Leaking of petroleum products from storage tanks is a commonly found cause of soil contamination. Among those petroleum products, diesel-oil contaminated soils are more difficult to treat compared to gasoline (a more volatile petroleum product). With the growing interest in environmental remediation, various approaches have been proposed for treating petroleum-hydrocarbon (PH) contaminated sites. Given that it is often not possible to remove the released oil or remediate the site completely within a short period of time, using the in situ remedial technology, soil excavation followed by more cost-effective technology should be applied to accelerate the efficiency of site cleanup. In the first-part of this study, laboratory degradation experiments were conducted to determine the optimal operational conditions to effectively and economically bioremediate diesel-fuel contaminated soils. In the second part of this study, a combined full-scale landfarming and biopile system was operated to cleanup diesel fuel-contaminated soils. In the laboratory study, except of frequent soil tilling for air replacement, different additives were added in the laboratory bioreactors to enhance the total petroleum hydrocarbon (TPH) removal efficiency. The additives included nutrients, TPH-degrading bacteria, activated sludge, fern chips, and kitchen waste composts. PH-degrading bacteria were isolated from PH-contaminated soils and activated sludge was collected from a wastewater treatment plant containing PH in the influent. PH-degrading bacteria and sludge were added to increase the microbial population and diversity. Fern chips and kitchen waste composts were added to increase the soil permeability. Results indicate that the bioreactor with kitchen waste compost addition had the highest TPH removal rate. The observed TPH-removal ratios for the compost, activated sludge, PH-degrading bacteria, fern chips, nutrients, TPH-degrading bacteria addition, and control (with HgCl2 addition) groups were 80.5%, 78.6%, 77.4%, 75.1%, 73.3%, 66.1%, and 1.6% respectively. In the field study, activated sludge was selected as the additive from the engineering point of view. With the addition of activated sludge, an increase of 20% was observed for TPH removal ratio. Results from the denaturing gradient gel electrophoresis (DGGE) tests show that the detected PH-degrading bacteria in the activated sludge included the following: Pseudomonas sp., Pseudoxanthomonas sp., Rhodocyclaceae bacterium, Variovorax sp., Acidovorax sp., Leptothrix sp., Alcaligenaceae bacterium, and Burkholderia sp. Some of these bacteria became dominant species in the field after a long-term operation, which was beneficial to the soil bioremediation. Results indicate that the in situ bioremediation has the potential to be developed into an environmentally and economically acceptable remediation technology.

MSc (Eng) dissertation - Faculty of Engineering and the Built Environment / Fertilizers are defined in the broadest sense as products that improve the levels of available plant nutrients or chemical and physical components that directly or indirectly enhance plant growth, yield and quality. The aim of this study was to produce slow controlled release fertilizers from oxidised coal. Two types of coals namely, Waterberg and Twistdraai (products, middlings) were utilised for the production of humic acids through slurry phase oxidation. The highest yields of humic acids were obtained in Waterberg and Twistdraai products samples. Subsequent to that, a nitrogen element was successfully inserted into the humic acid substrate. Humic acids are potential feedstock for modern manufacturing of organic fertilizers. The chemical substances regarded as hazardous to human consumption or those elements that negatively impact on the soil were significantly less detectable.