Abstract
In this study, granulated activated charcoal (GAC) and bio charcoal (BC) is used as a filler in P3 biosand bag filter to study their filtration performance against a range of fluoride impurities from 1–1400 mg/L. A set of experiments are done to analyze the filtration efficiency of the sandbag filter against fluoride impurities after incorporating different amounts (e.g., 0.2, 2 kg) and a combination of GAC and BC. A combination of filler GAC and BC (1 kg each) have exhibited excellent results with 100% fluoride removal efficiency against 5 mg/L fluoride impurities for an entire experimental time of 165 min. It is because of the synergetic effect of adsorption caused by the high surface area (739 m2/g) of GAC and hydroxyapatite groups in BC. The data from remediation experiments using individual GAC and BC are fitted into the Langmuir and Freundlich Isotherm Models to check their adsorption mechanism and determine GAC and BC’s maximum adsorption capacity (Qm). The remediation data for both GAC and BC have shown the better fitting to the Langmuir Isotherm Model with a high R2 value of 0.994 and 0.970, respectively, showing the excellent conformity with monolayer adsorption. While the GAC and BC have presented negative Kf values of −1.08 and −0.72, respectively, for Freundlich Model, showing the non-conformity to multilayer adsorption. The Qm values obtained from Langmuir Model for GAC is 6.23 mg/g, and for BC, it is 9.13 mg/g. The pH study on adsorption efficiency of individual GAC and BC against 5 mg/L of fluoride impurities indicates the decrease in removal efficiency with an increase in pH from 3 to 9. For example, BC has shown removal efficiency of 99.8% at pH 3 and 99.5% at pH 9, while GAC has exhibited removal efficiency of 96.1% at pH 3 and 95.9% at pH 9. Importantly, this study presents the significance of the synergetic application of GAC and BC in the filters, where GAC and BC are different in their origin, functionalities, and surface characteristics.
Highlights
The Fourier Transform Infra-Red Spectrometry (FTIR) spectra of hardwood granulated activated charcoal (GAC) showed the following major peaks: (I) 1698 cm−1 indicates the presence of C=O stretching shows the presence of conjugated ketones, (II) 1574 cm−1 peak relates to C=C stretching of aromatic components and lignin, (III) 1211 cm−1 indicate hydrogen-bonded phosphorous functional group linkages [21]
While the FTIR of bio charcoal (BC) presented the following characteristic peaks: (I) 871 cm−1 demonstrates the presence of carbonate groups in hydroxyapatite structure, (II) a broad and strong band of calcium (Ca2+ ) was at 560 and 610 cm−1 indicates the structure of calcium hydroxyapatite, (III) 1050 cm−1 stretching mode of phosphate (PO4 3− ) peak
These bands are characteristics of mineral calcium hydroxyapatite [Ca5 (PO4 )3 (OH)] which is the main constituent of teeth and bones [22]. These characteristic peaks remain maintained in dialyzed BC, the minor peaks at 1413 and ~800 cm−1 disappeared in BC after dialysis
Summary
If water is not made more affordable and accessible to all, it is estimated that half of the global population in 2025 will live in water-stressed conditions [1] This is largely concerning during the COVID-19 pandemic because 1.8 billion people who use or work in healthcare are at a higher risk of infection due to the lack of access to basic water services [2]. Most common are heavy metals impurities which are usually present in their charged forms such as cations and anions. They are widespread and can cause environmental toxicity in addition to a multitude of acute and chronic illnesses depending on the amount ingested over time. There is natural hydrogeological dissolution and distribution near marine sediments or volcanoes
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