Microbial decomposition

International audienceWithin aquatic ecosystems, microbial decomposition of organic matter plays a prominent role in the energy and mass transformation processes (Jorgensen, 1983a). Organic waste water discharge in a river results in dissolved oxygen uptake, either directly by chemical oxidation of the reducing pollutants (see Chap. 10), or by their metabolism by microorganisms, i.e. their biodégradation. Raising the temperature of rivers reduces oxygen solubility and accelerates the kinetics of chemical and microbiological oxygen and polluting load reduction...

Electrochemical properties of nicotinamide derivatives in aqueous solution - Part IV. Oxidation of N1 -alkyl-1,4-dihydronicotinamides

International audienceThe electrochemical reduction of nicotinamide—adenine-dinucleotide (NAD+) and model compounds has been extensively studied1-3 ; on the other hand very few papers have been published on the electrochemical oxidation of nicotinamide—adenine-dinucleotide reduced (NADH) in aqueous solution. Haas4 reported the occurrence of an oxidation wave of NADH at pH 8.6 at rotating platinum and glassy carbon disk electrodes (with respective half-wave potentials 0.90 ± 0.02 and 0.67 ± 0.03 V vs. NHE); macroscale electrolyses lead to NAD+ by a two-electron oxidation4'5. In this paper we shall present the features of the electrochemical oxidation of model compounds of NADH, namely Ni-benzyl-and NL-propyl-l,4-dihydronicotinamide (NBzNH and NPrNH) in aqueous solution, buffered within a large pH range; a possible mechanism is deduced from these data. Extensive studies have shown the occurrence of a "primary acid modification" of aqueous NADH solutions or its models below pH 7 (ref. 6); the common explanation put forward is a saturation of the 5-6 double bond in the pyridinic ring, the u.v. absorption band being shifted from 355 to 290 nm. Therefore the results and discussions presented here only concern the pH range 7 to 13. Experimental All products used were prepared in this laboratory, according to published methods, namely NBzNTP (ref. 7), NBzNH and NPrN+Br~ (ref. 8), NPrNH (ref. 9). The purity and concentration of the freshly prepared aqueous solutions were checked by u.v. spectrophotometry with a Cary 14 apparatus. Drop-time controlled portography and voltammetry were carried out with Tacussel equipment (PRT 500 LC\ Servovit 9 B, S6 RZ millivoltmeter) and a Sefram "Luxy trace" bigalvanometric recorder. A Tacussel IG 4-100 electronic integrator was used for coulometry. At the beginning of all macroelectrolyses a Fontaine A 60 power-supply was connected between the counter-electrode and the generator. All aqueous solutions were thermostated at 25.0 ± 0.1°C during the experiments

Caractérisation physico-chimique de tourbe utilisée en épuration d'eau usée urbaine

International audiencePeat beds are currently used for urban water treatment procedures, although reactions occuring within such beds are still unknown : filtration, ion exchange, adsorption or biodégradation by immobilized biomass. This work intends to characterize by physico-chemical parameters the evolution of peat used in water treatment. It is based upon comparison of 5 physical and 4 physico-chemical parameters on peat sampled either on 2 french treatment plants located in Queveauvillers (Somme department) and in Levis Saint Nom (Yvelynes department) or from 2 commercially available eutrophic and oligotrophic sources. Heurteauville and Floratorf, respectively.Among physical parameter tested, namely humidity and (M.O.T.) organic matter content, (R.A.) air and (R.F..) water retention values and (M.V.A.) apparent density, most significant changes were observed with organic matter content, i.e. its weight loss between 105 and 500 "C.Several physico-chemical parameter determinations have been tested, including equilibrium pH in peat suspensions, (C.E.P.) proton, (C.F.C.) alcaline and (C.E.M.) metallic cation exchange capacities. The first and most easily measured parameters, i.e. equilibrium pH within 40 g/1 peat suspensions, showed most significant variations when peat was used in treatment plants. Thus we recomend to compare organic matter content and/or equilibrium pH of peat sampled either on water treatment beds or on a reference source, i.e. « unused » peat, before deciding the renewal of such beds. Both parameters evolution may be related to inorganic deposition on beds, biodégradation of peat organic matter and/or partial dissolution of humic and fulvie acids in neutral or slightly basic pH waste waters, which all may play a prominent role in this treatment procedure.Des lits de tourbe sont couramment utilisés en assainissement urbain bien que la nature des phénomènes d'épuration soient encore inconnus : filtration, échange d'ions, adsorption ou biodégradation par biomasse immobilisée. Ce travail tente de caractériser l'évolution de la tourbe au cours de son utilisation en station à l'aide de paramètres physico-chimiques. Il repose sur la comparaison des valeurs de 5 paramètres physiques et 4 paramètres physico-chimiques d'échantillons de tourbe provenant soit de 2 stations françaises situées à Queveauvillers (Somme) et Levis Saint-Nom (Yvelynes), soit de 2 sources disponibles commercialement, à savoir une tourbe brune eutrophe d'Heurteauville et une tourbe blonde oligotrophe Floratorf. Parmi les paramètres physiques que nous avons testés, le taux d'humidité ou de matière organique (M.O.T.), de rétention d'air (R.A.) ou d'eau (R.E.) et la masse volumique apparente (M.V.A.), les variations les plus significatives ont été observées avec les taux de matière organique des échantillons de tourbe, c'est-à-dire leur perte de poids entre 105 et 500 "C. Nous avons mesuré plusieurs paramètres physico-chimiques, en particulier le pH d'équilibre, les capacités d'échange protonique (C.E.P.), canonique (C.E.C.) et métallique (C.E.M.) : la détermination du pH d'équilibre de suspensions de tourbe à 40 g/1 semble la méthode la plus simple à mettre en oeuvre et celle qui a permis de mettre en évidence les variations les plus significatives lors de l'utilisation de la tourbe en station. Nous suggérons par conséquent de comparer le taux de matière organique et/ou le pH d'équilibre d'échantillons de tourbe prélevés dans les lits et dans des lots de référence, c'est-à-dire non utilisés en station, avant de décider de renouveler ces lits. Les variations de ces deux paramètres lors de l'utilisation de la tourbe sont la conséquence de dépôts de matière minérale sur les lits, de biodégradation de la matière organique de la tourbe et/ou de la dissolution partielle des acides humiques et fulviques dans des eaux usées de pH neutre ou légèrement alcalin, phénomènes qui peuvent tous avoir un effet important sur ce procédé de traitement

BATCH METAL REMOVAL BY PEAT : KINETICS AND THERMODYNAMICS

International audiencePeat moss, a natural inexpensive material, is able to play an important rrle in treatment processes of metal-bearing industrial effluents since it adsorbs, complexes or exchanges various metal cations. This paper presents kinetics and thermodynamics of batch metal removal reactions by 50 g/l (dry wt) eutrophic or oligotrophic peat particles using Cu 2+, Cd 2÷, Zn 2÷ and Ni 2÷ concentrations ranging from 0.01 to 100 mM. Metal cation removal reactions are moderately rapid in l0 mM metal unbuffered solutions: the forward kinetic constant ranges between 0.005 and 0.17 M-1 s-1, and equilibrium is reached within about 1 h. Under these conditions of pH (2.2-4.2) and concentrations, apparent binding equilibrium constants were found to range between 2 and 3150 M-1 depending upon the peat origin and the metal cation. In 0-6.5 pH-buffered metal cation solutions, the four cations binding reactions behaved differently demonstrating that metal binding equilibrium constant decrease in the order Ni 2+ > Cu 2+ > Cd 2+ = Zn 2÷. When pH is higher than 6.7, more than 90% of a 10 mM metal cation solution is removed by 50 g/l peat particles and metal binding capacities equal 200 mmol kg-1 dry wt, whatever the metal nature and the peat origin. Except for nickel cation which is very strongly bound to peat, all metal cations are completely released when pH is fixed below 1.5

URBAN RUNOFF IMPACT ON COMPOSITION AND CONCENTRATION OF HYDROCARBONS IN RIVER SEINE SUSPENDED SOLIDS

International audienceIt is now well established that hydrocarbons are recognised like hazardous compounds, especially polynuclear aromatic hydrocarbon (PAH) [Bomboi and Hernandez, 1991; Hermann R, 1981], Urban runoff is a non negligible source of hydrocarbon that may damage the quality of receiving river. In this report, we present the first results of a study of the impact of combined sewer overflows (CSOs), during summer 1995, on the distribution of n-alkanes (C11-C37 ) in theSeine river. Figure 1 shows the site of Chatou, where suspended solids (SS) were sampled just before and during a week period following the moderate CSO event of September 7, 1995

Electrochemical Biosensors: Recommended Definitions and Classification

Two Divisions of the International Union of Pure and Applied Chemistry (IUPAC), namely Physical Chemistry (Commission I.7 on Biophysical Chemistry, formerly Steering Committee on Biophysical Chemistry) and Analytical Chemistry (Commission V.5 on Electroanalytical Chemistry), have prepared recommendations on the definition, classification and nomenclature related to electrochemical biosensors; these recommendations could, in the future, be extended to other types of biosensors. An electrochemical biosensor is a self-contained integrated device, which is capable of providing specific quantitative or semi-quantitative analytical information using a biological recognition element (biochemical receptor) which is retained in direct spatial contact with an electrochemical transduction element. Because of their ability to be repeatedly calibrated, we recommend that a biosensor should be clearly distinguished from a bioanalytical system, which requires additional processing steps, such as reagent addition. A device which is both disposable after one measurement, i.e. single use, and unable to monitor the analyte concentration continuously or after rapid and reproducible regeneration should be designated a single-use biosensor. Biosensors may be classified according to the biological specificity-conferring mechanism or, alternatively, the mode of physicochemical signal transduction. The biological recognition element may be based on a chemical reaction catalysed by, or on an equilibrium reaction with, macromolecules that have been isolated, engineered or present in their original biological environment. In the latter case, equilibrium is generally reached and there is no further, if any, net consumption of analyte(s) by the immobilized biocomplexing agent incorporated into the sensor. Biosensors may be further classified according to the analytes or reactions that they monitor: direct monitoring of analyte concentration or of reactions producing or consuming such analytes; alternatively, an indirect monitoring of inhibitor or activator of the biological recognition element (biochemical receptor) may be achieved. A rapid proliferation of biosensors and their diversity has led to a lack of rigour in defining their performance criteria. Although each biosensor can only truly be evaluated for a particular application, it is still useful to examine how standard protocols for performance criteria may be defined in accordance with standard IUPAC protocols or definitions. These criteria are recommended for authors, referees and educators and include calibration characteristics (sensitivity, operational and linear concentration range, detection and quantitative determination limits), selectivity, steady-state and transient response times, sample throughput, reproducibility, stability and lifetime

Covalent enzyme coupling on cellulose acetate membranes for glucose sensor development

International audienceMethods for immobilizing glucose oxidase (GOx) on cellulose acetate (CA) membranes are compared. The optimal method involves covalent coupling of bovine serum albumin (BSA) to CA membrane and a subsequent reaction of the membrane with GOx, which has previously been activated with an excess of p-benzoquinone. This coupling procedure is fairly reproducible and allows the preparation of thin membranes (5-20 µm) showing high surface activities (1-3 U/cm2) which are stable over a period of 1-3 months. Electrochemical and radiolabeling experiments show that enzyme inactivation as a result of immobilization is negligible. A good correlation between surface activity of membranes and their GOx load is observed

Propriétiés électrochimiques des dérivés polyconjugués hétérocycliques d'interêt biologique II. Effets des paramètres expérimentaux sur les caractéristiques des différentes vagues de réduction de la pyrimidine en solution aqueuse

International audienceThe characteristics of the different reduction waves of aqueous solutions of pyrimidine depend considerably on the following experimental parameters: pH, pyrimidine concentration, temperature, controlled drop-time. In relation to these observations, to logarithmic analysis of the shape of the waves and to drop-time curves, evidence is given of a dimerization step occurring between the two reduction steps in acid media; the existence of adsorption reactions is discussed.Les caractéristiques des différentes vagues de réduction polarographique de la pyrimidine en solution aqueuse dépendent considérablement des paramètres expérimentaux suivants: pH de la solution, concentration de pyrimidine, température, temps de goutte imposé. Cet ensemble d'observations et les résultats d'analyses logarithmiques de la forme des vagues et de courbes électrocapillaires conduisent d'une part à supposer l'existence d'une dimérisation radicalaire intercalée entre les deux premières étapes de réduction en milieu acide et d'autre part à discuter l'existence de réactions d'adsorption sur la surface de l'électrode