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Serena Randazzo a,b, Onofrio Scialdone b, Enric Brillas a, Ignasi Sirés a a Laboratori d’Electroquímica dels Materials i del Medi Ambient, Departament.

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Presentation on theme: "Serena Randazzo a,b, Onofrio Scialdone b, Enric Brillas a, Ignasi Sirés a a Laboratori d’Electroquímica dels Materials i del Medi Ambient, Departament."— Presentation transcript:

1 Serena Randazzo a,b, Onofrio Scialdone b, Enric Brillas a, Ignasi Sirés a a Laboratori d’Electroquímica dels Materials i del Medi Ambient, Departament de Química Física, Facultat de Química, Universitat de Barcelona, Martí i Franquès 1-11, Barcelona, Spain b Dipartimento di Ingegneria Chimica, Gestionale, Informatica e Meccanica, Università di Palermo, Viale delle Scienze, Palermo, Italy Comparative electrochemical treatments of two chlorinated aliphatic hydrocarbons. Time course of the main reaction by-products Introduction The nowadays society finds it difficult to ensure the clean water supply because domestic, agricultural and industrial activities are responsible for introducing refractory organic pollutants into the water streams. Aliphatic compounds conjugate toxicity with high chemical stability, bioaccumulation and long-range diffusivity [1]. Chloroethanes are particularly ubiquitous in the industry and in household products, and their entry into the environment may entail potential risks for the living beings [2]. To avoid the release of chloroethanes into the aqueous environment, powerful water treatment technologies such as the advanced oxidation processes (AOPs) must be applied in the wastewater treatment facilities. This work reports the degradation of acidic aqueous solutions of 1,2-dichloroethane (DCA) and 1,1,2,2-tetrachloroethane (TCA) under electro-Fenton (EF) conditions to study the synergistic oxidation at the anode surface (BDD(  OH)) and in the bulk (  OH) to minimize the diffusional limitations. The effect of various experimental parameters on the mineralization process was examined. The identification and evolution of the main accumulated organic by-products were ascertained by chromatographic techniques, allowing the proposal of original reaction pathways for DCA and TCA. In addition, the fate of chloride ions released during the degradation of chloroethanes was carefully studied. Results Fig. 4 Effect of several parameters on the mineralization of DCA (a,b) and TCA (c) solutions. (a,c) DOC decay vs electrolysis time for the treatment of 130 ml of 4 mM DCA or TCA in M Na 2 SO 4 medium, at pH 3.0 and at 10 ºC using a BDD/ADE cell. [Fe 2+ ] (mM): (  ) 0 (with N 2 supply to the cathode) and (,, ▲ ) 0.5; Current (mA): ( ) 100, ( ,,) 300, and ( ▲ ) 450. The inset in (a) shows the DOC decay vs the specific charge for the trials with Fe 2+. (b) Evolution of Δ(DOC) exp vs electrolysis time for ( ), which is shown in plot (a). In (b,c): (x) analogous to ( ), with 2 mM DCA or TCA (i.e., 48 mg l -1 DOC), and (+) analogous to ( ), using a Pt anode. [1] S. Rondinini, A. Vertova, Electroreduction of halogenated organic compounds, in: C. Comninellis, G. Chen (Eds.), Electrochemistry for the environment, Springer Science + Business Media, New York, 2010, pp. 279–306. [2] Chlorinated hydrocarbons, in: Ullmann’s Encyclopedia of Industrial Chemistry, Wiley-VCH Verlag GmbH & Co. KGaAed, 2002 (electronic edition). [3] E. Brillas, I. Sirés, M.A. Oturan, Electro-Fenton process and related electrochemical technologies based on Fenton’s reaction chemistry, Chem. Rev. 109 (2009) 6570–6631. REFERENCES 62 nd Annual Meeting of the ISE, Niigata, Japan, th September 2011 Mineralization of DCA and TCA solutions (c) Fig. 5 Time course of the concentration of the short-chain carboxylic acid intermediates accumulated during the treatment of 130 ml of 4 mM TCA (left) or DCA (right) in M Na 2 SO 4 medium, at pH 3.0 and at 10 ºC using a BDD/ADE cell. [Fe 2+ ] (mM). (a) Total amount of dichloroacetic (left) and chloroacetic + acetic (right) acids for different treatments as shown in Fig. 4. (b) Trends of (  ) chloroacetic + acetic, (  ) oxalic and (  ) formic for same conditions of ( ) (see Fig. 4). Fig. 6 General reaction schemes proposed for the complete mineralization of acidic aqueous solutions of DCA (upper) and TCA (lower) by EAOPs using a BDD/ADE cell.  OH not drawn in stoichiometric quantities. Fig. 7 Time course of the concentration of the chlorinated ions released during the treatment of 130 ml of (a) 4 mM DCA and (b) of TCA in M Na 2 SO 4 medium, at pH 3.0, at 10 ºC using a BDD/ADE cell, with a [Fe 2+ ] of 0.5 mM, at a current of 300 mA. Ions: ( ) Cl , ( ▲ ) ClO 3 , (  ) ClO 4 , and (x) sum of the three ions. Time course of the main reaction by-products Accumulation of electrogenerated H 2 O 2 in the electrolytic cell Materials and method The electrolyte solution was composed by 1,2-dichloroethane 99,8% or 1,1,2,2-tetrachloroethane 98%, Na 2 SO M as supporting electrolyte, FeSO 4 ·7H 2 O as source of Fe 2+ and H 2 SO 4 to obtain an initial pH of 3. The electro-Fenton treatments were performed using 0.5 mM Fe 2+ as catalyst. Comparative anodic oxidation experiments were made without Fe 2+ and feeding the cathode with pure N 2. All trials were performed under vigorous stirring with a magnetic bar to ensure a good mixing and reproducible mass transport conditions. The pH 3.0 was selected because it is the optimum value for Fenton’s reaction [3]. Colourimetric measurements were made with a Unicam UV4 Prisma double-beam UV/Vis spectrometer thermostated at 20 ºC. The concentration of H 2 O 2 was determined from the light absorption of the Ti(IV)-H 2 O 2 coloured complex at = 408 nm. The mineralization of the solutions was assessed from the decay of their dissolved organic carbon (DOC). The decay of the concentration of DCA and TCA was followed by gas chromatography/mass spectrometry (GC/MS). The time course of the carboxylic acid intermediates was followed by ion-exclusion HPLC. The chlorinated inorganic anions were determined by IC. Fig. 1 Scheme of a bench-scale undivided and thermostated cylindrical glass cell, where the carbon-PTFE ADE cathode was directly fed with air. Fig. 2 Time course of the accumulated H 2 O 2 during the electrolysis of 130 ml of a M Na 2 SO 4 solution, at 300 mA, pH 3.0, and at 10 ºC using a BDD/ADE cell. [Fe 2+ ] (mM): (  ) 0 and (,, ▲ ) 0.5; [DCA] (mM): ( , ) 0, ( ▲ ) 2, and ( ) 4. Fig. 3 Decay of the DCA concentration vs electrolysis time during the degradation of 130 ml of 4 mM DCA (i.e., 96 mg l -1 DOC) in M Na 2 SO 4 medium, at 300 mA, pH 3.0, and at 10 ºC, by (  ) pure anodic oxidation (i.e., 0 mM Fe 2+ and N 2 supply to the cathode) and ( ) electro-Fenton (i.e., 0.5 mM Fe 2+ and air supply to the cathode) using a BDD/ADE cell. Degradation of DCA solutions by EAOPs The anodic oxidation at BDD anode combined with the electro-Fenton process resulted in a higher abatement of DCA and TCA compared to anodic oxidation. The accumulated H 2 O 2 concentration increased during the first 240 min, reaching a value of about 120 mM. The accumulated H 2 O 2 concentration decreased when ferrous ions, DCA 2 mM and DCA 4 mM were respectively added to the solution. The mineralization of DCA and TCA solutions was enhanced working at higher current, higher initial concentration of the starting compounds, using BDD instead of Pt and with an electro-Fenton process compared to anodic oxidation. Università degli Studi di Palermo DICGIM – Dipartimento di Ingegneria Chimica, Gestionale, Informatica, Meccanica


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