Turbidity and chlorine demand reduction using locally available physical water clarification mechanisms before household chlorination in developing countries

Abstract

Over 1.1 billion people in the world lack access to improved drinking water. Diarrhoeal and other waterborne diseases cause an estimated 1.9 million deaths per year. The Safe Water System (SWS) is a proven household water treatment intervention that reduces diarrhoeal disease incidence among users in developing countries. Turbid waters pose a particular challenge to implementation of SWS programmes; although research shows that a 3.75 mg l 21 sodium hypochlorite dose effectively treats turbid waters, users sometimes object to the strong chlorine taste and prefer to drink water that is more aesthetically pleasing. This study investigated the efficacy of three locally available water clarification mechanisms-cloth filtration, settling/decanting and sand filtration-to reduce turbidity and chlorine demand at turbidities of 10, 30, 70, 100 and 300 NTU. All three mechanisms reduced turbidity (cloth filtration 21-60%, settling/decanting 78-88% and sand filtration 57-99%). Sand filtration ( P ¼ 0.002) and settling/decanting ( P ¼ 0.004), but not cloth filtration ( P ¼ 0.30), were effective at reducing chlorine demand compared with controls. Recommendations for implementing organizations based on these results are discussed.

Turbidity and chlorine demand reduction using alum and moringa flocculation before household chlorination in developing countries

“…However, other investigations have documented greater efficacy of settling and decanting alone as a pretreatment mechanism that significantly reduces turbidity and chlorine demand (Kotlarz et al 2009). The difference between the two studies is that water was settled for 24 hours in the settling and decanting efficacy study, while settling occurred for only 2 hours in this study.…”

Disinfection By-Product Formation and Mitigation Strategies in Point-of-Use Chlorination with Sodium Dichloroisocyanurate in Tanzania

“…Previous laboratory research investigating the turbidity and chlorine demand reduction of cloth filtration, sand filtration, and settling and decanting in 10-300 NTU waters found all three locally available physical filtration mechanisms were effective in reducing turbidity. 32 However, cloth filtration did not reduce turbidity at 10 NTU, but reduced turbidity more effectively as initial turbidity increased to 300 NTU. The cloth filtration turbidity reduction results are consistent with results presented herein, with no turbidity reduction seen in lowturbidity (< 20 NTU) sources.…”

“…Further research on locally available mechanisms to reduce chlorine demand and turbidity is not indicated in the laboratory setting because this research has already been well established in the literature. 32,33 Targeted research in specific locations where household chlorination is promoted with known high concentrations of THM precursors, such as bromine, is indicated. Bromine presence increases the health risks associated with THMs, as brominated THMs, with higher risk and therefore lower guideline values than chloroform, are formed.…”

Residual Maintenance Using Sodium Hypochlorite, Sodium Dichloroisocyanurate, and Chlorine Dioxide in Laboratory Waters of Varying Turbidity

“…To represent various turbidity types seen in surface water used for drinking in low-resource settings, reactors were spiked with laboratory-grade white kaolin clay (Lion China Clay USP, Charles B. Chrystal Co., Larchmont, NY, US) or creek bottom sediments collected from the Mystic River (Medford, MA, US). The 0, 10, 30, 100, and 300 NTU targets were set to be consistent with previous research and with chlorine dose breakpoints [16,32,33]. Pre-testing was conducted to determine the amount of clay/sediments required to obtain turbidity targets in reactors using a calibrated Hach 2100 portable turbidimeter (Loveland, CO, US).…”