Performance Monitoring of Indigenous Household Groundwater Filter for Iron and Fluoride Removal: A Case Study from Assam, India

Abstract

Groundwater in the north-eastern part of India contains high levels of iron and fluoride. However, due to lack of piped water supply, the rural people in Assam rely on groundwater for meeting their daily water needs. The groundwater is treated using different types of indigenous household groundwater filter units for removal of iron. IHGF units are fabricated based upon past experiences using layers of sand, gravel and sometimes wooden charcoal enclosed within a hollow reinforced cement concrete ring, tin container and plastic bucket. An attempt has been made to assess the levels of iron and fluoride in the groundwater of Amingaon—a selected rural locality for the study, the effectiveness of an IHGF unit in removal of iron and fluoride from the groundwater and suggestions for improving the service life of the unit. During the field survey in the area, groundwater samples collected from ten locations indicate Fe²⁺ and F⁻ concentrations in the range of 0.0–11.3 mg/L and 0.1–0.7 mg/L, respectively. Monitoring of an IHGF unit over a period of 170 days indicates almost Fe²⁺ free water with F⁻ removal of 30–40%. Upon continuous use, filter media of the IHGF unit get clogged leading to lower filtration rate requiring dismantling, cleaning of media and refabrication of the unit every 2–3 months. The batch studies indicate iron removal mechanism as oxidation of Fe²⁺ in the presence of DO to Fe³⁺ form. The groundwater devoid of DO is pre-treated by turning nine times from one bucket to the other from a height of approximately 1 m, thereby increasing DO levels close to 6 mg/L. The increased DO converts Fe²⁺ to Fe³⁺ which settles out easily within 25 min. The pre-treated and settled groundwater contains residual Fe²⁺ of 0.5–0.6 mg/L and is then applied to the IHGF unit over a period of 129 days producing almost Fe²⁺ free water. This helps in increasing the longevity of the service period of the unit as accumulation of Fe³⁺ reduces significantly due to pre-treatment of the groundwater.