Ozone-Based Technologies in Water and Wastewater Treatment

Ozone is a strong oxidant that can be used in the potabilization of surface or ground water as well as in wastewater treatment to remove microorganisms, inorganic ions and organic pollutants. The oldest use of ozone is as a biocide in drinking water potabilization. The integral ozone exposure required for a given degree of disinfection can be calculated from the deactivation kinetic constant of the microorganism. Ozone removes iron, manganese and arsenic from water by oxidation to an insoluble form that is further separated by filtration. Both processes require ozone in molecular form, but the removal of organic pollutants that are refractory to other treatments can be possible only by exploiting the indirect radical reactions that take place during ozonation. Ozone decomposes in water, especially when hydrogen peroxide is present, to yield the hydroxyl radical, the strongest oxidizer available in water treatment. Models for the ozonation process are required to adjust the ozone dosing to the desired degree of removal of a given pollutant or an aggregate measure of pollution. Mineralization, defined as the removal of organic carbon, has been accomplished in wastewaters from urban and domestic treatment plants. The results show that the logarithmic decrease of TOC as a function of the integral ozone exposure usually presents two zones with different kinetic parameters. Among advanced oxidation processes, a promising alternative currently under development is the use of ozone in combination with solid catalysts. The mechanism of catalytic ozonation is not clear, but in the case of metal oxides, the adsorption of ozone or organic compounds on Lewis acid sites is only possible near the point of zero charge of the surface. Activated carbon seems to behave as an initiator of ozone decomposition, a role that may also occur with other types of catalysts. Some results on the mineralization of water with the drugs naproxen (non-steroidal anti-inflammatory) and carbamazepine (anticonvulsant) are presented using titanium dioxide as catalyst.