Improved Solar Still for Water Purification

According to the 2010 Malawi Demographic and Health Survey (MDHS), about 65% of households in Malawi do not have access to treated water. Distillation is one technique used for treating water. Many distillation methods are available but they are either energy intensive or contribute to environmental degradation due to their nature. However, solar energy can be used as an alternative source of energy for water distillation. There are many designs of solar distillation systems but the most-widely used one is the conventional still. Internal surfaces of the walls of the conventional solar still (CSS) are commonly painted black to avert condensation of water vapor on the walls. However, the CSS suffers from low production of distilled water and there is, therefore, a need to improve its performance. In this study, two conventional stills were designed with an identical geometry but the internal surfaces of their walls were painted white. These solar stills were tested outdoors under the same meteorological conditions at the Malawi Polytechnic (15° 42' S, 35°02' E). Distillate output was measured during experimentation. It was found that the average daily distillate outputs were 2.55 kgm-2 and 2.38 kgm-2 for the experimental still and CSS respectively. In addition, the efficiency of the experimental solar still was 6.8% more than that of the CSS. It can therefore be concluded that painting the internal surfaces of the walls of the still white improves the distillate output of the still.