Research on Sustainable Conversion of Agriculture and Food Waste into Activated Carbons Devoted to Fluoride Removal from Drinking Water in Senegal

Abstract

The objective of this study was to investigate the production of activated carbons (AC) from cashew
shells, and millet stalks and their efficiency in fluoride retention. These agricultural residues are
collected from Senegal. It is known that some regions of Senegal, commonly called the groundnut
basin, are affected by a public health problem caused by an excess of fluoride in drinking water used
by these populations. The activated carbons were produced by a combined pyrolysis and activation
with water steam; no other chemical compounds were added. Then, activated carbonaceous materials
obtained from cashew shells and millet stalks were called CS-H2O and MS-H2O respectively. CS-
H2O and MS-H2O show very good adsorbent features, and present carbon content ranges between
71% and 86%. The BET surface areas are 942 m2:g????1 and 1234 m2:g????1 for CS-H2O and MS-H2O
respectively. A third activated carbon produced from food wastes and coagulation-flocculation sludge
(FW/CFS-H2O) was produced in the same conditions. Carbon and calcium content of FW/CFS-
H2O are 32.6 and 39.3% respectively. The kinetics sorption were performed with all these activated
carbons, then the pseudo-first equation was used to describe the kinetics sorption. Fluoride adsorption
isotherms were performed with synthetic and natural water with the best activated carbon from
kinetics sorption, Langmuir and Freundlich models were used to describe the experimental data.
Regarding equilibrium data, the experimental data are better described by Langmuir model than by
the Freundlich model. The results showed that carbonaceous materials obtained from CS-H2O and
MS-H2O were weakly efficient for fluoride removal. With FW/CFS-H2O, the adsorption capacity is
28:48 m2:g????1 with r2 = 0:99 with synthetic water.