A study of field performance and sustainability of Fluoride Nilogon in defluoridation in Yemen

Yemen faces a severe drinking water crisis due to rapidly declining groundwater and elevated fluoride concentrations exceeding WHO guidelines. In areas with fluoride contamination, such as Lahj and Al Dhale’a governorates, where groundwater is the only drinking water source available, the risks to public health are high. To address this, ZOA, an international relief and recovery organisation, in collaboration with Tezpur University, piloted the low-cost Fluoride Nilogon filter, developed by a Tezpur University group, across 300 households in Lahj governorate as phase I in 2021. Based on its demonstrated effectiveness, the intervention was expanded in Phase II to 400 additional households in Al Dhale’a and a communal scale unit (18,000 L size) treating ~7,000 L per batch, benefitting approximately 700 residents in Al Dhale’a governorate in 2024. This paper describes a study of the field performance of the filters in both phases, offering a scalable solution for decentralised fluoride alleviation in low-resource environments. The paper also includes a study of suitability of the crushed limestone for Fluoride Nilogon reactors for both phases of the intervention and the performance of the filters. The suitability of limestone for field use was analysed by obtaining four samples of limestone, viz ., A and B in Phase I; and C and D in Phase II, obtained from various localities of Yemen, to choose the better one for field use. The results of the fluoride removal abilities of the limestone samples were correlated with major physicochemical characteristics of limestone, such as porosity, density, and chemical impurities.