Development of Household Water Defluoridation Process Using Aluminium Hydroxide-Based Adsorbent
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 flow rate, 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 flow rate and higher bed depth. Thermodynamic evaluation using the Bed Depth Service Time (BDST) model indicated that the fluoride adsorption capacity was 25.8 mg F-/g of adsorbent, which is very high compared to commercially available activated alumina (1.8-1.9 mg/g) adsorbents. Kinetic studies showed that the rate of adsorption in continuous studies was in the range between 6.12 × 10-3 and 39.3 × 10-3 L/mg.h, under different operating conditions. The household defluoridation unit (HDU) was tested at an up-flow mode and it was found out that the HDU packed with 0.9 kg of adsorbent with 28.3 cm 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 22 2.0 USD/m3 of treated water with the potential to minimize further. Hence it is concluded that, the proposed method is simple and has superior performance for the treatment of fluoride contaminated water with potential for household application.
KEYWORDS: fluoride, adsorption, treated aluminium oxide hydroxide, household defluoridation unit.