Technical and social performances of an arsenic-removal technology—the sono arsenic filter—in rural areas of Bangladesh were investigated. Results of arsenic field-test showed that filtered water met the Bangladesh standard (<50 µg/L) after two years of continuous use. A questionnaire was administrated among 198 sono arsenic filter-user and 230 non-user families. Seventy-two percent of filters (n=198) were working at the time of the survey. Another 28% of the filters were abandoned due to breakage. The abandonment percentage (28%) was lower than other mitigation options currently implemented in Bangladesh. Households were reluctant to repair the broken filters on their own. High cost, problems with maintenance of filters, weak sludge-disposal guidance, and slow flow rate were the other demerits of the filter. These results indicate that the implementation approaches of the sono arsenic filter suffered from lack of ownership and long-term sustainability. Continuous use of arsenic-contaminated tubewells by the non-user households demonstrated the lack of alternative water supply in the survey area. Willingness of households to pay (about 30%) and preference of household filter (50%) suggest the need to develop a low-cost household arsenic filter. Development of community-based organization would be also necessary to implement a long-term, sustainable plan for household-based technology.

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The structure of water adjacent to silica is sensitive to the degree of deprotonation of surface silanol groups. As a result, close inspection of signals originating from these water molecules can be used to reveal the surface charge density. We have used nonlinear vibrational spectroscopy of the water O–H stretching band over a temperature range of 10–75 °C to account for the increase in surface potential from deprotonation. We demonstrate that the behavior at the silica surface is a balance between increasing surface charge and a decreasing contribution of water molecules aligned by the surface charge. Together with a model that accounts for two different types of silanol sites, we use our data to report the changes in enthalpy and entropy for deprotonation at each site. This is the first experimental determination of these thermodynamic parameters for hydrated silanol groups at the silica surface, critical to a wide range of geochemical and technological applications.

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The study of interfacial properties of thin films such as polymers is an important area of surface science. The application of visible-infrared sum-frequency generation spectroscopy to such systems requires a careful interpretation of the results, as the electric field magnitude and phase at each interface must be determined in a manner that takes thin film interference effects into account. Several schemes have been proposed for handling the local field corrections, and these methods all have their origins in linear optics. We first provide an extensive discussion of the cases in which the film is sufficiently thick that multiple beam interference can be ignored, or sufficiently thin in which the relevant expressions collapse to simple forms. Then we illustrate a straightforward method that has a concise analytic solution in the case of a single thin film that exhibits interference effects. We demonstrate a visualization technique that allows the experimental geometry to be tuned to select the interface of interest, and rapidly switch between the interfaces when the film thickness is chosen to accommodate this.