal could be achieved after one hour of the treatment, which resulted in
25% reduction in COD. Although, this process has been used widely for wastewater
treatment due to lower cost and ready availability of hydrogen peroxide but it suffers
from a number of drawbacks, which are illustrated below (Stasinakis 2008).
• H 2 O 2 has poor UV light absorption characteristics, because of which a lot of UV
light becomes absorbed by water matrix and thus most of the light input gets
wasted.
• It cannot utilize solar light as the source of UV light because UV energy required
for the photolysis of the oxidizer is not available in the solar spectrum
(Niaounakis and Halvadakis 2006).
• The UV light can also be absorbed by the interfering compounds and turbidity in
the wastewater as a result; the efficiency of the system is thus reduced.
10 Photo-oxidation Technologies for Advanced Water Treatment
227
high-pressure lights and as they possess high light intensity, they have the ability to
penetrate deeper. Therefore, the completion of reaction is done in a short span
of time.
The prime reason behind the combination of UV and H 2 O 2 for formation of
hydroxyl radicals is the cleavage of H 2 O 2 with UV light. This produces a quantum
yield of two hydroxyl radicals per unit of radiation absorbed (Glaze et al. 1987) as
shown in Eq. 10.4.
H 2 O 2 þ hγ ! 2
• OH
ð10:4Þ
Legrini et al. (1993) reported the sequence of the chemical reaction between
hydroxyl radicals and organic matter present in drinking matter. Hydroxyl radicals
react with organic compounds to produce organic radicals, which then further react
with the dissolved oxygen to produce hydroperoxyl radicals. Then, these formed
radicals initiate the oxidation reaction to form innocuous smaller weight fragments.
This technique can be compatibly used for the removal of hazardous waste from
groundwater, chemical process water, drinking water and industrial wastewater.
Various organic pollutants are efficiently degraded by the UV/H 2 O 2 process. In
literature, several successful applications of UV/H 2 O 2 have been reported. For
instance, Rivas et al. (1998) used this process for phenol oxidation while Zhang
et al. (2008) investigated the treatment of contaminated waters.
Furthermore, this UV/H 2 O 2 technology has also been employed for the remediation of ground water containing mixtures of hazardous aliphatic compound trichloroethylene (TCE) present in the concentration range of about 2000–10,000 (μg/L).
The contaminated water was irradiated with medium pressure Hg arc of 3000 W of
electric power followed by the addition of 50 mg/L of hydrogen peroxide. Under
these conditions, significant elimination of TCE was achieved from 3700–4000 (μg/
L) to 0.7 (μg/L) within 50 s of the irradiation (Sharma and Celin 2005). In order to
investigate the effectiveness of this process, water samples were collected from
paper pulp bleaching industries, distillery, and tomato processing plants. The extent
of waste removal could be achieved after one hour of the treatment, which resulted in
25% reduction in COD. Although, this process has been used widely for wastewater
treatment due to lower cost and ready availability of hydrogen peroxide but it suffers
from a number of drawbacks, which are illustrated below (Stasinakis 2008).
• H 2 O 2 has poor UV light absorption characteristics, because of which a lot of UV
light becomes absorbed by water matrix and thus most of the light input gets
wasted.
• It cannot utilize solar light as the source of UV light because UV energy required
for the photolysis of the oxidizer is not available in the solar spectrum
(Niaounakis and Halvadakis 2006).
• The UV light can also be absorbed by the interfering compounds and turbidity in
the wastewater as a result; the efficiency of the system is thus reduced.
10 Photo-oxidation Technologies for Advanced Water Treatment
227