Laddsula Tesha WSE

							               Fluoride removal using low cost adsorbents
                              Name: Ladslaus Modestus (Kimango-Tesha)
                                         Country: Tanzania

                                 Supervisor    Prof. Gary Amy (PhD, MSc)
                                    Mentor     Dr. Branislav Petrusevski (PhD, MSc)
                                    Mentor     Dr. Kebreab Ghebremichael (PhD, MSc)
                                Sponsor(s):    NFP


 An abstract of the thesis submitted for the partial fulfilment of requirements for the Master of Science
          degree at the UNESCO-IHE Institute for Water Education, Delft, the Netherlands

Some areas in the developing world have high content of fluoride in the water and this has resulted in
public health concerns related to dental or bone fluorosis. There is no way of reversing symptoms of
fluorosis and the best way to avoid the problem is to reduce fluoride concentration in drinking water
content to WHO standard of 1.5 mg/L. There are several fluoride removal methods widely applied in
practice: coagulation, adsorption, ion exchange, electrochemical methods and membrane techniques.
Many of these methods are expensive, particularly in developing countries and often produce residuals
which can not be readily disposed in the environment.. The search for low cost and appropriate
methods of fluoride removal has become of an interest. This study, focused on the removal of fluoride
using low cost adsorbents such as Aluminium Oxide Coated Pumice (AOCP), Aluminium Oxide
Coated Sand (AOCS), Moringa oleifera and Chitosan. The research included: 1) coating of sand and
pumice using aluminium sulphate solution, ii) characterization of the coated media using visual and
microscopic observation, iii) investigation of the stability of the coated material in varying pH range
(by leaching test) and iv) batch adsorption experiments to estimate the adsorption capacity of each
adsorbent for fluoride removal. Different coating procedures were used to maximize aluminium coating
on the surfaces of pumice and sand media.

The leaching experiments indicated that the coated surface was stable in a wide pH range, which states
that the coated adsorbent can be conveniently used in the normal pH ranges of water treatment. Based
on the different coating procedures, coating of the media in cycles (coating and recoating) by the
common procedure (aluminium sulphate coating and ammonium hydroxide oxidizing) resulted in a
significantly better adsorbent coating than a single coating procedure. Moreover this procedure resulted
in a better coating compared to a soaking and rinsing procedure that was conducted in several cycles.
This was observed from the amount of leached aluminium after boiling in an acid and also by the
results of batch adsorption experiments. Compared to a single cycle coating, the amount of coating in
recoated media was 2-3 times more higher. The results also indicated that high concentration of coating
solution was necessary to achieve significant coating.

Batch adsorption experiments indicated that the aluminium coated media (AOCP, AOCS) and the bio-
adsorbents (M. oleifera , chitosan) showed good adsorption capacity. Adsorption capacity of the
materials were estimated from Langmuir and Freundlich isotherm models. Based on Freundlich model
the adsorption capacity of the different adsorbents were 0.1228 mg/g, 0.5883 mg/g, 0.0554 mg/g and
0.4914 mg/g 0.4803 mg/g and 0.5900 mg/g for AOCP, recoated AOCP, AOCS, recoated AOCS,
M .oleifera and chitosan, respectively.

The study indicated that there is a potential to use low cost adsorbents for fluoride removal from water
sources.

Key words: Adsorption, Fluoride, Aluminium Oxide Coated Pumice / Sand, Moringa oleifera, Chitosan