Groundwater fluoride removal by novel activated carbon/aluminium oxide composite derived from raffia palm shells: Optimization of batch operations and field-scale point of use system evaluation

Abstract

Fluoride contamination of groundwater is endemic in several countries of the world. Ingestion of fluoride laden water is linked with varying human health consequences. However, deployment of efficient and optimally performing groundwater defluoridation systems in affected regions still require concerted research efforts. Thus in this study, Response Surface Methodology (RSM) is employed to infer the effects of process conditions including adsorbent dosage (0.5–2.5 g/L), contact time (30–150 min), solution pH (3–11) and starting fluoride concentration (2–10 mg/L) on the batch-mode fluoride removal using a novel raffia palm shell activated carbon-aluminium oxide composite. The predicted optimal conditions were used to verify its efficacy for F-removal in actual fluoride ladened groundwater. Furthermore Point of Use (PoU) adsorption filters made of the raffia palm shell activated carbon-aluminium oxide composite and a Commercial Activated Carbon (CAC) was tested for fluoride containment in groundwater. The optimum conditions for defluoridation of synthetic fluoride solution were 5.9, 4.0 mg/L, 2.0 g/L and 120 min for pH, initial fluoride concentration, adsorbent dosage and contact time respectively and resulted to F-removal efficiency of 99.1% and uptake capacity of 2.0 mg/g. Test with actual fluoride ladened groundwater at the suggested optimum conditions indicated removal efficiencies of 92.83 and 85.65% for groundwater sourced from Kaltungo and Langtang areas respectively. Performance of the raffia palm shell activated carbon-aluminium oxide composite-based and CAC-based PoU filters were found to be 14.0 and 7.8 mg/g, 700 and 500 L, 112 and 80 h and 55.88 and 54.47% for average adsorption capacity, treated volume at breakthrough, breakthrough time and average removal efficiency respectively. Exhausted raffia palm shell activated carbon-aluminium oxide composite was regenerated by recoating the spent media with aluminium oxide and was reused in the PoU filters for up to 5 cycles with a marginal decrease in all performance indices.Thus the novel raffia palm shell activated carbon-aluminium oxide composite was found to be an excellent groundwater defluoridation media in both the batch and PoU modes of operation.