Treatment of chlorinated organic compounds in waste gases is difficult because of several reasons: these compounds are dioxin precursors when incinerated, and also biological treatment is difficult because of a limited number of suitable microbial degradation pathways. On the other hand, since the 1990s, a new generation of chemical oxidation techniques has been introduced in water treatment. Advanced Oxidation Processes (AOPs) are based on a combination of UV/H2O2, UV/O3 or H2O2/O3. The combinations result in the generation of OH-radicals, which subsequently attack the organic pollutants. In this work, the treatment of a gas stream (240 L/h) loaded with 20-40 ppmv trichloroethylene (TCE) is presented. Therefore, a combination of an absorption process in a bubble column with a liquid H2O2/O3 initiated oxidation, was investigated. Removal efficiencies, depending on the dosed H2O2 and O3, up to 94% were found. The production of chloride ions was investigated: the Cl-atoms from the removed TCE could be found back as chloride ions. Next to the experimental work, attention was paid to the mechanisms taking place in the proposed concept. Here, a simulation model was developed, considering gas/liquid mass transfer of TCE and ozone, axial liquid dispersion, advective gas and liquid transport and about 29 chemical reaction steps. The modelling allowed a better understanding of the technique and gives insight in its possibilities and limitations. Finally, it can be concluded that the proposed technique shows interesting perspectives: it is able to transform chlorine in chlorinated solvents into chloride ions effectively at ambient temperature conditions.
Magnetic iron oxide/clay nanocomposites for adsorption and catalytic oxidation in water treatment applications
