Combination of advanced oxidation processes and gas absorption for the treatment of chlorinated solvents in waste gases

Treatment of chlorinated organic compounds in waste gases is difficult beca use of several reasons: these compounds are dioxin precursors when incinera ted, and also biological treatment is difficult because of a limited number of suitable microbial degradation pathways. On the other hand, since the 1 990s, a new generation of chemical oxidation techniques has been introduced in water treatment. Advanced Oxidation Processes (AOPs) are based on a com bination of UV/H2O2, UV/O-3 or H2O2/O-3. The combinations result in the gen eration of OH-radicals, which subsequently attack the organic pollutants, I n 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 absor ption process in a bubble column with a liquid H2O2/O-3 initiated oxidation , was investigated. Removal efficiencies, depending on the dosed H2O2 and O -3 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. Nex t to the experimental work, attention was paid to the mechanisms taking pla ce in the proposed concept. Here, a simulation model was developed, conside ring gas/liquid mass transfer of TCE and ozone, axial liquid dispersion, ad vective 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 th e proposed technique shows interesting perspectives: it is able to transfor m chlorine in chlorinated solvents into chloride ions effectively at ambien t temperature conditions.