Loretta Li


Relevant Thesis-Based Degree Programs


Graduate Student Supervision

Doctoral Student Supervision

Dissertations completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest dissertations.

Environmental fate and transformation of fluorotelomer compounds in landfill leachate (2020)

Fluorotelomer compounds (FTCs) and their transformation products are routinely detected inlandfill leachate, their environmental fate and transformation in leachate are unknown. This studyfocused on measuring bio- and phototransformation of spiked FTCs in landfill leachate, using lab-scale experiments under environmentally relevant conditions. Spiked 8:2 fluorotelomer alcohol(FTOH) and 6:2 fluorotelomer sulfonate (FTS) and their known biotransformation products werequantified in sediment-leachate microcosms and their headspaces over 90 days. The results showed that 8:2 FTOH and 6:2 FTS persisted (half-life >>30 d) in landfill leachate-sediment microcosms. Slower biotransformation led to significant partitioning of semi-volatile 8:2 FTOH to the gas phase, suggesting that landfills may act as secondary sources for semi-volatile FTOHs in the environment. C6 – C8 and C4 – C6 perfluorocarboxylic acids (PFCAs) were the most abundant products for 8:2 FTOH and 6:2 FTS, respectively.The effect of organic carbon and ammonia concentrations in 6:2 FTS biotransformation and PFCAformation were investigated with sediment microcosms, to which deionized water (DI) and variousamounts of leachate were added. Greater biotransformation of 6:2 FTS was observed in leachate added microcosms, compared to DI microcosms, likely reflecting substrate dependency of 6:2 FTS biotransformation. Substrate limiting conditions in DI microcosms resulted in a slightly higher formation of (C4 – C6) PFCAs compared with leachate added microcosms.To understand roles of microbial communities (e.g., heterotrophic, autotrophic) in 6:2 FTSbiotransformation and PFCA production, experiments were carried out with specific substrates(i.e., glucose, ammonia) and ammonia-oxidizing inhibitor (allylthiourea) using inoculum preparedfrom sediment. Both heterotrophic and autotrophic bacteria were able to biotransform 6:2 FTS tovarying extents. Greater biotransformation of 6:2 FTS and C4 – C6 PFCAs formation wereobserved in the presence of ammonia oxidizers, indicating that biological nitrification is likely toincrease 6:2 FTS biotransformation and PFCA production.Phototransformation of 6:2 FTS and PFCA production were investigated in leachate undersimulated sunlight. The results showed that 6:2 FTS was undergoing indirect photolysis in leachate (half-life of ∽15 days), suggesting indirect photolysis of 6:2 FTS is likely a relevant transformation pathway in sunlit aquatic environments.

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Role of heavy metals and organic matter on sorption and mobility of polycyclic aromatic hydrocarbons in soil: implications for remediation (2019)

Polycyclic aromatic hydrocarbons (PAHs) are a group of abundant contaminants in contaminated sites having many adverse effects on human health and the ecosystem. Due to the many common sources of PAHs and heavy metals, many sites are contaminated by both groups. Co-presence of these contaminants can affect their sorption/desorption in the soil environment, affecting their fate, transport, and remediation processes. This research project advanced the understanding of sorption behavior of PAHs co-existing with heavy metals in soil. Three types of artificially blended clay and clay minerals (kaolinite, kaolinite+sand, kaolinite+sand+bentonite) and a real spiked clayey soil sample were investigated. The synergistic effect of organic matter (humic acid) with heavy metals on enhancing the sorption of PAHs was tested and confirmed for the first time. Different single and combined solutions were used to enhance the desorption of PAHs from the soil. Two non-ionic surfactants (Triton X-100 and Tween 80) with EDTA showed the capability to simultaneously remove these PAHs (acenaphthene, fluorene and fluoranthene) and these prominent heavy metals (Ni, Pb, and Zn) from the soil sample. Results also showed that the co-presence of metal contaminants and soil organic matter can decrease the mobility and desorption of PAHs with the results that the efficiency of soil washing/flushing remediation could decrease in such cases. Our findings also show that the rate of desorption of PAHs is reduced by the co-presence of organic matter and heavy metals in soil. This affects the cost and time of remediation of sites contaminated by mixed heavy metals and PAHs. Our findings were confirmed through column soil flushing of a real natural soil sample by combined enhancing solutions.

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Acid rock drainage remediation with Bear River clinoptilolite in a slurry bubble column (2013)

Clinoptilolite, a natural zeolite, is capable of removing heavy metals from acid rock drainage (ARD). However, previous studies have predominantly been on artificial solutions, with no previous work on sorbent regeneration. This study investigated a novel process for capturing ARD and regenerating clinoptilolite based on a slurry bubble column (SBC) for enhanced mass transfer.Uptake tests were performed with natural ARD and various sorbent particle sizes from 300 to 1400 μm in average diameter, superficial gas velocity from 0.08 to 0.23 m/s, initial aqueous pH from 2 to 6, Zn concentrations from 15 to 215 ppm and sorbent/solution ratio from 25 to 400 g/kg to test zinc uptake.To obtain favorable regeneration, zinc in loaded clinoptilolite was displaced by NaCl as regenerant. Regenerant concentrations from 10 to 40 g/kg, regenerant/sorbent ratios from 100 to 400 g/kg, particle sizes from 300 to 1400 μm, and initial regenerant pH from 2 to 6 were tested to find suitable regeneration conditions.To test the long-term viability of clinoptilolite sorbent, repeated capture-regeneration cycles were tested. It was shown that NaCl regenerant could bereused to minimize waste volume. Three removal-only cycles after 10 full cycles continuously decreased the accumulated zinc in the clinoptilolite, allowing the uptake capacity to be almost fully recovered. When 10 full cycles were tested after three removal stages, results were similar to those for the first 10 cycles. Only one-quarter of the regenerant was required to achieve a similar total zinc uptake when reused NaCl solution was utilized.During the remediation, dealumination of clinoptilolite was observed, under certain circumstances. Increased Al in the aqueous phase led to co-precipitation of Zn-Al colloid, enhanced by abundant sulfate in solution. The unit zinc uptake of the Al colloid was much higher than that of the raw clinoptilolite. Adsorption isotherms were fitted to the Langmuir model, and the overall aqueous species and surface uptake were explored by the PHREEQC model. The cyclic capture/regeneration process is promising that further development work is warranted.

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Polybrominated diphenyl ethers in biosolids-amended soils (2011)

Polybrominated diphenyl ethers (PBDEs) are added to many consumer products as flame retardants. Their hydrophobic characteristics and high n-octanol-water coefficients make them partition in organic media such us sludge and biosolids, by-products of wastewater treatment which are commonly applied to agricultural soils to promote crop growth or discarded in landfills. Biosolids-amended soils have been found to contain up to 7x10⁶ pg PBDEs/g dry weight, whereas leachates from biosolids and flame-retarded products in landfills, contained up to 4,000 pg PBDEs/litre. PBDEs in the environment could potentially cause serious health effects.Research was conducted to determine the concentration and mobility of PBDEs in biosolids, biosolids-amended soil, and clay liners used to retain PBDEs. A field study investigated the degree of PBDE contamination due to the application of biosolids at an agricultural site near Kamloops and an agricultural field in Totem Field at the University of British Columbia in Vancouver. PBDEs were found to migrate downwards to depths of at least 0.85 m. Laboratory experiments determined leachability of PBDEs from biosolids. PBDEs sorbed on fine particles suspended in the leachate, allowing PBDEs to exceed their aqueous phase solubilities. Concentrations were much higher on ultra-fine than on fine particles. Leaching column tests demonstrated that PBDEs leached from biosolids-amended soils and migrated through the soils. PBDEs in soils upgradient and downgradient of solid waste facilities in Northern Canada varied widely from location to location. There was evidence that PBDE contamination in Iqaluit is due to long-range atmospheric transport, whereas that found at Yellowknife is mainly from the solid waste facility. Laboratory experiments showed that sand-bentonite partially retained PBDEs. The hydraulic conductivity decreased with leaching, and then gradually increased. The decrease is attributed to swelling, whereas the increase is due to shrinkage of the clay interlayer, owing to the hydrophobicity of the permeant. The research may be helpful in establishing regulations on land application of biosolids, regulating waste disposal and landfill design requirements.

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Phytoremediation and Metal Speciation in Highway Soils (2010)

Research was conducted to develop a cost effective and environmentally friendly technology to limit the dispersal of metal contaminants from highway traffic in the soil to the surrounding natural environment. The study comprised preliminary field measurements followed by two pot experiments and a field study. The first study evaluated the phytoextraction/ phytostabilisation potential of five plant species: Brassica napus L (rape), Helianthus annuus L. (sunflower), Lolium perenne L (perennial rye grass), Poa pratensis L (Kentucky blue grass) and Festuca rubra L (creeping red fescue) for metals (Cu, Mn, Pb and Zn), in soils with different metal contamination levels. The promising plant species identified were Lolium perenne, Festuca rubra and Poa pratensis. Total soil and plant metal concentrations, as well as the relative metal partitioning in different soil fractions and in plants were determined to provide an estimate of the mobility and potential bioavailability of metals in the soil. The second study evaluated the effectiveness of soil-plant-amendment interaction in immobilising metals in the soil. The amendments included lime, phosphate and compost individually and in combination, and were applied to the plant species: Lolium, Poa and Festuca. Maximum metal immobilisation was achieved in the soil by the combined application of amendments in conjunction with growth of Festuca for Cu, Poa for Pb and Zn and Lolium for Mn. The results obtained from first and second studies were confirmed by conducting field studies. A completely randomized factorial experiment in split plot design with three plant species (Lolium, Poa, and Festuca) individually and in combination, with and without soil amendments was conducted along Highway 17 soil in southwest British Columbia. The influence of root-soil interactions and seasonal influence on the solubility and bioavailability of metals in the soil with and without soil amendments was also evaluated. The best management practices (BMP) developed from the study have the applicability for phytostabilisation of metal contaminated sites and can be suggested as a risk management activity, reducing long-term associated risks.

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Master's Student Supervision

Theses completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest theses.

Removal of polycyclic aromatic hydrocarbons from deionized water and landfill leachate by using modified clinoptilolites (2018)

Polycyclic aromatic hydrocarbons (PAHs) are toxic, carcinogenic, and persistent in the environment. Clinoptilolite, a type of natural zeolite, was modified with cetylpridinium chloride (CPC), didodecyldimethylammonium bromide (DDAB), hexadecyltrimethylammonium bromide (HDTMA-Br), and tetramethylammonium chloride (TMA) separately as potential adsorbents for removal of PAHs. Leachability and thermal stability of modified clinoptilolites were investigated. Adsorption capacity, kinetics, sorbent dosage, pH, temperature, and competition effects were studied adopting batch adsorption tests using deionized water spiked with five PAHs (anthracene (50 µg/L), fluoranthene (100 µg/L), fluorene (100 µg/L), phenanthrene (100 µg/L), and pyrene (100 µg/L)). The leachability and thermal stability results indicated that CPC and DDAB modified clinoptilolites were less leachable and more stable compared to HDTMA modified clinoptilolites. The non-modified clinoptilolite, and TMA modified clinoptilolite exhibited 93 % of five PAHs after 24 hours at 1:100 solid: liquid ratio and met the local water quality criteria, except for fluorene on HDTMA modified clinoptilolite which retained >83%. For CPC and DDAB modified clinoptilolites, more than 80% of all PAHs were retained within 15 minutes and maximum adsorption was reached in 95%) from landfill leachate spiked with PAHs.

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Modification and utilization of sewage sludge-based activated carbon as metal adsorbants (2013)

Sewage sludge is the by-product of the wastewater treatment process. Its conventional disposal methods include incineration, landfill, and agricultural land application. As populations grow, the volume of sewage sludge likewise increases. The conventional disposal methods including incineration, landfill and application to agricultural land are unsustainable and have major limitations. Therefore, a more sustainable and economical alternative is needed by converting this waste material into the resource that can enhance environmental sustainability. Due to the carbonaceous nature of sewage sludge, the aims of this research are to convert a sewage sludge sample into activated carbon, to further explore the modification of sewage sludge based activated carbon (SBAC) to improve metal sorption capacity, and to investigate the effectiveness of the modified SBACs (MSBACs) by selecting the MSBAC with best adsorption performance to compare with other adsorbents.The SBAC was prepared through the chemical activation of ZnCl₂, followed by pyrolysis in an electric furance, and it was further modified by nitric acid. Batch sorption tests were conducted in which the SBAC and MSBACs were contacted with distilled water spiked with lead ions (Pb²⁺) to measure their adsorptivity for Pb²⁺. The Pb²⁺ sorption capacity of MSBACs was further compared with zeolite, grundite, kaolinite, and commercial activated carbon. Batch sorption tests were conducted in which MSBAC10 was contacted with natural acid rock drainage (ARD) and the ARD solution spiked with Al³⁺, Fe²⁺, Cu²⁺ and Zn²⁺ to further demonstrate its application of removing multiple-metal components.The batch sorption tests showed the great improvement of Pb²⁺ uptake capacity of the SBAC after modification. Compared with other MSBACs and adsorbents, MSBAC10 exhibited the strongest and fastest sorption behavior. The adsorptivity for lead ions in five minutes was ranked as: MSBAC10 > illite (grundite) > zeolite > commercial activated carbon (CAC) > kaolinite > perlite, and grundite ≥ zeolite ≥ MSBAC10 ≥ CAC > kaolinite > perlite over a 24-hour period, whereas, MSBAC’s application on the natural ARD solution, removed 98.88% of Cu, 42.60% of Zn and 34.63% of Al.  

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MTBE Gas Phase Diffusion in Subsurface Soil: Influence of Soil, Water, Clay, and Organic Content (2012)

Volatile organic compounds (VOCs) have adverse effects on human health upon short- and long-term exposure, causing allergy and asthma in adults and respiratory problems and immune system disorders in children. The most important mechanisms responsible for VOC migration and deposition in soil include diffusion, advection, adsorption, biodegradation and chemical reaction. MTBE (Methyl Tertiary-Butyl Ether), a very common VOC, detected in groundwater near landfills and hazardous waste dumps, can cause cancer in humans. Due to its specific physical and chemical properties such as high volatility, high water solubility, not much adsorptivity on soil particle and biodegradability, it is very mobile in the environment. The objectives of this research were to design and build a diffusivity apparatus, determine gas-phase diffusion of MTBE in soil, and investigate major factors affecting the effective diffusivity of MTBE such as particle size distribution, soil water and organic carbon content. Previously, sorbents and reservoir-based soil columns have been used to determine soil diffusion. A novel apparatus was designed which can overcome the limitations of conventional designs. Special features of the design include a three-segment body design stainless steel column and a very accurate humidity adjustment system, with humidity sensors at the inflow and outflow, giving the ability to determine the effective diffusivity of MTBE in soil more accurately and easily. Soil samples in this study were at 0 to 80% saturation, with 0 to 15% clay content (Kaolinite) and 0 to 15% organic content. They were compacted in a developed stainless steel one-flow reservoir-based column to a dry density of 1.6 to 1.7 g/cm³. Effective diffusivities were calculated based on Fick’s first law. Overall MTBE effective diffusivities ranged from 0.0004 to 0.003 cm²/s. The results demonstrate that higher water content of soil resulted in lower effective diffusivities. Increasing clay content of soil resulted in longer equilibrium time and lower effective diffusivity values. Variations of soil particle size had less effect on the effective diffusivity than changes in water content. It was also discovered that the organic content of soil has a significant capacity for adsorbing MTBE.

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Perfluorinated Compounds in Landfill Leachate from Discarded Carpets (2012)

Perfluorinated compounds (PFCs) are a class of anthropogenic chemicals incorporated over six decades into a wide range of industrial and consumer-use products including surface treatments for carpets and textiles, paper and packaging, non-stick cookware, firefighting foams and insecticides. The extremely strong carbon-fluorine bond, "the strongest in organic chemistry", makes them thermally and chemically stable, and resistant to degradation. Several studies on toxicology of PFCs demonstrate negative health effects of these compounds. Some PFCs were added to the Stockholm convention on Persistent Organic Pollutants (POPs) in 2009, due to their persistence, toxicity, and widespread occurrence in the environment. Stain-resistant carpets comprise a major part of global historical PFC production and use. Landfills are a major source of PFC emissions to the environment as final destinations for discarded consumer articles, including carpets. This thesis explores how various PFCs leach from carpets to landfill leachate, and how factors like temperature, pH and contacting efficiency affect the transfer of PFCs into aqueous media.Experiments were conducted in which a number of carpets manufactured in ~2000 to 2005 were contacted with landfill leachate and distilled water. Transfer of different PFCs into the aqueous phase increased with contacting time, with differences between 1 and 24 h much greater than between 24 and 168 h. A temperature increase from 5 to 35oC resulted in a significant increase in PFC leaching. Increasing the pH from 5 to 8 resulted in an increase followed by a decrease in leaching of most PFCs. The overall leaching rates of PFCAs into distilled water were somewhat greater than into landfill leachate. The majority of PFC exchange between carpets and leachate was more dependent on some factor (e.g. adsorption or desorption) rather than external mass transfer.

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Perfluorinated compounds in landfill leachate and their effect on the performance of sodium bentonite landfill liners (2011)

Perfluorinated compounds (PFCs) are a class of persistent organic pollutants (POPs) with potential major health and environmental concerns. PFCs are thermally and chemically stable, and do not readily degrade in the environment. PFCs have been detected in numerous environmental matrices, including surface water, ground water and sediment. PFCs are used for surface treatments for paper and textiles, industrial surfactants, insecticides and fire-fighting foams. Given their widespread use, products that contain PFCs have been, and continue to be disposed in landfills after their useful lives. Typical landfills have liners made of compacted clay (e.g. sodium bentonite) to prevent contaminants in leachate from migrating into the surrounding environment. Research was conducted to characterize geographic and temporal distributions of PFCs in landfill leachate in Canada and to investigate PFC retention on sodium bentonite. Landfill leachate was collected from 29 landfills across Canada and analyzed for up to 18 PFCs. PFCs were ubiquitous in landfill leachate samples from across Canada and varied considerably with concentrations, generally being lower in the North than in the South. At one landfill, PFCs were analyzed in landfill gas condensate and water from a nearby river. Concentrations in both of these matrices were less than the landfill leachate. At another landfill, PFCs in landfill leachate were monitored for five months. Some PFCs varied temporally, whereas others remained relatively constant. The temporal variations were attributed to the presence of PFC precursors. There were strong correlations between PFC precursors and corresponding major degradation end-products. PFCs of similar size were also well-correlated with each other. Batch adsorption tests were conducted in which sodium bentonite was contacted with water and landfill leachate spiked with PFCs to measure the sorption of PFCs on sodium bentonite. PFCs in landfill leachate do not readily bind to sodium bentonite. Leaching cell tests were conducted in which compacted sand-bentonite admix columns were permeated with water, landfill leachate and PFC spiked landfill leachate. Similar hydraulic conductivity values were produced under each condition, indicating that PFCs do not significantly compromise the performance of bentonite liners. The sand-bentonite admix also appears to retain PFCs under the leaching cell test conditions.

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Surfactant enhanced soil washing technique for removal of trace metals from contaminated soils (2010)

Increasingly stringent environmental regulations and legislation around the world are demanding the development of environmentally friendly technologies for contaminated site remediation. Researchers have recognized soil washing as an economically promising in-situ treatment method. Despite research indicating the effectiveness of soil washing with the aid of aqueous acids or chelating agents such as HCl and EDTA, the need to minimize the environmental impact of the remediation process itself has prompted investigations into alternative soil washing agents such as surfactants, particularly degradable compounds.This thesis examines two surfactants in their effectiveness of removing cadmium (Cd) and lead (Pb) from artificially contaminated kaolinite and illite clay minerals to determine the optimum conditions (concentration of surfactants and reaction time) for removing metals from contaminated urban sediments from two locations: a Wetland and a parking lot in Vancouver B.C. Selective sequential extraction was used to investigate geochemical fractionation before and after treatment of sediments by the surfactants. The optimum effective concentration for removing Cd and Pb from kaolinite and illite was 20 mM for Rhamnolipid for 0.5 h and Texapon at a concentration of 100 mM for 0.5 h. Thus, the concentration of 20 mM Rhamnolipid and 100 mM Texapon and reaction time of 0.5 h were selected to apply to remediate the two contaminated urban sediments. The removal of total metal content (Cu, Mn, Pb, and Zn) under laboratory conditions for the Wetland was 31%, 26%, 43%, and 27% after treatment by Rhamnolipid; and 31%, 27%, 58% and 31% after treatment with Texapon. The removal of these metals was 28%, 26%, 60%, and 31% by Rhamnolipid and 39%, 18%, 86%, and 40% by Texapon. Removal of metals from exchangeable and reducible fraction which have the potential to be released into environment approached up to 100%.Determination of Rhamnolipid and Texapon concentration remaining in Wetland and parking lot sediments after treatment revealed that more than 99% of remaining surfactants were removed from the two sediments after two washes with distilled water. The residual Rhamnolipid and Texapon were below the LD50/LC50 and toxicity limits for aquatic life.

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Trace metal contamination due to acid rock drainage and its impacts on the fish-bearing Pennask Creek watershed in British Columbia (2010)

Acid rock drainage (ARD) and associated metal leaching (ML) is a major pollution problem throughout the world, adversely affecting both surface and ground waters. The elevated concentrations of metals in the water column due to ARD/ML can be transferred to abiotic and biotic components of an ecosystem and adversely affect the health of aquatic life. The Pennask Creek watershed, one of the most important rainbow trout-producing environments in British Columbia (BC), has been contaminated with ARD/ML as a result of highway construction.This study was designed to comprehensively examine the Pennask Creek watershed ARD/ML problem and its environmental impacts by combining existing and newly gathered information. The overall objectives were to determine the extent of metal contamination of the water and sediments, the potential biological impacts of this contamination, the influence of local geology, and to estimate the potential risk to aquatic organisms.Results show that metal concentrations in the water and sediments downstream of the ARD/ML source are higher than concentrations elsewhere in the watershed. Analysis of historical water quality data indicates that the concentrations of these metals have decreased markedly since 2004, due to remediation efforts. Metals of concern include Al, As, Cu, Mn, Ni and Zn.Rock cuts along Highway 97C are generating ARD characterized by a low pH and high metal concentrations. Rock samples collected from the stream beds and banks were not found to be potentially acid-generating. However, these rock samples contained significant levels of metals of concern, which could continue to be leached under acidic conditions for many years to come.Al, Cu, and Zn levels consistently exceeded BC and Canadian water and sediment quality guideline values for the protection of aquatic life, indicating that adverse biological effects are probable at sites downstream of the ARD/ML source. Benthic invertebrate monitoring over a ten year period shows low abundance and diversity, and a complete absence of sensitive taxa at downstream sites. Risk quotients indicate a likelihood of adverse biological effects for aquatic organisms, including rainbow trout, due to metal contamination in the watershed.

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