Life Cycle Assessment to Inform the Sustainable Design of Constructed Wetlands

Constructed wetlands offer a natural solution for simultaneously improving water quality, increasing water supply and promoting ecosystem services. For this reason, constructed wetlands are increasingly being used as a part of wastewater treatment and stormwater management. Despite this technology being nature-based, multiple environmental impacts can occur throughout the system’s lifetime, including both direct emissions (e.g., direct greenhouse gas emissions to air, direct nutrient emissions to water) and indirect emissions (e.g., through material and energy consumption). The growing popularity of nature-based passive treatment technologies calls for a holistic understanding of how the specific design and operation of these systems translate into trade-offs and synergies regarding environmental impacts. To this end, the objective of this research is to estimate the potential global environmental impacts associated with both the construction and operation phases of constructed treatment wetland mesocosms using life cycle assessment (LCA). LCA – following the steps of goal and scope definition, inventory, impact assessment, and interpretation – was conducted for mesocosm wetlands with different designs (e.g., surface and subsurface flow regimes) that were established in 2022 in the city of Norman, Oklahoma, by researchers at the University of Oklahoma. The life cycle inventory for these mesocosms was based on material and construction data for these established systems. After the inventory was developed, impact assessment was conducted using the Tool for Reduction and Assessment of Chemicals and Other Environmental Impacts (TRACI), developed by the U.S. EPA. For the operation phase, a literature review was conducted to estimate direct greenhouse gas emissions that are produced during the system’s lifetime, assumed to be 20 years. To better understand the influence of specific design parameters, uncertainty and sensitivity analyses were conducted using Monte Carlo methods and Spearman’s rank correlation coefficients, respectively. The end goal of this research is to help inform sustainability decision-making regarding constructed wetlands for wastewater treatment and reuse.