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Abstract
Drinking water contamination is a major issue of public health concern in Anuradhapura, Sri Lanka, where dental and skeletal fluorosis can be resulted due to a prolonged exposure to excess fluoride. The study investigates use of Eichhornia crassipes (Water Hyacinth) biomass as a low-cost, eco-friendly biosorbent to extract fluoride in ground water (GW) and surface water (SW). Biomass samples were dried and powdered followed by conducting the batch adsorption experiment using water samples obtained in a Kahatagasdigiliya borehole (GW) and Nuwarawewa reservoir (SW). The adsorption experimentation was carried out at biosorbent dosages 0.10-4.00 g L -1 and 3 hours contact time (150 rpm). Removal efficiencies (RE) were established as per the spectrophotometric procedures of measuring fluoride levels. The results indicated difference in the fluoride extraction capability between GW and SW. The biomass of E. crassipes exhibited outstanding adsorption potentials in the SW with 99.17% of RE at dosage of 1.00 gL⁻¹ and adsorption capacity of 238 mg g -1. This was afforded statistically because Langmuir fitting of the isotherm plot showed good results (R2=0.95), which is indicative of monolayer adsorption event with a homogenous surface of the biosorbent. Conversely, the elimination of fluoride in GW was, not quite, as successful and 68.03 % RE occurred at a dosage of 0.50 gL⁻¹. It seems that complex GW chemistry which influence adsorption sites and the existence of competing ions are likely to explain why GW data showed poor model fitting with adverse and non-physical properties. Besides showing that E. crassipes biomass is a potential biosorbent to purify fluoride contaminated SW, these findings demonstrate that matrix water source affects biosorption activity. The study finds it appropriate to introduce E. crassipes biosorption in the economically rational and eco-friendly water purification adsorption systems to benefit the Sri Lankan villages which are affected by fluoride contamination.
Keywords: Adsorption isotherms, Biosorption, Eichhornia crassipes, Fluoride removal, Surface water
