Supercritical water oxidation (SCWO) could offer a viable
treatment alternative to destroy the
organic structure of ion-exchange resins (IER) that are radioactive
process wastes and which
contain radioactivity. The GC/MS technique was used successfully
to identify the low-concentration degradation compounds that are present in the cold liquid
effluent after SCWO
of polystyrenic IER at 380 °C (25.5 MPa). The study of the
behavior of these IER in supercritical
water enhances the role of temperature and the role of supercritical
water in the degradation
process. With the exception of acetic acid, the identified
compounds are aromatic. The functional
groups are released during the heating time, and they do not interfere
in the degradation process.
The oxidation involves a complex set of reaction pathways. A
mechanism including parallel
and competitive reactions is proposed.
A syntrophic consortium was enriched in a basal medium containing cinnamate as the carbon and energy source. It was found to consist of three morphologically distinct microbes, viz., a short, rod-shaped, non-motile bacterium with distinctly pointed ends, Papillibacter cinnamivorans; a rod-shaped, motile bacterium with rounded ends, Syntrophus sp.; and a methanoarchaeon, Methanobacterium sp. This methanogen was then replaced by a collection strain of Methanobacterium formicicum. A syntrophic interdependency of the three partners of the consortium was observed during growth on cinnamate. In the presence of bromoethanesulfonic acid (BESA), cinnamate was transformed to benzoate, whereas under methanogenic conditions without BESA, cinnamate was first transformed to benzoate via beta-oxidation and subsequently completely degraded into acetate, CH(4), and CO(2). Papillibacter cinnamivorans was responsible for benzoate production from cinnamate, whereas a syntrophic association between Syntrophus sp. and the methanogen degraded benzoate to acetate, CH(4), and CO(2). A new anaerobic degradation pathway of cinnamate into benzoate via beta-oxidation by a pure culture of P. cinnamivorans is proposed.
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