Developing a Cost-Effective Resilient Decarbonization Strategy: Lessons for Decision-Makers

Introduction
Wastewater utilities are working towards a circular economy by reducing energy consumption and other greenhouse gas (GHG) emissions. To support these goals utilities may create a long-term decarbonization strategy. However, the complexity of wastewater infrastructure and treatment processes necessitates a tailored, case-by-case approach to guide decision-making. York Region in Ontario, Canada has developed a cost-effective resilient wastewater decarbonization strategy and its experience provides valuable insights to other utility decision-makers on the challenges, approaches, and lessons learned in this important endeavor.

Boundary Definition
Deciding which emissions are within the boundary of the strategy is an important step. Table 1 summarizes the emissions that York Region included, organized by scope. This choice was informed by a global scan, other local municipalities, regulatory agency reporting requirements, and previous studies. For example, York Region included sewer generated methane in its inventory owing to having a previous assessment to build on.

Baseline Conditions and Business-as-Usual Projection
Baseline emissions were quantified for historical years using the OWWA/WEAO GHG Inventory Tool for Water Utilities supplemented by additional quantifications such as for sewer-generated methane. Using the baseline conditions and existing systems as a guide, the project team developed a business-as-usual (BAU) projection that assumes existing practices are continued accounting for additional flow. The BAU conditions starting at the baseline year of 2014 to 2050 are presented in Figure 1, suggesting emissions could nearly double.

Mitigation Activities Long-listing and Refinement
The project team brainstormed a long list of potential mitigation projects based on a global scan and team knowledge. The overall approach to filter the long list is illustrated in Figure 2. The project team then refined this long list into a short-list of feasible-by-2050 activities and programs. This feasibility assessment considered: technology availability and anticipated development before 2050, alignment with stakeholders, alignment with the existing wastewater master plan and alignment with co-owned facilities.

The feasible options were then categorized as a mitigation activity or a supporting activity. Mitigation activities are those where a cost and GHG reduction could be quantified such as changes to fugitive emissions or reducing the consumption of electricity. Supporting activities are those that cannot be numerically quantified but provide support to achieving GHG reductions, such as measuring emission factors, increasing staff capacity through training, and developing different purchasing policies. For each mitigation activity, capital and O&M costs were estimated and GHG emissions over the project service life were estimated. From these values the cost of abatement was calculated by dividing the net present value lifecycle cost by the total tons of carbon dioxide equivalent (CO2e) mitigated (i.e. $/t-CO2e). Mitigation projects exceeding $1,000 CAD/t-CO2e were deemed not cost-effective. Of the 17 projects that were considered cost-effective, a multi-criteria analysis (MCA) was used to rank them using the criteria listed in Table 2.

Results and Outcomes
A marginal abatement cost (MAC) curve was generated from the 17 feasible and cost-effective mitigation projects. This MAC curve is shown in Figure 3 while the same projects sorted by MCA rank is shown in Figure 4. These two plots highlight that despite some projects having a negative abatement cost, these projects are not necessarily optimal when considering the criteria in Table 2. These plots indicate the cost-effective mitigations would reduce the 2050 BAU emissions by approximately 45 percent.

Getting to zero GHG emissions was found to be not feasible at the present time even if all cost-effective mitigation projects were implemented. Figure 5 shows the projected emissions of the BAU case, and the decarbonization projections with and without constraints. Owing to York Region's planned doubling of the service population by 2050, the decarbonization pathway would keep the total emissions at roughly the same magnitude as historical emissions. As an alternative that can better communicate decarbonization progress even with population growth, the GHG emissions can be normalized per volume of wastewater treated. In this view, the benefit of decarbonization action is clearly seen and offers another communication tool that utilities can use with their stakeholders.

Significance
Although York Region found that decarbonizing to zero GHG emissions is not yet cost-effective to achieve, there are many mitigations available that do achieve significant reductions supporting a more sustainable and circular wastewater infrastructure. This presentation will further identify the lessons for utility decision-makers when pursuing a comprehensive decarbonization strategy that is feasible and cost-effective. In addition, the presentation will explain how adapting and improving resilience to climate change was also incorporated into the project.