Chlorinated aliphatic hydrocarbons (CAH’s) are a diverse group of industrial chemicals that play a significant role as pollutants of soil and groundwater. They are recalcitrant and resist degradation in most waste treatment systems. Furthermore, physical removal techniques used for CAHs are often very expensive, labour intensive and time consuming. Microbial communities native to contaminated areas are known to participate in biodegradation of these CAHs to an extent. The main focus of this study was therefore to investigate the bioremediation of soil contaminated with a mixture of CAHs, namely carbon tetrachloride (CCl4), dichloromethane (DCM) and 1, 2 dichloroethane (1, 2-DCA). Two different laboratory-scale microcosm types, a stationary microcosm (Type S) and microcosms that received a continuous circulation of groundwater (Type C) were used to determine the effects of 3 different bioremediation approaches, viz, biostimulation, bioaugmentation and a combination of biostimulation and bioaugmentation on the degradation process. For both microcosm types, gas chromatography analysis revealed that the greatest decreases in CAH concentrations occurred in soil that was biostimulated. 1, 2-DCA was rapidly biodegraded in Type C microcosms that contained glucose, with a 57% net degradation in 15 days. Consortia comprising of aerobic Bacillus and Alcaligenes sp. were used for bioaugmenting contaminated soil. However, this approach did not promote biodegradation as significantly as biostimulation experiments. A combination of biostimulation and bioaugmentation revealed that the addition of nutrients was still unable to induce the degradative ability of the introduced microorganisms to produce degradation values comparable to those of biostimulated soil microcosms. Common intermediates of CAH metabolism viz., chloroform, dichloromethane and carbon dioxide were detected by gas chromatography/mass spectrometry. The detection of chloroform and dichloromethane is sufficient evidence to assume that anaerobic conditions had developed, and that biodegradation was occurring under oxygen-limiting or oxygen-free conditions. An aerobic environment was initially created, but soil microbial respiration had probably led to the rapid development of anaerobic conditions and in all likelihood, enhanced degradation. The prevalence of anaerobic conditions can also account for the lack of appreciable degradation by the bacterial consortium used during bioaugmentation. Phospholipid phosphate analysis was conducted and used as an indicator of microbial biomass. It was noted that phospholipid phosphates did not always correlate with the degradation of CAHs in some microcosms. In this regard, different patterns were noted for Type S and Type C microcosms. Microbial biomass patterns for Type C biostimulated and bioaugmented soil microcosms increased within the first 5 days of sampling. This could have been as a result of the larger volume of groundwater required for the circulating microcosm possibly concealing actual CAH concentrations. In contrast, in Type S microcosms, for most treatments, a sharp decline in biomass within the first week was observed. This study clearly demonstrates that the bioremediation of certain chlorinated solvents can be a function of their water solubility. It must also be emphasized that the biodegradation of some CAHs in a mixture can affect the concentrations of others present in the mixture as well, warranting further study with mixtures of CAHs. Furthermore, the development and use of bioreactors, similar to the Type C microcosm can provide novel, simple ways to hasten remediation of chlorinated solvents like 1, 2-DCA. / Thesis (M.Sc.) - University of KwaZulu-Natal, Durban, 2008.

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The objectives achieved in this thesis are: (1) to develop a new method for measuring the most important acid buffering mechanism within a soil ecosystem-mineral weathering and (2) to test a soil acidification simulation model against actual field data to determine which soil acidifying or buffering mechanisms seem to be understood and which mechanisms need more detailed analysis. First, a new method was developed that allows for quantification of H$ sp+$ consumption due to weathering and H$ sp+$ consumption due to cation exchange. Initial results yield mineral weathering rates that are well within the range of results obtained by other workers. This technique permits the analysis of multiple soil samples in a relatively short time, allowing for better quantification of spatial variability of mineral weathering within a soil ecosystem. Secondly, it was demonstrated that the acid simulation model generally underestimates soil chemistry values for pH, base cation saturation and soil solution base cations, and overestimates soil solution nitrate concentrations. Problems with obtaining accurate measurements of atmospheric dry deposition, a lack of data on cycling of nutrient elements and the absence of a sub-model to deal with the accumulation and mineralization of organic matter are reasons thought to explain the differences between model and field results.

The platinum microelectrode technique for measuring oxygen flux in soils has been reviewed. Shortcomings in the existing technique and instrumentation have been discussed. The new instrumentation, electrode standardization and measurement techniques developed enable the method to be used with confidence in unsaturated soil systems. Measurements of oxygen flux index in four soil samples showed a very highly significant regression relationship between oxygen flux index and air space within the range 3 - 15% air space on each soil. There was no significant difference in the regression relation between soils. A field penetrometer, designed to measure the presence and strength of subsurface pans in field soils has been described. Measurements with the penetrometer on three depth of ploughing treatments (100, 230 and 355 mm) on tillage trials at four sites with different clay contents showed that hard layers were present on all the treatments. Except on the shallowest ploughing depth treatment on the fine-textured soil, where the pan was 225 mm below the nominal ploughing depth, the hard layers were present between a few mm and 150 mm below the nominal ploughing depth, and had strengths of between 16 and 24 bars. The theory and factors affecting measurement of soil strength with needle penetrometers have been investigated. The design and operation of a laboratory penetrometer used to measure soil strength under closely controlled laboratory conditions has been discussed. Physical factors likely to affect root growth, viz. soil texture, air space, bulk density, soil strength and available moisture, have been measured in a comprehensive range of undisturbed cores taken from the four tillage trials. High soil strength is considered as being the soil physical factor most likely to restrict root growth in these soils. Physical factors affecting soil strength have been investigated. Soil strength is shown to be highly dependent upon bulk density, matric potential and soil texture. The hard pans shown to exist in all the tillage trial soils exhibit many of the characteristics of tillage pans, but their existence cannot be attributed exclusively to the ploughing depth treatments imposed in the tillage trials. Rather, the pans have resulted from a combination of interacting factors, including the previous history of the soils, the imposed tillage treatments, crop, and climatic factors. A study of some of the data from the literature on root growth and soil strength shows that root growth is severely restricted by soil strengths of the order of 20 to 30 bars. In order to determine whether root growth was being restricted in the tillage trials, root profiles were extracted from one of the trials. These showed that the pans severely restricted root growth. Analysis of maize yield data from the tillage trials showed that on the three coarse-textured sites yield increased with increased depth of ploughing, and that there was a marked seasonal effect, ploughing depth having a relatively greater effect on maize yield in dry seasons than in wet. On the fine-textured site, however, where no pan existed near the surface in the shallow ploughed treatment, the ploughing depth effect was not significant, nor was there any marked seasonal effect of ploughing depth on maize yield. Evidence presented shows that the pans, by restricting root growth are reducing the amount of water available to the plant. This effect is greater in dry seasons, and in soils with low available water . / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1976.

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An estimation method for predicting the saturated hydraulic conductivity (Ksat) of the soil was developed for common Nova Scotia soil types by examination of historical Ksat records. Detailed statistical analysis was performed to develop useful predictive models for Ksat based on soil physical properties and to determine the confidence limits for specific horizon-soil type combinations. Sensitivity analysis of the Hooghoudt equation was then performed to establish Ksat classes to which the confidence limits could be assigned to complete the development of the estimation method. / Model development processes proved unsuccessful due to the influence of factors not considered by the model due to their qualitative nature. Independent field testing of the estimation method with respect to core and Guelph permeameter measurement techniques produced measured values within the same class as the estimated value 34% of the time for both techniques and values within one estimated class or less 70 and 76% of the time for core and permeameter techniques respectively.

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