Oxidation with ozone is an innovative chemical process which is spreading throughout wastewater treatment technologies. Within the PerFORM WATER 2030 project, the oxidation with ozone is going to be studied and tested at plant scale to achieve emerging micropollutants removal.
Ozone is an inorganic molecule formed by three oxygen atoms (O3) that has a very high oxidizing capacity, i.e. it is a molecule with a high tendency to steal electrons from other chemical species leading to the breakdown of chemical bonds among the atoms. The split molecule is called oxidized, while the chemical reaction is called oxidation.
Oxygen also participates in numerous oxidation reactions (such as combustion), but it has not enough oxidizing power to destroy organic compounds present in water such as emerging micropollutants. Micropollutants' reaction with ozone cause the destruction of compounds into simpler, biodegradable and less harmful for the environment substances.
The action of ozone, however, is not selective towards micropollutants, therefore the ozone has to bo applied to a partially purified water in order to increase its efficiency and reduce undesired consumption (scavenger effect).
Moreover, ozone is a very unstable gas that cannot be stored in cylinders, but is produced on the spot by a specific generator starting from pure oxygen or oxygen present in the air.
The PerFORM WATER 2030 project is going to test the use of ozone for the removal of micropollutants present in the wastewater treated by the San Giuliano Milanese West treatment plant.
The most important critical aspect is the ozone transferring from the gas phase to the liquid phase, also called gas dissolution. Indeed, only ozone dissolved in water can exhibit its oxidizing action towards MIEs, while what remains in the gas phase does not participate in the reaction.
Therefore an ad hoc pilot plant has been built in order to test the oxidation process with ozone and identify the optimal operating parameters to ensure the sustainability of the full-scale process.
The contact reactor of the PerFORM WATER 2030 project was designed by SIAD and is composed by two high columns up to 6 meters. The main characteristic of the reactor is to enhance the transfer of ozone from the gas phase and to the liquid phase.
In order to maximize the ozone exchange, the reactor was designed in a way that maximize the contact surface between the liquid phase and gas phase: ozone is fed at the bottom of the reactor as fine bubbles, in the same way as how air is fed inside aquariums. Ozone is produced by a generator starting from pure oxygen, which is located in a tank positioned specifically for this experimentation. The reactor is fed by a flow rate of 1 m3/h, while ozone dosages vary from 4 to 50 g/h.
Chemical oxidation with ozone is a rising technology in wastewater treatment.
Actually, it is an innovative technology whose benefits are already known, such as some countries, like Switzerland, are going to upgrade their existing wastewater treatment plants with final oxidation with ozone, especially for the reduction of micropollutants.
In Italy instead, the use of ozone is widespread in the treatment of primary waters, also thanks to its disinfectant properties.
Other applications, i.e. in the industrial field, indicate ozone as the ideal solution for discoloration and/or the improving of biodegradable properties of wastewater.
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