Optimizing the solar water disinfection (SODIS) method by decreasing turbidity with NaCl

Abstract

Abstract.Solar water disinfection (SODIS) has proven to be effective at reducing diarrheal incidence in epidemiological intervention studies. However, the SODIS method is limited to waters of low turbidity (<30NTU). This study investigates the use of common table salt (NaCl) to reduce the turbidity of water containing suspended colloidal clay particles for use in the SODIS method. Three representative clays found in tropical soils (kaolinite, illite, and bentonite) were tested at three levels of turbidity (50, 100, and 200 NTU) for their flocculating behaviour with multiple NaCl concentrations to find the optimum. Supernatants were tested for sodium concentration for comparison against health and taste thresholds. Results show that unlike kaolinite and illite, pure bentonite solutions were shown to be very responsive to NaCl and produced supernatants with as low as 4 NTU (98% particle removal efficiency). This study has shown that NaCl, in combination with high-activity clay particles in solution, may effectively reduce turbidity to levels suitable for SODIS treatment, thereby expanding the number of people who can utilize the technology effectively.Keywords: clay, drinking water, flocculation, sanitation, SODIS, sodium, turbidity To be published: Brittney Dawney and Joshua M. Pearce, "Optimizing the solar water disinfection (SODIS) method by decreasing turbidity with NaCl",

Evaluating the geographic viability of the solar water disinfection (SODIS) method by decreasing turbidity with NaCl: A case study of South Sudan

“…However, at the household level in developing countries, the high cost of conventional coagulants such as alum and ferric salts, or a lack of availability of natural coagulants such as Moringa Oleifera, often makes coagulation-flocculation an impractical option (Sobsey 2002). The flocculating behavior of different types of clay in aqueous solutions containing NaCl has been explored (Hsi & Clifton 1960;Gibbs 1983Gibbs , 1985Akther et al 2008;Panayiotopoulos et al 2004;Dawney & Pearce 2012). The use of NaCl as a means of reducing turbidity prior to SODIS treatment was examined by Dawney and Pearce (2012), when it was shown that NaCl in combination with sodium bentonite (a high-activity clay) can significantly reduce turbidity to as low as 4 NTU.…”

“…The flocculating behavior of different types of clay in aqueous solutions containing NaCl has been explored (Hsi & Clifton 1960;Gibbs 1983Gibbs , 1985Akther et al 2008;Panayiotopoulos et al 2004;Dawney & Pearce 2012). The use of NaCl as a means of reducing turbidity prior to SODIS treatment was examined by Dawney and Pearce (2012), when it was shown that NaCl in combination with sodium bentonite (a high-activity clay) can significantly reduce turbidity to as low as 4 NTU. In particular, the application of this technology to water that is to be used for hygiene and sanitation purposes shows promise, as the sodium content remaining in the supernatant is not as limiting (Dawney & Pearce, 2012).…”

“…This study investigates the use of table salt (NaCl) in reducing turbidity in water caused by colloidal clay particles common to certain developing rural regions in Africa, India, and South America. The potential use of NaCl to reduce turbidity has been explored and shown to be effective (Dawney & Pearce, 2012), particularly in samples containing a high concentration of high-activity clay. The current study aims to examine this phenomenon further by investigating the effectiveness of NaCl at reducing turbidity in water containing a mixture of high-and low-activity clays, simulating naturally occurring soils of the Vertisol type.…”

Design Optimization of Polymer Heat Exchanger for Automated Household-Scale Solar Water Pasteurizer

“…There have been various methods attempted to provide drinking water in rural areas of undeveloped nations using solar technologies, including: (i) solar desalination; (ii) solar detoxification; and (iii) solar disinfection [7,8]. These methods include the use of basic solar stills [9,10], solar stills with improved output from compound parabolic reflectors [11], phase change material [12], a hemispherical solar still [13], efficient heat exchange mechanisms [14] and an inclined wick solar still [15], and progressively more sophisticated variations of the solar water disinfection (SODIS) method [16], using common chemicals to decrease turbidity to enable SODIS to work [17] and photocatalysts [18]. SODIS is low-cost, simple, and is available for large geographic regions (e.g., from Haiti [19] to South Sudan [20]), but becomes less effective in high-turbidity water, which can be challenging in some communities [16].…”

Purifying Drinking Water with Sun, Salt, and Limes

“…The more turbid solutions of bentonite, which flocculated more easily than the other clays, required less salt (1,000 mg/L) to achieve the same; the greater proximity of the clay particles to one another makes flocculation easier. The more turbid kaolinite and illite suspensions required the addition of a bentonite “jumpstarter” in order to be brought below the SODIS threshold 4 . None of the treated samples in the study had salt concentrations below the taste threshold of 256 mg/L, but several had less residual salt than a typical sports drink.…”