High Iron and Manganese in Groundwater of Brahmaputra River Plains: concerns for drinking water quality and remediation

Apart from the health risks associated with the consumption of contaminated water, the suitability of water, based on its visual appeal, taste, and odor, is a matter of paramount importance. Elevated levels of Iron (Fe) and Manganese (Mn) lead to the discoloration of sanitary wares and laundry, besides resulting in deposits within distribution systems and contributing to an undesirable taste in drinking water. The mobilization of Fe and Mn in groundwater is predominantly governed by redox processes. In this study, we conducted an analysis of shallow groundwater (n=145) in the Brahmaputra River Plains (BRP), India, which shows that 85 percent (n=123) and 80 percent (n=116) of the groundwater exceed the WHO acceptable limit of Fe (0.3 mg/L) and Mn (0.1 mg/L), respectively. The highest concentration of Iron (II) is 7 mg/L with a median value of 3 mg/L (n=35). However, they are heterogeneously distributed among the Piedmont deposits, Older Alluviums, and Younger Alluviums. Spearman’s correlation shows that total Fe has a strong correlation (0.89) with Fe (II), and a comparison between them reveals that Fe (II) is the dominant species. The reducing nature of the groundwater with low dissolved oxygen and a high dissolved organic carbon suggests reductive dissolution of Fe and Mn oxyhydroxides as a possible mechanism of Fe and Mn release in the groundwater. Therefore, there is a need to mitigate the high Fe and Mn levels in the groundwater-sourced drinking water to avoid health and suitability concerns. Treatment facilities, including the use of iron-removal sand filters and aeration, have been installed across the region to mitigate the problem. Investigation of Fe (II) concentrations in the treated household-supplied water shows a considerable decrease in the Fe (II). Implementing effective mitigation measures, such as the use of iron-removal filters, is crucial to ensure the provision of safe drinking water.