Development of a Household Water Defluoridation Process Using Aluminium Hydroxide Based Adsorbent Eyobel Mulugeta 1 , Feleke Zewge 2* , and Bhagwan Singh Chandravanshi 3 ABSTRACT: In this study, the removal of fluoride from water using aluminium hydroxide based adsorbent has been investigated in continuous operation. The effect of fluoride influent concentration, feed flowrate, and adsorbent bed height onto the breakthrough characteristics of the adsorption system were examined. The fixed-bed adsorption system was found to perform better with lower influent fluoride concentration, lower flowrate, and higher bed depth. Thermodynamic evaluation using the bed depth service time model indicated that the fluoride adsorption capacity was 25.8 mg F  /g of adsorbent, which is high compared to commercially available activated alumina (1.8 to 1.9 mg/g). Kinetic studies showed that the rate of adsorption in continuous studies was in the range of 6.12 3 10 3 to 39.3 3 10 3 L/mg . h under different operating conditions. The household defluoridation unit (HDU) was tested at an up-flow mode and it was determined that the HDU packed with 0.9 kg of adsorbent with 28.3 cm of bed depth resulted in a specific safe water yield of 823.79 L. Regeneration of the exhaust media using 1% NaOH and 0.1 M HCl showed that the adsorbent could be reused. The estimated running cost of the unit was 2.0 U.S. dollar/m 3 of treated water, with the potential to minimize further. Hence, it was concluded that the proposed method is simple and exhibits superior performance for the treatment of fluoride-contaminated water with the potential for household application. Water Environ. Res., 87, 524 (2015). KEYWORDS: fluoride, adsorption, treated aluminium hydroxide, household defluoridation unit. doi:10.2175/106143014X13975035525627 Introduction Fluoride has certain physiological properties that are of great interest in terms of how they relate to human health and well being at low levels (Harrison, 2005; Heikens et al., 2005; Miretzky and Cirelli, 2011; WHO, 2011). The role of fluoride in the normal process of mineralization of certain (hard) tissues is highly evident (Heikens et al., 2005). In addition to beneficial effects, fluoride also has pathological effects when its presence exceeds the threshold limit (WHO, 2011). Mottling of teeth is one of the earliest and most easily recognized symptoms of dental fluorosis (Chen et al., 2010; Nie et al., 2012; WHO, 2011). In severe fluorosis, some victims can experience deformation of bones (skeletal fluorosis), which eventually becomes crippling. Prevalence of dental and skeletal fluorosis has been reported in several parts of the world, including Ethiopia, where fluoride concentration in drinking water exceeded the guideline level (1.5 mg/L) (Ayoob and Gupta, 2006; Feleke, 2005; Jagtap et al., 2012; Mohapatra et al., 2009; Tekle-Haimanot et al., 2006). The World Health Organization (1996) guidelines set a maximum amount of fluoride in drinking water at 1.5 mg/L to protect humans from fluorosis. However, up to 33 mg/L of fluoride concentrations were reported in water samples from boreholes in Ethiopia. Such high levels are found in the Rift Valley Region, which is characterized by relatively high volcanic activity in the country (Kloos and Tekle-Haimanot, 1999). Volcanic deposits are the main natural source of fluoride in the Ethiopian Rift Valley and contributions from anthropogenic activities are negligible in this area. Consequently, problems related to the intake of high fluoride water are prevalent in this region of the country (Tekle- Haimanot et al., 2006). Several attempts have been made over the years to reduce fluoride to an acceptable level in drinking water using a wide variety of materials. Presently, there are few treatment methods that are used for controlling excessive levels of fluoride in drinking water. Based on the mechanism of fluoride removal, the methods can be categorized into chemical precipitation by lime and alum (Meenakshi and Maheshwari, 2006), adsorption on to activated alumina, clay materials, and industrial waste residue (Feleke, 2001; Ghorai and Pant, 2005; Maliyekkal et al., 2008; Moges et al., 1996; Nigussie et al., 2007); ion exchange by membranes, synthetic resins, and bone char (Ayoob et al., 2008; Kaseva, 2006; Mjengera and Mkongo, 2003; Solangi et al., 2009; Viswanathan and Meenakshi, 2009); and by membrane technol- ogies such as reverse osmosis and electro-dialysis (Kabay et al., 2008; Sehn, 2008). The methods used by industrialized countries such reverse osmosis, electro-dialysis, and ion exchange require more technical support for operation and maintenance and the capital investment cost is high (Meenakshi and Maheshwari, 2006). Despite such efforts, rural communities in the several regions of developing countries are consuming water with fluoride content that exceeds the recommended level. The purpose of this study was to develop efficient household water defluoridation techniques based on aluminium hydroxide as an alternative method and to establish process parameters. Materials and Methods Defluoridation Material. Hydrated aluminium sulfate (Al 2 (SO 4 ) 3 14H 2 O), which is locally produced in Ethiopia, was used to prepare aluminium hydroxide. In a typical procedure, 1,2*,3 Department of Chemistry, Faculty of Science, Addis Ababa University, P.O. Box 1176, Addis Ababa, Ethiopia; e-mail: fbeshah@ yahoo.com; telephone: þ 251 1 11 23 94 66; facsimile: þ 251 1 11 23 94 70 524 Water Environment Research, Volume 87, Number 6