Fluoride Removal From Water With Aluminium Oxide Hydroxide A Pilot Study For Household Application

Health problems occurring due to high fluoride concentrations in drinking water are a widespread problem inrnthe East African Rift system including the Ethiopian Rift Valley. Excessive fluoride in groundwater is the mostrnserious water quality problem and many people are being affected by both dental and skeletal fluorosis. ThernWHO and national standard (ES 261:2001) permit only 1.5 mg/l as a safe limit for human consumptionrnwhereas several residents of Rift Valley region of Ethiopia are consuming water with fluoride concentrationrnmuch more than the permissible limit.rnCurrent methods of fluoride removal from water include adsorption onto activated alumina, bone char and clay,rnprecipitation with lime, dolomite and aluminium sulfate, the Nalgonda technique, ion exchange and membranernprocesses such as reverse osmosis, electrodialysis and nano filtration. Most of the available materials forrndefluoridation are expensive and technically non-feasible in rural communities in Ethiopia. Hence therndevelopment of defluoridation method based on locally available materials is desirable. The technology must berntechnically simple, cost effective, easily transferable, use local resources and must be accessible to the ruralrncommunity.rnThe present work has been undertaken to explore the feasibility of aluminium oxide hydroxide for the removal ofrnfluoride from water. Aluminium hydroxide was prepared by the reaction between aluminium sulfate (Alum) andrnsodium hydroxide at room temperature. The white preciptate of aluminium hydroxide was dried at 50 oC in airrncirculated oven and heated at 300 oC in oxidizing atmosphere to produce two forms of aluminium hydroxidesrnrespectively. The products were characterized by XRD and BET SA measurements by BET-nitrogen method. Arnsurface area of 110 m2/g and pore volume of 0.29 cm3/g was obtained for the sample prepared at 300 oCrn(Boehmite) where as a surface area of 37 m2/g and pore volume of 0.19 cm3/g was obtained for the samplernprepared at ordinary conditions (Pseudo-boehmite structure).XRD results show that heat treated aluminiumrnhydroxide comprised AlOOH as the major component and traces of FeO(OH), Fe (OH) 2 and Al2O3..rnThe Langmuir sorption capacity, qm, and adsorption coefficient, b, are 101.63 mg/g and 4.0 × 10-2 L mg -1 forrnpsedoboehmite and 72.72 mg/g and 2.11×10 –1 L mg -1 for boehmite, respectively. The D-R isotherm adsorptionrnenergy values of 6.04 and 13.35 kJ mol-1 are noted for F –adsorption onto pseudoboehmite and AlOOH,rnrespectively which indicates the sorption process is predominantly physisorption. The Temkin constant, KT, ofrnboehmite and pseudoboehmite for F - are 20,735.34 l mg -1 and 7,369.996 l mg -1, respectively indicating a lowerrnadsorbent/fluoride ion potential (interaction) for pseudoboehmite. The Temkin adsorption potential, 1/bT, wasrn0.00742 and 0.00116 for AlOOH and pseudoboehmite, respectively. The relatively higher adsorption potentialrnfor AlOOH was probably due to the high surface coverage of F- ions onto its surface.rn.rnThe AlOOH media used has the capability of producing water with a residual fluoride concentration of less thanrn0.05 mg/l from an initial fluoride of 20.0 mg/l. In the previous fluoride adsorption studies using this material,rnthe adsorption capacity of AlOOH for fluoride ions has been tested in batch and continuous mode and found outrnas 23.7 mg F - /g and 25.79 mg F -/g , respectively.rnA comparable breakthrough time, t, was observed between a laboratory scale column (down flow) experimentrnand mini column(up flow) of the previous adsorption experimental results with breakthrough time values 1150rnmin and 1350 minutes, respectively.rnThe presence of certain cations may be effective in fluoride retention. Exchangeable cations such as Na, Ca andrnMg may form solid precipitate with fluoride.rnA domestic defluoridator has been developed and tested at a pilot domestic unit. AlOOH particles with 1.0 – 2.0rnmm size were used as filter media in this unit. Upward flow technique has been used in the defluoridationrnprocess. The performance of the pilot defluoridator has been monitored at regular intervals to evaluate itsrnfluoride removal performance. The pilot household defluoridator has a capacity of treating about 20 L of waterrnand this quantity of water could be used by a family of five each consuming four liters per day for cooking andrndrinking purposes. About 0.785 Kg of AlOOH granules has reached breakthrough in 1.4 month when thernfluoride concentration in water was around 20 mg/l. The defluoridation price per liter of water was estimated asrn0.55 birr/L.rnHence it is concluded from the pilot study that the developed technology is simple, efficient, effective andrnfeasible for defluoridation of water for fluoride affected regions both at the remote and rural settlements atrnlarge and urban households in Ethiopia.rnKey words: Fluoride, defluoridation, Pseudo-boehmite, boehmite, adsorption, Bed Depth Service Time

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