Civil and Environmental Engineering

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Browsing Civil and Environmental Engineering by Author "Anderson, William"

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    Conventional and Oxidant-amended Biofiltration to Improve Treatment Resilience in Drinking Water Systems Vulnerable to Wildfire
    (University of Waterloo, 2024-01-26) McGregor, Lauren; Emelko, Monica; Anderson, William
    Climate-change-exacerbated landscape disturbances can create obstacles for the provision of safe drinking water. The threats posed by wildfires are of particular concern due not only to the potentially extreme nature of their effects, but also because millions of people worldwide depend on water sourced from forested watersheds. Wildfire may lead to major shifts in the concentration and character of dissolved organic carbon (DOC), which may impair drinking water treatment processes to the point of causing service disruptions or outages. Resource-limited small systems can be especially vulnerable to variable water quality, underscoring a need for wildfire-resilient treatment strategies that are cost-effective and less operationally demanding than conventional processes. Biofiltration technologies—especially slow sand filtration—have been proposed as sustainable, low-cost strategies to remove DOC; however, their effectiveness has not been thoroughly investigated during periods of extreme source water quality change such as the episodic deteriorations possible following severe wildfire. Despite the operational simplicity of biofiltration, it is often described as a “black box” process due to our limited knowledge of its biological treatment mechanisms. A better understanding of biofiltration response to wildfire-associated source water disturbances at both the treatment performance and microbial community levels may increase the adaptability of biofiltration processes to climate change effects. Furthermore, biofiltration enhancement is an emerging area of research focused on the customization of biofiltration processes through exerting greater control at the design, process, and influent stream levels. Potential benefits include increased biodegradation of organics and lower incidences of hydraulic challenges. For many of these strategies, there has been little investigation in slow sand filtration. This work aims to advance knowledge in these areas through the execution of two main objectives: 1) assess DOC removal capacity in conventional and peroxide-amended biological sand filters when treating wildfire-ash-impacted water at bench-scale, and 2) evaluate the impacts of wildfire-associated disturbances and peroxide exposure on biofilter bacterial communities. Challenge testing with severely wildfire-ash-impacted water was conducted on biofilters operated in duplicate under conditions closely resembling slow sand filtration. Filters were subjected to two-, four-, and seven-day disturbance periods, each followed by a five-day return to “baseline” source water quality. One of these pairs, as well as another pair not undergoing ash challenge testing, received intermittent low-dose hydrogen peroxide amendment. Effluent DOC concentrations were elevated, and DOC removal declined during challenge periods; however, DOC characterization analysis showed this was likely the result of a higher proportion of slowly biodegradable humic and aromatic organic matter in the ash-impacted water. No significant evidence of impairment to biodegradation was observed. Biofilter performance was consistent within each disturbance period and recovered within hours of the return to baseline conditions. Over the 30-day experimental phase, the impacts of hydrogen peroxide amendment on organic matter accumulation and DOC removal were not significant to practice. Amplicon sequencing was carried out on filter media samples collected throughout the experimental phase. Community composition and diversity were compared across experimental conditions and were assessed alongside biofilter performance to identify potential connections. DNA sequencing was also conducted on media samples collected from a similar set of biological sand filters in a previous ash challenge experiment, which used a distinctly different source water. The lack of compositional differences between microbial communities in filters under different experimental conditions supported the assertion that ash-impacted water and peroxide amendment did not severely disrupt the biological communities in the long-term. Comparison of the two filter sets, however, demonstrated the significant impact of source water character on biological filter community characteristics and dynamics. Collectively, the two components of this work provided process insights into biofilter disturbance response and resilience from multiple perspectives.
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    Evaluation of Potential Health Risks from Microplastics in Drinking Water
    (University of Waterloo, 2021-05-03) Chowdhury, Omar; Emelko, Monica; Anderson, William
    Microplastics have been detected, often abundantly, in freshwater environments over the past decade. While understanding of the ecological health implications of microplastics in aquatic environments has advanced considerably, the health risks of microplastics in drinking water are not well understood. Direct health impacts are attributed to the ingestion of microplastics materials themselves. In contrast, indirect health impacts are attributed to the chemical contaminants that sorb on and in microplastics in the aquatic environment and are concurrently ingested. While it is desirable to evaluate both types of health risks, there are currently no available and conclusive toxicological investigations of the health implications of microplastics ingestion by humans; current understanding is limited to microplastics impacts on small organisms or cell cultures. In contrast, considerable information regarding the health effects of some contaminants that sorb on or in microplastics is available. Although this information has not been integrated to inform health risks associated with microplastics ingestion via contaminated drinking water, this integration is pressingly needed to guide risk management. Here, the potential health risks attributable to chemical contaminants retained on or in microplastics in the aquatic environment and ingested via contaminated drinking water were assessed using a new concept developed in this research: the Threshold Microplastics Concentration (TMC). The TMC indicates the total number of microplastics particles per liter of water that, if ingested, constitutes exposure to potentially harmful concentrations of chemical contaminants retained on or in microplastics via sorption mechanisms. A TMC of 0.024 microplastics particles per liter was identified given currently available contaminant sorption data; this value increased to 2.550 microplastics particles per L in absence of antimony. Thus, these respective values indicate that source water concentrations of 24 or 2,550 microplastics particles per L or less should not pose health concerns attributable to sorbed chemical contaminants for well-operated conventional treatment systems in which a 3-log (i.e., 99.9%) reduction in microplastics concentration can be reasonably expected by physico-chemical filtration. Critically, a source water microplastics concentration that exceeds the TMC is not necessarily indicative of health risks from microplastics in drinking water; rather, it indicates that more detailed analysis may be warranted. For example, system specifics such as types of treatment implemented, sorbed contaminants present in the source water, size distribution of the microplastics, etc. affect the TMC. Notably, antimony was identified as a potential sentinel indicator of potential health risk from microplastics because it is especially toxic. Similarly, PVC was identified as a key microplastics type because of its contaminant sorption propensity. Only 11 contaminants and seven common microplastics materials were included in this analysis because of limited sorption and toxicity data for known chemical contaminants of human health concern; however, the “Microplastics Calculator” developed herein to calculate TMCs can be easily updated as chemical, plastics, and treatment data become available. Microplastics are particles—in many ways they are not different than other particles removed during drinking water treatment. Their removal can therefore be explained by the physico-chemical processes that are involved in particle removal during filtration. Here, a synthesis of the current knowledge regarding the treatment of particulate contaminants including microplastics and a limited series of surface charge assessments and bench-scale coagulation and filtration experiments were conducted to confirm microplastics removal expectations during drinking water treatment. These experiments demonstrated the size dependency that would be expected by classical filtration theory: the order of particle removal efficiency by filtration was 45 μm > 10 μm > 1 μm. The surface charge of several common microplastics (polyethylene, polystyrene, acrylic, and polyetheretherketone) varied considerably and was impacted by the quality of the matrix in which they were suspended, as would be expected. Notably, however, coagulant addition at doses sufficient for achieving optimal particle destabilization in absence of the microplastics was also sufficient for destabilizing microplastics suspended at environmentally relevant concentrations in all matrices investigated (i.e., distilled deionized MilliQTM water; 100 mM KCl electrolyte solution; low turbidity, low dissolved organic carbon (DOC) Lake Ontario water; and moderate DOC, higher turbidity Grand River water). Overall, this analysis confirmed that the removal of microplastics particles by engineered physico-chemical filtration processes should be consistent with that which would be expected of other particles and particulate contaminants.