Le péroxyde d'hydrogène en désodorisation physico-chimique : Rôle de la composition de la solution de lavage dans le mécanisme d'action

La désodorisation physico-chimique en stations d'épuration s'effectue généralement par lavage basique oxydant pour piéger les espèces soufrées réduites telles que H2 S ou CH3 SH. L'utilisation du peroxyde d'hydrogène n'est pas encore répandue en comparaison de celle du chlore. Cette étude a été menée afin de déterminer le comportement de H2O2 en fonction de la composition de l'eau de lavage. L'influence des paramètres : concentration en métaux (fer, manganèse, cuivre et zinc), pH, [H2O2], [CO32-], [HS-] a été étudiée en utilisant un plan d'expériences. La décomposition de H2O2 et la concentration de radicaux libres ont été mesurées pour chaque expérience. En présence de métaux, un pH élevé et une forte concentration en peroxyde sont les deux paramètres principalement responsables d'une forte décomposition. Cette décomposition serait accompagnée d'une production de radicaux avec [HO°]max =10-13 M. Cette valeur mesurée de radicaux dans le milieu n'explique qu'une petite part de la décomposition de peroxyde observée. Par conséquent, la majorité de la décomposition est due à des réactions soit à la surface des oxydes, soit en solution avec les cations dissous. Le mélange de métaux et de carbonates à pH 10,5 présente un effet de synergie sur la décomposition de H2O2. Ces résultats démontrent que malgré le pouvoir oxydant des radicaux HO° formés, l'utilisation de H2O2 en désodorisation ne sera possible qu'avec l'ajout de stabilisant.Deodorization of wastewater treatment plants involves the elimination of molecules such as NH3, amines and sulphur compounds like H2 S and mercaptans. In classical physico-chemical processes, NH3 and amines are trapped in acid solution by washing air in a scrubbing tower, while sulphides are eliminated in basic oxidising solutions. The oxidant usually used is sodium hypochlorite. Elimination of sulphides and organosulphides generally demands two scrubbers: one at pH 9 and the other at pH 11. Because chlorine in deodorization generates the formation of organochlorinated species, it should soon become necessary to replace this oxidant in order to avoid the formation of such compounds. The present study follows the behaviour in wash conditions not of chlorine, but hydrogen peroxide, in order to discover the deodorization capacity of this molecule.The kinetics of H2 S oxidation by H2O2 are well known; the constant is given by log k = 12.04 - (2641/T) - 0.186 x pH (Millero et al., 1989). Unfortunately H2O2 shows strong decomposition in alkaline medium, due to the presence of metals and carbonates in the solution. Initiating a homolytic reaction results in the decomposition of peroxide. However, increasing the concentration of free radicals may improve H2 S oxidation and consequently, the efficiency of the process.To better understand the behaviour of H2O2 in wash conditions, various parameters were studied, namely pH (9 and 10.5), [H2O2] (1 and 5 g L-1), metal concentrations (iron, manganese, copper and zinc) (20 and 200 µg L-1), [CO32-] (0 and 100 mg L-1) and [HS-] (0 and 2 mg L-1). Four experimental designs, one for each metal, were employed to reduce the number of experiments and benefit from statistical laws. H2O2 decomposition and HO° concentration were measured and empirical equations established. All experiments were performed in closed-batch reactors with ultra-pure reactants and water. Measurements of HO° concentrations necessitated the addition of atrazine to the solution. The oxidation of this pesticide by HO° is well known. Using atrazine concentrations measured through time, the HO° concentrations were calculated according to the equationln ([Atz]0/[Atz]) = k[HO∘]twith k=2.1 × 109 M-1 s-1 (De Laat et al., 1997). Oxidation of atrazine was halted by extraction onto a Ct18 Sep-Pack resin and samples were analysed by liquid chromatography.The results showed that in the presence of metals H2O2 decomposition was maximal at high pH and with high peroxide concentrations. The decomposition was accompanied by HO° production. However, the presence of metals generated the decomposition of H2O2 with a reduced production of free radicals compared with ultra-pure water, which indicates that metal oxides were not only decomposition catalysts, but also radical inhibitors. Comparison of simplified radical decomposition, calculated according to the equation([H2O2]/[H2O2]0)=e-k[HO∘]t,and observed decomposition showed that under these conditions H2O2 consumption was mainly due to metal reactivity. Nonetheless, increasing iron and copper concentrations from 20 to 200 µg L-1 did not modify the decomposition rate of H2O2. For this reason we postulate a Fenton-like reaction between H2O2 and dissolved metals in which concentrations are determined by solubility products. It follows that the kinetics of H2O2 decomposition can be summarised by r=-k1 [oxide][H2O2] - k2[ Mn+][H2O2] - k3 [HO°][H2O2], with [metal]Tot =[Mn+] + [oxide] and, in the case of Cu and Fe, k1 [oxide][H2O2] << k2[ Mn+][H2O2].To conclude, the addition of four metals with [CO32-]=1 g L-1 at pH 10.5 produces a synergetic effect, resulting in a much faster decomposition. These conditions, unfortunately, resemble deodorization conditions. The use of a stabiliser that inhibits not only free radicals but also decomposition catalysts is therefore necessary for deodorization

Relativistic and retardation effects in the two--photon ionization of hydrogen--like ions

The non-resonant two-photon ionization of hydrogen-like ions is studied in second-order perturbation theory, based on the Dirac equation. To carry out the summation over the complete Coulomb spectrum, a Green function approach has been applied to the computation of the ionization cross sections. Exact second-order relativistic cross sections are compared with data as obtained from a relativistic long-wavelength approximation as well as from the scaling of non-relativistic results. For high-Z ions, the relativistic wavefunction contraction may lower the two-photon ionization cross sections by a factor of two or more, while retardation effects appear less pronounced but still give rise to non-negligible contributions.Comment: 6 pages, 2 figure

On waiting for something to happen

This paper seeks to examine two particular and peculiar practices in which the mediation of apparently direct encounters is made explicit and is systematically theorized: that of the psychoanalytic dialogue with its inward focus and private secluded setting, and that of theatre and live performance, with its public focus. Both these practices are concerned with ways in which “live encounters” impact on their participants, and hence with the conditions under which, and the processes whereby, the coming-together of human subjects results in recognizable personal or social change. Through the rudimentary analysis of two anecdotes, we aim to think these encounters together in a way that explores what each borrows from the other, the psychoanalytic in the theatrical, the theatrical in the psychoanalytic, figuring each practice as differently committed to what we call the “publication of liveness”. We argue that these “redundant” forms of human contact continue to provide respite from group acceptance of narcissistic failure in the post-democratic era through their offer of a practice of waiting

Is there still a place for the concept of therapeutic regression in psychoanalysis?

The author uses his own failure to find a place for the idea of therapeutic regression in his clinical thinking or practice as the basis for an investigation into its meaning and usefulness. He makes a distinction between three ways the term ‘regression’ is used in psychoanalytic discourse: as a way of evoking a primitive level of experience; as a reminder in some clinical situations of the value of non-intervention on the part of the analyst; and as a description of a phase of an analytic treatment with some patients where the analyst needs to put aside normal analytic technique in order to foster a regression in the patient. It is this third meaning, which the author terms “therapeutic regression” that this paper examines, principally by means of an extended discussion of two clinical examples of a patient making a so-called therapeutic regression, one given by Winnicott and the other by Masud Khan. The author argues that in these examples the introduction of the concept of therapeutic regression obscures rather than clarifies the clinical process. He concludes that, as a substantial clinical concept, the idea of therapeutic regression has outlived its usefulness. However he also notes that many psychoanalytic writers continue to find a use for the more generic concept of regression, and that the very engagement with the more particular idea of therapeutic regression has value in provoking questions as to what is truly therapeutic in psychoanalytic treatment

Psychoanalysis as the Patient: High in Feeling, Low in Energy

This paper examines the increasingly important role that affect is assuming in psychoanalytic research and practice. This rise in the centrality of affect has been at the expense of an independent role for motivation and a dismissal of any energy concept. Difficulties with this affect-first approach are identified and an alternative offered that accords motivation an independent role and accommodates a useful energy concept. Research on esophageal atresia, addiction, and infant suckling are cited in support of this position.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66624/2/10.1177_00030651970450031101.pd

Technical design and performance of the NEMO3 detector

The development of the NEMO3 detector, which is now running in the Frejus Underground Laboratory (L.S.M. Laboratoire Souterrain de Modane), was begun more than ten years ago. The NEMO3 detector uses a tracking-calorimeter technique in order to investigate double beta decay processes for several isotopes. The technical description of the detector is followed by the presentation of its performance.Comment: Preprint submitted to Nucl. Instrum. Methods A Corresponding author: Corinne Augier ([email protected]