Standard addition method for the determination of pharmaceutical residues in drinking water by SPE-LC-MS/MS

International audienceThe study of the occurrence and fate of pharmaceutical compounds in drinking or waste water processes has become very popular in recent years. Liquid chromatography with tandem mass spectrometry is a powerful analytical tool often used to determine pharmaceutical residues at trace level in water. However, many steps may disrupt the analytical procedure and bias the results. A list of 27 environmentally relevant molecules, including various therapeutic classes and (cardiovascular, veterinary and human antibiotics, neuroleptics, non-steroidal anti-inflammatory drugs, hormones and other miscellaneous pharmaceutical compounds), was selected. In this work, a method was developed using ultra performance liquid chromatography coupled to tandem mass spectrometry (UPLC-MS/MS) and solid-phase extraction to determine the concentration of the 27 targeted pharmaceutical compounds at the nanogram per litre level. The matrix effect was evaluated from water sampled at different treatment stages. Conventional methods with external calibration and internal standard correction were compared with the standard addition method (SAM). An accurate determination of pharmaceutical compounds in drinking water was obtained by the SAM associated with UPLC-MS/MS. The developed method was used to evaluate the occurrence and fate of pharmaceutical compounds in some drinking water treatment plants in the west of France

Mineralization of synthetic and industrial pharmaceutical effluent containing trimethoprim by combining electro-Fenton and activated sludge treatment

International audienceA combined process coupling of an electro-Fenton and a biological degradation was investigated in order to mineralize synthetic and industrial pharmaceutical effluent containing trimethoprim, a bacteriostatic antibiotic. Electro-Fenton degradation of trimethoprim was optimized by means of a Doehlert experimental design, showing that 0.69 mM Fe2+, 466 mA and 30 min electrolysis time were optimal, leading to total trimethoprim removal, while mineralization remained limited, 12% for 30 min electrolysis times. The aromatic and aliphatic by-products were identified and a plausible degradation pathway was proposed. Biodegradability was improved, since the BOD5/COD ratio increased from 0.11 initially to 0.32 and 0.52 after 30 and 60 min electrolysis times respectively, confirmed by activated sludge culture, 47 and 59% mineralization of the byproducts from electrolysis.The relevance of the proposed combined process was then confirmed on an industrial pharmaceutical effluent. Its electrolysis under the above conditions showed an almost total removal of trimethoprim after 180 min of electrolysis, while TOC removal remained low, 14 and 16% for 180 and 300 min reaction times, respectively. Overall removal yields of the industrial effluent during the combined process were therefore 80 and 89% for 180 and 300 min of effluent pretreatment followed by 15 days activated sludge culture, respectively

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%

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

Electro-Fenton pretreatment for the improvement of tylosin biodegradability

International audienceThe feasibility of an electro-Fenton process to treat tylosin (TYL), a non-biodegradable antibiotic, was examined in a discontinuous electrochemical cell with divided cathodic and anodic compartments. Only 15 min electrolysis was needed for total tylosin degradation using a carbon felt cathode and a platinum anode; while 6 h electrolysis was needed to achieve high oxidation and mineralization yields, 96 and 88 % respectively. Biodegradability improvement was shown since BOD5/COD increased from 0 initially to 0.6 after 6 h electrolysis (for 100 mg L−1 initial TYL). With the aim of combining electro-Fenton with a biological treatment, an oxidation time in the range 2 to 4 h has been however considered. Results of AOS (average oxidation state) and COD/TOC suggested that the pretreatment could be stopped after 2 h rather than 4 h; while in the same time, the increase of biodegradability between 2 and 4 h suggested that this latter duration seemed more appropriate. In order to conclude, biological cultures have been therefore carried out for various electrolysis times. TYL solutions electrolyzed during 2 and 4 h were then treated with activated sludge during 25 days, showing 57 and 67 % total organic carbon (TOC) removal, respectively, namely 77 and 88 % overall TOC removal if both processes were considered. Activated sludge cultures appeared, therefore, in agreement with the assessment made from the analysis of physico-chemical parameters (AOS and COD/TOC), since the gain in terms of mineralization expected from increasing electrolysis duration appeared too low to balance the additional energy consumption

Indirect electroreduction as pretreatment to enhance biodegradability of metronidazole.

International audienceThe removal of metronidazole, a biorecalcitrant antibiotic, by coupling an electrochemical reduction with a biological treatment was examined. Electroreduction was performed in a home-made flow cell at -1.2V/SCE on graphite felt. After only one pass through the cell, analysis of the electrolyzed solution showed a total degradation of metronidazole. The biodegradability estimated from the BOD5/COD ratio increased from 0.07 to 0.2, namely below the value usually considered as the limit of biodegradability (0.4). In order to improve these results, indirect electrolysis of metronidazole was performed with a titanium complex known to reduce selectively nitro compounds into amine. The catalytic activity of the titanium complex towards electroreduction of metronidazole was shown by cyclic voltammetry analyses. Indirect electrolysis led to an improvement of the biodegradability from 0.07 to 0.42. To confirm the interest of indirect electroreduction to improve the electrochemical pretreatment, biological treatment was then carried out on activated sludge after direct and indirect electrolyses; different parameters were followed during the culture such as pH, TOC and metronidazole concentration. Both electrochemical processes led to a more efficient biodegradation of metronidazole compared with the single biological treatment, leading to an overall mineralization yield for the coupling process of 85%

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)

Improvement of the activated sludge treatment by its combination with electro Fenton for the mineralization of sulfamethazine

International audienceA combined process coupling an electro-Fenton pretreatment and a biological degradation in order to mineralize sulfamethazine (SMT) was investigated. The electro-Fenton pretreatment of SMT was first examined and the intermediates products were identified for an initial SMT amount of 0.36 mM, after 1 h electrolysis at pH 3, 18 °C, 200 mA. 94.2% SMT was degraded but the level of mineralization remained low (6.5%), ensuring significant residual organic content for a subsequent biological treatment. Two possible degradation reaction pathways involving all the identified and quantified intermediates are proposed. In a second part, biological treatments with fresh activated sludge were performed to complete the mineralization of the electrolyzed solution of SMT, showing an increase of the mineralization yield with time duration of the pretreatment. For an initial SMT concentration of 0.2 mM, a ferrous ions concentration of 0.5 mM, at pH 3, 18 °C and 500 mA, the mineralization yield during the biological treatment increased as follows: 61.4, 78.8 and 93.9% for 0.5, 1 and 4 h pretreatment, confirming the relevance of the proposed combined process

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

Combined electrochemical treatment/biological process for the removal of a commercial herbicide solution, U46D

International audienceThe removal of a commercial solution of 2,4-D, U46D , was carried out by coupling an electrochemical oxidation and a biological process involving activated sludge. The similar electrochemical behavior of 2,4-D and U46D highlighted their oxidation around 1.6 V/SCE and the feasibility of an electrochemical pretreatment. It was based on a home-made flow cell involving bare graphite felt electrode. To propose a consistent mechanism for 2,4-D oxidation, the indirect determination of OH has been performed and the absence of radicals formation during 2,4-D electrolysis was confirmed. Consequently, the proposed pretreatment can be considered as a 'direct' electrochemical process instead of an advanced electrochemical oxidation process. The impact of the flow rate on the pretreatment showed that 3 mL min 1 was a good compromise between the pretreatment time and the electrolysis efficiency, since it led to an almost total degradation of the pollutant while its mineralization remained limited. At this flow rate and for 500 mg L 1 of 2,4-D, the energy cost was estimated at 5 kWh m 3. The biodegradability of U46D solution was not significantly modified after electrolysis, most likely due to the presence of dimethylamine salt in U46D . Owing to the significant BOD5/COD ratio measured, a biological treatment of the commercial U46D solution was however considered. The electrochemical pretreatment shortened the duration of the biodegradation. For non-pretreated U46D (100 mg L 1 2,4-D), mineralization remained limited until 6 days of culture (33.7% DOC removal), and total removal of the DOC was observed after 8 days. For pretreated U46D , 63.7% decrease until the fifth day of culture was observed but total mineralization was not reached at the end of culture (72.1%). An overall mineralization yield during the coupled process of 82.1% was therefore reached. The presence of refractory compounds generated during the electrochemical pretreatment in small concentration was therefore show