[Show abstract][Hide abstract] ABSTRACT: 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.
[Show abstract][Hide abstract] ABSTRACT: The aim of this work is to optimize the degradation yield of an activated sludge and to study the reaction mechanism on a cellulose model compound. This optimization is performed with a Simplex design with four parameters: reaction temperature (280-350 °C), injected air pressure (40-60 MPa), reaction time (10-45 minutes) and COD concentration (0.5-5 g L-1). The better yield obtained on TOC concentration is 82 5% at 330 °C. Over this temperature, the yield substantially decreases. The use of cellulose as a model compound for activated sludge confirms optimization results and leads to the identification of by-products and free radical species participating in the reaction. Two major organic compounds have been detected: 4-oxo pentanoïc acid and 3-oxo butanoïc acid, and three types of radicals: HO°, CO2°- and °CH(OH)CH3.
[Show abstract][Hide abstract] ABSTRACT: The stability of 18 herbicides (ten organonitrogens and eight phenylureas, including four degradation products), selected for the frequency of their detection in the environment, was evaluated under a variety of storage conditions. Large volumes of surface water (4 L) were extracted using large-particle-size graphitized carbon black cartridges (Carbopack B 60-80 mesh). The effects of temperature, matrix type, drying and solvent-washing of cartridges on the recovery of these contaminants, after different storage periods, were studied and compared to the conservation of surface water in bottles. After two months, there was no significant difference between the conserved surface water and the stored cartridges for the selected compounds. Cartridges kept at -20 °C were better than those stored at 4 °C and 20 °C. The type of matrix water selected, in this case St. Lawrence surface water, appears to have a minor effect on the recovery of the target pesticides after cartridge storage. No improvement was observed in the recovery of any of the chemicals when the cartridges were dried or washed and stored in a solvent. After immediate surface-water extraction, the most practical storage condition for the target herbicides was found to be storage on cartridges in the dark at - 20 °C, with no solvent drying or washing of the Carbopack B material.