Defluoridation of Water Supplies Using Coconut Shells Activated Carbon: Batch Studies

Abstract

Drinking water with elevated fluoride levels results in serious irreparable health problem that has attained an alarming dimension all over the world, Tanzania being one of the affected countries; techniques have been under study for years. Batch experiments were carried out to determine the effect of various adsorbent factors such as adsorbent dose, initial pH, particle size and contact time on adsorption process. Adsorption efficiency was observed to increase with decrease in particle size, the highest efficiency recorded was 68.2 and 65.9% for field and synthetic water respectively when particle size less than 150μ of coconut shells activated carbon were used. Adsorption was observed to be favoured by pH in acidic range and the maximum efficiency of 58.4% was recorded at pH of 2.0 and particle sizes between 4.18-2.36mm. The pH of the effluent was lowered to acidic range which necessitates further treatment of the effluent or coupling with other materials for pH elevation before use. Adsorption increases with adsorbent dose hence at a smaller influent concentration; the required standard of 1.5mg-F- /l can be met. Equilibrium isotherms have been analysed using Langmuir and Freundlich isotherm models, and both of the models fit to explain the adsorption behaviour of fluoride ions onto Coconut shell activated carbons, during this study it was established that when properly activated; coconut shells can be appropriate for use household filters that could be cost effective in rural areas of Tanzania due its local availability and its colour adsorption property.