Abstract

The Kanchan Arsenic Filter (KAF) is an intermittent, point-of-use, affordable drinking water technology for the removal arsenic from groundwater. Performance of KAFs in Nepal has been variable, with high removal in some settings and low removal in others. This study consisting of two parts (laboratory and field research) was conducted to improve the perfomance of the KAFs.In the laboratory research, four different synthetic groundwaters spiked with arsenic were fed to the filters once a day for 35 days to evaluate the effect of water components on corrosion of iron nails and of arsenic removal in downscaled KAFs. Composition of water samples collected from those filters was analyzed using UV-Vis spectroscopy, Flame - atomic absorption spectrophotometry (F-AAS), and inductively coupled plasma mass spectrometry (ICP-MS). Morphology of iron nail surface was done by scanning electron microscopy – energy dispersive spectroscopy (SEM-EDS), followed by a characterization of iron rust powder using X-ray powder diffraction (XRD). Colloids of iron corrosion products were analyzed using transmission electron microscopy (TEM) for their phase, images and structure. Batch tests were conducted to examine iron corrosion rates of iron nails in the presence of 2,2-bipyridine under different testing conditions. The field research in Nepal containing water quality assessments, filter checks, and household interviews was carried out to explore potential factors causing a bias and inadequate filter performance.
Results from the lab research showed remarkable impacts of water conditions on iron corrosion and arsenic removal by the KAFs, with the strong enhancing effect of hardness surpassing the inhibiting effect of phosphate. Filters running hardness-rich water (200 mg/L Ca) removed arsenic (initial concentration of 2000 µg/L) to under the limit of Nepali water standard (50 µg/L) while filters running low hardness water (40 mg/L Ca) removed much less arsenic, especially in the presence of phosphate. On average, 35.7 to 47.9% of arsenic was removed after contacting with iron nails while total arsenic removal was 85.2 to 99.5% over the duration of this study.
The field research revealed that inconsistencies in performance of the full-scale KAFs were mostly resulting from variations of groundwater quality, improper methods of maintenance and operation of the filter users and unfavorable water conditions. A change in nail type showed a moderate difference on filter performance. Addition of embedded nails in filter media significantly facilitated arsenic removal and is a promising solution for enhancing the KAF performance.