Abstract
Fluoride pollution (with concentration >1.0 mg/L) in groundwater has become a global threat in the recent past due to the lesser availability of potable groundwater resource. In between several defluoridation techniques discovered so far, the adsorption process proved to be most economic and efficient. This study is an effort to evaluate defluoridation efficiency of powdered rice husk, fine chopped rice husk and sawdust by the batch adsorption process. Optimum defluoridation capacity is achieved by optimizing various parameters, viz. dose of adsorbent, pH, contact time and initial concentration. It was found that all three materials can be employed for the defluoridation technique, but powdered rice husk is the best adsorbent in the midst of all three. Powdered rice husk showed fluoride removal efficiency ranging between 85 and 90 % in the contact period of 7 h only in conditions of all optimized parameter. Following this parameter optimization, adsorption efficiency was also evaluated at natural pH of groundwater to minimize the cost of defluoridation. No significant difference was found between fluoride adsorption at optimized pH (pH = 4) and natural one (pH = 7), which concludes that powdered rice husk can be efficiently used for the defluoridation technique at field scale. The adsorption isotherm using this adsorbent perfectly followed Langmuir isotherms. The value of calculated separation factor also suggests the favourable adsorption of fluoride onto this adsorbent under the conditions used for the experiments. The field application for defluoridation of groundwater using this adsorbent (based on pH of natural groundwater there and seasonal variation of temperature) showed the high success rate.
Highlights
Fluoride is a normal constituent of natural water because of its high reactivity
No significant difference was found between fluoride adsorption at optimized pH and natural one, which concludes that powdered rice husk can be efficiently used for the defluoridation technique at field scale
Fluoride pollution in groundwater is a global concern as ingestion of water with fluoride concentration more than 1.5 mg/L may result in dental or skeletal fluorosis and, in the recent past, the defluoridation from groundwater has become a major thrust area of investigation for the scientific community
Summary
Fluoride is a normal constituent of natural water because of its high reactivity. Normally, fluorine exists in the form of fluoride in natural waters (Leung and Hrudey 1985). In this study an effort is made to observe the adsorption of fluoride from groundwater of Mehsana District, Gujarat, India, on finely chopped rice husk, powdered rice husk and sawdust. These adsorbents are chosen on the basis of availability (very commonly available) as well as affordability (very cheap) with local residents there. All the experiments of batch adsorption are piloted to examine the effect of various parameters like dose of adsorbent, pH of working media, initial concentration of fluoride in the working sample, and contact time for which the adsorbent was kept in the working media. The constants qm and Ka can be determined from a linearized form of Eq (2) by the slope of the linear plot of Ce/qe versus Ce
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