Multilevel integration of exploration units : beyond the ambidextrous organization

How firms combine incremental and radical innovation? The ambidextrous model suggests to differentiate exploration units from exploitation units. We show the importance of integration between these entities in outlining the tensions between them. We suggest that integration takes place on a multilevel basis and relies on various mechanisms.Modèle ambidextre

Combined electrochemical and biological treatment for pesticide degradation - Application to phosmet

International audienceThe aim of this study was to determine the feasibility of coupling an electrochemical process with a biological treatment in order to degrade phosmet, an organophosphorous pesticide. The absence of biodegradability of phosmet by Pseudomonas fluorescens and activated sludge was verified in our operational conditions. So, a conventional biological treatment is not appropriate for phosmet polluted effluents. Electrochemical behavior of phosmet was studied by cyclic voltammetry and the feasibility of an electrochemical pretreatment was thus demonstrated. Preliminary results with activated sludge showed a diminution of 26% for COD (chemical oxygen demand) measured when the electrolyzed solution was used as the sole carbon and nitrogen sources. When glucose and ammonium were added as supplementary carbon and nitrogen sources, the COD diminution reached 34% after 79 h of culture. This study demonstrates the feasibility of an electrochemical pre-treatment prior to biotreatment

Electrocatalytic reduction of metronidazole using titanocene/Nafion®-modified graphite felt electrode

International audienceThe main objective of this study was to examine the feasibility of an electrocatalytic reduction on titanocene/Nafion®-modified graphite felt electrode, as pretreatment, before a biological treatment, for the degradation of metronidazole, a nitro biorecalcitrant pollutant. A titanium complex, know as an effective catalyst in the reduction of nitro groups, was immobilized on the electrode surface by encapsulation into a Nafion® film. The different operating conditions used to prepare the modified electrode, i. e. the initial concentrations of catalyst and Nafion® and the sonication time, were optimized and the modification of the electrode was highlighted by cyclic voltammetry and electronic scanning microscopy coupled with energy dispersive spectroscopy analysis. The results show a good stability and reproducibility of the modified electrode. Flow heterogeneous catalytic reduction of metronidazole was then carried out with the titanocene/Nafion®-modified graphite felt as working electrode. The HPLC analysis underlined the total reduction of metronidazole after 1 hour and the evolution of the biological oxygen demand to chemical oxygen demand ratio showed a significant increase of biodegradability from 0.06 before pretreatment to 0.35 ± 0.05 after electrolysis on the modified graphite felt electrode. The comparison of both homogeneous and heterogeneous reactions underlined the interest of the immobilization process that led to a higher stability of the catalyst, giving rise to a higher turnover number and an improvement of biodegradability. The stability of the modified electrode was investigated after electrolysis by cyclic voltammetry and successive electrolyses

Direct electrochemical oxidation of a pesticide, 2,4-dichlorophenoxyacetic acid, at the surface of a graphite felt electrode: Biodegradability improvement

International audiencePesticides' biorecalcitrance can be related to the presence of a complex aromatic chains or of specific bonds, such as halogenated bonds, which are the most widespread. In order to treat this pollution at its source, namely in the case of highly concentrated solutions, selective processes, such as electrochemical processes, can appear especially relevant to avoid the possible generation of toxic degradation products and to improve biodegradability in view of a subsequent biological mineralization. 2,4-D was found to be electroactive in oxidation, but not in reduction, and the absence of hydroxyl radicals formation during the electrochemical step was demonstrated, showing that the pretreatment can be considered as a "direct" electrochemical process instead of an advanced electrochemical oxidation process. The presence of several degradation products in the oxidized effluent showed that the pretreatment was not as selective as expected. However, the relevance of the proposed combined process was confirmed since the overall mineralization yield was close to 93%

Enhancement of the biodegradability of a mixture of dyes (methylene blue and basic yellow 28) using the electrochemical process on a glassy carbon electrode

International audienceThe coupling of an electrochemical process with a biological treatment for the degradation of methylene blue (MB) and basic yellow 28 (BY28) considered separately or in mixture on a glassy carbon electrode was examined in this study. It was shown that color removal efficiency and mineralization yield of MB, BY28, and their mixture increased with the working potential and decreased with the initial dye concentration. The optimal conditions were found to be E=2.4V/SCE, [MB](0)=50mg L-1, [BY28](0)=50mg L-1, pH=2, T=25 degrees C, and =600rpm, which led to 100% color removal after 120 and 240min of reaction time for BY28 and MB, respectively. Under these optimal conditions, the mineralization yield of BY28, MB, and their mixture (50mg L-1 of each dye) was close to 59, 57, and 54% within 360min of reaction time, respectively. The biological oxygen demand (BOD5)/chemical oxygen demand (COD) ratio increased substantially after 360min of pre-treatment from 0.04 to 0.27 for the dyes mixture. Microbial degradation was therefore performed for the pre-treated mixture solution and the results showed significant mineralization yield leading to an overall dissolved organic carbon decrease of 78% for the coupled process. It was therefore shown the presence of residual refractory compounds at the end of the culture which was illustrated by the decrease of the BOD5/COD ratio (0.045) obtained for the final solution. However, biodegradability was improved after a recycling of the solution in the electrochemical oxidation pre-treatment during 180min leading to a BOD5/COD ratio of 0.73

Reductive dehalogenation of 1,3-dichloropropane by a [Ni(tetramethylcyclam)]Br2-Nafion modified electrode

International audienceDechlorination reaction of 1,3-dichloropropane, a contaminant solvent, was investigated by electrochemical reduction in aqueous medium using a Ni(tmc)Br2 complex, known as effective catalyst in dehalogenation reactions. The catalytic activity of the complex was first investigated by cyclic voltammetry and flow homogeneous redox catalysis using a graphite felt as working electrode. A total degradation of 1,3-dichloropropane was obtained after 5 h of electrolysis with a substrate/catalyst ratio of 2.3. The concentration of chloride ions determined by ion chromatography analysis showed a dechlorination yield of 98%. The complex was then immobilized on the graphite felt electrode in a Nafion® film. Flow heterogeneous catalytic reduction of 1,3-dichloropropane was then carried out with the [Ni(tmc)]Br2-modified Nafion® electrode. GC analyses underlined the total degradation of the substrate in only 3.5 h with a substrate/catalyst ratio of 100. A dechlorination yield of 80% was obtained, as seen with ion chromatography analyses of chloride ion. Comparison of both homogeneous and heterogeneous reactions highlighted the interest of the [Ni(tmc)]Br2-modified Nafion® electrode that led to a higher stability of the catalyst with a turnover number of 180 and a higher current efficiency

Combined process for removal of tetracycline antibiotic - Coupling pre-treatment with a nickel-modified graphite felt electrode and a biological treatment.

International audienceBiodegradability improvement of tetracycline-contg. solns. after an electrochem. pre-treatment was examd. Cyclic voltammetry with a nickel electrode revealed a significant electrochem. activity of tetracycline, in both oxidn. and redn. Electrochem. treatment was therefore performed in a home-made flow cell using a nickel-modified graphite felt electrode as the working electrode. Optimal conditions, namely 100 mg l-1 initial tetracycline, above 0.45 V potential, and between 1 and 6 mL min-1 flow rate, led to a more than 99% conversion yield of tetracycline in oxidn. in alk. conditions, after only a single pass through the percolation cell. However, total org. carbon (TOC) analyses revealed a low mineralization level, i.e., always below 31%, underscoring the importance of a combined electrochem. and biol. treatment. This was confirmed by the favorable trends of the COD/TOC ratio, decreasing from 2.7 to 1.9, and the av. oxidn. state, increasing from 0.044 to 1.15, before and after oxidn. pretreatment at 0.7 V and 3 mL min-1 flow rate. Electrolyzed solns. appeared biodegradable, since BOD5/COD increased from 0 to 0.46 for untreated and pretreated TC at 0.7 V/SCE. Biol. treatment showed only biosorption for non-pretreated tetracycline, while after 11.5 days of culture, the mineralization of solns. electrolyzed in oxidn. was 54%, leading to a 69% overall TOC decrease during the combined process

Combined process for 2,4-Dichlorophenoxyacetic acid treatment-Coupling of an electrochemical system with a biological treatment

International audienceA coupled process was studied for the removal of a chlorinated pesticide: 2,4-Dichlorophenoxyacetic acid (2,4-D). A home-made electrochemical flow cell was used for the pre-treatment and a biological treatment was then carried out using activated sludge supplied by a local wastewater treatment plant. 2,4-D was used as a target compound for the study. Several parameters were monitored during the biological treatment, like dissolved organic carbon (DOC), the target compound and the major by-product. Pretreatment led to a quick decrease of DOC during the biological process, since a 66% mineralization yield was measured after the second day, and 79% after the seventh day of culture. After two days of treatment, HPLC results revealed a total degradation of Chlorohydroquinone, the major by-product. The electrochemical pretreatment shortened the length of the biological treatment, since DOC measurements showed that in the case of non-pretreated 2,4-D, no mineralization was observed before day 7. These promising results should be subsequently confirmed on commercial 2,4-D-containing solutions and then on real effluents

Flow electrolysis on high surface electrode for biodegradability enhancement of sulfamethazine solutions

International audienceThe main objective of this study was to examine the feasibility of coupling an electrochemical process with a biological treatment for the degradation of sulfamethazine, a biorecalcitrant antibiotic. The electrochemical behavior of sulfamethazine was examined by cyclic voltammetry, showing an electroactivity in oxidation. The pre-treatment was carried out using an electrochemical flow cell involving a graphite felt electrode of high specific area. After a single pass through the cell, the analysis of the electrolyzed solution showed a promising trend in view of the proposed combined process, namely a high degradation of the target compound (more than 90%) while the mineralization level remained low (it did not exceed 20%). The optimization of the operating conditions, viz. flow rate and applied potential, allowed to improve the biodegradability of sulfamethazine solutions. Indeed, under optimal conditions, the biodegradability based on the BOD5 on COD ratio measurement was improved from 0.08 to 0.58, namely above the threshold limit value (0.4)

Degradation of enoxacin antibiotic by the electro-Fenton process: Optimization, biodegradability improvement and degradation mechanism

International audienceThis study aims to investigate the effectiveness of the electro-Fenton process on the removal of a second generation of fluoroquinolone, enoxacin. The electrochemical reactor involved a carbon-felt cathode and a platinum anode. The influence of some experimental parameters, namely the initial enoxacin concentration, the applied current intensity and the Fe(II) amount, was examined. The degradation of the target molecule was accompanied by an increase of the biodegradability, assessed from the BOD5 on COD ratio, which increased from 0 before treatment until 0.5 after 180 min of electrolysis at 50 mg L−1 initial enoxacin concentration, 0.2 mmol L−1 Fe(II) concentration and 300 mA applied current intensity. TOC and COD time-courses were also evaluated during electrolysis and reached maximum residual yields of 54% and 43% after 120 min of treatment, respectively. Moreover, a simultaneous generation of inorganic ions (fluorides, ammonium and nitrates) were observed and 3 short chain carboxylic acids (formic, acetic and oxalic acids) were identified and monitored during 180 min of electrolysis. By-products were identified according to UPLC-MS/MS results and a degradation pathway was propose