Dr. Susanne Walford

Environmental considerations for wet mining peatlands in Northwestern Ontario

SUPERVISOR: Dr. Peter Lee  (Biology)    
ABSTRACTSignificant changes in water quality were detected using a Before-After-Control-Impact (BACI) experimental design. Porewater showed increases in pH, alkalinity, conductivity (including Ca, Mg, K, Na), some metals (Sr, Ba, Mn, Fe) and total nitrogen (TN) in the mined and restored plot. Change in surface water total mercury (THg) was linked to total suspended solids (TSS) and limited to active phases of wet mining. The season mining ceased, TSS and THg concentrations in impacted surface waters were similar to reference site water (<5 mg/L and <4 ng/L, respectively). Experimentally derived 28 day dry weight Biota-Sediment Bioaccumulation Factors (BSAFs) for THg using Lumbriculus variegatus exposed to site sediment ranged from 0.91 to 1.59, while indigenous benthos ranged from 1.2 to 6.8. The BSAFs for methylmercury (MeHg) ranged from 9.92 to 67.4 and benthos from 21.8 to 106. A kinetic trial with inorganic mercury (iHg) spiked sediment, showed tissue THg reached steady state (11.5 d, model BSAF=3.12). Both tissue and sediment MeHg for the same trial showed linear increases (model BSAF=8.38), suggesting an increase in MeHg concentration in sediment would result in a corresponding MeHg increase in L. variegatus tissue. Sugar flotation methodology reduced recovery time and increased percent recovery of L. variegatus from site sediment. Tissue THg did not differ in aqueous only exposures to sugar solution and tissue MeHg did not differ when organisms were extracted from sediment by sugar flotation. However, MeHg tissue concentrations in aqueous only exposures were 27% higher than controls. Mechanical dewatering of wet mined peat produced peat mining process water (PMPW) with low pH (5.55) and high TSS (432 mg/L), Al (1.39 mg/L), Fe (4.36 mg/L), Hg (37.1 ng/L), MeHg (0.485 ng/L), Zn (55 mg/L), TN (7.92 mg/L), total phosphorus (TP) (303 mg/L) and colour (532 TCU). In mesocosm studies, high removal efficiencies were calculated for acrotelm peat filters (TSS 45-83%, particulate organic carbon (POC) 47-89%, metals 52.9-100%, TN 84.4%, TP 80.8%), though leachate concentrations did not all achieve water quality guidelines. Colour and dissolved organic carbon (DOC) also leached from mesocosms. An initial removal of solids from PMPW is required before peatlands be considered further as primary treatment systems.

Dr. Weijue Gao

Submerged anaerobic membrane bioreators for wastewater treatment and membrane fouling characterization and control

SUPERVISOR: Dr. Baoqiang Liao  (Chemical Engineering)    
ABSTRACT: This thesis focused on effects of transient conditions (pH shocks, temperature variation and temperature shocks) on the performance and membrane fouling characterization and control of submerged anaerobic membrane bioreactors (SAnMBR) for pulp and paper effluent treatment (thermomechanical whitewater and pressate). A comprehensive characterization of cake layer formed on membrane surfaces was conducted using various techniques. Results show that a pH 8.0 shock had a minor impact, while pH 9.1 and 10.0 shocks exerted significant long-lasting negative impacts on performance of the SAnMBR. The SAnMBR system was highly resilient and could successfully tolerate the 5 °C/10 °C temperatures shocks at 37 °C and the temperature variations from 37 to 45 °C. The temperature shock of 5 °C and 10 °C at 45 °C led to slight disturbance and significant disturbance of the performance, respectively. A new insight was achieved on fundamental understanding of membrane fouling with regard to cake layer structure that changes significantly from the top layer to the bottom layer. Additionally, the freshly formed cake layers (2 days) were thinner, higher in EPS concentration, high in porosity, but much lower in particle size distributions (PSDs), as compared to the cake layers of 25 days at 55 °C. The elevated pH shocks, high operating temperatures and temperature shocks induced dispersion and breakage of large sludge flocs. Smaller flocs had a higher tendency to accumulate on membrane surfaces. PSDs act as a key factor to generate high fouling resistance. EPS, SMP, and colloidal particles contents in supernatant were increased with an increase in operating temperature and were positively correlated to the membrane filtration resistance that increased with an increase in operating temperature. PCR-DGGE study showed that there were significant differences in microbial community population density along the cake layer depth. Temperature not only affected the richness of the microbial populations but also the diversity of the microbial community. The results suggest that SAnMBR is a promising technology for pulp and paper effluent treatment and for system closure. However, membrane fouling, particularly cake layer formation, should be minimized. Operating SAnMBR at mesophilic temperatures is more attractive than that at thermophilic temperature, from a membrane fouling point of view.

Dr. Asieh Ahmadalinezhad

Nanomaterial-based electrochemical sensors for the detection of biological compounds

SUPERVISOR: Dr. A. Chen  (formerly in Chemistry)    
ABSTRACT: Electrochemical detection methods are highly attractive for the monitoring of glucose, cholesterol, cancer, infectious diseases, and biological warfare agents due to their low cost, high sensitivity, functionality despite sample turbidity, easy miniaturization via microfabrication, low power requirements, and a relatively simple control infrastructure. The development of implantable biosensors is laden with great challenges, which include longevity and inherent biocompatibility, coupled with the continuous monitoring of analytes. Deficiencies in any of these areas will necessitate their surgical replacement. In addition, random signals arising from non-specific adsorption events can cause problems in diagnostic assays. Hence, a great deal of effort has been devoted to the specific control of surface structures. Nanotechnology involves the creation and design of structures with at least one dimension that is below 100 nm. The optical, magnetic, and electrical properties of nanostructures may be manipulated by altering their size, shape, and composition. These attributes may facilitate improvements in biocompatibility, sensitivity and the specific attachment of biomaterials. Thus, the central theme of this dissertation pertains to highlighting the critical roles that are played by the morphology and intrinsic properties of nanomaterials when they are applied in the development of electrochemical biosensors. For this PhD project, we initially designed and fabricated a novel amperometric glucose biosensor based on the immobilization of glucose oxidase (GOx) on a Prussian blue modified nanoporous gold surface, which exhibited a rapid response and a low detection limit of 2.5 μM glucose. The sensitivity of the biosensor was found to be very high (177 μA/mM) and the apparent Michaelis–Menten constant was calculated to be 2.1 mM. Our study has demonstrated that nanoporous gold provides an excellent matrix for enzyme immobilization. To adopt these advanced properties, we fabricated a highly sensitive and mediator-free electrochemical biosensor for the determination of total cholesterol. The developed biosensor possessed high selectivity and sensitivity (29.33 μA mM−1 cm−2). The apparent Michaelis–Menten constant, of this biosensor was very low (0.64 mM), which originated from both the effective immobilization process and the nanoporous structure of the substrate. The biosensor exhibited a wide linear range, up to 300 mg dL−1, in a physiological environment (pH 7.4); making it a promising candidate for the clinical determination of cholesterol. The fabricated biosensor was tested further by utilizing actual food samples (e.g., margarine, butter and fish oil). The results indicated that it has the potential capacity to be employed as a facile cholesterol detection tool in the food industry and for supplement quality control. To enhance the stability of the biosensors in the continuous monitoring of glucose, we designed a novel platform that was based on buckypaper. The fabricated biosensor responded to glucose with a considerable functional lifetime of over 80 days and detected glucose with a dynamic linear range of over 9 mM with a detection limit of 0.01 mM. To investigate the effects of the physical dimensions of nanomaterials on electrochemical biosensing, we synthesized TiO2 nanowires with controllable dimensions via a facile thermal oxidation treatment of a Ti substrate. To improve the conductivity of the TiO2 nanowires and to facilitate the immobilization of enzymes, a thin layer of carbon was deposited onto the TiO2 nanowires via a chemical vapour deposition method. Upon the immobilization of glucose oxidase as a model protein, direct electron transfer was observed in a mediator-free biosensing environment. Our electrochemical studies have revealed that the electron transfer rate of the immobilized glucose oxidase is strongly dependent on the dimensions of the carbonized TiO2 nanowires, and that the designed glucose biosensor exhibits a wide linear range, up to 18 mM glucose, as well as high sensitivity and selectivity. Glucose measurements of human serum using the developed biosensor showed excellent agreement with the data recorded by a commercial blood glucose monitoring assay. Finally, we fabricated an enzyme-free glucose sensor based on nanoporous palladium-cadmium (PdCd) networks. A hydrothermal method was applied in the synthesis of PdCd nanomaterials. The effect of the composition of the PdCd nanomaterials on the performance of the electrode was investigated by cyclic voltammetry (CV). Amperometric studies showed that the nanoporous PdCd electrode was responsive to the direct oxidation of glucose with high electrocatalytic activity. The sensitivity of the sensor for continuous glucose monitoring was 146.21 μAmM−1cm−2, with linearity up to 10 mM and a detection limit of 0.05 mM. In summary, the electrochemical biosensors proposed in my PhD study exhibited high sensitivity and selectivity for the continuous monitoring of analytes in the presence of common interference species. Our results have shown that the performance of the biosensors is significantly dependent on the dimensions and morphologies of nanostructured materials. The unique nanomaterials-based platforms proposed in this dissertation open the door to the design and fabrication of high-performance electrochemical biosensors for medical diagnostics.