Efficiency of Declining Head Sand Filters for Household Level Water Purification

Abstract

Installation of conventional water treatment processes in the rural and suburban areas of developing countries is, at present, impractical due to economic reasons and the settlement characteristics of the population. Small-scale water treatment processes seem to be the most suitable methods to provide relatively clean water for those who draw their water supplies from unprotected streams, wells and ponds. In this study, a household sand filter has been designed that can be made from locally available materials, and that can be operated and maintained by the householder. The unit is designed to work at declining rate taking into account economic factors and the intermittent trend of collecting water in rural areas. The filter unit has a capacity sufficient to treat the quantity of water required for a typical household of 7 per uns at 15 litres per person per day. The cost of materials and labor required for a sing' tank is Eth. Birr 215 but mass production results in a considerable cost offset. The filter produces effluent that satisfies the World Health Organization (WHO) recommendations for turbidity, color, odor, taste, pH and total dissolved solids (TDS). It is also capable of removing most of the bacterial load, thus reducing the probability of contracting water-borne diseases. It can treat raw water turbidity of 100 Nephelometric Turbidity Unit (NTU) for three weeks without losing its capacity and efficiency but for higher turbidities, simple pretreatment methods are recommended.