Chemical oxidation includes the technologies based on:
- ozonation (O3)
- UV light with oxidants (e.g. hydrogen peroxide)
- Fenton mechanisms
- on the different combinations of these treatment technologies
- catalytical oxidation
- advanced oxidation nanotechnology
- photocatalysis under visible light
- LED-based photocatalysis
The efficiency of the technology and the consumption of oxidants are influenced by various factors, including the properties and concentrations of the compounds of interest, as well as the general characteristics of the matrix treated. The matrix also impacts on the type and distribution of intermediates and by-products. In particular pH, turbidity, alkalinity, temperature and the nature and amount of the organic and inorganic matter are important properties.
Chemical oxidation technologies have numerous advantages, e.g.
- disinfection (bacterias, molds, viruses, biofilm)
- enhancement of processes
- oxidation of toxic and refractory compounds
- minimizing the sludge production
- the improvement of biological processes
- sum effects (e.g. colour, odour, microbes, toxicity, organics)
Examples of case studies done in the laboratory: 
- Integrated technologies for the treatment of contaminated soils (PAHs, CPs, Syanides), ground
waters and industrial landfill leachates
- Ozone treatment of circulation waters and effluents in the pulp and paper industry – removal of resin acids, EDTA and microorganisms
- Impact of ozonation on the colour and COD of pulp and paper mill waters
- Inactivation of microbes and fungus in a Finnish fish farm (O3, UV ja H2O2)
- The oxidation of malodorous odours from compost (prestudy)
- The oxidation of quicksilver wastes (prestudy)
Ozonation
Ozone (O3) has been used as a chemical reagent, an industrial chemical and as an oxidant for water treatment over a century. Ozone is a powerful oxidant and disinfectant, with the highest thermodynamic oxidation potential of the common oxidants. In principle, ozone should be able to oxidize some of the organic substances to their highest stable oxidation states and organic compounds to carbon dioxide and water. Hence, ozonation rarely results the mineralization to CO2, salts and water under the conditions typically present in practical processes. Recently the treatment of industrial effluents and landfill leachates including refractory and ”hard” COD compounds is expected to be one of the most promising use of ozone.
Advanced Oxidation Processes
The processes that are based on the utilization of secondary oxidants, such as hydroxyl radicals are called advanced oxidation processes (AOPs). AOPs have been suggested as an alternative, particularly for the treatment of landfill leachates and biorefractory organic pollutants, such as aromatics. By AOPs it is possible to oxidize a larger spectrum of compounds, by the highly reactive and unselective radical pathway than by direct ozonation. The generation hydroxyl radicals (.OH) can be considerably intensified via various combination of oxidants, radiation and catalyst. Especially in water remediation, a number of OH-radical generating systems are currently in use, or under study eg. O3/H2O2, UV/H2O2, Fe2+/ H2O2, Fe2+/H2O2 + hv, UV/O3, UV/TiO2 and ionizing radiation. The efficiency by which hydroxyl radicals are formed during reactions between ozone and H2O2 depend on the pH and on the amount of scavengers.
Ongoing research in laboratory
Advanced oxidation nanotechnology (AON)
In AON, catalyst used for photodegradation is prepared by methods of nanotechnology. Among AONs, nanosize and nanostructured semiconductors are of particular interest because of their environmentally friendly features. In general, due to rapid OH-radical based oxidation reactions, AONs are characterized by high reaction rates and short treatment times. Other advances of AONs are that they do not produce any polycyclic intermediate products and can oxidize pollutants in ppb level when no further treatment is necessary.
Photocatalysis under visible light
The use of visible/solar light in photodegradation of pollutants has become an emerging field due to the lack of the pure water and conventional energy sources in many parts of the earth. The utilization of solar light in degrading of pollutants requires catalytic materials, which work in the wavelengths of the visible light. Development of such materials is currently of LAEC’s interest.
LED-based photocatalysis for water treatment
TiO2-based photocatalytic water treatment under UV-light has gained attention in both degrading organic contaminants and disinfection. However, this procedure needs to be enhanced in various ways. UV lights exhibit short-term intensity fluctuations and substantial deterioration of performance over time. TiO2-catalyst in power form is hard to separate from the reaction mixture and in thin film form has low surface area, which decreases the catalytic efficiency. To enhance the photocatalytic process, UV-lamps are replaced by long-lasting, mechanically stable, and environmentally safe LED-lamps (light emitting diodes) and the catalysts’ surface areas increased by the methods of nanotechnology. ALD-technique (atomic layer deposition) is used in coating of nano-sized surface structures.