Evaluation of the KanchanTM Arsenic Filter under various water quality conditions of the Nawalparasi District, Nepal

Abstract

In 2002, the Massachusetts Institute of Technology Department of Civil and Environmental Engineering partnered with the Environment and Public Health Organization to develop and disseminate the KanchanTM Arsenic Filter (KAF) for the low-cost removal of arsenic from drinking water in rural Nepal. In this system, arsenic is removed via absorption onto the surface of ferric hydroxide, or rust, through the integration of locally available iron nails into a BioSand Filter setup. Since 2002, the KAF filter has been successfully disseminated in approximately 24,000 Nepali households. However, recent studies have indicated that under certain raw water conditions, the KAF may inadequately reduce groundwater arsenic concentrations to levels below the Nepali government guideline of 50 ptg/L. The present study focused on identifying and determining the impact of raw water parameters on the arsenic removal efficiency of the KAF. These parameters included arsenic, ferrous iron, dissolved oxygen, silica, phosphorous, pH, hardness, chloride, manganese, and electrical conductivity concentrations. In addition, filter flow rate, installation date, location, and user survey results were recorded. A total of 100 filters, of ages from less than one year to seven years, from 79 groundwater sources and 15 villages - primarily in the Nawalparasi District - were tested. Data showed that poorly performing KAFs resulted from groundwater conditions that did not promote the corrosion of the iron nails. These conditions included low groundwater ferrous iron levels (<3mg/L), low ferrous iron levels after water had passed though the nails (<1.1 mg/L), low chloride concentrations (<7 mg/L), and low hardness concentrations (<350 mg/L of CaCO3). In order for the filter to be promoted in areas with various groundwater conditions, it is recommended that future studies explore the incorporation of local components into the KAF system to increase iron corrosion.