Unique Geochemistry of Arsenic-Contaminated Groundwater and Corresponding Mitigation Efforts in Southern Nepal

Abstract

In the lowlands of Nepal, as well as in several other South Asian countries, the level of arsenic in groundwater extracted from Quaternary alluvial sediments frequently exceeds the World Health Organization (WHO) drinking water guideline of 10 μg/L. The widely accepted explanation refers to the reductive dissolution of Fe-bearing minerals releasing As-oxyanions from the soil minerals. However, this hypothesis is only to some extent applicable. Given that arsenic and iron in the groundwater are weakly correlated or decoupled and iron(III) (hydr)oxides are scarcely present, a substantial portion of As and Fe has to be retained in clay minerals. The low concentration of iron in groundwater can be explained by the origin of As and Fe in the rocks (leucogranites); in the High Himalayas, they are low in Fe but considerably enriched in Li, B, As, Se, Br, Sr, Mo, Cd, P, and U. This unique geochemical setting has a major impact on the performance of the Kanchan Arsenic Filters (KAFs) used to eliminate As from groundwater in Nepal. Lack of sufficient Fe in groundwater, combined with limited release of iron by corrosion of iron nails, call for an adapted version of these filters. The first results from 20 modified filters show a clear increase in As removal efficiency, achieved mainly by the replacement of old nails, an added upper sand layer over the nails, and elongation of the outlet tube to avoid wet–dry cycles and to keep the nail bed immersed. Proper instructions to the users on the operation and maintenance of filters, by replacing the reactive materials (iron nails) and the lower sand bed regularly, are imperative.

A Simplified and Affordable Arsenic Filter to Prevent Arsenic Poisoning: Lab-Scale Study and Pilot Experiment

“…The finding of the study confirmed the negligible impact of Cl − , SO 4 2− , and NO 3 − on the arsenic adsorption process at both low and high concentrations. The presence of HCO 3 − and PO 4 3− has negligible interference when present at low concentration (<1 mg L −1 ); however, it affects the removal efficiency at high concentrations (at 10 mg L −1 of phosphate and 500 mg L −1 of bicarbonate).…”

“…Arsenic contamination of groundwater is undoubtedly one of the detrimental global issues that mankind is suffering from. Since its first report in the early 1980s, more than 150 million people worldwide have been reported to be exposed, and the spread of arsenic contamination in groundwater has continued to grow with every new survey. , Considering the serious health risks associated with chronic consumption of arsenic-contaminated water, such as hypertension, keratosis, and skin and bladder cancer, − the development of a robust arsenic removal technology is of a pressing need.…”

Influence of Water Salinity on the Efficiency of Fe0-Based Systems for Water Treatment

“…Despite a growing interest in the applications of Fe 0 for environmental remediation [14,22,23] and safe drinking water supply [87][88][89][90], little progress has been made in characterizing the variability in reactivity among Fe 0 samples from different sources [19,34,86,91,92]. The most important lesson from Figure 5 is that the extent to which saltwater affects the performance of a Fe 0 /H 2 O system depends on the used Fe 0 source used (Fe 0 quality).…”

Effects of solid additives and inorganic ligands on the efficiency of metallic iron- based water treatment system

“…While this difference is difficult to justify, the overall results reaffirm the importance of characterizing the diversity among the Fe 0 materials of environmental interest (Miehr et al 2004. Despite a growing interest in the applications of Fe 0 for environmental remediation (Guan et al 2015, Plessl et al 2022, Singh et al 2023) and safe drinking water supply (Tepong-Tsindé et al 2019, Tepong-Tsindé 2021, Mueller et al 2023, little progress has been made in characterizing the variability in reactivity among Fe 0 samples from different sources , Ranjan et al 2006, Naseri et al 2017. The most important lesson from Figure 5.5 is that the extent to which saltwater affects the performance of a Fe 0 /H2O system depends on the used Fe 0 source used (Fe 0 quality).…”

“…Currently, Fe 0 -based filtration is also considered to be one of the most affordable and applicable technologies for decentralized safe drinking water supply (Naseri et al 2017, Noubactep 2018a, Mueller et al 2023, Bandyopadhyay 2024. In other words, the Fe 0 technology can significantly contribute to achieving the two United Nations (UN) Sustainable Development Goals (SDGs) focusing explicitly on freshwater: (i) Goal 6 "Ensure availability and sustainable management of water and sanitation for all", and (ii) Goal 14 "Conserve and sustainably use the oceans, seas and marine resources for sustainable development" (Hering et al 2016).…”