Abstract
Abstract. Bio-sand filters (BSFs) are point-of-use (POU) potable water filtration systems commonly used in low-income communities at household level. The principle of operation is similar to that of a slow sand filter and the major difference is that they are operated intermittently at the POU. It is one of the emerging low-cost technologies which makes use of readily and locally available construction materials but is poor in the removal of nitrates. In order to enhance the removal of nitrates through denitrification, a modified BSF with ethanol as an external carbon source at C / N ratios of 1.1 and 1.8 was investigated. In the absence of an external carbon source, the nitrate removal efficiency was 32 %, whilst removal efficiencies at C / N ratios of 1.1 and 1.8 were 44 and 53 % respectively. The inflow rate reduced significantly from an initial flow rate of 0.04 to 0.01 m3 h−1. The reduction in the inflow rate was mainly due to the growth of the biological layer on the filter media. The study showed that the use of an external carbon source like ethanol in bio-sand filtration enhances the removal of nitrates in potable water.
Highlights
Bios-sand filters (BSFs) are intermittent slow sand filters designed for household use and called point-of-use (POU) water filtration systems, with principal filtration mechanisms being physical, chemical and biological (Murphy et al, 2010)
BSFs are widely applied in the treatment of water at household level, few studies have been conducted on the removal of chemical contaminants
These two ratios were selected based on the optimum range of carbonto-nitrogen ratio which was established by Aslan and Cakici (2007), Gomez et al (2000) and Callado (2001) for denitrification in slow sand filtration, which ranged from 1.08 to 2.5
Summary
Bios-sand filters (BSFs) are intermittent slow sand filters designed for household use and called point-of-use (POU) water filtration systems, with principal filtration mechanisms being physical, chemical and biological (Murphy et al, 2010). BSFs are widely applied in the treatment of water at household level, few studies have been conducted on the removal of chemical contaminants. One chemical of major concern is nitrate-nitrogen contamination (NO3-N) on surface and ground water as it poses serious health problems (Almasiri and Kaluarachchi, 2007). Presence of nitrates in drinking water results in the formation of nitrosomines in the stomach, which are carcinogenic (Shuval and Gruener, 1977; Aslan and Cakici, 2007; Speijers and Fawell, 2011). Nitrate poisoning has been reported in livestock when concentrations exceeded 100 mg L−1 (Tredoux et al, 2000) and other problems related to nitrate in drinking water are well documented in the literature (Moraes, 1996; Fan and Steinberg, 1996; Lin et al, 2002; Forman, 2004)
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