Aplicação do dióxido de cloro no tratamento de água para consumo humano: desinfecção para controle de oocistos de Cryptosporidium sp., formação de subprodutos e manutenção de residuais desinfetantes em sistemas de distribuição / Chlorine dioxide use in drinking-water treatment: disinfection control of Cryptosporidium sp., byproducts formation, and maintenance of disinfectant residuals in distribution systems

Rosane Cristina de Andrade

This work aimed at evaluating the use of chlorine dioxide in drinking-water treatment, with emphasis on byproducts formation, maintenance of disinfectant residuals in distribution systems and removal of Cryptosporidium oocysts. In jar test experiments, the application of chlorine dioxide in samples of raw water (simulating pre-oxidation), settled and filtered water (simulating disinfection) led to oxidant demand and chlorite and chlorate formation according to the water characteristics, expressed by turbidity and color. Chlorine dioxide residuals and chlorate concentrations were associated with chlorine dioxide doses, but the chlorite concentrations were not. Reaction times were associated with chlorine dioxide residuals, but not with the resulting chlorite and chlorate concentrations. The application of 2.5- 6 mg ClO2.L-1 led to chlorite formation always above the maximum contaminant level established in the Brazilian drinking-water standard (0.2 mg ClO2 - L-1), but only a few times above the maximum contaminant level goal (0.8 mg.L-1), and rarely above the maximum contaminant level (1 mg.L-1) set by the US Environmental Protection Agency. In the experiments using a contact chamber and a distribution system (both in pilot scale), the application of 3-6 mg ClO2.L-1 in filtered water samples (0.2-0.3 NTU and 5-10 color units) led to oxidant demand of 0.9-1.3 mg.L-1, and chlorine dioxide residuals at the contact chamber outlet of 4,7 mg.L-1 (when dosing 6 mg ClO2.L-1) and around 2 mg.L-1 (when dosing 3 mg ClO2.L-1); these residuals tended to decrease in the distribution system, staying however rather stable. Chlorite concentrations at the contact chamber outlet ranged from 0.2 to 0.4 mg.L-1, also tended todecrease in the distribution system, but stayed always below 0.9 mg.L-1. Chlorate concentrations in the distribution system ranged from 0.8 to 2.4 mg.L-1 (average of 1.7 mg.L-1) when dosing 6 mg ClO2.L-1 and from 0.7 to 1.4 mg.L-1 (average of 1.1 mg.L-1) when dosing 3 mg ClO2.L-1. In jar test experiments involving the inoculation of 103 and 104 Cryptosporidium oocysts per liter, several combinations of chlorine dioxide residuals (C) and contact times (T) were tried. Overall, it was confirmed that chlorine dioxide is effective for Cryptosporidium control, but the results varied widely and it was not possible to fit a model to predict Cryptosporidium oocysts removal as a function of CT values. Nevertheless, the results were consistent with the range reported in the literature.

AUTOR(ES)

FONTE

DATA DE PUBLICAÇÃO

RESUMO

ASSUNTO(S)

ACESSO AO ARTIGO

Documentos Relacionados