Defluoridation of drinking water and rainwater harvesting using a solar still

Abstract

When people drink water having a fluoride (F^–) concentration >1–1.5 mg/L for a long period of time, various ailments that are collectively referred to as fluorosis occur. Based on the design of Thomas (http://www.planetkerala.org), an inclined basin-type solar still containing sand and water has been used at Bangalore for defluoridation. For water samples having a fluoride concentration in the range 5–20 mg/L, the fluoride concentration in the distillate was usually <1.5 mg/L. During the periods October 2006–May 2007 and October 2007–May 2008, the volume of distillate showed a significant diurnal variation, ranging from 0.3 to 4.0 L/m²·day. Based on the figures for 2006, the cost of the still was about Rs. 850 (US$16) for collector areas in the range 0.50–0.57 m². The occurrence of F^– in the distillate merits further investigation. Overall, the still effectively removes F^–, but a large area of the collector, in the range 2.5–25 m², is needed to produce about 10 L of distilled water for cooking and drinking. Rainwater falling on the upper surface of the still was collected, and its fluoride concentration was found to be below the desirable limit of 1 mg/L. Hence it can also be used for cooking and drinking.