No abstract

The size distribution, band gap energy, and photoluminescence of silicon nanocrystals embedded in SiO2 have been measured by direct and independent methods. The size distribution is measured by coupling high-resolution and conventional electron microscopy in special imaging conditions. The band gap is calculated from photoluminescence excitation measurements and agrees with theoretical predictions. Their correlation allows us to report the experimental Stokes shift between absorption and emission, which is 0.26±0.03 eV, independent of average size. This is almost exactly twice the energy of the Si–O vibration (0.134 eV). These results suggest that the dominant emission is a fundamental transition spatially located at the Si–SiO2 interface with the assistance of a local Si–O vibration.

Abstract. Epidemiologic investigations of the Latin America cholera epidemic have repeatedly implicated untreated drinking water and water touched by hands during storage as important vehicles for disease transmission. To prevent such transmission, we provided a new narrow-mouthed, plastic, water storage vessel and 5% calcium hypochlorite solution for home disinfection of stored water to a Bolivian Aymara Indian community at risk for cholera. We evaluated acceptance of this intervention and its effect on water quality. Each of 42 families in the study obtained water from a household well; fecal coliform bacteria were found in water from 39 (93%) of 42 wells and 33 (79%) of 42 usual water storage vessels. One group of families received the special vessels and chlorine (group A), a second received only the special vessels (group B), and a third served as a control group (group C). Water samples collected every three weeks from group A special vessels had lower geometric mean fecal coliform colony counts (P < 0.0001) and lower geometric mean Escherichia coil colony counts (P < 0.0001) than water from group B or C vessels. Adequate levels of free chlorine persisted in these vessels for at least 5 hr. The special vessels and chlorine solution were well accepted and continued to be used for at least six months. Use of the vessel and chlorine solution produced drinking water from nonpotable sources that met World Health Organization standards for microbiologic quality.

No abstract

No abstract

No abstract

No abstract

The presence of thousands of microcontaminants in wastewaters and their potential risks has drawn a large attention of the scientific community during the last years. The presence of these contaminants is especially controversial when wastewater is considered for reuse because a large number of microcontaminants are frequently not totally removed by conventional wastewater treatment processes. As a contribution to the knowledge in this field, this chapter focuses on the application of four well-known and widely used technologies to the elimination of microcontaminants. Membranes, activated carbon, ozonation, and advanced oxidation processes (AOPs) are deeply reviewed to assess their efficiency and safety in the elimination of these contaminants from wastewater effluents. A brief description of each technology is presented together with a review of their real application, mostly in wastewater treatment plants (WWTPs). A deep analysis of the found data allows to conclude that the four presented alternatives can be useful for microcontaminant mitigation although none of them seem to be a universal barrier for microcontaminants when used separately. In addition, each technology presents drawbacks which demand further research to be overcome. Depending on the final use of reclaimed water, the treatment may require the combination of several of the studied technologies although that results in an economic impact which cannot be neglected.