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

Addition of weak acids in electrolytes to prevent osmosis in aqueous organic redox flow batteries

International audienceWater transfer issues related to unbalanced ionic strengths in aqueous organic redox flow batteries (AORFBs) are often overlooked. In this work, a simple strategy based on the addition of a weak acid in the negolyte was studied to prevent osmosis in AORFBs. Ferrocyanide [Fe(CN)6]4- and anthraquinone-2,7-disulfonic acid disodium salt (AQDS) were used as positive and negative active materials, respectively, and aspartic acid was chosen as a weak acid. The addition of acid aspartic as well as strong bases such as KOH, NaOH or LiOH to reach the complete deprotonation of the acid and the desired pH contributes to balancing the cations total concentration of both compartments. Battery cycling experiments were carried out with 0.2 – 0.3 M AQDS and 0.4 – 0.6 M [Fe(CN)6]4−. When no weak acid was used, osmosis quickly leading to a shortage of negative electrolyte was observed, while in presence of aspartic acid both electrolyte volumes remained unchanged during the time of experiment. © 202

Metallic nanoparticles for electrocatalytic reduction of halogenated organic compounds: A review

International audienceIncreasing attention is paid to the degradation of refractory halogenated organic compounds in wastewaters. For this purpose, electrocatalytic reduction process constitutes a promising technology due to its high selectivity. Owing to their well-controlled structure and high specific surface area, nanoparticles have been the subject of many investigations in electrocatalysis. This study presents a general review on nanoparticles-modified electrodes to achieve reductive dehalogenation. The role of the electrode support, especially 3-D Carbon and metallic porous electrodes are first discussed. Then, the methods to prepare metallic nanoparticles on the electrode supports included spontaneous deposition and/or electrodeposition are summarized and the commonly used characterization methods of nanoparticles modified electrodes are also presented. The influence of the electrode material, Ag, Pd, and Cu, as representatives, on electro-dehalogenation process is discussed and compared. Finally, this review also highlights the recent applications of these nanoparticles-modified electrodes for the treatment of halogenated organic compounds in aqueous solutions

A new hydroxyanthraquinone derivative with a low and reversible capacity fading process as negolyte in alkaline aqueous redox flow batteries

International audience2,3-dihydroxylated anthraquinone (2,3-DHAQ) is evaluated for the first time in a redox flow battery. This compound exhibits a good solubility in alkaline media (0.7 M in KOH at pH andgt; 13.5) and a suitable potential (−0.85 V vs Ag/AgCl) leading to a 1.11 V theoretical open circuit voltage at 50% state of charge with potassium ferrocyanide as posolyte. It is implemented in a 25 cm2 cell during 180 cycles with a capacity fading of 0.022% per cycle and a current efficiency higher than 99.7%. Owing to its high solubility, an initial energy density up to 17 Wh L−1 (7.7 Wh L−1 when both posolyte and negolyte are considered) is obtained. 2,3-DHAQ exhibits a good chemical stability compared with other dihydroxyanthraquinone (around 0.1% per cycle). After more than 3000 cycles, 2,3-DHAQ is observed as the main product, showing its high chemical stability. Moreover, the capacity fading process is reversible since changing the discharge conditions allows a full recovery of the initial capacity. This opens up new perspectives as the capacity loss is often used to evaluate the relevance of new molecules. A wider range of active materials in AORFB can be considered if the capacity fading they exhibit can be reversible. © 2022 Elsevier B.V