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No description available.

The intrusive and expensive nature of soil cleanup technologies like excavation and incineration created a need to search for alternative remediation technologies. Rhizoremediation and its associated microorganisms has the potential to cleanup contaminated soil in a ‘non invasive’ and cost-effective manner. The literature cites many benefits of the technology if implemented correctly. However, there is still a lack of knowledge concerning the interaction of the plants and microorganisms that are responsible for degrading the organic pollutants. In this study, the potential for degrading Poly aromatic hydrocarbons (PAH’S) by rhizosphere bacteria was investigated. In addition, the hydrocarbon removal efficiencies of different plant rhizospheres were investigated. The metabolic and genetic profiles of soil bacteria in vegetated and non- vegetated soils were determined. The results of the removal efficiencies of different plant rhizospheres showed that the removal of hydrocarbons was more effective in soil vegetated by different plant species. By using co-occurring (different) plant species, hydrocarbons were removed faster than when monoplanted were used. The number of hydrocarbon degrading bacteria in the rhizosphere increased during rhizoremediation of PAH’s contaminated soil. Analysis of the functional and genetic diversity in PAH’s contaminated and non-contaminated rhizosphere and non-rhizosphere soil, using Biolog (physiological community level) and genetic diversity (polymerase chain reaction- denaturant gradient gel electrophoresis) was determined. The biolog did not revealed clear difference on substrate utilization profiles of the microbial communities in the rhizosphere and bulk soil. However, unlike the Biolog DGGE revealed slightly differences in both the metabolic and genetic profiles of the different soil samples. The study on the feasibility of seeding bacteria capable of colonizing and surviving on the rhizosphere showed that Pseudomonas putida successfully colonized the rhizosphere of Eleusine corocana. The number of P putida increased during rhizoremediation of PAH’s. These results suggest that bacteria with the ability to adhere and survive in the root zone can be engineered and seeded for rhizoremediation purposes. However, other factors such as the influence of soil type and organic matter content must be investigated to improve rhizoremediation technology. / Dissertation (MSc)--University of Pretoria, 2009. / Microbiology and Plant Pathology / unrestricted

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No description available.

This study examined biological mercury removal from soil using mercury-resistant bacteria in soil microcosms. Mercuric chloride was used to artificially contaminate Kidman soil to mercury concentrations of 5 ppm and 10 ppm. Soil moisture content was maintained at three levels, 20%, 30% and 50%. Mercury resistant-bacteria were added to soil samples and the mercury removal rate was compared to control samples without added bacteria. Mercury removal rate was initially enhanced by the addition of bacteria. After 30 days, no difference was observed between samples and controls with initial mercury concentration of 5 ppm when soil moisture content was 20%. At an initial mercury concentration of 10 ppm, soil samples had less mercury remaining than controls after 30 days. Autoclaved soil had a decreased mercury removal rate compared to soil not autoclaved. Addition of nutrient (sucrose) did not increase the mercury removal rate. A slurry-type bioreactor was found to be more efficient than a non-stir type. After 30 days of continuous stirring, 85-90% of the added mercury (10 ppm) was removed, while under the same conditions except no stirring, only around 60% of the mercury was removed. Overall, biological detoxification of mercury from contaminated soil can be achieved by using a slurry-type bioreactor with additon of mercury-resistant bacteria.

Although the pesticide DDT has been banned from use in Canada for more than three decades, DDT still persists in Canadian farmlands at detectable levels. Much effort, such as incineration, thermal desorption, and bioremediation, has been used to remediate DDT contaminated soils, but so far it is either too expensive or impractically slow. In this study, a three-year period of field trials was performed to investigate phytoremediation of DDT contaminated soil. In the field trials, millet, fall rye, sugar beet, potato, and pumpkin, treated with plant growth-promoting rhizobacteria (PGPR) were planted on two sites. As well, untreated plants were planted as a control. Plant growth, and 4,4’-DDT plus 4,4’-DDE concentrations in plant tissues and soil were monitored regularly. Comparing the plant growth between PGPR treated and untreated, PGPR significantly promoted the plant growth. On site 1, the root length and root weight of fall rye treated with PGPR were 16% and 44% greater, respectively, compared to the untreated plants. The root and shoot dry weights of millet treated with PGPR were 38% and 47% greater than those untreated plants. Root dry weight of sugar beet treated with PGPR was increased by 74% compared to untreated sugar beet. A significant effect of growth promotion was also observed in pumpkin and potato treated with PGPR. Following plant growth, DDT detection in plants was performed. 4,4’-DDT and 4,4’-DDE were found in plant tissues of fall rye, millet, sugar beet, and pumpkin. The concentrations of 4,4’-DDT and 4,4’-DDE in fall rye roots were 0.61 and 0.59 μg/g, respectively. In pumpkin tissues at harvest, 4,4’-DDT and 4,4’-DDE concentrations were 0.67 and 1.64 μg/g in roots, 1.06 and 2.05 μg/g in the lower stems, and 0.2 and 0.32 μg/g in the upper stems. The data indicated that it is feasible to phytoremediate DDT from contaminated soil. In addition, 4,4’-DDT concentrations in soils with different plant species were determined. In millet plot on site 1, 4,4’-DDT concentration in rhizosphere soil dropped by 41% in 2006 compared to 4,4’-DDT concentration at t0. In sugar beet plot on site 1, 28% of 4,4’-DDT dropped in rhizosphere soil in 2007. In pumpkin plot on site 1, 4,4’-DDT in rhizosphere soil was decreased by 22% in 2007. The results show that 4,4’-DDT concentration in rhizosphere soil was significantly lower than the initial level of DDT. Based on the data of 4,4’-DDT in soils and plant tissues, a mass balance was constructed and calculated. The preliminary mass balance shows that the total amount that DDT decreased in rhizopshere soil approximately equals to the total amount of DDT accumulated in plant tissues. This indicates that phytoextraction is the mechanism of DDT phytoremediation. In addition, PGPR promoted plant growth and then enhanced the phytoremediation efficiency of DDT. Therefore, the research indicates that PGPR assisted phytoremediation has a great potential for remediation of DDT and other chlorinated aromatics from impacted soil.

Although the pesticide DDT has been banned from use in Canada for more than three decades, DDT still persists in Canadian farmlands at detectable levels. Much effort, such as incineration, thermal desorption, and bioremediation, has been used to remediate DDT contaminated soils, but so far it is either too expensive or impractically slow. In this study, a three-year period of field trials was performed to investigate phytoremediation of DDT contaminated soil. In the field trials, millet, fall rye, sugar beet, potato, and pumpkin, treated with plant growth-promoting rhizobacteria (PGPR) were planted on two sites. As well, untreated plants were planted as a control. Plant growth, and 4,4’-DDT plus 4,4’-DDE concentrations in plant tissues and soil were monitored regularly. Comparing the plant growth between PGPR treated and untreated, PGPR significantly promoted the plant growth. On site 1, the root length and root weight of fall rye treated with PGPR were 16% and 44% greater, respectively, compared to the untreated plants. The root and shoot dry weights of millet treated with PGPR were 38% and 47% greater than those untreated plants. Root dry weight of sugar beet treated with PGPR was increased by 74% compared to untreated sugar beet. A significant effect of growth promotion was also observed in pumpkin and potato treated with PGPR. Following plant growth, DDT detection in plants was performed. 4,4’-DDT and 4,4’-DDE were found in plant tissues of fall rye, millet, sugar beet, and pumpkin. The concentrations of 4,4’-DDT and 4,4’-DDE in fall rye roots were 0.61 and 0.59 μg/g, respectively. In pumpkin tissues at harvest, 4,4’-DDT and 4,4’-DDE concentrations were 0.67 and 1.64 μg/g in roots, 1.06 and 2.05 μg/g in the lower stems, and 0.2 and 0.32 μg/g in the upper stems. The data indicated that it is feasible to phytoremediate DDT from contaminated soil. In addition, 4,4’-DDT concentrations in soils with different plant species were determined. In millet plot on site 1, 4,4’-DDT concentration in rhizosphere soil dropped by 41% in 2006 compared to 4,4’-DDT concentration at t0. In sugar beet plot on site 1, 28% of 4,4’-DDT dropped in rhizosphere soil in 2007. In pumpkin plot on site 1, 4,4’-DDT in rhizosphere soil was decreased by 22% in 2007. The results show that 4,4’-DDT concentration in rhizosphere soil was significantly lower than the initial level of DDT. Based on the data of 4,4’-DDT in soils and plant tissues, a mass balance was constructed and calculated. The preliminary mass balance shows that the total amount that DDT decreased in rhizopshere soil approximately equals to the total amount of DDT accumulated in plant tissues. This indicates that phytoextraction is the mechanism of DDT phytoremediation. In addition, PGPR promoted plant growth and then enhanced the phytoremediation efficiency of DDT. Therefore, the research indicates that PGPR assisted phytoremediation has a great potential for remediation of DDT and other chlorinated aromatics from impacted soil.

Soil and groundwater at many existing and former industrial areas and disposal sites is contaminated by petroleum hydrocarbons that were released into the environment. Among those petroleum hydrocarbons, fuel oil is more difficult to treat compared to gasoline and diesel fuel due to its characteristics of low volatility, low biodegradability, and low mobility. Thus, a combination of several different treatment technologies is required to remediate fuel oil contaminated soil or groundwater. The objective of this study was to assess the potential of applying Fenton-like oxidation process to remediate fuel-oil contaminated soils. The following tasks were performed in this study: (1) determination of the optimal oxidation conditions, (2) evaluation of the efficiency of chemical by Fenton-like process after the pretreatment of surfactant flushing, and (3) evaluation of the stability of H2O2 by the addition of potassium dihydrogen phosphate (KH2PO4). Total petroleum hydrocarbons (TPH) in soil were analyzed to determine the effectiveness of the oxidation treatment. Results from this study show that the highest TPH removal efficiency (84.8%) was obtained for soils containing 3%(w/w) of fuel oil when 3% of H2O2 was applied followed by 0.05% of H2O2 with 56.7% of TPH removal. Results also show that approximately 69.1% of TPH removal was detected with soils containing 5%(w/w) of fuel oil when 6% of H2O2 was applied followed by 3% of H2O2 with 56.7% of TPH removal and 0.05% of H2O2 with 32.6% of TPH removal. Results also indicate that Fenton-like process has much higher oxidation efficiency than using H2O2 alone. The oxidation efficiency was significantly affected when the contaminated soils were pretreated with surfactant. Results reveal that the maximum allowable surfactant addition was approximately 0.7% (w/w) for soils containing 0.5% (w/w) of fuel oil when 6% of H2O2 was applied. Addition of 2.2 mM of potassium dihydrogen phosphate influence could increase the stability of H2O2, but caused the decrease in the efficiency of TPH removal. During the Fenton-like reaction, pH values were close to 6 to 7. The neutral to slightly acidic conditions caused the decreased dissolution rate of iron minerals. This would also cause the decreased production of hydroxyl radicals from the surface of iron minerals. Results from the byproduct analysis show that the oxidation potential of Fenton-like process is not strong enough to completely destroy the fuel oil to non-toxic end products. The oxidation process produced byproducts containing carboxyl groups with molecular weights similar to their parent compounds.

Toxic metals contaminate soil worldwide and thus serve as sever environmental threat. Therefore the purposes of this study were to investigate in which soil fractions that different heavy metals (Fe, As, Cu, Zn and Pb) could be found in contaminated soils and if it is possible to use sieving as a method for decontamination. Soil samples were collected from three different locations, the Nasa silver mine, the Blaiken-mine and Svalget environmental station. The samples were oven dried and later on sieved into six different fractions 8mm, 4 mm, 0.5 mm, 0.250mm, 0.063 mm and <0.063 mm. The fractions 4 mm, 0.5 mm and <0.063 mm from each location were analyzed in an x-ray fluorescence detector. The results showed that in general the smallest fractions contained the highest concentration of heavy metals which was very clear for Pb where 5 out of 6 samples had the highest concentration in the smallest fraction. The highest concentration of Cu (1147 ppm) and Zn (1117 ppm) were found in the smallest fraction in samples from the location Svalget. The highest concentration of Pb (10042 ppm) was also found in the smallest fraction in samples from Blaiken. In similarity the highest concentration of As (13305 ppm) was found in the smallest fraction in samples from the Nasa mine. However, in most samples the difference between the smallest fractions and the coarser material was small. Sieving may therefore not be the best way to decontaminate soil because even the larger fractions contained high concentrations of heavy metals.