ABSTRACT
204 Aluminum oxide coated media (AOCM) have been found capable of water defluoridation. The fluoride removal performance of AOCM, however, require further enhancement in order to improve on the economic and practical viability, for sustainability. AOCM defluoridation materials were produced by surface modification of indigenous materials by aluminium coating and, so far using bauxite and pumice as base materials. The specific surface areas of AOCMs produced from the pumice and bauxite base materials were, however, found to be low which may be attributable to the low specific areas of these precursor base materials. In this component of the study, the ‘possibility of using wood charcoal (WC) as an alternate indigenous base materialfor producing a high-surface-area fluoride adsorbent, with enhanced performance was investigated. Aluminol functionalized wood charcoal (AFWC) were found capable of reducingfluoride concentration of 5 ± 0.2 mg/L in model to < 1.5 mg/ L, in laboratory-scale columns. The number of bed volumes of water treated by AFWC was found to be 30% higher than that of aluminium oxide coated pumice (AOCP). The superior performance of AFWC over that of AOCP may be due to differences in the textural properties (surface area and’porosity) of the precursor base materials (virgin pumice versus wood charcoal), used in the fluoride adsorbent synthesis process. It was further observed that, different starting/precursor wood charcoal (i.e. WC 1, WC 2, and WC 3 & WC 4) used as base marerialfor the surface functionalization process had an influence on the fluoride adsorption capabilities of the produced AFWCs. Four aluminol functionalized wood charcoals (AFWCs) were produced: AFWC 1, AFWC 2, AFWC 3 and AFWC 4, using WC 1, WC 2, WC 3 and WC 4 as precursor wood charcoal, respectively. Theirfluoride removal efficiencies as well as kinetics in terms of contact times for reducing the fluoride concentration in model water to the WHO guideline value was in the order: AFWC 1 < AFWC 2 < AFWC 3 < AFWC 4. AFWC 3, which was usedfor further work, wasfound capable of reducing fluoride concentration of 4.88 mg/L in natural groundwater in the field to < 1.5 mg/L (WHO guideline value), indicating its laboratory performance was reproducible under field conditions. A comparison of the performance of AFWC with that of activated alumina (AA) under similar field conditions, indicated a higher performance of the later. The fluoride adsorption capacity of AFWC therefore require further improvements. The particle size range of the AA grade usedfor the field assessment was, however, much finer (0.21 — 0.63 mm) than that of AFWC (0.8 — 1.12mm), which might have contributed to its better performance. Moreover the grade of AA tested was said not be regenerable and has to be used only once and disposed off. The use AA for treatement of fluoride-contaminated groundwater in developing countries 205can, however, only be cost-effective when it can be usedfor multiple cycles. On the other hand AFWC was found to be regenerable. Regenerated AFWC (RAFWC) was further observed to perform by 30% better in the field than the freshly produced AFWC. The field performance of AFWC and RAFWC were therefore found encouraging and it could be too early to conclude on the superiority of the performance of AA over that of AFWC, since the former (i.e. AA) can not be regenerated.
