Fabrication of Macadamia Nutshell Powder-AI/Fe Metal Oxide Modified Diatomaceous Earth Composite Beads for Fluoride and Pathogen Removal Groundwater

Abstract

Contamination of drinking water due to fluoride and pathogens is a severe health hazard problem. Excess of fluoride (>1.5 mg/L) in drinking water leads to dental and skeletal fluorosis whereas the presence of pathogens in water can lead to adverse health effects, including gastrointestinal illness, reproductive problems, and neurological disorders. This study aims to fabricate macadamia nutshell powder-Al/Fe metal oxide modified DE composite beads for removal of fluoride, pathogen from groundwater. The physicochemical compositions of the material were characterized using Scanning Electron Microscope, Fourier Transform Infrared Spectroscopy, Brunauer Emmett Teller and X-Ray Fluorescence and X-Ray Diffraction. The fluoride removal was evaluated using batch and column experiment and the pathogen removal was done using Well disc diffusion assay method. First chapter of results focused on physiochemical characterization of macadamia nutshell powder and further evaluates its efficiency in fluoride and pathogens removal from water. Physicochemical characterization revealed that MNS mainly consist of O, C, H and N as the main elements. This was further confirmed by FTIR which showed OH, C-H, C=O, C-C, C-OH together with the band of C-O. The XRD revealed that MNS is crystalline. The batch experiments showed a maximum fluoride sorption capacity of 1.26 mg/g which was achieved at initial fluoride concentration of 5 mg/L, adsorbent dosage of 0.5 g/100 mL, pH 6 and shaking time of 120 min agitation time. The adsorption isotherm data fitted well to Langmuir than to Freundlich isotherm indicating adsorption occurred on monolayer surface. The value ΔG0 was found to be negative indicating that adsorption of fluoride onto MNS was spontaneous and favourable. The regeneration studies of MNS demonstrated that the adsorbent can be regenerated for up to 7 cycles using 0.01 M HCl and this clearly indicates the reuse potential of the adsorbent. MNS show no zone of inhibition (bacterial activity) towards the Escherichia Coli and Staphylococcus Aureus and Klebsiella Pneumoniae. Second chapter focused on fabrication of macadamia nutshell powder-Al/Fe metal oxide Modified diatomaceous earth composite beads for fluoride and pathogen removal and to further evaluate their properties and efficiency of fluoride and pathogens removal. The optimum ratio for fabricating the beads was found to be 1:3 (1 MNS: 3 Modified DE) which yield the high fluoride removal. The MNS-Al/Fe metal oxide modified DE beads consist of Al2O3 and FeO3 as major chemical components. Batch experiments showed a maximum fluoride removal capacity of 2.61 mg/g with initial fluoride concentration of 5 mg/L and adsorbent dosage of 0.9 g/ 100 mL at a pH of 4 and equilibration time of 120 mins. The adsorption kinetics data fitted better to pseudo second order than pseudo first order of reaction kinetics indicating that the rate limiting factor is chemisorption. The adsorption isotherm data fitted better to Langmuir isotherm model indicating that adsorption occurred on monolayer surface. The thermodynamics parameters such as ΔGᴼ and ΔHᴼ revealed that adsorption of fluoride by the composite adsorbent is endothermic and spontaneous and ΔSᴼ indicated that fluoride ions were randomly distributed on the surface of the adsorbent. The presence of Mg2+, Ca2+, SO42-, NO3-, Cl-, and CO32- reduced the percentage fluoride uptake by the prepared beads. The adsorbent was regenerated up to 5 cycle using deionised water and this clearly indicates the reuse potential of the adsorbent. The column experiments showed that increasing bed height from 30 mm to 40 mm increases the volume of water treated at breakthrough point from 1.3 To 1.8 L. Moreover, the breakthrough capacity for 40 mm bed height was found to be 0.49 mg/g. Antimicrobial potency study showed that the prepared composite beads have a potency against Klebsiella Pneumoniae with 10 mm diameter of inhibition zone. Based on the findings, it can be concluded that MNS and MNS-Al/Fe metal oxide modified DE beads can be used for fluoride removal from ground water with about 48% (MNS) and 70% (MNS and MNS-Al/Fe metal oxide modified DE beads). MNS and MNS-Al/Fe metal oxide modified DE beads also show microbial potency towards Klebsiella Pneumoniae. Moreover, MNS show no microbial potency and the fluoride removal is below 1.5 mg/L as recommended by WHO. Therefore, it is recommended that further study should investigate modification of MNS using inorganic and organic chemical species in order to enhance its performance towards fluoride and pathogen removal. Although MNS-Al/Fe metal oxide modified DE beads showed potency towards Klebsiella Pneumoniae, further research must be done use Ag and Au nanoparticles to enhance its effectiveness to bacteria.