Thesis (MSc. Agriculture (Soil Science)) -- University of Limpopo, 2019 / Global shortage of fresh quality water has led to the use of treated wastewater in arid
and semi-arid regions. Although, the treated wastewater has proven to be the best
solution in ameliorating pressures brought by water shortage, it contains toxic heavy
metals, some in high concentrations that could possibly pose health risks and
degrade soil quality. Therefore, the objectives of the study were to determine the
vertical and horizontal distribution of bioavailable heavy metals on virgin, cultivated
and fallowed fields and to investigate the bioremediation abilities of selected soil
microbes on non-essential heavy metals in cultivated and fallowed soils following
irrigation with treated wastewater at University of Limpopo (UL) Experimental Farm.
Three fields, namely, virgin field (VF), cultivated field (CF) and fallowed field (FF),
each being 6.4 ha, were each divided into 40 equal grids, equivalent to 40 m × 40 m,
which were used in vertical assessment of heavy metals.
Soil profiles were established inside each grid and soil samples collected at 0-20;
20-40 and 40-60 cm soil depth for further laboratory analysis. The soil samples were
analyzed for basic soil physico-chemicals, namely, particle size distribution, soil pH
(H20 and KCl), electrical conductivity (EC), reduction potential (Eh), organic carbon
(OC) and cation exchange capacity (CEC). Five essential heavy metals namely zinc
(Zn), iron (Fe), copper (Cu), cobalt (Co), manganese (Mn) and five non-essential
heavy metals, namely, arsenic (As), chromium (Cr), lead (Pb), aluminium (Al), and
cadmium (Cd), were also extracted from the soil samples. Heavy metal resistant
Gram-negative (–) and Gram-positive (+) bacteria were isolated from the soil and
identified as Providencia rettgeri (–), Enterobacter cloacae (–), Bacillus cereus (+)
and Arthrobacter aurescens (+).
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The isolated bacteria were cultured and inoculated in heavy metal-contaminated
soils and incubated for 12 weeks to bioremediate the non-essential heavy metals.
Results obtained suggested that the treatments had no significant (P ≤ 0.05) effects
on vertical distribution of all the essential and non-essential heavy metals among the
three fields. However, on average Co was above the permissible level at 53 mg/kg in
CF at 0-20 cm and although all the other essential heavy metals increased, they
were still within the permissible levels. The concentration of As was also above the
permissible levels in CF with an average concentration of 4.30 mg/kg. Cadmium
levels were also above the permissible levels in CF with an average concentration of
1.146 mg/kg in CF and this increased by 0.46 units from VF which had an average
value of 1 mg/kg. However, fallowing reduced Cd to 0.51 mg/kg which was below or
within the expected limits in soil previously irrigated with treated waste water.
Gram-positive bacteria reduced more concentrations of non-essential heavy metals
separately and combined, especially in the fallowed field. Irrigation with treated
wastewater has shown to have both negative and positive effects on the
concentration of essential and non-essential heavy metals in cultivated and fallowed
fields. Bioremediation coupled with fallowing has been proven to be the best solution
in ameliorating heavy metal toxicity while naturally improving the quality of the soil. / National Research Foundation (NRF)
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ul/oai:ulspace.ul.ac.za:10386/2886 |
| Date | January 2019 |
| Creators | Phadu, Moedisha Lorraine |
| Contributors | Manyevere, A., Kgopa, P. M., Mashela, P. W. |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | xix, 112 leaves |
| Relation | Adobe Acrobat Reader |
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