Remoção de Oocistos de Cryptosporidium por filtração direta: Influência de alguns aspectos operacionais / Removal of Cryptosporidium Oocysts by direct filtration: the influence some operational aspects

AUTOR(ES)
DATA DE PUBLICAÇÃO

2006

RESUMO

The present work deal with the removal of Cryptosporidium oocysts by downflow direct filtration with almost uniform filter bed to verify the influence of operational aspects such as coagulant dosage, filtration flow rate and raw waters characteristcs. The experimental work was carried out in pilot-plant comprised by a hydraulic flash mixing device and a rapid downflow sand filter column. The studies in pilot-scale were preceded by benches studies (Jar Tests) for the definition of the coagulant dosages and the pH values to be used in the filtration experiments. Fifteen filtration experiments had been carried out, using aluminum sulphate as coagulant. Three different dosage levels were used: suboptimal, "optimal" and overoptimal dosages of coagulant. Raw waters from the Paranoá lake and from the Torto stream were used. During filtration experiments these waters were spiked with Cryptosporidium sp. oocysts in the order of 103 to 102 oocysts/L and the filter was operated with constant flow rates of 210 m/day and 105 m/day. Independently of the filtration flow rate and the raw water tested, when "optimal" and overoptimal coagulant dosages were used, the filter effluents presented turbidity values lower than 0,5 NTU and values of chlorophyll-a lower than 1,5μg/L. Regarding the removal of Cryptosporidium oocysts, for the studied filter, no appreciable differences on the removal of these protozoan were observed with the utilization of conservatives flow rates, 105 m/day, when comparing with 210 m/day.. On the other hand, for the raw waters studied, the use of overoptimal coagulant dosages tends to improve the removal of the Cryptosporidium oocysts, when comparing with optimal dosages. Similarly, it was observed that the removal of the Cryptosporidium oocysts was lower during ripening period when comparing with the stable filtration operation. However, the operational aspect that placed more influence on the removal of Cryptosporidium oocysts was the use suboptimal coagulation dosage. When this condition was adopted, it was verified that, independently of the raw water.used, the removal was significant lower. So, failures in the coagulation process, such the use of suboptimal coagulant dosages and the ripening filter period may be considered as the two major operational risk factors. viii

ASSUNTO(S)

sulfato de alumínio tratamento de água remoção de oocistos de cryptosporidium filtração direta descendente recursos hidricos

ACESSO AO ARTIGO

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