Articleshttp://hdl.handle.net/11602/21392024-03-29T10:43:03Z2024-03-29T10:43:03ZEffect of hysteresis on water flow in the vadose zone under natural boundary conditions, Siloam Village case study, South AfricaArrey, I. A.Odiyo, J. O.Makungo, R.Kataka, M. O.http://hdl.handle.net/11602/23252022-11-04T20:15:05Z2017-10-17T00:00:00ZEffect of hysteresis on water flow in the vadose zone under natural boundary conditions, Siloam Village case study, South Africa
Arrey, I. A.; Odiyo, J. O.; Makungo, R.; Kataka, M. O.
A one-dimensional vadose zone model was used to simulate flow under natural boundary
conditions. The effects of hysteresis and temporal variability of meteorological conditions were
evaluated. Simulations were performed in HYDRUS-1D code for the period April 2013–January 2014
(6601 hours) at three different locations in a delineated portion of the sub-quaternary catchment
A80A of Nzhelele with different soil textures. Soil hydraulic characteristics were estimated in a
Rosetta library dynamically linked to the HYDRUS-1D model which is based on the numerical solution
of a one-dimensional Richard’s equation. Analysis of the simulation results suggests that ignoring
hysteresis for soils of similar textural class does not lead to any significant deviation of the model
predicted soil moisture, unlike for soils with different textural classes
2017-10-17T00:00:00ZBiosynthesis of Ultrasonically Modified Ag-MgO Nanocomposite and Its Potential for Antimicrobial ActivityAyinde, Wasiu BGitari, Mugera W.Muchindu, MunkombweSamie, Amidouhttp://hdl.handle.net/11602/23232022-11-04T18:39:48Z2018-08-29T00:00:00ZBiosynthesis of Ultrasonically Modified Ag-MgO Nanocomposite and Its Potential for Antimicrobial Activity
Ayinde, Wasiu B; Gitari, Mugera W.; Muchindu, Munkombwe; Samie, Amidou
This study reports a green synthesis route for a bilayered Ag-MgO nanocomposite using aqueous peel extract of Citrus paradisi
(grapefruit red) under an accelerated uniform heating technique and its antibacterial potency against Escherichia coli. Surface
modifications and composition of the nanocomposite were examined using a UV-visible spectrophotometer, transmission
electron microscopy (TEM), X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, and scanning electron
microscopy (SEM) equipped with an energy dispersive X-ray (EDX) analyzer. (e efficiencies of the as-synthesized Ag-MgO
nanocomposite against Escherichia coli were examined. (e synthesized Ag-MgO nanocomposite showed characteristic synergetic
bands at 290nm for MgO nanoparticle and at around 440nm for Ag nanoparticle which blue-shifted to 380nm in the
composite. A spherically dispersed nanocomposite with cubical crystal lattice network with a diameter of about 20–100nm
comprising Ag nanoparticle embedded within MgO nanoparticles was obtained. (e nanocomposite produced stronger antibacterial
activity against Escherichia coli as compared to MgO nanoparticle, indicating a higher interaction between Ag and MgO
ions. (e nanocomposite was successfully synthesized via an efficient modified method by bioreductive agents with an improved
synergistic antibacterial property towards water purification.
2018-08-29T00:00:00ZThe Presence of Toxic and Non-Toxic Cyanobacteria in the Sediments of the Limpopo River Basin: Implications for Human HealthMagonono, MurendeniOberholster, Paul JohanShonhai, AddmoreMakumire, StanleyGumbo, Jabulani Rayhttp://hdl.handle.net/11602/23172022-11-03T03:06:29Z2018-07-03T00:00:00ZThe Presence of Toxic and Non-Toxic Cyanobacteria in the Sediments of the Limpopo River Basin: Implications for Human Health
Magonono, Murendeni; Oberholster, Paul Johan; Shonhai, Addmore; Makumire, Stanley; Gumbo, Jabulani Ray
The presence of harmful algal blooms (HABs) and cyanotoxins in drinking water sources
poses a great threat to human health. The current study employed molecular techniques to determine
the occurrence of non-toxic and toxic cyanobacteria species in the Limpopo River basin based on the
phylogenetic analysis of the 16S rRNA gene. Bottom sediment samples were collected from selected
rivers: Limpopo, Crocodile, Mokolo, Mogalakwena, Nzhelele, Lephalale, Sand Rivers (South Africa);
Notwane (Botswana); and Shashe River and Mzingwane River (Zimbabwe). A physical-chemical
analysis of the bottom sediments showed the availability of nutrients, nitrates and phosphates,
in excess of 0.5 mg/L, in most of the river sediments, while alkalinity, pH and salinity were in excess
of 500 mg/L. The FlowCam showed the dominant cyanobacteria species that were identified from
the sediment samples, and these were the Microcystis species, followed by Raphidiopsis raciborskii,
Phormidium and Planktothrix species. The latter species were also confirmed by molecular techniques.
Nevertheless, two samples showed an amplification of the cylindrospermopsin polyketide synthetase
gene (S3 and S9), while the other two samples showed an amplification for the microcystin/nodularin
synthetase genes (S8 and S13). Thus, these findings may imply the presence of toxic cyanobacteria
species in the studied river sediments. The presence of cyanobacteria may be hazardous to humans
because rural communities and farmers abstract water from the Limpopo river catchment for human
consumption, livestock and wildlife watering and irrigation.
2018-07-03T00:00:00ZMobility and Attenuation Dynamics of Potentially Toxic Chemical Species at an Abandoned Copper Mine Tailings DumpGitari, Wilson MugeraThobakgale, RendaniAkinyemi, Segun Ajayihttp://hdl.handle.net/11602/23162022-11-03T02:01:36Z2018-02-12T00:00:00ZMobility and Attenuation Dynamics of Potentially Toxic Chemical Species at an Abandoned Copper Mine Tailings Dump
Gitari, Wilson Mugera; Thobakgale, Rendani; Akinyemi, Segun Ajayi
Large volumes of disposed mine tailings abound in several regions of South Africa, as a consequence of unregulated, unsustainable long years of mining activities. Tailings dumps occupy a large volume of valuable land, and present a potential risk for aquatic systems, through leaching of potentially toxic chemical species. This paper reports on the evaluation of the geochemical processes controlling the mobility of potentially toxic chemical species within the tailings profile, and their potential risk with regard to surface and groundwater systems. Combination of X-ray fluorescence (XRF), X-ray diffraction (XRD), and scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) techniques, show that the tailing profiles are uniform, weakly altered, and vary slightly with depth in both physical and geochemical properties, as well as mineralogical composition. Mineralogical analysis showed the following order of abundance: quartz > epidote > chlorite > muscovite > calcite > hematite within the tailings profiles. The neutralization of the dominant alumino-silicate minerals and the absence of sulfidic minerals, have produced medium alkaline pH conditions (7.97–8.37) at all depths and low concentrations of dissolved Cu (20.21–47.9 μg/L), Zn (0.88–1.80 μg/L), Pb (0.27–0.34 μg/L), and SO42− (15.71–55.94 mg/L) in the tailings profile leachates. The relative percentage leach for the potentially toxic chemical species was low in the aqueous phase (Ni 0.081%, Cu 0.006%, and Zn 0.05%). This indicates that the transport load of potentially toxic chemical species from tailings to the aqueous phase is very low. The precipitation of secondary hematite has an important known ability to trap and attenuate the mobility of potentially toxic chemical species (Cu, Zn, and Pb) by adsorption on the surface area. Geochemical modelling MINTEQA2 showed that the tailings leachates were below saturation regarding oxyhydroxide minerals, but oversaturated with Cu bearing mineral (i.e., cuprite). Most of the potentially toxic chemical species occur as free ions in the tailings leachates. The precipitation of secondary hematite and cuprite, and geochemical condition such as pH of the tailings were the main solubility and mobility controls for the potentially toxic chemical species, and their potential transfer from tailings to the aqueous phase.
2018-02-12T00:00:00Z