Shabnam Sharifyazd

Topic

Nature-Based Redox Systems for Air Quality and Greywater Treatment: From Plant-Mediated Hydrogen Peroxide Generation to Bioelectrochemical Wetlands

Department of Civil Engineering

Date & location

• Wednesday, September 9, 2026
• 8:00 A.M.
• Virtual Defence

Examining Committee

Supervisory Committee

• Dr. Kristian Dubrawski, Department of Civil Engineering, University of Victoria (Supervisor)
• Dr. Caetano Dorea, Department of Civil Engineering, UVic (Member)
• Dr. Barbara Hawkins, Department of Biology, UVic (Outside Member)

External Examiner

• Dr. Boris Tartakovsky, Biotechnoogy Research Institute, National Research Council

Chair of Oral Examination

• Dr. Christina Chakanyuka, School of Nursing, UVic

Abstract

Nature-based solutions offer promising pathways for improving water and air quality with lower energy and chemical demands, but their performance depends on redox processes that are often localized, dynamic, and difficult to control. This dissertation investigated how plant-mediated and electrochemically controlled redox processes at environmental interfaces can be characterized and leveraged for treatment applications. Three complementary experimental studies examined the leaf-air-condensate interface and the plant-water-electrode-biofilm interface. First, controlled chamber experiments were conducted to determine whether active plant transpiration and near leaf condensation could generate exogenous hydrogen peroxide (H₂O₂). Condensate collected near plant leaves contained approximately 1-5 ppm H₂O₂, confirmed using test strips and spectrophotometric analysis. Formation occurred under light conditions when plants were actively transpiring, was not detected in no-plant, no-light, or cut-plant controls, and decreased with distance from the leaves. A preliminary Escherichia coli assessment showed no clear reduction in colony recovery following passive exposure to the plant-containing environment or direct application of collected condensate, demonstrating that oxidant formation alone does not ensure biologically effective delivery. Second, controlled anode potential was evaluated as a redox management variable in unplanted sand-packed bioelectrochemical wetland systems (BWSs) operated in 250 mL and 1 L reactor configurations. Chemical oxygen demand (COD) removal responded non-monotonically to anode potential, with the highest removals occurring within favourable intermediate negative-potential regions that differed between reactor configurations. In the 1 L system, operation at -1.29 V versus the standard hydrogen electrode achieved approximately 86% COD removal while limiting overlying-water dissolved oxygen depletion to approximately 2 mg L⁻¹, indicating that organic removal and oxygen preservation can be considered together. Third, Java moss and Amazon sword were integrated into BWSs to determine how plant species, biomass, photoperiod, anode potential, and reactor configuration influenced treatment. Plant integration improved COD removal under selected conditions, including 89% removal in a 250 mL Java moss-integrated BWS at -0.23 V, compared with 54% in the unplanted non-bioelectrochemical control. However, plant responses were condition-dependent: a significant plant-treatment-by-operating-condition interaction in the 1 L plant-species experiment (p = 0.027) showed that the direction and magnitude of plant-associated effects differed among operating conditions. The unplanted BWS achieved the highest COD removal at -1.29 V vs SHE, while higher observed removal in planted treatments occurred only under selected operating conditions. Electrochemical, water-quality, and microbial-community measurements showed that effective performance emerged from coupled biological and redox conditions rather than current magnitude or a single universal microbial community. Overall, this dissertation advances a process-based framework for nature-based environmental engineering in which oxidizing or electron-accepting capacity is evaluated through its generation, transport, persistence, contact, and functional outcome. The findings establish a new direction for plant-associated condensate chemistry and provide experimentally supported operating principles for performance-driven bioelectrochemical wetland treatment.