No description available.

No description available.

Chromium contamination of groundwater and soils continues to pose a major environmental concern. Soils may have become contaminated with chromium through former industrial activities geochemical enrichment. The nature of the industrial activity will determine the form and concentration of the chromium as well as the presence of co-contaminants and the pH and redox of the soil. Chemical reductants have been widely used for the transformation of hexavalent chromium in the environment. Over recent decades attention focused on the chemical reductant calcium polysulphide which has performed effectively in the treatment of groundwater and soil samples contaminated with Cr(VI). Yet a detailed understanding of calcium polysulphide (CaSx) performance has not yet been established. Hexavalent chromium concentrations in aqueous and groundwater samples were significantly reduced by calcium polysulphide and CaSx:chromate molar ratio of 1.5 was sufficient to prevent partitioning of Cr(VI) into solution and to precipitate the solution phase. Calcium polysulphide was used for the remediation of solid chromite ore processing residue (COPR) samples. Prior to the application of calcium polysulphide to COPR, each of the key steps were optimized. A range-finding experiment was conducted to understand the dosage and treatment regime at which Cr(VI) immobilization within COPR was optimal. The results indicated that unsaturated deployment of CaSx into the medium outperformed that in saturated systems. A higher polysulphide amendment dose of 5% w/v concentration enhanced the final treatment of Cr(VI) within COPR. The toxicity and carcinogenicity of Cr(VI) over Cr(III) requires a technique capable of discriminating between valencies. The EPA Method 7196A specifically quantifies the concentrations of Cr(VI) in environmental samples and was used for all analysis to differentiate between Cr(VI) and Cr(III). Cr(III) was calculated as the difference between the Cr(VI) and Cr-total concentrations. In addition to the EPA 7196A, a novel ion exchange resin (IER) procedure was developed to differentiate the two species of chromium. After optimisation, Amberlite resins IRA 400 and IR-120 were used for the specific sorption and subsequent analysis of aqueous Cr(VI) and Cr(III) solutions. For the selective removal of chromate from groundwater, waste water and soil samples, Amberlite IRA 400 achieved a consistent performance of >97% removal in a range of trials. The IERs in this work were applied as analytical tools however they could be applied as remediation tools. While aqueous treatment of chromium contaminated media using CaSx was very successful, COPR treatment proved to be difficult due to the complex nature of the system. An understanding of stoichiometric responses to CaSX has been established, but the nuances of soil physicochemical interactions require more thorough investigation.

Hydrocarbon contamination of soils has increased worldwide and bioremediation offers an attractive and environmentally friendly solution to this problem. However, the efficiency and completion of remediation must be assessed using environmental risk assessment criteria. As a result, a variety of indicators have become essential for determining and evaluating recovery of contaminated soils. In this study, microbiological and toxicological assays are used to support traditional chemical analyses, to identify a suite of assays suitable for determining a Soil Recovery Index from Pollution (SRIP). Microbiological assays used are microbial biomass carbon (Cmic), plate counts for culturable degraders and general heterotrophs enzyme activities (dehydrogenase and phosphatase), basal respiration, Substrate Induced Respiration (SIR), and bacterial biosensor. Toxicological response assays of higher organisms include two species of earthworms (Eisenia fetida and Lumbricus terrestris), also, plant assays, including seed germination, root elongation, germination index and plant shoot height performed using two species of plant wheat (Triticum aestivum L.) and white mustard (Brassica alba L.). All assays were applied sequentially to kerosene and diesel amended soils for both incubated and non–incubated treatments. The indicators were discriminated in terms of their sensitivity using a ranking system. The data collected were integrated into a single numeric value to reflect a ‘level of concern’ for each soil treatment. Soil characteristics and hydrocarbon types play key roles in the response of these indicators. The soil that had high organic matter and clay content was less affected by hydrocarbons. For the freshly hydrocarbon amended soils, kerosene was more toxic than diesel, however the opposite was found in the incubated hydrocarbon amended treatments. The most sensitive and robust indicators were basal respiration, bacterial heterotrophs and degraders counts, bacterial biosensors (methanol extracted soils), earthworm survival, mustard root elongation and mustard plant shoot height. Sensitive indicators were inserted into the SRIP. The SRIP indicates the “level of concern” for each soil treatment in a single value.

No description available.

More than 30,000 potential Superfund sites have been identified. Heavy metals are contaminants at many of these Superfund sites. The average cost of cleanup a single-typical Superfund site currently stands at $20 million, and it is expected that the cost may escalate to $50 million within the next decade. Problems have already been encountered during the inspection of sites, and available technologies have not been effective in treating all sites. Lack of innovative strategies for dealing with contaminated soils is a major obstacle to completing Superfund site cleanup. The characteristics of low molecular weight (LMW) organic acids (citric, oxalic, and succinic acids) can be utilized as an agent in soil washing and flushing to develop an innovative technology in the remediation of the soil contaminated with heavy metals. The objective of the work was the testing of a new remediation technology involving soil flushing and washing with LMW organic acids, designed to permanently remove heavy metals from contaminated soil at Superfund sited. Significant amounts of heavy metals (Cu, Pb, Zn) were removed and formed soluble metal-organic complexes at higher concentrations of organic ligands. At a citric concentration of 100 mM, over 70~80% of copper, lead, and zinc were mobilized and all metals extracted were complexed with citrate ions as various forms. Therefore, the use of citric acid to remove heavy metals from contaminated soils would be less costly that using EDTA. The subsequent pH elevation by hydrated lime, Ca(OH)₂, causes the decomplexation of Pb-citrate and initiates precipitation of lead hydroxide. Results showed that slightly alkaline conditions (pH 8.5), which are much lower than that used with EDTA, are needed for substantial precipitative removal of the lead. Increasing calcium nitrate concentration significantly improved the Pb(II) desorption via a cation exchange reaction, That is, the time required to recover lead from the contaminated soil during a soil column experiment was greatly reduced as the concentration of calcium nitrate in the influent was increased. Varying influent pH had little effort on the rate of lead mobilization in the soil columns due to the buffering capacity of the soil, which maintained the effluent pH at the soil pH. The effluent flow rate had no effect on mobilizing Pb(II) from the soil. A higher concentration of citric acid resulted in a much faster rate of lead mobilization from the contaminated soil. Differences in lead desorption rates between influent pHs of 4.5 and 6 were significantly high. However, lead desorption curves for citrate solution at a lower pH value (pH < 4.5) were nearly identical. The flow rate of effluent has no effect at removing lead in the range of 0.1~1.0 mL/min. Also, lead transport model was developed under the assumption of one-dimensional flow through a homogeneous porous medium. A simplified model was also developed by assuming no dispersion effect, no immobile aqueous-phase zone, and linear desorption kinetics. An analytical solution of the simplified equation was obtained by solving a partial differential equation. The computer simulations were fitted to experimental data using estimates for model parameters which were not obtainable independently in experiments. At higher concentrations and pH of the influent, this model presented here fitted well with the experimental data. / Graduation date: 2013

published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy

The Redwater Production Area (RPA) is an established oil field located north of Edmonton in central Alberta. Recent assessments indicate that substantial amounts of hydrocarbon contaminated soil exist in the RPA as a result of the use of flare pits, ecological ponds, product spills and pipeline leaks. Alternative remedial technologies may reduce the quantity, cost, and ultimately the long-term liabilities associated with the current practice of landfill disposal. The purpose of this thesis is to assess the viability of accelerated biopile soil treatment as a remedial methodology in the rehabilitation of contaminated soil in the RPA. The thesis includes a literature search, a bench scale treatability and pilot biopile experiment and concludes with a summary of the viability of biopiling to be employed as part of a multi-year/multi-site remedial initiative. Construction of the Redwater Soil Treatment Facility began in 2008 with treatment and recycling operations commencing in early 2009.

A laboratory study was conducted to bioremediate a fine textured soil contaminated with diesel. The local microorganisms were stimulated by supplying nutrients with the aid of a water table management system. A fine textured soil, contaminated for more than 20 years, with more than 6500 mg/kg of diesel was packed in fifteen columns, 2 m long and 0.2 m in diameter. Twelve out of fifteen soil columns were subjected to bioremediaton, by supplying nutrients, water and air at desired depths. Three columns were used as a control to monitor passive degradation of contaminant without intervention. / The experiment was designed to employ three different treatments in triplicates. In the first treatment, nutrients, air and water were supplied. In the second, only nutrients and water were applied and in the third, water alone was applied. These treatments were applied by two different water table management strategies. In the first, three columns were remediated by following a full column remediation strategy, while in the second, nine columns were treated in a stagewise manner, by maintaining the water table at 1 m depth from surface. (Abstract shortened by UMI.)

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.