Fluoride Removal from Water by Locally Produced Aluminum Hydroxide

Feleke, Beneberu Shimelis (2005) Fluoride Removal from Water by Locally Produced Aluminum Hydroxide. Masters thesis, Addis Ababa University.

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People in several regions of the Rift Valley of Ethiopia are consuming water with fluoride up to 33 mg/L, which has resulted in both skeletal and non-skeletal fluorosis. Due to the unavailability of effective therapeutic measures, defluoridation of drinking water appears to be the best method for combating the disease. Several methods, using a variety of materials, have been suggested from time to time. However, most of these methods have one or more short-comings with regards to the defluoridation capacity, cost effectiveness, operational at community level and quality of treated water. In view of this, search for more suitable material and method is still in progress. Among tested and used method adsorption of fluoride by (activated) alumina is the most effective and widely used material. However, it is expensive to be applied particularly in developing countries like Ethiopia where the material is not available/ produced. In the present study, aluminum hydroxide (or hydrated alumina) was prepared from locally manufactured aluminum sulfate and used for fluoride removal in batch and continuous operation. The fluoride removal performance was investigated as a function of the contact time, amount of adsorbent dose, thermal pretreatment of adsorbent, concentration of fluoride and pH in batch mode. The adsorption was rapid during the initial 20 min, but significant amount (> 90 %) was removed with in 1 h at an optimum adsorbent dose of 1.6 g/L for initial concentration of 20 mg/L.The removal efficiency of fluoride was increased with adsorbent dosage. Samples of the adsorbent were treated at a temperature range from 200 to 600 oC. An adsorbent treated at 300 0C was selected for fluoride removal studies, in addition to the untreated adsorbent. The removal of fluoride from water depends on initial fluoride concentration. For a given adsorbent dose, the adsorption of fluoride was rapid and efficient, but lower capacity for the more diluted solution. The pH of the water affected the fluoride removal efficiencies of both untreated hydrated alumina (UHA) and treated hydrated alumina (THA), but defluoridation capacity was appreciable with in a pH range of 4.0 to 9.0, which suggests that hydrated alumina have great potential applications. The adsorption data at ambient pH were well fitted to the Freundlich isotherm model with a minimum capacity of 23.7 mg/g and 7.0 mg/g for THA and UHA, respectively. The kinetic studies showed that the adsorption reaction of fluoride removal by hydrated alumina can be well described by a pseudo-second-order rate equation with an average rate constant of 6.60 x 10-3 g min-1mg-1 and 1.87 X 10-3 g min-1mg-1 for UHA and THA, respectively. Filtration through THA in continuous column reduced the fluoride concentration in both simulated as well as ground water. The sorption capacity of THA was 23.2 mg/g and 3.1 mg/g at breakthrough fluoride concentration of 1.5 mg/L; and 38.7 mg/g and 7.1mg/g at point of saturation for simulated water and ground water, respectively. The capacity at breakthrough for simulated water was comparable with the minimum fluoride adsorption capacity of 23.7 mg/g obtained from batch experiment. Thus, the studied method can be operational at household as well as small community level.

Item Type: Thesis (Masters)
Uncontrolled Keywords: Fluoride, Batch defluoridation, Continuous Defluoridation, Hydrated alumina, Fluoride removal efficiency, Adsorption capacity, Breakthrough.
Subjects: G Geography. Anthropology. Recreation > GE Environmental Sciences
Q Science > Q Science (General)
Q Science > QD Chemistry
T Technology > TD Environmental technology. Sanitary engineering
Divisions: Africana
Depositing User: Selom Ghislain
Date Deposited: 11 Sep 2018 11:29
Last Modified: 11 Sep 2018 11:29
URI: http://thesisbank.jhia.ac.ke/id/eprint/5234

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