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Effluents or liquids of percolation from the discharges (leachates) are charged bacteriologically and especially chemically of mineral substances (mineral ions and heavy metals) and organic (volatile fatty acids, humic substances), which can contaminate soil, surface waters and ground waters. The humic substances, called also refractories, are not easily biodegradable and require concentrating them and/or adsorbing them by implementation of expensive processes. Scientists are looking for alternatives to eliminate or recover these substances. The present study investigates the elimination of humic acid from waste water using supported liquid membrane containing trioctyl phosphine oxide (TOPO) in toluene, as extractant. The supported liquid membrane is composed of a flat sheet of cross-linked polydimethylsiloxane (PDMS). In this study we have: (i) optimized the conditions for humic acid species transfer from feed aqueous phase to stripping phase across PDMS/TOPO/toluene supported liquid membrane; (ii) characterized the membrane by using FTIR technique and by determining the flux J, permeability P and diffusion coefficient of the complexed species D. Speciation of the humic acid species in the membrane organic carrier (extractant) phase has also been carried out using theoretically derived equations to elucidate the stoichiometry and mechanism of transport of humic acid across the PDMS/TOPO/toluene supported liquid membrane. Optimum conditions of transport for humic acid have been found to be: pH=3, [NaOH]=0.4 M, Eextraction = 94.67%, E diffusion = 32.5%, J = 1.34 × 10 −4 mg cm −2 s −1 , D = 1.16 × 10 −2 cm 2 s −1 and P = 2.64 cm s −1 . Kinetic parameters calculated from the experimental data have been determined. Thermodynamic functions of the several species transfer from the feed solution to the stripping one through the supported liquid membrane, such us enthalpy, entropy and Gibbs free energies, were determined. Positive values of ∆H and negative values of ∆G indicate respectively the endothermic and the spontaneous nature of the humic acid extraction in aqueous solution.

Abstract. The kinetics of Kjeldahl's digestion for nitrogen determination was compared between microwave and classical heating conditions. Various parameters (micr owave power, concentrations, time) of micr owave digestion were studied in order to define the optimal digestion conditions. Finally, the Kjeldahl's analysis of nitrogen using microwave digestion was applied to various pharmaceutical, agricultural and food products. Key words.Microwave -Kjeldahl -nitrogen -digestion. Analusis, 1998, 26, 205-209 © EDP Sciences, Wiley-VCH Article available at http://analusis.edpsciences.org or http://dx.doi.org/10.1051/analusis:1998133 digest because of the high nitrogen concentration 32.18 g per 100 g. Classical procedureAccording to the french standard method AFNOR [12][13][14][15], 0.2 g of the sample was added to 20 mL of sulphuric acid and 2 g of a catalyst (composed of 1 g of selenium, 10 g of CuSO 4 and 100 g of K 2 SO 4 ). The digestion is the principal phase in the protocol and takes several hours. The success of the analysis depends on the efficiency of this digestion process. It must be conducted with the highest rigour and it is necessary that all the nitrogeneous forms are transformed into ammoniacal nitrogen. The digestion was carried out using an electrical heating block "Büchi 430". The distillation stage allows to shift the ammoniac from the digestion solution to a boric acid solution using a distillation block "Büchi 315". Finally, titration gave the nitrogen concentration of the analysed samples. Microwave procedureMicrowave digestion was reached at atmospheric pressure in a Prolabo Maxidigest 350 monomode microwave oven cavity operating at 2.45 GHz with a power range from 0 to 300 watts. The borosilicate reactor has a capacity of 20 to 150 mL. The incident microwave power is controlled with a programmer which allows to work with one or several steps of microwave incident power according to the durat i o n expressed in minutes [1].A microwave digestion protocol was adopted from several scientific works in this field [8][9][10]. First, the sample was mixed with 20 mL of sulphuric acid without heating. Then, microwave carbonisation of the organic matrix was carried out. The carbonisation duration represents 80 to 90% of the digestion time. After that , hy d rogen peroxide wa s added without heating. Finally, microwave oxidation permits the destruction of the most resistant molecules. This step represents only 20% of the total duration.Microwave digestion was conducted without a catalyst or antifoaming agent, to avoid pollution problems and to reduce chemical reagents. The hydrogen peroxide was selected as an oxidant agent to complete the digestion [3,10]. At the end, the solution was distilled then proportioned according to the standard method AFNOR. The degree of nitroge n rep o rted in this study is given from the ave rage of thre e identical tests. Results and discussion Kinetic study of the arginine digestionThis kinetic study has been realised following the degree of nitrogen during the arginine ...