No presente trabalho foi avaliado o papel de íons metálicos tais como: Cr(VI), Cr(III), Cd(II), V(V) e do íon cloreto, no processo de oxidação do S(IV) em solução aquosa. As concentrações dos íons metálicos, íon cloreto e do S(IV) foram escolhidas de modo a representarem as frações solúveis destes em aerossóis urbanos. Os estudos relativos ao processo de oxidação do S(IV) foram conduzidos em condições experimentais controladas tais como: (pH (2,1-4,5), T (11,0-35,0 °C), vazão de O2, concentração de reagentes, etc...). A constante cinética, K, determinada a 25,0 °C e na faixa de pH estudada (2,1-4,5), utilizando-se água pura, apresentou um valor médio de 8,0 ± 0,5 x 10-4 s-1 , e este valor foi tomado como referência para reação de oxidação não catalisada. Os valores das constantes cinéticas determinadas, na presença de Cr(VI), revelaram que a reação de oxidação do S(IV) é bastante influenciada pela acidez do meio. Em pH 2,1 (K = 2,3 x 10-2 mg-1 L s-1) a reação se processa com velocidade específica cinco vezes superior quando comparado a pH 2,6 (K = 4,3 x 10-3 mg-1 L s-1) e trinta vezes superior quando comparada a pH 3,4 (K = 8,0 x 10-4 mg-1 L s-1). A seguinte expressão de velocidade foi obtida para o sistema envolvendo Cr(VI) em pH 2,6:-r S(IV) = K [Cr(VI)] [S(IV)] e a energia de ativação encontrada foi: Ea = 70,3 kJ/ mol. Não foi observado efeito catalítico para o íon metálico Cd(II) e para cloreto, porém efeitos catalíticos inibitórios foram observados para os íons Cr(III) e V(V). Catalytic effect of metal ions: Cr(VI), Cr(III), Cd(II), V(V) and chloride anion, on the oxidation of S(IV) in aqueous solution, at concentrations of metal ions and S(IV) usually found in urban atmospheres, were studied under controlled experimental conditions (pH (2.1-4,5), T (25.0-35.0°C), air flow rate, concentration of reactants, etc...). The kinetic constant determined at 25.0 °C and pH range (2.1-4.5), using ultra pure water was 8.0 ± 0.5 x 10-4 s-1. This value was considered as a reference for the oxidation reaction rate. The kinetic constants determined in the presence of Cr(VI) revealed that the oxidation reaction of S(IV) is quite influenced by the acidity. At pH = 2.1 (K = 2.3 x 10-2 mg-1 L s-1) the reaction is carried out with a rate five times greater when compared to pH = 2.6 (K = 4.3 x 10-3 mg-1 L s-1) and thirty times greater when compared to pH = 3.4 (K= 8.0 x 10-4 mg-1 L s-1). The following rate expression was obtained at pH = 2.6:-r(S(IV) =K [Cr(VI)] [S(IV)] and the activation energy found was: Ea =70.3KJ/mol. No catalytic effects were observed for Cd(II) or chloride ion, while inhibitory effects were observed for Cr(III) and V(V) ions.

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The yeast Saccharomyces cerevisiae, a microorganism with cell walls resistant to many types of treatments, was chosen as a model to study electrochemical disinfection process using dimensionally stable anodes (DSA). DSA electrodes with nominal composition of Ti/RuOTiO and Ti/RuOTiOIrO were evaluated in 0.05 mol L NaSO containing yeast. The results showed inactivation about of 100 % of the microorganisms at Ti/RuOTiO by applying 20 and 60 mA cm after 120 min of electrolysis, while a complete inactivation at Ti/RuOIrOTiO electrode was achieved after 180 min at 60 mA cm. When chloride ions were added in the electrolyte solution, 100 % of the yeast was inactivated at 20 mA cm after 120 min of electrolysis, independent of the anode used. In the absence of chloride, the energy consumption (EC) was of 34.80 kWh m, at 20 mA cm by using Ti/RuOTiO anode. Meanwhile, in the presence of chloride, EC was reduced, requiring 30.24 and 30.99 kWh m at 20 mA cm, for Ti/RuOTiO and Ti/RuOIrOTiO electrodes, respectively, The best performance for cell lysis was obtained in the presence of chloride with EC of 88.80 kWh m (Ti/RuOTiO) and 91.85 kWh m (Ti/RuOIrOTiO) to remove, respectively, 92 and 95 % of density yeast. The results clearly showed that yeast, as a model adopted, was efficiently inactivated and lysed by electrolysis disinfection using DSA-type electrodes.

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This study investigated the electrochemical oxidation of organic matter present in shrimp farming effluent using three types of electrocatalytic materials: Ti/RuTiO, Ti/Pt, and boron-doped diamond (BDD). An electrochemical cell with 300 mL under stirring agitation was used by applying 20, 40, and 60 mA cm. A Ti/RuTiO anode showed a reduction of chemical oxygen demand (COD) about 84 % after 1 h of electrolysis, while at the same time, 71 % of COD decay was achieved at Ti/Pt. Conversely, only 71 % of COD was removed after 2 h with a BDD anode. Regarding the temperature effect, BDD showed better performances than those achieved for Ti/RuTiO and Ti/Pt anodes during an electrochemical treatment of a shrimp farming effluent, obtaining 72 % of COD removal by applying 20 mA cm at 40 °C after 15 min. Energy consumption and cost were estimated in order to established the engineering applicability of this alternative process.