User acceptance: the key to evaluating SODIS and other methods for household water treatment and safe storage

Household water treatment has been identified as one effective strategy to interrupt transmission routes of diarrhoea causing pathogens, and thus to mitigate the global burden of waterborne diseases. And yet, the commitment of governments and international organizations to integrate household water treatment and safe storage (HWTS) into their water supply, sanitation, and hygiene promotion programmes remains limited. More efforts are required to scale up the initial successes in the promotion of HWTS methods, and to achieve sustainable application at user level. This article illustrates the experience with the promotion of one particular HWTS approach solar water disinfection (SODIS) as an input to the debate on effectiveness, user acceptance, and integrated planning in the context of HWTS approaches

User acceptance: the key to evaluating SODIS and other methods for household water treatment and safe storage

Household water treatment has been identified as one effective strategy to interrupt transmission routes of diarrhoea causing pathogens, and thus to mitigate the global burden of waterborne diseases. And yet, the commitment of governments and international organizations to integrate household water treatment and safe storage (HWTS) into their water supply, sanitation, and hygiene promotion programmes remains limited. More efforts are required to scale up the initial successes in the promotion of HWTS methods, and to achieve sustainable application at user level. This article illustrates the experience with the promotion of one particular HWTS approach solar water disinfection (SODIS) as an input to the debate on effectiveness, user acceptance, and integrated planning in the context of HWTS approaches

Arsenic Removal from Groundwater by Household Sand Filters: Comparative Field Study, Model Calculations, and Health Benefits

Arsenic removal efficiencies of 43 household sand filters were studied in rural areas of the Red River Delta in Vietnam. Simultaneously, raw groundwater from the same households and additional 31 tubewells was sampled to investigate arsenic coprecipitation with hydrous ferric iron from solution, i.e., without contact to sand surfaces. From the groundwaters containing 10−382 μg/L As, <0.1−48 mg/L Fe, <0.01−3.7 mg/L P, and 0.05−3.3 mg/L Mn, similar average removal rates of 80% and 76% were found for the sand filter and coprecipitation experiments, respectively. The filtering process requires only a few minutes. Removal efficiencies of Fe, phosphate, and Mn were >99%, 90%, and 71%, respectively. The concentration of dissolved iron in groundwater was the decisive factor for the removal of arsenic. Residual arsenic levels below 50 μg/L were achieved by 90% of the studied sand filters, and 40% were even below 10 μg/L. Fe/As ratios of ≥50 or ≥250 were required to ensure arsenic removal to levels below 50 or 10 μg/L, respectively. Phosphate concentrations >2.5 mg P/L slightly hampered the sand filter and coprecipitation efficiencies. Interestingly, the overall arsenic elimination was higher than predicted from model calculations based on sorption constants determined from coprecipitation experiments with artificial groundwater. This observation is assumed to result from As(III) oxidation involving Mn, microorganisms, and possibly dissolved organic matter present in the natural groundwaters. Clear evidence of lowered arsenic burden for people consuming sand-filtered water is demonstrated from hair analyses. The investigated sand filters proved to operate fast and robust for a broad range of groundwater composition and are thus also a viable option for mitigation in other arsenic affected regions. An estimation conducted for Bangladesh indicates that a median residual level of 25 μg/L arsenic could be reached in 84% of the polluted groundwater. The easily observable removal of iron from the pumped water makes the effect of a sand filter immediately recognizable even to people who are not aware of the arsenic problem

Arsenic Removal from Groundwater by Household Sand Filters: Comparative Field Study, Model Calculations, and Health Benefits

Arsenic removal efficiencies of 43 household sand filters were studied in rural areas of the Red River Delta in Vietnam. Simultaneously, raw groundwater from the same households and additional 31 tubewells was sampled to investigate arsenic coprecipitation with hydrous ferric iron from solution, i.e., without contact to sand surfaces. From the groundwaters containing 10−382 μg/L As, <0.1−48 mg/L Fe, <0.01−3.7 mg/L P, and 0.05−3.3 mg/L Mn, similar average removal rates of 80% and 76% were found for the sand filter and coprecipitation experiments, respectively. The filtering process requires only a few minutes. Removal efficiencies of Fe, phosphate, and Mn were >99%, 90%, and 71%, respectively. The concentration of dissolved iron in groundwater was the decisive factor for the removal of arsenic. Residual arsenic levels below 50 μg/L were achieved by 90% of the studied sand filters, and 40% were even below 10 μg/L. Fe/As ratios of ≥50 or ≥250 were required to ensure arsenic removal to levels below 50 or 10 μg/L, respectively. Phosphate concentrations >2.5 mg P/L slightly hampered the sand filter and coprecipitation efficiencies. Interestingly, the overall arsenic elimination was higher than predicted from model calculations based on sorption constants determined from coprecipitation experiments with artificial groundwater. This observation is assumed to result from As(III) oxidation involving Mn, microorganisms, and possibly dissolved organic matter present in the natural groundwaters. Clear evidence of lowered arsenic burden for people consuming sand-filtered water is demonstrated from hair analyses. The investigated sand filters proved to operate fast and robust for a broad range of groundwater composition and are thus also a viable option for mitigation in other arsenic affected regions. An estimation conducted for Bangladesh indicates that a median residual level of 25 μg/L arsenic could be reached in 84% of the polluted groundwater. The easily observable removal of iron from the pumped water makes the effect of a sand filter immediately recognizable even to people who are not aware of the arsenic problem

Mechanisms and Products of Surface-Mediated Reductive Dehalogenation of Carbon Tetrachloride by Fe(II) on Goethite

Natural attenuation processes of chlorinated solvents in soils and groundwaters are increasingly considered as options to manage contaminated sites. Under anoxic conditions, reactions with ferrous iron sorbed at iron(hyro)xides may dominate the overall transformation of carbon tetrachloride (CCl4) and other chlorinated aliphatic hydrocarbons. We investigated mechanisms and product formation of CCl4 reduction by Fe(II) sorbed to goethite, which may lead to completely dehalogenated products or to chloroform (CHCl3), a toxic product which is fairly persistent under anoxic conditions. A simultaneous transfer of two electrons and cleavage of two C−Cl bonds of CCl4 would completely circumvent chloroform production. To distinguish between initial one- or two-bond cleavage, 13C-isotope fractionation of CCl4 was studied for reactions with Fe(II)/goethite (isotopic enrichment factor ε = −26.5‰) and with model systems for one C−Cl bond cleavage and either single-electron transfer (Fe(II) porphyrin, ε = −26.1‰) or partial two-electron transfer (polysulfide, ε = −22.2‰). These ε values differ significantly from calculations for simultaneous cleavage of two C−Cl bonds (ε ≈ −50‰), indicating that only one C−Cl bond is broken in the critical first step of the reaction. At pH 7, reduction of CCl4 by Fe(II)/goethite produced ∼33% CHCl3, 20% carbon monoxide (CO), and up to 40% formate (HCOO-). Addition of 2-propanol-d8 resulted in 33% CDCl3 and only 4% CO, indicating that both products were generated from trichloromethyl radicals (•CCl3), chloroform by reaction with hydrogen radical donors and CO by an alternative pathway likely to involve surface-bound intermediates. Hydrolysis of CO to HCOO- was surface-catalyzed by goethite but was too slow to account for the measured formate concentrations. Chloroform yields slightly increased with pH at constant Fe(II) sorption density, suggesting that pH-dependent surface processes direct product branching ratios. Surface-stabilized intermediates may thus facilitate abiotic mineralization of CCl4, whereas the presence of H radical donors, such as natural organic matter, enhances formation of toxic CHCl3