The increase in population and car fleets has led to a sharp rise in the generation of carwash wastewater (CWW). CWW contains heavy metals, detergents, oil and grease, and suspended solids, and is considered one of the most polluting industries in terms of water consumption and wastewater production. In various parts of the world CWW is not treated but left to drain and impair receiving waters. Numerous jurisdictions are examining how simple green infrastructure like low impact development (LID) technologies, such as rain gardens that treat polluted urban stormwater may be used to help treat the pollutant loads in CWW. Given that many of these green technologies use trees, this thesis examines how poplar trees are impacted by and remediate heavy metals that exist in CWW. The study was conducted at the University of Victoria, BC, Canada, and involved both laboratory work and field work conducted from 2021 to 2022. The research focused on tree health and heavy metal uptake and evaluated the performance of the designed treatment field in removing contaminants from CWW. The proposed methodology is grounded in a low-impact development (LID) approach tailored for wastewater treatment, particularly suited to remote, rural, and underserved areas, including developing nations like India, Malaysia, and other countries in the Middle East. The results demonstrate a decreasing trend in the concentration of zinc, cadmium, nickel, iron, copper, and lead from the point of application (point 1) at the field site to the effluent point (point 4), indicating good performance for removing these heavy metals. The removal rates for zinc, nickel, lead, iron, copper, and cadmium were 78.4%, 61.9%, 82.4%, 86.4%, 78.1%, and 98.95% respectively.

The study assessed the uptake of heavy metals by poplar trees by analyzing the concentrations in tree leaves. The data showed variations in heavy metal concentrations between different trees and leaf positions, with some metals exhibiting higher concentrations in the bottom leaves and others showing higher concentrations in the top leaves. The concentrations of heavy metals in the leaves were also influenced by seasonal variations and leaf turnover. Overall, the research findings indicate the impact to poplar trees in systems that use poplar trees for treating carwash wastewater, highlighting the importance of considering seasonal variations and leaf turnover when studying heavy metal uptake in trees. These findings carry significance for enhancing wastewater treatment procedures and encouraging responsible approaches across a range of industrial and environmental contexts.