Factors affecting the operation and maintenance of biosand filters for rainwater treatment in developing countries

Waterborne diseases kill more than 2 million people, mostly children, around the world annually. More than a billion people worldwide do not have access to improved, safe water. Two simple inexpensive solutions to provide clean water are the use of biosand filters for water treatment, and using rainwater instead of river water as the water supply. Combining the two technologies of using rainwater supply and using biosand filters can produce high quality water.; The objectives of the research are to identify and quantify the factors affecting the performance of biological sand filters for surface water and rainwater treatment in the Amazon region. This will allow engineers to know the best possible sand depth and flow rate for a biological sand filter. The primary objective of this research is to identify the optimum sand depth for removal. To obtain this objective percent removal of total and fecal coliforms and total solids at ten, twenty, and thirty inches of sand were determined.; Some initial studies of biosand filters at the University of Arkansas indicated that adequate filtration for drinking water was not possible at some sand depths. These initial studies were done in filters built in 5 gallon buckets, and 55 gallon drums. The five gallon prototypes removed some solids, but reduction of fecal or total coliforms was not significant. The likely causes for this failure are insufficient sand depth and/or insufficient residence time; therefore more depth than 3-5 inches of sand is needed to remove these organisms. Then, 55-Gallon Drum Prototypes were built, but this system also had its faults. Because of the temperature variance during the fall and early winter the microorganisms were not performing as well as they would in warmer climates. In the rainforest this will not be a problem, because according to literature the microorganisms function well from 1°C--45°C, or 33.8°F--113°F, with higher efficiency at higher temperatures. At night in Fayetteville, the temperature was dropping below 32°C causing stress to the microorganisms.; In order to evaluate the effect of filter depth in constant temperature conditions and because we were unsure what adequate height of sand we needed from the first experiment, a filter was built so that sand height would be the variable, and the temperature would remain constant inside one of the Environmental Engineering Labs in the basement of Bell Engineering Center.; The results of this study show that a 20 inch sand depth is adequate, but the 30 inch sand bed performed slightly better. However the 30 inch sand depth had less of a head than the other depths when the water was fed at a constant rate, and thus will require less maintenance.