Polycyclic aromatic hydrocarbons (PAHs) and heavy metals are often present together at contaminated sites. These sites are considered difficult to clean-up using bioremediation technologies because of the toxicity of heavy metals to microorganisms. Laboratory experiments were conducted to verify if biodegradation of a model PAH, naphthalene, could be sustained over a long time-period (weeks) in the presence of a common heavy metal contaminant, Cr (VI). Complete reduction of Cr (VI) at concentrations up to 6.3 mg/L was achieved by Pseudomonas putida ATCC 17484 in the presence of naphthalene that was continuously released from an immiscible organic liquid, 2,2,4,4,6,8,8-heptamethylnonane (HMN). The presence of Cr (VI) inhibited bacterial growth and reduced naphthalene biodegradation rates. Despite this the microorganisms were able to degrade significant masses of naphthalene, quantities much greater than those reported in earlier studies. The addition of 1,2-Naphthoquinone, a possible by-product of naphthalene degradation and an oxidizing agent, resulted in improved naphthalene biodegradation rates in the presence of Cr (VI).

A dense nonaqueous phase liquid, o-dichlorobenzene (o-DCB) was removed by surfactant-enhanced electrokinetic remediation from saturated bentonite clay. The surfactant was Antarox BL-236, a nonionic surfactant with a solubilization capacity of 0.052 g DCB/g surfactant. The 9 cm long bed, which initially contained 10 wt % bentonite and a dispersion of o-DCB (2910 or 5821 ppm) in water, was placed in a horizontal cylinder (5 cm ID) and held at each end by a supported filter paper. Carbon disk electrodes were located in compartments at each end of the bed. Surfactant solution or distilled water was fed to the anode compartment and effluent was withdrawn from the cathode compartment to maintain liquid levels. A constant direct current of 1.53 mA/cm2 of bed cross sectional area was applied. The current generated hydrogen ions at the anode, hydroxyl ions at the cathode, and an electroosmotic flow from the anode to the cathode. Stainless steel pin electrodes placed in the bed and pH electrodes inserted into the bed and the electrode compartments gave continuous measurements of voltage differences and pH changes. Experimental runs were 48 to 96 hours in duration. / To prevent cracking of the bed, which increased the energy requirements, the cathode compartment was flushed continuously with 0.01 M HNO3, a procedure called cathode rinse. An anode feed of 10 wt % surfactant solution removed six times more DCB in 4 days than distilled water. About 20% of the solubilization capacity of the surfactant was utilized at 2910 ppm initial DCB, increasing to 34% for 5820 ppm. DCB was detected in the effluent after about 1.5 pore volumes of liquid passed through the bed; thereafter the rate of DCB removal was approximately constant. The effects of surfactant concentration and NAPL concentration on DCB removal and the energy expenditure were determined.

A common wastewater treatment process practised in zinc production plants is the single stage mixing of acidic wastewaters with slaked lime, inducing the reactive precipitation of fine (∼1 mum) gypsum (CaSO 4·2H2O) and other solids with a solids density of less than 10%. These solids report to tailings ponds for containment. / The solid-liquid separation step would be more efficient if the size and density of the precipitated solids were increased. Tailings pond life would be increased if the solids density of the precipitated solids was improved. It is the scope of this thesis to report on how high density and clean gypsum may be produced by implementing staging and product recycling. According to this work a staged neutralisation process (each neutralisation reactor operating at different pH) leads to production of large sized gypsum crystals with a high solids density. A continuous lab scale circuit run with synthetic zinc plant effluent produced large (∼100 mum) gypsum crystals with a solids density of 35%. / The effect of various metal impurities (such as Zn, Mn, Mg, Fe(II), Cd, Na) in concentrations ranging from 0.1 g/l to 10 g/l on the morphology of gypsum and their uptake by gypsum is investigated with the view of ultimately controlling gypsum contamination. By implementing staging and product recycling gypsum was produced containing less than 0.025% zinc and minor quantities of other elements hence meeting all industrial specifications for synthetic gypsum.

One major task facing the geoenvironmental engineering today is the development of methods to assess the long term changes, release and transport of contaminants from waste disposal sites, considering the hydrochemical interaction of the contaminants with the clay barrier. / Modelling of the leaching processes, which take place in a landfill, is an invaluable tool as it is often not possible to conduct experiments over sufficiently long timescales to observe the long term leaching behaviour of wastes. In this study the multi-component transport of heavy metals into a clay barrier has been investigated experimentally and theoretically by coupled solute transport and geo-chemical reaction. An experimental design for coupled solute transport and chemical reaction, based on the column leaching test in association with the batch equilibrium test for comparison, is proposed to examine the Cl and EDTA effects on the partitioning of Zn and Pb (dissolved, adsorbed, precipitated) into uncontaminated or; precontaminated kaolinite or; kaolinite mixtures with silica gel and calcium carbonate (K, KS, KC, KSC). / A COupled Solute Transport and CHemical Equilibrium SPeciation (COSTCHESP) model was developed to simulate the transport of multiple thermodynamically reacting chemical substances through clay barrier systems. It consists of two main modules; a finite difference transport module (COST), and an equilibrium geochemistry module (CHESP). This simplifies the coupling between the physical and chemical processes and leads to a simple and efficient model to simulate the simultaneous processes of advective-dispersive transport (advection; diffusion, osmotic and ion restriction effect) and geochemical reactions (complexation, exchange, precipitation, adsorption and desorption). The reliability of the model has been verified by laboratory experiments. / The proposed model accounts for most of the hydro-geochemical interactions of the multi-components with the clay liner. The model will lead to proper identification of the form of specific ions (i.e. adsorbed and precipitated on solid, and available in solution) and can be a useful tool for (i) assessing the importance of geochemical reactions on the transport of heavy metals in groundwater; (ii) predicting the forms by which the metals are partitioned in the clay barrier, and (iii) indicating the potential availability of the heavy metals from contaminated soil through the chemical processes, particularly, if one recognizes that the local equilibrium pH environment is neither stagnant nor uniform throughout the subsurface underlying the waste landfill. (Abstract shortened by UMI.)

One of the challenges mine operators have to face in large surface tailings disposal projects is to keep high tailings deposition rates under allowable values, while ensuring a sound and stable surface impoundment This is particularly important in the case of the upstream method of construction, in which perimeter dikes overlay soft unconsolidated deposits of fine materials (usually silts and days), where loss of shear strength could develop due to excess pore water pressure build-up. / This study offers a new approach for investigating the influence of tailings deposition rate over the structural behavior of upstream tailings dams, and its relation to the construction sequence and pond operation. A complex, yet practical method uses a nonlinear numerical algorithm, integrating a 1-dimensional self-weight consolidation model for fine grained materials, with a 2-dimensional stress-deformation finite element program for consolidation of earth structures. A beach profile equation is used to complete the structural geometry of the dam at various operating stages. The dam behavior is evaluated based on excess pore water pressure profiles, principal effective stress levels, and mobilized material strength. The time-dependent pond filling operation process and staged dam construction are simulated. / A case study from a large operating South African gold mine is used to perform simulations and parametric analyses. The behavior of the upstream tailings dam is assessed under both normal and increased slurry discharge rates. It is shown that under variable deposition rates, the present approach can help identify weak structural zones, and hence, improve the assessment of the structural dam safety. From such analyses, adequate tailings deposition rates conditions could be determined in advance for a variety of mill or pond operating conditions.

Biosorption is a property of certain types of inactive, dead biomass to bind and concentrate heavy metals from even very dilute aqueous solutions. It may be used for purification of metal containing industrial waste effluents. The issues related to the biosorption process design and optimization were addressed by (1) equilibrium isotherm relationships, (2) biosorption process rate and (3) breakthrough time in a continuous-flow biosorption column. This work investigates these three aspects for the biosorption of the heavy metals uranium and cadmium on protonated Sargassum fluitans seaweed biomass. / Biosorption uptakes of uranium and cadmium were evaluated by determining their isotherms at different solution pH values. It was established that the state of uranium in aqueous solution and ion exchange play an important role in the biosorption of uranium. A new equilibrium biosorption isotherm model based on ion exchange of uranium complex ion species was developed. The new model is capable of predicting the effect of proton as an exchanged species and of the metal speciation on the biosorption uptake for a equilibrium batch biosorption system. / The end-point titration method was applied in the experimental determination of the biosorption uptake rates of uranium and cadmium at different pH levels. A one-dimensional intraparticle diffusion rate model reflected well the controlling step in the uranium and cadmium ion transport inside the biosorbent. The PDEs of this new model were solved numerically by the Galerkin Finite Element Method (GFEM). / Biosorption of uranium was examined in a continuous-flow fixed-bed column at the feed pH 2.5. The biomass binding capacity for the uranium before the breakthrough was as high as 105 mg/g biomass. The elution with diluted hydrochloric acid produced an overall uranium concentration factor of about 25--30. A mass transfer model based on the external and intraparticle diffusion was developed to describe the column sorption performance. The model equations were solved by the Orthogonal Collocation (OC) numerical method. The model-calculated breakthrough curves agreed well with the experimental ones, indicating the potential of the model for process design and optimization.

Bioavailability is often considered to be the rate limiting process in the bioremediation of sites contaminated with hydrophobic organic compounds (HOCs). In order to meet the need for a direct measurement technique for microbial bioavailability, the whole-cell bioluminescent biosensor PpF1G4 was developed. To create PpF1G4, bioluminescent reporter genes (lux) were placed under the control of the promoter region of the solvent efflux pump genes (sep) in Pseudomonas putida F1. In screening experiments, it was determined that biosensor PpF1G4 produced a bioluminescent response to a wide range of aromatic compounds. / PpF1G4 was used to evaluate how three nonionic surfactants (Triton X-100, Brij 30 and Brij 35) influence the bioavailability of three different HOCs (toluene, naphthalene, and phenanthrene). Nonionic surfactants were used because they are in general less toxic to bacteria. The increased bioluminescent response of PpF1G4 in micellar solutions of Triton X-100 and Brij 35 indicated higher intra-cellular concentrations of the test compounds, toluene, naphthalene and phenanthrene, compared to control systems with no surfactants present. In contrast, Brij 30 caused a decrease in the bioluminescent response to the test compounds. The effect of the micellar solutions on the toluene biodegradation rate was consistent with the bioluminescent response. Thus, the bioluminescent response of PpF1G4 was an accurate indicator of bioavailability. The results suggest that nonionic surfactants enhance biodegradation in two ways: (1) by augmenting membrane permeability through binding of surfactant monomers; and (2) by increasing the mass flux of substrates present in the micellar pseudophase to the cells. / PpF1G4 was also employed to evaluate the bioavailability of HOCs partitioned from multicomponent NAPLs (gasoline, crude oil, and creosote) into surfactant solutions. All three surfactants tested increased the bioavailability of HOCs partitioned from creosote and crude oil. None of the surfactants significantly enhanced the response to gasoline-equilibrated solutions. The suppression of bioluminescence in Brij 30 solutions containing single test compounds did not occur in Brij 30 solutions containing multiple HOCs. This research sheds some light on how certain nonionic surfactants may increase the bioavailability of HOCs and thus enhance bioremediation.

Peroxidase enzymes oxidise phenolic compounds to produce free radicals which spontaneously polymerize and precipitate from solution. In order to be able to compare the performance of the various enzymes, a technique for the evaluation of the kinetic constants governing the reactions was developed. In order to do so, the reactions which occur between horseradish peroxidase, phenol, peroxide and aminoantipyrine in an assay were first defined then mathematically modeled. The kinetic model was applied to reactions conducted under a range of initial concentrations of peroxide and phenol. The model was calibrated against experimental data using a genetic algorithm. Based on this approach, an optimal set of kinetic parameters was determined which accurately reflect the trends in experimental data. Due to assumptions used in the development of the model and observations made on the laboratory and modeled data, it was found that the model was applicable to reactions in which the initial phenol concentration was above 1 mM and the peroxide concentration over 0.15 mM. These conditions can now be used to extend the application of the model to evaluate the kinetic parameters associated with other peroxidase enzymes.

The Activated Sludge Process is the most widely used wastewater treatment process in the pulp and paper industry. Black liquor from the Kraft Pulping Process is characterized by high inorganic and organic load; it also contains toxic compounds. Upsets in the plant operation lead to disturbances in the activated sludge process and the process fails to produce effluents that meet regulatory standards. In this project, the effect of black liquor on the activated sludge was studied. / Experiments were carried out in batch reactors and growth kinetics for the activated sludge were studied for each condition. In addition, the removal of chemical oxygen demand (COD), total organic carbon (TOC) and soluble lignin was studied with respect to time. Results from initial rate were compared. Characterization of activated sludge was done using the 'Biolog' technique. An attempt was made to correlate the results of the kinetic study and the activated sludge population. / Results from the specific rates indicate that for 0% black liquor, initial specific rates of COD (or TOC) removal (or the activity of microorganisms) were different for different initial biomass concentration. This trend however was not clear for the black liquor concentrations. For all conditions of biomass concentration, the specific rate was nearly the same. Due to the toxicity of black liquor, microorganisms that can survive the toxicity shock or those that can adapt to black liquor, may lead to a similar population in the system resulting in the same specific rate or the activity of the microorganisms. This was confirmed by the sludge characterization technique.

Recent laboratory studies have reported on the success of electro-kinetic extraction of heavy metals from contaminated test samples, and have suggested that this would be a useful in-situ remediation technique. However, field studies have shown limited success and some contradictory results. The basis for successful application appears to be a judicious choice of soil type and parametric constraints. / In this study, the surface charges of two soils (kaolinite and illite soils) are used as the primary control in the investigation of electro-osmotic extraction of lead---introduced as a contaminant into the soils. Four types of soils were used: pure kaolinite, illite soil, illite and sand as a mixture, and kaolinite and sand as a mixture. The contaminating lead concentrations, ranging from 100 mg/kg to 5000 mg/kg, were all below the CEC (cation exchange capacity) of the pure soils and their mixtures. / Electro-kinetic extraction tests showed that more than 60% of Pb was transported to the cathode in kaolinite, while there was little removal in the illite or sand/illite mixtures. Laboratory results demonstrated that the surface charges of the soils had important effects on the electro-kinetic extraction. / In addition, a modified technique, based on electro-chemical processes, was developed to maximize the contaminant extraction and to minimize precipitation at the cathodic region. The study's approach relies on combining electro-kinetics with conditioning fluids and acidification of the cathodic reservoir to enhance the efficiency of contaminant removal. An experimental testing program indicated that the success of electro-kinetic removal was governed by the quantity of H+ ions available in the system. It was also noticed that the hydraulic conductivity (in the same direction of electro-osmotic flow), the conditioning fluid, and acidification of the cathodic reservoir had positive effects on the removal of lead, while the OH- ions produced at the cathode and/or other anions induced during the acidification of the cathodic reservoir had negative effects on lead removal. / A modified model, based on interaction energies, was also presented for ion distribution next to the soil particle surface. The removal predictions of this model, through isotherm values, were compared with the results from batch equilibrium tests. A good correlation was noted.