(505c) Comparison of Advanced Oxidation Technologies
Advanced oxidation processes AOPs cover a variety of technologies and combinations of. The basic principles of technologies are of physical/mechanical nature such as UV-radiation, sonication or corona discharge and chemical nature such as ozone treatment, hydrogen peroxide application or oxygen admixture. The oxidizing power is achieved by admixture of oxidizers to the effluent and activation by either chemical or physical measures such as the Fenton processes or several UV-radiation processes or combination of chemical and physical measure as provided by corona discharge. The major obstacle for successful industrial application of advanced oxidation processes is caused by the composition of effluents. Except fresh water preparation effluents from any production source are rarely specified as contaminated by a specific constituent only. Overwhelmingly effluents are composed of a diffuse organic and/or inorganic basic load and dilute target constituents. Latter actually need to be addressed in application of advanced oxidation processes. As a consequence treatment may be very costly or even too expensive because cost of treatment is determined by the effluent matrix and not by the target constituent. With these limitations in mind a selection of advanced oxidation processes was investigated in a long term project of nearly one decade and compared, based on the treatment of synthetic effluents spiked with test constituents. The experimental part of technology evaluation considered the Fenton reaction, the Photo-Fenton Reaction, UV-H2O2 oxidation, selected photocatalytic processes, anodic oxidation and corona discharge/ozone treatment. Comparison of technologies was carried out with phenol, acetone and EDTA. Investigations considered degradation as well as TOC-depletion. Comparison was carried out by determining the specific energy demand per mass unit of constituent and peripheral process specifications such as fouling. Beside net cost evaluation, technology selection for practical application of AOPs also has to consider maintenance of equipment which is governed fouling control. Anodic oxidation processes for example are fouling sensitive. Fouling prevention mainly depends on the setup of equipment. Fouling prevention of photochemical reactors needs separation of the radiation source from the effluent, limiting the quantum yield due to scattering. Corona discharge, a gas phase process, enables separation of the power source from the effluent on account of the operation principle. When applicable, corona discharge treatment is therefore preferred over radiation based processes. Several Fenton reactions are sensitive to process poisoning by adsorption, precipitation or formation of stable complexes or overdosing of Fe2+.
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