Douglas W. Miwa

Decolourisation of real textile waste using electrochemical techniques: Effect of electrode composition

The present paper presents the study of the decolourisation of real textile effluent by constant current electrolysis in a flow-cell using a DSA type material. The effect of using different anode materials (Ti/Ru(0.3)Ti(0.7)O(2); Ti/Ir(0.3)Ti(0.7)O(2); Ti/Ru(X)Sn(1-X)O(2), where X=0.1, 0.2 or 0.3) on the efficiency of colour removal is discussed. Attempts to perform galvanostatic oxidation (40 and 60 mA cm(-2)) on the as-received effluent demonstrate that colour removal and total organic carbon (TOC) removal are limited. In this case the greatest degree of colour removal is achieved when anode containing 90% SnO(2) is used. If the conductivity of the effluent is increased by adding NaCl (0.1 mol L(-1)) appreciable colour/TOC removal is observed. The efficiencies of colour and TOC removal are discussed in terms of the energy per order (E(EO)/kW h m(-3)order(-1)) and energy consumption (E(C)/kW h kg(-1)TOC), respectively. Finally, the extent of colour removal is compared to consent levels presented in the literature.

Electrochemical degradation of the dimethyl phthalate ester on a fluoride-doped Ti/β-PbO2 anode.

The electrooxidation of the dimethyl phthalate (DMP) ester was galvanostatically carried out in a filter-press reactor using a fluoride-doped lead dioxide (β-PbO2,F) film electrodeposited on a Ti substrate. The variables investigated were the nature of the supporting electrolyte (NaCl and Na2SO4), pH (3, 7, and 10), current density (10, 20, 40, 60, and 80mAcm(-2)), and temperature (10, 20, 30, 40, and 50°C). The removal of DMP was monitored through high performance liquid chromatography (HPLC) and total organic carbon (TOC) analysis. The best conditions were obtained using Na2SO4 and at low current densities, independent of the solution pH or temperature. These conditions led to the highest levels of current efficiencies and complete combustion. However, the TOC removal levels were low, due to the generation of highly oxidized intermediates, which was confirmed by the intermediates detected by HPLC.

SnO2-based materials for pesticide degradation.

This study presents the results of the degradation of the pesticide atrazine using electrochemical and photo-assisted electrochemical degradation techniques using SnO(2)-containing electrode of nominal composition electrodes of composition Ti/Ru(X)Sn(1-X)O(2) (where X=0.10, 0.15, 0.20, 0.25 and 0.30). The materials were characterized ex situ and in situ in order to correlate the observed atrazine removal rates with electrode morphology/composition. The results obtained demonstrate the effectiveness of the photo-assisted electrochemical degradation. Using purely electrochemical methods the rate of atrazine removal is almost zero at all the electrodes studied. However, the application of photo-assisted degradation results in almost complete atrazine removal in 1h of electrolysis. The efficiency of atrazine degradation does not seem to be greatly affected by the electrode material or by SnO(2) content, but the overall COD removal is dependent on the SnO(2) content. Overall, the SnO(2)-containing electrodes do not reach the level of COD removal (maximum approximately 21%) seen for the Ti/Ru(0.3)Ti(0.7)O(2) electrode. An interesting correlation between the morphology factor (phi) and chemical oxygen demand removal is observed.

Study of photo-assisted electrochemical degradation of carbaryl at dimensionally stable anodes (DSA®)

This paper presents the results concerning the degradation of the pesticide carbaryl comparing two methods: electrochemical (EC) and photo-assisted electrochemical (PAEC). The experimental variables of applied current density, electrolyte flow-rate and initial carbaryl concentration were investigated. The results demonstrate that the electrochemical degradation of carbaryl was greatly enhanced when simultaneous UV light was applied. The greatest difference between the PAEC and EC method was apparent when lower current densities were applied. The extent of COD removal was much enhanced for the combined method, independent of the applied current density. It should be noted that the complete removal of carbaryl was achieved with out the need to add NaCl to the reaction mixture, avoiding the risk of chlorinated organic species formation.

Comparing atrazine and cyanuric acid electro-oxidation on mixed oxide and boron-doped diamond electrodes

The breakdown of pesticides has been promoted by many methods for clean up of contaminated soil and wastewaters. The main goal is to decrease the toxicity of the parent compound to achieve non-toxic compounds or even, when complete mineralization occurs, carbon dioxide and water. Therefore, electrochemical degradation (potentiostatic and galvanostatic) of both the pesticide atrazine and cyanuric acid (CA) at boron-doped diamond (BDD) and Ti/Ru0.3Ti0.7O2 dimensionally stable anode (DSA®) electrodes, in different supporting electrolytes (NaCl and Na2SO4), is presented with the aim of establishing the influence of the operational parameters on the process efficiency. The results demonstrate that both the electrode material and the supporting electrolyte have a strong influence on the rate of atrazine removal. In the chloride medium, the rate of atrazine removal is always greater than in sulfate under all conditions employed. Furthermore, in the sulfate medium, atrazine degradation was significant only at the BDD electrode. The total organic carbon (TOC) load decreased by 79% and 56% at the BDD and DSA® electrodes, respectively, in the chloride medium. This trend was maintained in the sulfate medium but the TOC removal was lower (i.e. 33% and 13% at BDD and DSA® electrodes, respectively). CA, a stable atrazine degradation intermediate, was also studied and it is efficiently removed using the BDD electrode in both media, mainly when high current densities are employed. The use of the BDD electrode in the chloride medium not only degrades atrazine but also mineralized cyanuric acid leading to the higher TOC removal.

Electrochemical degradation of the dye reactive orange 16 using electrochemical flow-cell

Electrochemical removals of color and organic load from solutions containing the dye reactive orange 16 (RO16) were performed in an electrochemical flow-cell, using a platinum working electrode. The influence of the process variables flow-rate, such as NaCl concentration, applied potential and solution pH, were studied. The best color removal achieved was 93% (λ = 493 nm) after 60 min at 2.2 V vs. RHE electrolysis, using 1.00 g L-1 NaCl as supporting electrolyte. The rises in the concentration of NaCl and applied potential increased the color removal rate. The best total organic carbon removal (57%) was obtained at 1.8 V, without the separating membrane, indicating that the ideal conditions for the color removal are not necessarily the same as those to remove the total organic carbon. The degradation efficiency decreased with the solution pH decrease.

Electrochemical degradation of dimethyl phthalate ester on a DSA® electrode

The electrochemical degradation of dimethyl phthalate (DMP) using a one-compartment filter press flow cell and a commercial dimensionally stable anode (DSA®) is presented. The best electrolysis conditions were determined by the analysis of the influence of the nature and concentration of the support electrolyte, pH, current density and temperature. The abatement of DMP concentration and total organic carbon (TOC) removal were superior in the presence of NaCl, as well as the apparent first order kinetic constants. Using constant ionic strength at 0.15 mol dm-3 by adding Na2SO4, DMP concentration decreases faster at relative low NaCl concentrations while the TOC removal after 1 h of electrolysis increases with NaCl concentration. The DMP removal was very similar for all the current densities investigated at acidic solutions. When electric energy saving is considered, since the electrochemical system was under mass transport conditions, the best operational option is to use low current density values.

Photo-assisted electrochemical degradation of the commercial herbicide atrazine.

This paper presents a degradation study of the pesticide atrazine using photo-assisted electrochemical methods at a dimensionally stable anode (DSA(®)) of nominal composition Ti/Ru(0.3)Ti(0.7)O(2) in a prototype reactor. The effects of current density, electrolyte flow-rate, as well as the use of different atrazine concentrations are reported. The results indicate that the energy consumption is substantially reduced for the combined photochemical and electrochemical processes when compared to the isolated systems. It is observed that complete atrazine removal is achieved at low current densities when using the combined method, thus reducing the energy required to operate the electrochemical system. The results also include the investigation of the phytotoxicity of the treated solutions.

A microgravimetric study of simultaneous adsorption of anions and copper on polycrystalline Pt surfaces

A deposicao em subtensao de Cu foi estudada em quatro diferentes eletrolitos acidos, por meio de medidas simultâneas de voltametria ciclica e microgravimetria, usando uma microbalanca eletroquimica de cristal de quartzo. A influencia dos ânions na formacao da monocamada de Cu foi determinada. Entre os tres picos de dessorcao observados, encontrou-se que o primeiro e muito sensivel a natureza do anion presente em solucao. Este comportamento foi relacionado com o baixo recobrimento da superficie da Pt com os ad-atomos, na faixa de potenciais correspondente, que resulta apenas em interacoes muito fracas entre os ad-atomos de Cu. A monocamada e composta de uma primeira camada de Cu adsorvido sobre Pt e uma segunda camada de ânions adsorvidos sobre os ad-atomos de Cu, com cada ânion ocupando dois ad-atomos adjacentes, com excecao do Cl-, que se depositou na forma de um ânion para cada ad-atomo de Cu. Esta estrutura forma, consequentemente, uma bi-camada. A modificacao dos perfis dos massogramas e voltamogramas pelo acrescimo do Cl- no eletrolito de perclorato tambem foi analisada.

Electrochemical removal of CuII in the presence of humic acid

The removal of CuII (10 mg L-1) complexed by commercial humic acid (100 mg L-1) was studied at different current densities (30-80 mA cm-2) using a filter-press cell, Ti/Ru0.3Ti0.7O2 anode and stainless steel cathode. The electrolyses were performed with and without membrane separating the cell compartments [(homogeneous anionic (Nafion R117), heterogeneous cationic (Ionac MC-3470) and heterogeneous anionic (Ionac MA-3475)]. The influence of the membrane on the rate of CuII removal was bigger for cationic membranes. Current efficiencies up to ca. 55% (Ionac MC-3470) for CuII removal at 30 mA cm-2 were obtained. By combining oxidation and reduction, 100% CuII removal was achieved at current efficiencies of 75%. The main path for the removal is the electrostatic interaction with the anode followed by diffusion through the membrane and deposition at the cathode. Additionally, the oxidative degradation of humic acid contributes to the rate of CuII removal.