Flouride levels in water sources of Gilgil area in Kenya: Deflouridation using locally available geomaterials
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Date
2015
Authors
Wambu, Enos Wamalwa
Journal Title
Journal ISSN
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Publisher
Kenyatta University
Abstract
ABSTRACT
High prevalence of fluorosis resulting from consumption of drinking water containing excessive fluoride levels continues to affect many communities in Kenya. Low in come rural communities are most affected because of inadequate water treatment and high costs of necessary medication. As part of the on-going search for efficient and ffordable water defluoridation protocol, which has intensified in the most recent past, soil dsorbents have attracted a near-global acclaim as the most promising low cost media for water defluoridation. Nevertheless, it is still unclear whether certain Kenyan clays and soil minerals could be applied as inexpensive adsorbents in dcfluoridation of household water. The present study was, therefore, designed to assess the capacities of selected locally available geomaterials (LAGs) to remove fluoride from water with a view to develop an efficient and affordable water defluoridation technology. The adsorbent materials, which included a naturally occurring siliceous mineral (NSIM), a diatomaceous earth (DIME), a ferric polymineral (pEPM) and iron enriched lateritic soils (FELS) were sampled from their natural deposits in Bungoma and Nakuru counties of Kenya. The minerals were pulverized to pass through O.S-mm sieves and less than 1.0-J.lm fractions isolated by mechanical agitation and sedimentation of the pulverized samples in doubly deionized water (DDW). After the initial pre-treatment in dilute HCI solution, the chemistry and mineralogy of the LAGs were analyzed by atomic absorption spectrophotometry (AAS) and by X-ray Diffraction Analysis (XRD). The fluoride adsorption properties of the LAGs were then assessed with respect to changes in initial fluoride concentration, contact time, mixing ratios, presence of interfering ions, and solution pH and temperature. The efficacy of the LAGs to sorb fluoride from natural high-fluoride water was verified in batch and column tests. Fluoride adsorption onto the acidified LAGs was found to be controlled by the mineralogy and chemical composition of the adsorbents as well as by the solution parameters. The equilibrium fluoride adsorption onto the LAGs was adequately fitted by the Langmuir and the Freundlich adsorption isotherms indicating heterogeneity in the fluoride
adsorption mechanisms. Acidified DIME had highest fluoride adsorption capacity (51.1 mg/g) and the capacities of NSIM, FEPM and FELS to sorb fluoride from simulated batch solutions were in range of 10-13 mg/g. The adsorption kinetic data showed that for fluoride adsorption by NSIM and FEPM followed both pseudo-first order and pseudo-second order kinetic models. The adsorption of fluoride onto DIME could, however, be described by intraparticle diffusion kinetics whereas that for FELS by both the pseudo-second order and intraparticle diffusion models. Highest fluoride removal from high-fluoride natural water was achieved using FELS. Fluorides desorption from the LAGs, which was assessed using aqueous solutions of NaCI and
Na2C03, demonstrated the reversibility of the processes. The LAGs showed good fluoride adsorption capacities and they could be utilised as inexpensive adsorbents to defluoridate high fluoride drinking waters and help to alleviate endemic of fluorosis among the communities. Results of this study will be useful as a basis for future scale up using these inexpensive materials as low-cost adsorbents to develop affordable technology for easy and safe defluoridation and sustainable cleaning of drinking water.
Description
A thesis submitted in partial fulfilment of the requirements for the Award of the degree of doctor of philosophy (chemistry) in the School of pure and applied sciences, Kenyatta University, TD 430 .W3