As more contaminated sites are being discovered, new in situ remediation techniques need to be developed. Chemically treating soil with lime to increase soil pH is a method that may decrease the bioavailability of the contaminant. To test the usefulness of rendering metal-contaminated soils alkaline with dolomitic lime, to improve crop performance, field trials at a site in Port Colborne, ON, with soil nickel concentration (as high as 5000 mg/kg) from refinery emissions were completed. Oat and soybean yield, as well as plant uptake and bioavailabilty of nickel in soil were evaluated. Liming Ni-contaminated soils decreased soybean foliar Ni concentrations from 36.68 µg/g in unlimed fields to 19.98 µg/g in 50 t/ha limed fields in the 2007 growing season; yield of both oat and soybean in unlimed soils was the same (p>0.05) as at a reference site, suggesting that for these soils, remediation is not necessary for yield.

A laboratory scale study was conducted to evaluate the thermal remediation of trichloroethylene (TCE) in a saturated groundwater system using electrical resistance heating (ERH). Two experiments were conducted using a two-dimensional polycarbonate test cell, the first consisting of a single pool of TCE perched above a capillary barrier, the second consisting of two pools of TCE each perched on separate capillary barriers. Temperature data was collected during the heating process from an array of 32 thermocouples located throughout the test cell. Visualization of the vaporization of liquid phase TCE, as well as the upward migration of the produced vapour was recorded using a digital camera. Chemical testing was performed 48 hours after experiment termination to measure post heating soil concentrations. A co-boiling plateau in temperature was found to be a clear and evident earmark of an ongoing phase change in the pooled TCE. Temperature was found to increase more rapidly in the second experiment that included a fully spanning barrier. As temperatures increased above the co-boiling plateau, vapour rise originating from the source zone was observed, and was found to create a high saturation gas zone beneath the upper capillary barrier when no clear pathway was available for it to escape upwards. When the source zones had reached the target temperature of 100°C and the ERH process stopped, this high saturation gas zone condensed, leading to elevated TCE concentrations below as well as within the capillary barrier itself. The water table within the experimental cell was also noted to drop measurably when the gas zone collapsed. Post-testing chemical analysis showed reductions in TCE concentrations of over 99.04% compared to the source zone, although due to condensation of entrapped gas and convective mixing, there was a net redistribution of TCE within the experimental domain, especially within confined areas below the capillary barriers. A secondary set of experiments were conducted using a homogenous silica sand pack with no chemical contaminants to determine the effect, if any, of the wave shape of electrical input on the ERH process. It was found that in early time heating, square wave inputs consistently produced a more localized heating pattern when compared to the standard sine wave electrical input. This effect equalized between the two experiments as the ERH process went on, perhaps due to the increased dominance of conduction and convection as the mode of heat transfer in the test cell at higher temperatures. It is believed that the localization of heating in square wave experiments is due to a consistent power supply due to the lack of a sinusoidal ramping in power delivery. / Thesis (Master, Civil Engineering) -- Queen's University, 2009-03-18 14:40:46.019

Weak organic acids and/or their salts were tested as soil washing or flushing agents for the ex- or in-situ remediation of soils polluted by heavy metals. Three soils naturally with heavy metals were used for the tea. / The three soils were characterized as a clay loam, loam and sandy clay loam. Their organic matter, pH, saturated hydraulic conductivity, cation exchange capacity, particle density and heavy metal contents were also characterized. The different retention forms of heavy metals in all 3 soils were studied by sequential extraction. The clay loam was contaminated with Cr, Hg, Mn and Pb while the loam and sandy clay loam were contaminated with Cd, Pb, Cu and Zn. Weak organic adds and/or their salts and chelating agents (EDTA and DTPA) were used at different pH, levels of concentration and leaching time in batch experiments to establish optimum conditions for maximum removal of heavy metals from the three soils. Citrate and tartarate were found to be quite effective, in leaching heavy metals from these soils. The rate of leaching of heavy metals from soils with citrate, tartarate and EDTA was modeled using two-reaction model at a constant pH and temperature. / Three contaminated soils of different textures were flushed in a column at optimum pH with a salt of weak organic acids, namely, citrate, tartarate, citrate+oxalate or a chelating agent such as EDTA and DTPA. The citrate and tartarate (ammonium salts) were found to be quite effective in removing heavy metals from the three contaminated soils while leaching little macronutrients and improving the soil's structure. An in-situ soil remediation simulation was also successfully tested using the sandy clay loam at large scale level in a tub (plastic container) using citrate as a flushing liquid. EDTA and DTPA were effective in removing the heavy metals except for Hg, but these strong chelating agents extracted important quantities of macronutrients from the soil. These chelating agents are also known to pollute the soil by being adsorbed on the soil particles. / A bioremediation process was developed using the fungus Aspergillus niger to produce weak organic acids (mainly citrate and partly oxalate depending on pH) for the leaching of heavy metals from contaminated soils. The fungus was cultivated on the surface of the three contaminated soils for 15 days at 30°C and a pH ≤ 4 to enhance the production of citric acid rather than oxalic acid which hinders Pb leaching. By extrapolating the result, the three contaminated soils were expected to be sufficiently remediated to meet the A category (Quebec clean up criteria for cleaning soils contaminated by heavy metals) after 20 to 25 days of leaching using this technique. / Finally, the leachate, collected following the soil remediation using weak organic acids and/or their salts, EDTA and DTPA was treated effectively using granular activated carbon.

The primary objective of this study was to investigate the use of water table management (WTM) as a microbial delivery system for in-situ bioaugmentation of contaminated soils. In addition, the use of Rhizobium ( R.) for PCB degradation in soils was evaluated. / First, the presence and isolation of a variety of strains of Rhizobium meliloti was demonstrated using plant nodulation tests on alfalfa plants in soils that were contaminated for over 15 years with PCBs, PAHs and heavy metals. Next, R. meliloti, strain A-025, was selected based on its membrane (hydrophobicity, adhesion) characteristics and its potential to transform PCBs. This strain was delivered and implanted in sod columns, 200 mm in diameter x 1000 mm in length, packed with a sandy loam soil, using surface and subirrigation. The results of this study showed that subirrigation led to a higher number and a more uniform distribution of the bacterial cells in the soil at 60, 300, 500, and 700 mm depths, than surface irrigation. / In a different setup, similar column were packed with a PCB contaminated soil. These soil columns were bioaugmented with three bacterial cultures, i.e., R. meliloti (strain A-025), Comomonas testosteroni (strain B-356) and an indigenous bacterial consortium using subirrigation. The results indicated that bioaugmentation of the PCB contaminated soil was possible by using subirrigation. Bioaugmentation with the indigenous culture was observed to be more effective in the biodegradation of PCBs than with A-025 and B-356 cultures at 140 and 340 mm depths. However, at 590 mm depth, bioaugmentation with strain A-025 was observed to be better than the other treatments. Sequential aerobic and anaerobic cycles appear to be of significance for effective dechlorination of PCB congeners to lower chlorinated congeners. / In a separate exploratory study, the rhizospheric effects of alfalfa plants on R. meliloti for PCB depletion were investigated. The results suggest that the growth of alfalfa plants and bioaugmentation of soil with R. meliloti, strain A-025, increased the depletion of PCB congeners in the soil as compared to bioaugmentation alone. In other preliminary studies, the results showed that the presence of PCBs in a sandy loam soil increases the filtration of bacterial cells. Also, soil type and the presence of PCBs affected water infiltration, moisture, and hardness of the soil. Furthermore, water table management system along with bioaugmentation of soil columns with R. meliloti, strain A-025, decreased the concentration of atrazine by 31% during anaerobic and aerobic cycles and reduced the concentration of nitrate by 87% and 78% in the absence and presence of atrazine, respectively, in the drainage water. / The overall results of this work indicate that water table management (subirrigation) can be used for bioaugmentation of contaminated soils. Also, use of R. meliloti may prove to be an interesting option for soils contaminated with PCBs, atrazine and nitrate.

A possible remediation strategy that involved washing with complexing reagents(s) [disodium ethylenediaminetetraacetate (Na2EDTA) alone or in combination with bis-(2-hydroxyethyl)dithiocarbamate (HEDC)] was evaluated with an urban soil that had been field contaminated with excesses of heavy metal (HMs). Heavy metals (Cd, Cu, Mn, Ni, Pb and Zn) were targeted for removal. The aqueous solution that resulted from, washing was treated with zero-valent (ZV) magnesium (Mg0) or bimetallic mixture (Pd0/Mg 0 or Ag0/Mg0) to release the chelating reagent(s) from their heavy metal complexes. During this reaction, the heavy metals were precipitated from solution as hydroxides or became plated on to the surface of the excess ZV reagent. Thus, an appreciable fraction of the mobilized Pb and Cu and a portion of Zn became cemented to the surface of the ZV metal whereas most of the Fe and Mn were removed from solution as insoluble hydroxides. After filtration and pH re-adjustment, the demetallized solution was then returned to the soil to extract more heavy metals. After three washing cycles with the same reagent, it was observed that the sparing quantity of EDTA (10 mmoles) had mobilized 32--54% of the soil burden heavy metals (5 mmoles), but only 0.1% of the iron had been removed. / A 1:1 (mol/mol) mixture of EDTA and HEDC proved to be approximately equally efficient at HM extraction despite more than a three-fold reduction (3 mmoles) in the quantity of reagents. Three washing with the same reagent mobilized some 49% of the Pb, 18% of the Zn and 19% of the Mn but only 7% of the Cu and 1% of the Fe from the test soil.

Remediation of trace element-contaminated sites must consider both the nature of the contaminants and environmental surroundings. This thesis examined treatments for two contamination scenarios. The first study characterized chromium dynamics during the redox-sorption treatment of aqueous hexavalent chromium with the reducing agent sodium dithionite and two iron oxides. Results showed that chromium was successfully removed from solution by precipitation and sorption. The iron oxide derived from ferric chloride had a greater sorption capacity for hexavalent chromium than the oxide derived from ferrous chloride. The second study examined the phytoextraction treatment of soils contaminated with multiple trace elements. Deschampsia caespitosa plants had better early growth in the contaminated high-organic matter soil than three Brassica species. However, D. caespitosa plants did not take up sufficient amounts of trace elements during the study to be considered useful for short-term phytoextraction. These findings are applicable to the development of effective trace element remediation methods.

No description available.

The Microwave-Assisted Process (MAP$ sp{ rm TM}$) is an enhanced extraction technology patented by Environment Canada. MAP uses microwaves to rapidly transfer target compounds from one phase to another by selectively heating the phase containing the target compounds. This thesis presents the results of research performed to determine whether the MAP technique can be further developed into a large-scale soil treatment process that overcomes the limitations of conventional remediation technologies. / The dielectric properties of several mixtures of acetone and hexane over a temperature range from 25$ sp circ$C to 50$ sp circ$C were measured. The dielectric constants of these mixtures were found not to vary significantly with temperature. / A study of microwave absorption by heterogeneous mixtures showed that adding a solid material to a low dielectric constant solvent resulted in energy being preferentially absorbed by the solid. / The results of laboratory extraction tests showed that the ability of the MAP technique to extract contaminants was affected by the organic matter content of soil, particularly in the presence of water. / Use of a closed-vessel system yielded a 60% to 175% increase in the extraction of PAHs from a low organic-content soil relative to that achieved in an open-vessel system. (Abstract shortened by UMI.)

Chemical treatment of contaminated soils (in-situ or ex-situ) is the current most practical option for remediation. The degree of metal complexation by organic acids depends on the type, concentration, metal type, pH and temperature. The influence of pH, temperature on the extraction efficiency of lead, zinc and copper was evaluated using Sodium citrate and sodium acetate buffers. Sodium citrate buffer was selected for the soil treatment. The soil was characterized for its pH, total metal content and the distribution of target heavy metals in soil fractions. Optimal conditions for Pb extraction with 0.5M citrate buffer was used to treat soil in batches and in columns, to evaluate their extraction efficiency and possible use for in-situ remediation. / Chitosan, a derivative of chitin is a versatile biopolymer with metal uptake capabilities. Due to the large amounts of chitosan required to treat heavily contaminated leachates, magnesium (Mg) and iron (Fe) metals granules were evaluated for stripping the heavy metals from solution before the use of chitosan at optimized conditions to effectively polish the soil washing. (Abstract shortened by UMI.)

Phytoremediation, i.e., the use of plants to clean up contaminated soil, may serve as a feasible alternative if a high-biomass crop can be found that accumulates metals to a high.degree. Two plant species, corn (Zea mays) and Indian mustard (Brassica juncea), were grown in soil from a Superfund site contaminated with Pb and Cd (PbTota, = 65,200 mg/kg and CdTotI = 52 mglkg) over two croppings. Soil treatments consisted of composted sewage sludge (CSS), ethylenediaminetetraacetic acid (EDTA), and sodium citrate at two concentrations. In most cases, the EDTA and citrate treatments were superior in terms of extracting soil Pb into root tissue, and translocation of Pb into aboveground biomass. The CSS treatment typically resulted in the lowest Pb removal efficiencies. The high pH (7.4) and high exchange capacity of the CSS may have immobilized soil Pb. Soil Cd was generally more mobile than soil Pb. The EDTA2 treatment was most effective in removing soil Pb into roots, and translocation to shoots. Lead remaining in the soil after two croppings was mainly associated with the carbonate, organic, and residual fractions, which represent the less bioavailable form of this metal. / Department of Natural Resources and Environmental Management