ITRI Rosenfeld Postdoctoral Fellow, Lawrence Berkeley National Laboratory
Providing safe drinking water to low income communities by developing low-cost technologies
Globally, 200 million people drink groundwater contaminated with fluoride concentrations exceeding the World Health Organization’s recommended level (1.5 ppm). While low levels (<1.0 ppm) of fluoride have been shown to improve dental health, levels substantially exceeding 1.5 ppm have strong adverse health effects. In more extreme forms, skeletal fluorosis leads to spinal fusion and limb deformation, leaving victims severely disabled and often with chronic pain.
Existing technologies to remove fluoride from water are energy intensive, resulting in significant greenhouse gas emissions. Further, approaches such as reverse osmosis and filtration with activated alumina (which is processed from raw bauxite in an energy- and carbon-intensive manner) are expensive and are not attainable for low-income communities.
We have demonstrated that minimally-processed bauxite ores can remove fluoride to safe levels at a fraction of the cost of activated alumina. However, several technical challenges must be addressed in order to ensure that this technology will deploy reliably in the field. This work addresses challenges in safe material selection, competition from co-occurring ions, and adsorption reversibility; understanding all of these phenomena is crucial to overcoming the "valley of death" between an exciting discovery and a lifesaving innovation.
Abstract: Fluoride contamination of drinking water, which causes fluorosis and neurological damage, is an exigent worldwide problem. Adsorption by metal oxyhydroxides is an attractive technology for water defluorination, although the removal efficiency is restricted by protonation of the oxygen binding sites (M-OH and M-O-M) for F−. Herein, hollow Fe-Al binary metal oxyhydroxide micro-boxes (FeAl-OOH MB) were prepared by annealing derivatives of Prussian blue analogues (PBAs). XRD and 27Al MAS NMR analyses showed that the hollow structures were composed of Al oxyhydroxides (Al(O)6, Al(O)4) and Al-incorporated ferrihydrite. The surface oxygen was easily protonated in the presence of Al oxyhydroxides; with the introduction of Al into the lattice, the extent of protonation on the surface of the ferrihydrite was intensified via weakening the electronegativity of Fe sites. Therefore the limitation on adsorption efficiency was alleviated through tuning the surface charge. Together with large specific surface area (242 m2 g−1) and good mass diffusion, hollow FeAl-OOH MB exhibited outstanding maximum F− adsorption capacity (146.59 mg g−1) and adsorption rate (20 min was needed to reach equilibrium for initial F− concentration of 10 mg L−1), outperforming comparable metal oxyhydroxide/oxide adsorbents. Meanwhile, except for PO43−, co-existing anions (NO3−, Cl−, SO42− and HCO3−) showed negligible influence on the adsorption of F− on FeAl-OOH MB. Furthermore, the F− adsorbed on FeAl-OOH MB could be effectively desorbed using 0.1 M NaOH, and the desorption efficiency for reuse was 94.38%. The results illustrate the potential utility of hollow FeAl-OOH MB as an effective adsorbent for practical defluorination in drinking water treatment.
Pub.: 06 Feb '17, Pinned: 28 Jun '17
Abstract: A sustainable approach to produce graphene sheets from seaweeds which can remove 75−87% of fluoride from contaminated drinking water is demonstrated.Herein we present a sustainable and cost-effective approach for the preparation of functionalized graphene nanosheets (GNs) directly from seaweed and deep eutectic solvents (DESs). The seaweed granules remained after the recovery of juice from fresh brown seaweed, Sargassum tenerrimum, was utilized as a raw material and DESs generated by the complexation of choline chloride and metal salts were employed as solvent and catalyst for the large scale and facile production of metal oxide functionalized GNs. Moreover considering the biological application of such GNs, where nontoxic nature of substrates is desirable, we have also evaluated the cytotoxicity of the functionalized GNs (Fe3O4/Fe, SnO2/SnO/Sn, or ZnO/Zn-functionalized GNs), and most of them were found to be nontoxic against human lung carcinoma cells (A549). Thereafter, efficiency of these GNs was assessed for the removal of F– from fluoride contaminated groundwater (2.72–6.71 mg L–1) used for drinking purposes. After treatment with GNs, the concentration of fluoride was found to reduce to 0.36–1.69 mg L–1 (75–87% removal efficiency). Moreover, after recovery of GNs from the water, no significant contamination of metal ions was found in the remaining water. Thus, seaweed-derived nontoxic GNs can be utilized to produce safe drinking water with permissible fluoride content as per World Health Organization (WHO) norms.
Pub.: 08 Mar '17, Pinned: 28 Jun '17
Abstract: This study used fixed-bed column experiments to examine the potential and effectiveness of modified magnetite with aluminum or lanthanum to remove fluoride ions from fluoride solutions and drinking water. A fixed bed column test was conducted to simulate the actual condition of adsorption in a continuous manner in a filtration process. Fixed-bed column experiments were carried out at a bed depth of 1.3 cm and a flow rate of 1 mL min−1. The breakthrough curves obtained for fluoride ion adsorption from aqueous solutions and drinking water were fitted to Thomas, Bohart-Adams, Yoon and Nelson, and Yan models. The significant influence of bed height, flow rate, empty bed contact time, and initial fluoride concentration on removal were used for simulation of breakthrough curves. The impact of common ions present in drinking water on the adsorption of fluoride was investigated. The regeneration of the column was performed by eluting with 0.01 M Ca(OH)2, NaCl, NaOH or Na2SO4 solution after the adsorption studies. Thomas, Yoon–Nelson and Yan models were found suitable for the normal description of breakthrough curves in the experimental conditions, whereas the Adams–Bohart model was able to explain only the initial part of the dynamic behavior of the column system. Simulation results indicate that the breakthrough point (tp) decreases as the flow rate and initial fluoride concentration increase, and bed height is directly proportional to fluoride removal. It was concluded that modified magnetite can be effectively used as a sorbent for the removal of fluoride ions.
Pub.: 04 Apr '17, Pinned: 28 Jun '17
Abstract: Synthesized magnetic core-shell Ce-Ti@Fe3O4 nanoparticles were tested, as an adsorbent, for fluoride removal and the adsorption studies were optimized. Adsorption capacity was compared with the synthesized Ce-Ti oxide nanoparticles. The adsorption equilibrium for the Ce-Ti@Fe3O4 adsorbent was found to occur in <15min and it was demonstrated to be stable and efficient in a wide pH range of 5-11 with high fluoride removal efficiency over 80% of all cases. Furthermore, isotherm data were fitted using Langmuir and Freundlich models, and the adsorption capacities resulted in 44.37 and 91.04mg/g, at pH7, for Ce-Ti oxides and Ce-Ti@Fe3O4 nanoparticles, respectively. The physical sorption mechanism was estimated using the Dubinin-Radushkevich model. An anionic exchange process between the OH(-) group on the surface of the Ce-Ti@Fe3O4 nanomaterial and the F(-) was involved in the adsorption. Moreover, thermodynamic parameters proved the spontaneous process for the adsorption of fluoride on Ce-Ti@Fe3O4 nanoparticles. The reusability of the material through magnetic recovery was demonstrated for five cycles of adsorption-desorption. Although the nanoparticles suffer slight structure modifications after their reusability, they keep their adsorption capacity. Likewise, the efficiency of the Ce-Ti@Fe3O4 was demonstrated when applied to real water to obtain a residual concentration of F(-) below the maximum contaminated level, 1.5mg/L (WHO, 2006).
Pub.: 05 May '17, Pinned: 28 Jun '17