a b s t r a c tCyanobacterium Cylindrospermopsis raciborskii may cause problems in drinking water treatment plants if specific attention is not focused on removing the cyanobacteria. Slow sand filtration possesses a good capacity for cyanobacteria removal and is a simple alternative to more expensive treatments. However, high cyanobacteria concentrations can correspond to an operational problem for slow sand filters by reducing the filter running time, and therefore rough filtration is necessary. In this study, two similar upflow slow sand filters were used to evaluate C. raciborskii removal. Water with 9.1 × 10 5 cells/mL was used and an average of 99% of cells were removed. Nevertheless, average concentrations of 1.4 × 10 4 and 2.1 × 10 4 cells/mL were observed after filtration, and this could continue to act as a problem for water treatment. The system also indicated good results in terms of removing total coliforms, colour and turbidity. The average turbidity was below 1.0 NTU, which is the maximum value permitted by Brazilian regulations and WHO recommendations. The major advantage of the upflow slow sand filter involved the high removal of C. raciborskii without compromising the running time of the filter with the filters operating for almost 80 days without the use of rough filters. However, it is necessary to use a complementary treatment process to achieve better water quality results.
Slow sand filters are considered as a great alternative for supplying drinking water in rural and/or isolated areas where raw water that is treatable with this technique is available. Some studies used backwashing as an alternative for cleaning the slow sand filter with the goal of applying the technology in small communities, since filters that supply water to a small number of people do not require much space. In this study the influence of the effective diameter on water quality in the filters and cleaning system was evaluated. A pilot system with six filters was built: three filters were conventionally cleaned by scraping and the other three were cleaned by backwashing, each with a different effective diameter of filter medium. Most filters had an average turbidity of less than 1.0 NTU, the turbidity required at the output of the filters by the Brazilian Ministry of Health Ordinance. In the study, the filters cleaned by scraping with smaller-diameter filter beds effectively filtered water better but had worse effective production. The opposite occurs in the case of backwashed filters.
Diagnóstico e discussão sobre uso da Filtração Lenta para abastecimento público em Santa Catarina, Brasil
A diagnosis and discussion about the use of Slow Sand Filtration for public drinking water supply in Santa Catarina, BrazilResumo A filtração lenta é uma técnica simples para o tratamento de água e uma das mais antigas utilizadas no abastecimento público. Com o tempo, essa tecnologia perdeu espaço para sistemas que demandam, relativamente, menor área útil de ocupação, como a coagulação e a filtração rápida ou direta. Portanto, considera-se que há pouca informação sobre o uso atual dessa técnica de filtração para estudos na área. Em vista disso, esse estudo foi realizado com o intuito de fazer um levantamento e diagnóstico do uso da filtração lenta no estado de Santa Catarina. Estações de tratamento de água com filtros lentos foram identificadas e visitadas em todo o estado; os resultados de questionários aplicados in loco e observações em visitas técnicas são apresentados. Embora simples, observou-se que os problemas encontrados na aplicação da tecnologia estão relacionados à falta de conhecimento específico sobre o assunto. Concluiu-se que a filtração lenta ainda é aplicada no estado e a disseminação de conhecimento sobre a tecnologia é de suma importância para sua preservação, manutenção, melhor aplicação e disseminação em prol de seu uso. Palavras-chave: Abastecimento público. Filtro lento. Operação de ETA.
Abstract
Slow sand filtration is a simple technique for drinking water treatment and one of the oldest used for drinking water assessment. Over time, it lost its place for systems with coagulation and rapid filtration that demand smaller area prints relatively. Little information about the current application of this technology is found in studies in this field. This study was performed with the intention of making a survey and diagnosis of the use of slow sand filtration in
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