Results of the First Improvement Step Regarding Removal Efficiency of Kanchan Arsenic Filters in the Lowlands of Nepal—A Case Study

Abstract

In Nepal as well as in other countries in Southeast Asia, the World Health Organization drinking water guideline of 10 µg/L concerning arsenic concentrations in ground water hosted in Quaternary alluvial sediments is often regionally exceeded. The commonly accepted theories include that arsenic in ground water stems from reductive dissolution of As-rich Fe(III)hydr(oxides) including microbial degradation of sedimentary organic matter. On the contrary, the influence of clay minerals in the sediments as hosts for As was clearly underestimated, as geochemical analysis depicted that As was generally associated with specific elements such as Na, K, Al, and Li. Moreover, there was a very weak correlation or decoupling between As and Fe in the ground water in Nepal, and this fact points to consequences for water treatment. The so-called Kanchan filters, used for the removal of As, installed in the lowlands of Nepal often exhibited effluent As concentrations well above Nepal’s drinking water quality standard value (i.e., 50 μg/L). Ground water concentrations of Fe and As proved to be the most important geochemical factors regarding the performance of the filters. Moreover, the flow rate as well as the contact time to the rusty nails in the filter, intended to adsorb As on their surface, influenced the removal efficiency. The removal rate was severely influenced by the handling of the filters, too. This short communication provides an overview of the removal efficiency of 30 filters, their drawbacks, the influence of the aging material in the filters as well as measures of improvements to enhance the efficiency of the filters. Proper instruction for users of Kanchan filters is a major point that needs to be addressed in the future.