destroy poorly biodegradable organic compounds such as pharmaceutics, surfactants, detergents, dyes, herbicides and pesticides, aromatic and aliphatic
organohalogens, saturated aliphatic carboxylic acids, nitroaromatics, or in the ability
to improve the biological degradability of wastewater samples containing these
compounds.
Another interesting combination is heterogeneous photocatalysis with US,
because this process hinders the inactivation of the catalyst by reaction intermediates, which usually block the catalyst. US also reduces mass transfer limitations
occurring in the case of immobilized catalysts (see Gogate and Pandit 2004a for a
detailed description of this combined process).
Photocatalysis can be combined also with ferrate (see, e.g., Sharma et al. 2015
and Sharma et al. 2010).
7.4 Conclusions
Chemical oxidation processes, and particularly AOPs, represent a powerful means
for the abatement of refractory and/or toxic pollutants in wastewaters. Different AOP
techniques have been developed and their use either alone or combined allows
choosing the most appropriate procedure for the treatment of specific systems.
These technologies can process wastewaters resistant to conventional treatments
and are complementary to them.
A generalization on the application of an AOT can never be made. Each effluent
must be previously characterized, and treatability tests at laboratory scale must be
performed to choose the most appropriate method. Knowledge of kinetics, with
establishment of the limiting step and limiting reagent(s), and comparison with other
conventional treatments should be available before applying the technology. Obviously, a complex chemical composition always presents a greater difficulty than
simple mixtures, and HO
• scavengers are usually the main source of efficiency
reduction.
In general, AOPs are more adequate for treating small flows (or volumes) and not
too high concentrations of pollutants. Small COD contents, not higher than 5 g/L,
can be suitably treated. Higher concentrations would require high concentrations of
expensive reagents and/or high electrical power consumption.
Each AOT has an optimum working pH value and the pH variation during the
reaction must be continuously controlled. At the end of the process, another pH
adjustment will be needed in many cases before the biological treatment or to
comply with local regulations before discharging the effluent to the receiving bodies.
The use of toxicological tests (Microtox, Amphitox, etc.) to control the formation
of noxious byproducts along the process is mandatory. The purpose is to use the
technology until toxicity is reduced to a certain level, beyond which a conventional,
less expensive method can bring about the mineralization process with the obvious
reduction of costs.
7 Introduction to Oxidative Technologies for Water Treatment
161
organohalogens, saturated aliphatic carboxylic acids, nitroaromatics, or in the ability
to improve the biological degradability of wastewater samples containing these
compounds.
Another interesting combination is heterogeneous photocatalysis with US,
because this process hinders the inactivation of the catalyst by reaction intermediates, which usually block the catalyst. US also reduces mass transfer limitations
occurring in the case of immobilized catalysts (see Gogate and Pandit 2004a for a
detailed description of this combined process).
Photocatalysis can be combined also with ferrate (see, e.g., Sharma et al. 2015
and Sharma et al. 2010).
7.4 Conclusions
Chemical oxidation processes, and particularly AOPs, represent a powerful means
for the abatement of refractory and/or toxic pollutants in wastewaters. Different AOP
techniques have been developed and their use either alone or combined allows
choosing the most appropriate procedure for the treatment of specific systems.
These technologies can process wastewaters resistant to conventional treatments
and are complementary to them.
A generalization on the application of an AOT can never be made. Each effluent
must be previously characterized, and treatability tests at laboratory scale must be
performed to choose the most appropriate method. Knowledge of kinetics, with
establishment of the limiting step and limiting reagent(s), and comparison with other
conventional treatments should be available before applying the technology. Obviously, a complex chemical composition always presents a greater difficulty than
simple mixtures, and HO
• scavengers are usually the main source of efficiency
reduction.
In general, AOPs are more adequate for treating small flows (or volumes) and not
too high concentrations of pollutants. Small COD contents, not higher than 5 g/L,
can be suitably treated. Higher concentrations would require high concentrations of
expensive reagents and/or high electrical power consumption.
Each AOT has an optimum working pH value and the pH variation during the
reaction must be continuously controlled. At the end of the process, another pH
adjustment will be needed in many cases before the biological treatment or to
comply with local regulations before discharging the effluent to the receiving bodies.
The use of toxicological tests (Microtox, Amphitox, etc.) to control the formation
of noxious byproducts along the process is mandatory. The purpose is to use the
technology until toxicity is reduced to a certain level, beyond which a conventional,
less expensive method can bring about the mineralization process with the obvious
reduction of costs.
7 Introduction to Oxidative Technologies for Water Treatment
161