Disposal of animal by-products by wet air oxidation: performance optimization and kinetics.

This paper describes the application of subcritical wet oxidation to the disposal of sheep animal by-products originating from slaughterhouse. Animal by-products (ABPs) from categories 1 and 3 (gall, head, tail, spinal cord, offal, ileum and blood) were oxidized at high pressure and moderate temperature (P=12.5-20 MPa, T=200-320 degrees C). The oxidation experiments were performed on individual samples or on a reconstituted mixture representing the ABPs of a slaughtered sheep. The oxidation kinetics of a representative sample was studied and the apparent activation energy was found to be 42.9 kJmol(-1). The chemical by-products were also identified and quantified in the final oxidized solution: acetic acid and ammonia were identified in all samples as the major by-products representing around 31% and 69%, respectively, of residual TOC and initial nitrogen after the oxidation of a representative sample of ABPs containing initially 5 gL(-1) of total organic carbon (TOC). The contribution of the experimental factors temperature, reaction time and concentration of the feed solution to remove the organic matter was assessed and optimized using an experimental design based on the response surface methodology. Fitting of the experimental data showed that the 2nd order polynomial model represented the data best. A multicriteria optimization, using the desirability function, allowed the determination of the best region of the experimental domain to optimise the TOC removal and the energy consumption.

Degradation of cinnamate via beta-oxidation to benzoate by a defined, syntrophic consortium of anaerobic bacteria.

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.

Intermediates in wet oxidation of cellulose: identification of hydroxyl radical and characterization of hydrogen peroxide.

Some intermediates were identified during the course of non-catalytic wet air oxidation (WAO) of cellulose. Concentrations of by-products were determined in function of temperature and reaction time. This study also showed that hydroxyl radicals (HO*) and hydrogen peroxide (H2O2) play the role of intermediates in the initial phase of the oxidation reactions. Hydroxyl radicals were detected by the electron spin resonance spectroscopy coupled to the spin trapping technique using the 5,5-dimethyl 1-pyrroline N-oxide (DMPO) as spin trap agent. The spin adduct (DMPO/ HO*), resulting from the trapping of HO* with DMPO, showed a characteristic electron spin resonance signal which was inhibited when catalase was added, indicating that HO* was provided from H2O2. These transient species were only observed at the beginning of the reaction and were not oxygen dependent.