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Addis Ababa University Libraries Electronic Thesis and Dissertations: AAU-ETD! >
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Thesis - Anaesthesiology >
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http://hdl.handle.net/123456789/108
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| Title: | REMOVAL OF FLUORIDE FROM WATER USING GRANULAR ALUMINIUM HYDROXIDE: ADSORPTION IN A FIXED-BED COLUMN |
| Authors: | Eyobel, Mulugeta |
| Keywords: | Fluoride
Adsorption
Breakthrough
Fixed-bed column
Aluminium hydroxide
Bed |
| Date Added: | 7-Sep-2007 |
| Abstract: | Excessive and undesirable level of fluoride in drinking water supplies is a major problem in the
Rift Valley of Ethiopia. It has been reported that people in the Rift Valley of Ethiopia are
consuming water up to 33 mg L-1 of fluoride. The WHO has set 1.5 mg L-1 as the maximum
permissible limit for fluoride in potable water. Sustained intake of fluoride beyond this limit can
cause dental or skeletal fluorosis, which is a chronic disease manifested by mottling of teeth in
mild cases, softening of bones and neurological damage in severe cases, therefore adequate
measures for the reduction of the level are important.
It is also expected that the fluoride concentration may increase mainly because of the excessive
utilization of ground water as these area are characterized by water scarcity. In areas where
alternative water sources are not available, physical or chemical treatment of water is the best
option to control fluorosis. The methods of fluoride removal used by industrialized countries
require more technical support for operation and maintenance than is possible in the rural areas
of developing countries.
In this study, the removal of fluoride using aluminium hydroxide was studied in a fixed bed
column system. The Bed Depth Service Time design model, Empty Bed Residence Time and
Thomas model were used to analyze the performance of the column and the effect of the different
operating variables such as bed depth, flow rate and initial concentration were tested on these
simplified fixed bed design models. Desorption experiments were conducted to evaluate the
possibilities of regeneration and reuse of the media. The effects of co-existing ions on the
adsorption capacity of aluminium hydroxide were also investigated in batch mode.
The breakthrough curves for the adsorption of fluoride on to aluminium hydroxide confirmed that
the breakthrough volume and breakthrough time were decreased with increasing flow rate and
initial fluoride concentration or decreasing bed depth. The data estimated from bed depth service
time model showed that the adsorption capacity (No) of the adsorbent were found to be 24.07,
25.79 and 12.7 mg g-1 for 12, 23 and 40 mL min-1 flow rate, respectively. The operating line
seems flatten and no significant reduction in adsorbent exhaustion rate is gained with contact
time greater than about 3, 6 and 7 min for 40, 23 and 12 mL min-1 flow rates, respectively, with
the corresponding usage rate of 2.2, 0.9 and 1.3 g L-1. The optimum dose for batch system was
1.6 g L-1 and it is close to the adsorbent exhaustion rate of 12 mL min-1. The application of
Thomas model has showed that the adsorption capacity is strongly dependent on the flow rate,
initial fluoride concentration, and bed depth and is greater under conditions of a lower
concentration of fluoride, lower flow rate and higher bed depth. And the Thomas rate constant
decreases with increasing bed depth, decreasing initial concentration, and flow rate. Results
concerning the effects of anions on the adsorption of fluoride on to the aluminium hydroxide
showed that Cl- and SO4
2- have very little effect on the fluoride removal capacity of adsorbent but
HCO3
- and PO4
3- had a profound effect on the removal capacity of the adsorbent.
Hence it is concluded that using granular aluminium hydroxide as an adsorbent for fluoride
removal in a fixed-bed adsorption process is feasible. |
| Description: | A Thesis Submitted to
The School of Graduate Studies of Addis Ababa University
in Partial Fulfillment of the Requirement for
the Degree of Masters of Science
in Environmental Science |
| URI: | http://hdl.handle.net/123456789/108 |
| Appears in: | Thesis - Environmental Sciences
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