Household slow sand filters with and without water level control: continuous and intermittent flow efficiencies

ABSTRACT

Four household slow sand filters were made out of PVC and operated in continuous and intermittent flows, with and without using a float to control the maximum level of water inside the units. The efficiency was evaluated as a function of Escherichia coli reduction and turbidity in water from the study prepared with kaolinite and E. coli suspension. The correlation of the efficiencies with the following operational parameters was evaluated: operating time, time after maintenance, filtration rate and head loss divided by bed thickness. The filters were classified as intermittent with float (IFF), intermittent without float (IF), continuous with float (CFF) and continuous without float (CF). IFF, CFF and CF had a non-woven blanket installed on top of the media. The results indicated that no significant statistical differences were found in E. coli reduction and turbidity between IFF and IF, however the former had filter runs over 80 days and the latter almost a quarter of this value. CFF matured faster and had less turbidity remaining in relation to CF. When comparing IFF with CFF, the former presented lower turbidity remaining (0.89 ± 0.44 NTU versus 1.24 ± 0.91NTU), but a lower reduction of E. coli (1.40 ± 0.61 log versus 2.29 ± 0.74 log). The time after maintenance was the most important operational parameter when evaluating the efficiencies. The float helped to mature the filter more quickly in a continuous flow and, together with a non-woven blanket, extended the filter runs in the intermittent flow.

GRAPHICAL ABSTRACT

KEYWORDS:

• Biosand filter
• drinking water
• Escherichia coli
• point-of-use treatment
• turbidity

Acknowledgements

The authors would like to thank the São Paulo Research Foundation (FAPESP - Brazil), Process n° 2014/12712-8 and the National Council for Scientific and Technological Development (CNPq), Process 442163/2014-2 for the funding; and CNPq for the doctoral scholarship granted to Paulo Marcos Faria Maciel.

Disclosure statement

No potential conflict of interest was reported by the authors.

ORCID

Paulo Marcos Faria Maciel http://orcid.org/0000-0002-1864-3149

Lyda Patricia Sabogal-Paz http://orcid.org/0000-0003-2753-3248

Additional information

Funding

This work was supported by the Fundação de Amparo à Pesquisa do Estado de São Paulo under Grant Process 2014/12712-8; by the Conselho Nacional de Desenvolvimento Científico e Tecnológico under Grant Process 442163/2014-2 and by CNPq for the PhD scholarship awarded to Paulo Marcos Faria Maciel.