Ozone is industrially applied to water treatment either alone or in combination
with hydrogen peroxide and/or activated carbon. Improvements of the ozone technology, including combinations with catalysts and AOTs have been described
(Kasprzyk-Hordern et al. 2003; von Gunten 2003a, b). O 3 is characterized by a
short lifetime and low solubility in aqueous media.
Ozonation is a very well-known commercialized technology for water treatment.
It has been successfully used in the discoloration of kaolin and cellulose pulp and, in
general, in the treatment of extremely polluted aqueous effluents. Ozonation is a
good pretreatment before a biological treatment because complex organics are
transformed into aldehydes, ketones, or carboxylic acids, all easily biodegradable.
Ozonation is versatile, and it allows combining with other conventional methods or
AOTs. Ozone can be simply produced in situ by electric discharge in current of
oxygen or air, leaving neither odors nor residual tastes. In contrast, from the
operational point of view, the use of ozone is complicated because there are mass
transfer limitations due to the difficult access of the gaseous molecule to the aqueous
phase (Roche et al. 1994). To overcome the low solubility, the process requires
efficient stirring; some techniques like fixed beds of porous glass or metals, solid
catalysts, stirring, line mixers, contact towers and increase of retention time by large
bubble columns or diffusers have also been explored to enhance the process
(Boczkaj and Fernandes 2017). Another way to improve the process is to increase
the retention time in the reactor by large bubble columns or to increase the solubility
of ozone by increasing the pressure to several atmospheres. However, any additional
modifications raise the investment costs. Furthermore, a rather high O 3 /pollutant
molar ratio (more than 5:1) is generally needed for the complete destruction of the
compound, which makes the treatment even more expensive. Further to this, in some
cases, the method does not lead to the complete mineralization. The temperature
must be controlled because of the risk of volatilization of the initial or the intermediate compounds. Final degassing devices in the circuit are necessary to deplete the
ozone completely, which will be deleterious in a potential biological posttreatment;
this also increases the costs. In conclusion, the use of ozone implies high capital
costs and additional equipment for destroying the remaining ozone, together with
safety and health problems and mass transfer limitation due to the low solubility of
O 3 in water and danger of escape of volatile organic compounds (VOCs) to the
atmosphere caused by the bubbling of the reagent.
Recent advances for ozone applications in treatment of recalcitrant contaminants
have been driven in endocrine disrupting compounds, pharmaceutical, pesticides,
and personal care products (Gerrity et al. 2018).
7.2.3 O 3 /H 2 O 2
Combination of hydrogen peroxide and O 3 produces an enhancement of ozonation
(Domènech et al. 2004; Litter 2005; Hoigné and Bader 1976) in a process called
126
M. I. Litter
with hydrogen peroxide and/or activated carbon. Improvements of the ozone technology, including combinations with catalysts and AOTs have been described
(Kasprzyk-Hordern et al. 2003; von Gunten 2003a, b). O 3 is characterized by a
short lifetime and low solubility in aqueous media.
Ozonation is a very well-known commercialized technology for water treatment.
It has been successfully used in the discoloration of kaolin and cellulose pulp and, in
general, in the treatment of extremely polluted aqueous effluents. Ozonation is a
good pretreatment before a biological treatment because complex organics are
transformed into aldehydes, ketones, or carboxylic acids, all easily biodegradable.
Ozonation is versatile, and it allows combining with other conventional methods or
AOTs. Ozone can be simply produced in situ by electric discharge in current of
oxygen or air, leaving neither odors nor residual tastes. In contrast, from the
operational point of view, the use of ozone is complicated because there are mass
transfer limitations due to the difficult access of the gaseous molecule to the aqueous
phase (Roche et al. 1994). To overcome the low solubility, the process requires
efficient stirring; some techniques like fixed beds of porous glass or metals, solid
catalysts, stirring, line mixers, contact towers and increase of retention time by large
bubble columns or diffusers have also been explored to enhance the process
(Boczkaj and Fernandes 2017). Another way to improve the process is to increase
the retention time in the reactor by large bubble columns or to increase the solubility
of ozone by increasing the pressure to several atmospheres. However, any additional
modifications raise the investment costs. Furthermore, a rather high O 3 /pollutant
molar ratio (more than 5:1) is generally needed for the complete destruction of the
compound, which makes the treatment even more expensive. Further to this, in some
cases, the method does not lead to the complete mineralization. The temperature
must be controlled because of the risk of volatilization of the initial or the intermediate compounds. Final degassing devices in the circuit are necessary to deplete the
ozone completely, which will be deleterious in a potential biological posttreatment;
this also increases the costs. In conclusion, the use of ozone implies high capital
costs and additional equipment for destroying the remaining ozone, together with
safety and health problems and mass transfer limitation due to the low solubility of
O 3 in water and danger of escape of volatile organic compounds (VOCs) to the
atmosphere caused by the bubbling of the reagent.
Recent advances for ozone applications in treatment of recalcitrant contaminants
have been driven in endocrine disrupting compounds, pharmaceutical, pesticides,
and personal care products (Gerrity et al. 2018).
7.2.3 O 3 /H 2 O 2
Combination of hydrogen peroxide and O 3 produces an enhancement of ozonation
(Domènech et al. 2004; Litter 2005; Hoigné and Bader 1976) in a process called
126
M. I. Litter