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Wet air oxidation (WAO) and catalytic wet air oxidation (CWAO) of slaughtered animal byproducts (ABPs) were investigated. Two step experiment was carried out consisting of a non-catalysed WAO run followed by a CWAO run at 170-275 degrees C, 20 MPa, and reaction time 180 min. The WAO (1st step) of sample (5 g/L total organic carbon (TOC)) yielded (82.0 +/- 4)% TOC removal and (78.4 +/- 13.2)% conversion of the initial organic-N into NH4(+)-N. Four metal catalysts (Pd, Pt, Rh, Ru) supported over alumina have been tested in catalytic WAO (2nd step) at elevated pH to enhance ammonia conversion and organic matter removal, particularly acetic acid. It was found that the catalysts Ru, Pt, and Rh had significant effects on the TOC removal (95.1%, 99.5% and 96.7%, respectively) and on the abatement of ammonia (93.4%, 96.7% and 96.3%, respectively) with high nitrogen selectivity. The catalyst Pd was found to have the less activity while Pt had the best performance. The X-Ray diffraction analysis showed that the support of catalyst was not stable under the experimental conditions since it reacted with phosphate present in solution. Nitrite and nitrate ions were monitored during the oxidation reaction and it was concluded that CWAO of ammonia in real waste treatment framework was in good agreement with the results obtained from the literature for ideal solutions of ammonia.

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.