Filter media depth and its effect on the efficiency of Household Slow Sand Filter in continuous flow

• Published in: Journal of environmental management Vol. 288; p. 112412
• Main Authors: Freitas, Bárbara Luíza Souza, Terin, Ulisses Costa, Fava, Natália de Melo Nasser, Sabogal-Paz, Lyda Patricia
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 15-06-2021
• Subjects: Biosand filter; Decentralized treatment; Drinking water; Escherichia coli; Family Characteristics; Filtration; Fine sand; River water; Sand; Silicon Dioxide; Water Purification; Drinking water; Biosand filter; T-HSSF; C-HSSF; Decentralized treatment; Fine sand; HWTS; River water; HSSF
• ISSN: 0301-4797; 1095-8630
• DOI: 10.1016/j.jenvman.2021.112412

This study evaluated the impact of a 50% reduction of filter media depth in Household Slow Sand Filters (HSSFs) on continuous flow to remove physicochemical and microbiological parameters from river water. Furthermore, simple pre-treatment and disinfection processes were evaluated as additional treatments. Two filter models with different filtration layer depths were evaluated: a traditional one with 50 cm media depth (T-HSSF) and a compact one (C-HSSF) with 25 cm. HSSFs were fed with pre-treated river water (24-h water sedimentation followed by synthetic fabric filtration) for 436 days at a constant filtration rate of 0.90 m3 m−2 day−1 with a daily production of 48 L day−1. Sodium hypochlorite (2.0 mg L−1 of NaOCl 2.5% for 30 min) was used to disinfect the filtered water. Water samples were analysed weekly for parameters such as turbidity, organic matter, colour and E. coli, among others. Removal of protozoan cysts and oocysts by the HSSFs were also evaluated. After pretreatment, turbidity from the HSSF river water was reduced to 13.2 ± 14.6 NTU, allowing the filters to operate. Statistical analysis indicated no significant difference (p > 0.05) between T-HSSF and C-HSSF efficiencies in all evaluated parameters throughout operation time. Hence, media depth reduction did not hinder continuous HSSF performance for almost all the evaluated parameters. However, it may have affected Giardia cysts retaining, which passed through the thinner media on one evaluation day. Disinfection was effective in reducing remaining bacteria from filtered water; however, it was ineffective to inactivate protozoa. The reduction in the filtration layer did not affect the overall filtered water quality or quantity showing that a compact HSSF model may be a viable option for decentralized water treatment.
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•Reduced filter media depth did not affect HSSF efficiency.•Pre-treatment was effective to reduce river water turbidity.•HSSFs removed >87% of turbidity and reduced >2.97 log of E. coli.•HSSFs reduced >2.82 log of Giardia cyst and >1.13 log of Cryptosporidium oocyst.•Disinfection was effective in reducing bacteria and ineffective for protozoa.