A Holistic Look At Infrastructure Replacement: The Madison Metropolitan Sewerage District's Energy Management Master Plan

Relevance
Energy efficiency and sustainability are becoming top priorities for utility operations as evidenced by the growing number of energy management and renewable energy projects across the country. Utilities are combating rising energy costs and making good on their promise to be responsible environmental stewards while maintaining compliance with stringent discharge limits. This talk will walk through the development of and findings from the Madison Metropolitan Sewerage District's (District) 2020 Energy Management Master Plan (Plan), a comprehensive document that recommends targeted improvements to the Wisconsin-based utility's energy infrastructure and energy-management approaches over the next two decades.
Energy Planning Drivers, Goals and Approach
The Plan was born out of the District's need to upgrade or replace aging energy-producing and -consuming infrastructure at the Nine Springs Wastewater Treatment Plant (NSWTP), an effort that was estimated to cost approximately $88 million to$93 million without any process or energy optimization. To make strategic use of their resources and funding, the District decided to pursue improvements that would not only rehabilitate the NSWTP's energy infrastructure but also reduce its energy footprint by decreasing overall energy demands and increasing the generation and use of renewable energy. To this end, the Plan began with seven energy goals, which were influenced by the EnvisionTM scoring system: 1. Reduce fossil-fuel-based greenhouse gas (GHG) emissions by at least 10 percent within 10 years. 2. Reduce the cost of peak electricity demand by at least 5 percent within 10 years. 3. Reduce operational energy consumption by at least 10 percent within 10 years. 4. Use renewable energy to meet 50 percent of energy demands within 10 years. 5. Reduce the Class B biosolids processing and reuse program's energy demand or produce higher-value biosolids without significantly increasing energy demand. 6. Improve the resiliency and reliability of energy supply sources. 7. Improve the reliability of energy-using and -consuming infrastructure. In collaboration with the District and an industry-wide energy expert panel, the project team identified 'the universe of technology and energy options' that were grouped into the following major categories: co-digestion, biosolids, biogas, thermal, renewable energy, and effluent pumping as shown in Figure 1. Using a systematic screening process, the project team and the District then pared down 133 unique concepts into 26 strategic and feasible alternatives that were evaluated against criteria relevant to the District, including energy efficiency, resilience, reliability, cost, and operation and maintenance. This process generated 11 alternatives, which were merged into four synergistic combinations called 'scenarios.'
Analysis of Synergistic Alternative Combinations
The project team identified the following combinations of energy alternatives:
- Enhanced Baseline (Alternative 1a): Upgrades the plant's heat and power systems and partners with Madison Gas and Electric (MGE) to procure solar energy through their Renewable Energy Rider (RER) program.
- Maximize Renewable Energy Production (Alternative 2): Contains the same components as the Enhanced Baseline and includes new processes to capture and beneficially use additional waste heat energy.
- Energy Grid Resilience (Alternative 3): Upgrades heat systems and expands on-site power generation by using both biogas and natural gas in large co-generation systems, thus operating the plant 'off-grid.'
- Reduce Infrastructure Complexity (Alternative 4a): Simplifies infrastructure by upgrading heat systems, partnering with MGE through the RER program, and exporting renewable natural gas (RNG) to the renewable fuels market instead of using it for onsite power production.
To reduce the labor and transportation fuel needed for biosolids distribution, all four scenarios also included reconfigurations to the NSWTP's biosolids treatment processes and a new dewatering facility with expanded biosolids storage. After thorough alternatives evaluations and sensitivity analyses, the project team recommended that the Enhanced Baseline and Reduce Infrastructure Complexity alternatives be considered further. As shown in Table 1, both alternative combinations offer significant benefits over the baseline (i.e., continuing to rehabilitate and maintain existing infrastructure) with little to no drawbacks and at similar or even lower lifecycle costs.
Both alternatives have relatively similar capital costs, though the Reduce Infrastructure Complexity scenario has the potential for higher revenue production depending on the value of renewable identification numbers (RINs) in the U.S. Environmental Protection Agency's (EPA) Renewable Fuel Standard (RFS) program. In fact, revenues from the sale of RNG are projected to offset this scenario's increased costs in peak energy demand. In either case, Figure 2 shows that both recommended alternatives have considerably lower capital and 20-year net present value (NPV) costs compared to the other alternatives.
Energy Goals Achieved
The Enhanced Baseline scenario maintains the District's current operational philosophy (i.e., cogeneration and renewable electricity production) and meets all seven of the Plan's energy goals. The Reduce Infrastructure Complexity scenario offers a lower lifecycle cost potential, simplified infrastructure and lower operational complexity but does not meet the goal of reduced peak demand costs since it converts biogas to RNG rather than on-site electricity. With that being said, this scenario has the potential for high revenue production depending on the value of renewable identification numbers in the EPA's Renewable Fuel Standard program. In fact, revenues from RNG sales are projected to offset this scenario's increased costs in peak energy demand. Insights Gained (Lessons Learned)
During the 20-month development process of the Plan, the project team gained insights, both expected and unexpected, that will serve as valuable knowledge on future projects.
What does 'net-zero' really mean?
Although the Plan's focus wasn't on achieving 'net-zero,' grid independence was considered to help guide future policy decisions. A key lesson learned in this endeavor was that capturing all available energy on site (e.g., thermal, solar, carbon), especially with the goal of 'net-zero,' is not always cost-effective or practical.
The consequence here is to always question: What does 'net-zero' mean for the project at hand? Is it net-zero electricity use? Net-zero carbon? Thermal? For facilities like the NSWTP where net-zero electricity use may be impractical, net-zero carbon is a realistic goal that may become even more feasible over time as various electric utilities source greener energy.
Community energy partnerships can achieve multiple goals
The Plan was crucial in showing the District that, by establishing partnerships with the local electric utility or other entities, they can advance their goals to increase generation and use of renewable energy without having to bear the sole burden of owning and operating renewable energy infrastructure.
What's Next?
In their future facility planning efforts, the District will further evaluate the options recommended in the Plan to determine a path forward. In the process, the District will engage stakeholders and community partners to earn their support in developing effective, responsible, and transparent projects that bring value to the community.