Luna, Becky

Becky Luna is a Senior Vice President and Client Services Director at Carollo Engineers. She has a B.S. in Civil Engineering and an M.S. in Civil and Environmental Engineering from the University of Illinois at Urbana-Champaign. Becky joined Carollo in 2002 and has focused on the planning and design of biosolids facilities and secondary treatment processes for nutrient removal. Becky has worked with multiple municipalities to implement the beneficial use of biogas, including serving as project manager for two renewable natural gas projects that were awarded the WEF Project Excellence Awards.

Titles from this speaker

Comparison of Life Cycle Costs at Operating Cogeneration and RNG Facilities

Abstract

An increasing number of water resource recovery facilities (WRRFs) are considering options for beneficial use of biogas due to an increasing focus, both internally and externally, on resource recovery and sustainability. Conversion of biogas to electricity (through cogeneration) and to renewable natural gas (RNG) (for pipeline injection or vehicle fueling) are often considered side by side as alternatives that can produce revenue and reduce the greenhouse gas footprint of WRRFs. While there are a large number of WRRFs across the country that have operated cogeneration systems over the last decades, operating costs can vary significantly depending upon the technology selected, condition of the raw biogas, and age of the system. In addition, while the technology used to convert biogas to RNG is established, pipeline injection and vehicle fueling projects remain relatively few and far between in the U.S. These unknowns make it difficult to quantify O&M costs for utilities considering a biogas utilization project. This complicates the evaluations of these systems, since long-term operating and maintenance (O&M) costs are a significant factor in selection of a recommended alternative.

The conversion of biogas to electricity through cogeneration or to renewable natural gas (RNG) for pipeline injection or vehicle fueling has received increasing interest at water resource recovery facilities (WRRFs). For both uses, operation and maintenance (O&M) data from facilities is limited, making it difficult for WRRFs to accurately assess life cycle costs. WRRFs often rely on O&M costs provided by manufacturers. This paper compares manufacturer O&M cost estimates to operational data at ten facilities that run either cogeneration or RNG upgrading facilities and finds that actual O&M costs are higher than manufacturer O&M estimates, despite conservative assumptions.

SpeakerLuna, Becky

Presentation time

13:45:00

14:00:00

Session time

13:30:00

14:30:00

SessionBiogas: Market-based Decisions for Resource Recovery

Session number507

TopicBiosolids and Residuals, Energy Production, Conservation, and Management, Policy and Regulation

Author(s)

Becky Luna

Author(s)B.J. Luna2; T.G. Mossinger3; T. Dougherty4;E. Charbonnet1;

Author affiliation(s)Carollo Engineers, Broomfield, CO 1,2,4Carollo Engineers, Portland OR3

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2021

DOI10.2175/193864718825158136

Volume / Issue

Content sourceWEFTEC

Word count12

Description: Maximizing Operator Involvement Through CMAR: Keeping Avon WWTF Running Through 3...

Maximizing Operator Involvement Through CMAR: Keeping Avon WWTF Running Through 3 Years of Construction

Abstract

Eagle River Water and Sanitation District’s (ERWSD) $49.6M Nutrient Upgrades Project at the 4.3 million gallon per day (mgd) Avon Wastewater Treatment Facility (WWTF) implemented a plan for sequencing nutrient removal improvements at the three interconnected WWTFs. Key challenges for this project included: 1) maintaining effluent permit compliance with units out of service while handling seasonal loading peaks, 2) improving access to underground and inaccessible aeration basins while maintaining structural integrity, and 3) sequencing work while mitigating impacts to neighbors. The project was delivered using the Construction Manager at Risk (CMAR) model, with collaboration from key team members at Moltz Construction, ERWSD, and Carollo. The Avon project, which achieved substantial completion in May 2023 after five years of planning, design, and construction, serves as a strong example of the value of operator involvement and CMAR delivery in maintaining operations during construction.

The Nutrient Upgrades Project at Avon WWTF (near Vail, Colorado) faced key challenges: 1) maintaining compliance with units out of service while handling seasonal loading, 2) improving access to underground basins while maintaining structural integrity, and 3) sequencing work while mitigating impacts to neighbors. The project achieved substantial completion in May 2023, serving as a strong example of the value of operator involvement and CMAR delivery in operations during construction.

SpeakerBerlin, Jeffrey

Presentation time

10:30:00

11:00:00

Session time

10:30:00

11:30:00

SessionProject Delivery Challenges: Continued Operations and Commissioning

Session locationRoom S404c - Level 4

TopicFacility Operations and Maintenance, Intermediate Level, Municipal Wastewater Treatment Design, Utility Management and Leadership

Author(s)

Berlin, Jeffrey

Author(s)J. Berlin 1; T. Drescher 2 ; B. Luna 1; J. Berlin 1;

Author affiliation(s)Carollo Engineers, Inc. 1; Eagle River Water and Sanitation District 2 ; Carollo Engineers, Inc. 1; Carollo Engineers, Inc. 1;

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2023

DOI10.2175/193864718825159185

Volume / Issue

Content sourceWEFTEC

Word count15

Next Evolution of Biogas Upgrading -- RNG System with Heat Recovery

Abstract

Over the last fifty years, anaerobic digestion has become common practice at medium to large water resource recovery facilities (WRRFs) in the United States, providing a sustainable source of biogas while achieving significant improvements in sludge stabilization. With more installations, facilities are being presented with a larger array of biogas end use choices to meet their cost and sustainability goals. After four decades of operating a cogeneration facility to produce electricity and heat, Metro Water Recovery (Metro) and Carollo Engineers, Inc. (Carollo) completed a Biogas Utilization Study in 2021 to consider new beneficial uses of biogas at the Robert W. Hite Treatment Facility (RHWTF) that serves Colorado's Denver metropolitan area. The study compared replacing the existing cogeneration system with new cogeneration equipment versus installing biogas upgrading equipment to generate renewable natural gas (RNG) for pipeline injection. Through a detailed comparison of the biogas utilization alternatives that included financial analysis, operational considerations, and sustainable attributes, Metro selected RNG as the biogas utilization pathway which would provide the highest social, environmental, and financial benefit to Metro. In 2022, Metro and Carollo began design of the Biogas Utilization Project, including a biogas upgrading system for pipeline injection of RNG and a Boiler Mechanical Facility to replace the heat currently supplied by the cogeneration system. The initial phase of this project included further analysis into the available technologies for biogas upgrading. Most WRRFs in the United States have selected membrane or pressure swing adsorption technologies for the separation of methane and carbon dioxide due to their cost effectiveness at relatively small biogas flow rates. Although these approaches do not have technical limitations at higher flow rates, amine wash and water wash were determined to be more appropriate from a financial and physical layout perspective at Metro's design biogas flow of 3,000 standard cubic feet per minute (scfm). As part of the preliminary design effort, the team collected information on these two systems and conducted a triple bottom line alternatives analysis to support an informed technology selection. The detailed information included: - Equipment budgetary proposals (including capital and operating costs, equipment layouts, and equipment lead times) from multiple manufacturers. - Site visits to operating equipment installations. - Phone interviews with past and current RNG system operators. - Conceptual system layouts. - Conceptual design and construction costs. - Greenhouse gas (GHG) emissions. - Local natural gas utility's RNG quality requirements. A comparison of the water wash and amine upgrading systems is summarized in Table 1. Based on Metro's evaluation of the two technologies, site visits, and feedback from reference installations, the design team determined that both the amine and water wash upgrading systems could reliably produce RNG that meets the natural gas utility's quality requirements. While water wash systems contain fewer mechanical components and higher levels of redundancy (based on the equipment manufacturer's two-train proposal), the amine system offers slightly higher methane capture, a higher purity tail gas stream that may be more amenable to future beneficial use, lower GHG emissions, and the ability to recover a significant portion of the input heat to offset natural gas required for heating the digesters and buildings on site. Based on this evaluation, Metro selected the amine upgrading system for final design. In an amine upgrading system, raw biogas is boosted and conveyed into a counter-flow reactor tower where the carbon dioxide is solubilized into the amine solution at relatively low pressure (12 pounds per square inch). The methane flows out the top of the reactor tower while the carbon dioxide-rich amine solution is pumped to a stripping tower. Heat is added to the stripping tower to break the bond between the carbon dioxide and amine in solution, releasing carbon dioxide gas and regenerating the amine solution, which is pumped back to the reactor tower. The heat used by the amine upgrading system will be supplied by new hot water boilers that are being constructed as part of the project to heat the digesters and buildings (replacing heat that was previously supplied by the cogeneration system). The carbon dioxide separation process requires a high temperature to regenerate the amine solution. While the heat is often supplied by steam, in this case, the design includes superheated water pressurized to 125 pounds per square inch gauge (psig) and heated to 275 degrees, avoiding separate steam boilers, reducing overall system complexity, and improving redundancy. Up to 90 percent of the heat required by the amine upgrading system can be recovered and used elsewhere on the plant-site. However, the recoverable heat is 'low grade' in that it is not hot enough to be usable at the temperatures supplied from the amine skid for traditional digester process or building heating applications. To utilize heat recovery from this system, Metro and Carollo evaluated the use of industrial water-to-water heat pumps to upgrade the low-quality recovered heat to higher quality heat for use in the digestion process, the largest heat demand at the RWHTF. To better understand the costs and benefits of a heat pump heat recovery system, the team developed a 20-year net present value and estimated GHG emissions reductions associated with the heat recovery system. The capital cost of the heat pump system was developed by the construction manager at risk (CMAR) contractor, Moltz Construction, Inc. The total construction cost for the heat recovery system, including the building it is housed in, is estimated to be $9.2 million. If this system were to qualify for Inflation Reduction Act (IRA) funding (which is anticipated based on discussions with Metro's tax advisor), the capital cost would be reduced to approximately $6.4 million. While the heat pump system has a significant electrical demand, its high coefficient of performance means the energy output is more than five times the electrical energy input. The heat pumps will directly offset approximately $1.5 million in annual natural gas usage in the boilers and reduce GHG emissions by 30 percent compared to solely using natural gas for digester heating (Figure 1). The calculated 20-year NPV of the heat recovery system is approximately $3.1 million with a payback period of roughly 15 years. With the IRA's capital cost reduction (assumed to be a 30 percent discount) the 20-year NPV increases to $5.9 million and the payback period decreases to approximately 10 years. A graph comparing the 20-year NPV with and without the IRA reduction is shown in Figure 2. Construction of Phase 1 of the Biogas Utilization Project began in October 2024. Phase 1 includes construction of the Boiler Mechanical Facility, which will house the hot water boilers required to supply heat to the digesters, the amine upgrading system, and other process and building heating demands at the RWHTF. Construction of Phase 2 will begin in 2026 and includes demolition of the cogeneration facility and installation of the amine upgrading and heat recovery systems. At an inlet design flow rate of 3,000 scfm, the RWHTF's biogas upgrading system will be the second largest RNG system and the first installation of an amine upgrading system at a WRRF in the United States. Figure 3 presents a rendering of the proposed facilities. WRRFs are under increasing pressure to recover resources and make sustainable decisions related to energy use. This project showcases how a large regional WRRF pivoted from cogeneration to pipeline injection of renewable natural gas with a focus on maximizing resource recovery and minimizing natural gas use. This novel application of amine upgrading paired with a heat pump system provides a road map for other utilities to follow. The project's use of triple bottom line evaluations provides a solid business case for decision making.

This paper was presented at the WEF Residuals & Biosolids and Innovations in Treatment Technology Joint Conference, May 6-9, 2025.

SpeakerLuna, Becky

Presentation time

10:55:00

11:15:00

Session time

10:15:00

11:45:00

SessionAdvancing Biogas and RNG: Innovations and Regulatory Challenges

Session number26

Session locationBaltimore Convention Center, Baltimore, Maryland, USA

TopicAerobic Digestion, Alternative Delivery Systems (Design-Build-Operate-Transfer), Biogas, Biogas To Biomethane, Biogas Utilization, Greenhouse Gases, Heat recovery, Renewable Natural Gas

Author(s)

Luna, Becky, Dougherty, Tyler, Buhman, Darrell, Norford, A.D., Freedman, Daniel

Author(s)B. Luna1, T. Dougherty D. Buhman1, A. Norford2, D. Freedman2

Author affiliation(s)Carollo Engineers, Inc., 1Metro Water Recovery, 2

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date May 2025

DOI10.2175/193864718825159788

Volume / Issue

Content sourceResiduals and Biosolids Conference

Word count12

Policy Outlook Informs Sensitivity Analyses of Biogas Alternatives

Abstract

Introduction After four decades of operating a cogeneration facility to produce electricity and heat, Metro Water Recovery (Metro) commissioned a Biogas Utilization Study in 2021 to consider historical and new beneficial uses of biogas at their Robert W. Hite Treatment Facility (RHWTF) that serves Colorado's Denver metropolitan area. While cogeneration has been the industry standard for biogas utilization at water resource recovery facilities (WRRFs) for decades, biogas upgrading to renewable natural gas (RNG) has become more prevalent due to federal incentives available under the Renewable Fuel Standard (RFS) program created under the Energy Policy Act of 2005. And while the RFS program has been the historic driving force behind the shift to RNG, a drive by major companies to reduce the carbon footprint of their operations are leading to further incentives for biogas, potentially mitigating the risk of relying on a single revenue stream. This study investigated two alternatives for beneficial reuse of the biogas resource at Metro's RWHTF: - Upgrade and continue to operate the Cogeneration Facility to generate electricity and heat using biogas. - Construct a new facility that converts biogas into RNG for direct injection into a natural gas pipeline owned by Xcel Energy (Xcel) and monetize the RNG. While WRRFs across the country have embarked on similar evaluations; this project was unique in that it included an in-depth evaluation of the long-term viability of financial incentive markets, sustainability impacts, future natural gas demand, and the potential impact from current and future state policies. This evaluation was then used to inform sensitivity evaluations of the two alternatives to facilitate decision making. Monetizing RNG The study evaluated four pathways for Metro to generate a revenue source from their RNG. These revenue sources included: 1. Sale of brown gas, 2. Participation in the Renewable Fuel Standard (RFS) program, 3. Participation in state-specific Low Carbon Fuel Standard (LCFS) programs, and 4. Participation in the voluntary market. The sale of brown gas is typically tied to regional natural gas indices, with revenue calculated based on the amount of gas injected into the natural gas utilities' pipeline. The sale of brown gas can be paired with renewable credits as shown in Figure 1. The study evaluated the long-term viability of the RFS program, considered the potential for an LCFS program in the State of Colorado, state legislature geared towards the reduction of the carbon footprint of building heat, and reviewed the strength of voluntary markets. The renewable volume obligations (RVO) under the RFS are set to expire at the end of 2022, and members of Congress have voiced support for the replacement of the RFS with a national LCFS program (similar to California) that provides incentives for a wider range of low carbon fuels. To date, there remains a significant gap in RNG supply to meet the originally planned renewable volume obligations. Whether the RFS program is continued or replaced by an LCFS program, it is anticipated that a system of federal renewable credits will remain in place for the foreseeable future for RNG. The viability of an electric renewable identification number (e-RIN) pathway was also considered; however, the EPA has not approved any such project, despite receiving approval requests. The Colorado Energy Office recently evaluated the viability of an LCFS program for the State of Colorado. This report (Low Carbon Fuel Standard Feasibility Study, September 2020, ICF Resources, L.L.C.) stated that, 'Experience in California, Oregon and British Columbia has shown that LCFS programs can deliver on the above policy objectives, and that LCFS programs are a cost-effective mechanism to reduce GHG emissions and increase the share of lower carbon fuels in the transportation sector, while having a smaller cost impact on retail fuel prices relative to other decarbonization policies.' No movement has been made to date by the State legislature to introduce such a program. Many corporations and utilities have established 'carbon-free' energy goals, which has created a voluntary market for RNG. Due to the higher RIN pricing, increasing RNG demands in the voluntary markets have resulted in increasing value and revenue potential. Table 1 shows the pricing variability for the voluntary markets and illustrates the increases in the market based on current conditions and drivers towards RNG sustainability goals. Long-term Natural Gas Demand As the energy sector transitions to meet renewable energy goals, there is increasing demand for natural gas that is anticipated to continue through 2050. The U.S. Energy Information Administration (EIA) projects increasing demand for compressed natural gas (CNG) over the next 30 years at 1 percent compounded annually. CNG demand is also expected to remain strong in the transportation sector, despite the focus on electrification of light-duty vehicles. CNG continues to be the major fuel source for heavy-duty vehicles. Figure 2 expands on the uses of CNG in the transportation sector and demonstrates there is a steady increase in CNG consumption through 2050. As Xcel, the local electric and natural gas utility, further develops their renewable energy portfolio to meet their 2050 carbon-free electricity goals, natural gas is anticipated to remain the backbone of reliable energy sources and backup emergency power for the next 20 years. State of Colorado Policy Impacts The State of Colorado is targeting a reduction of greenhouse gas emissions by 90 percent of the 2005 values by the year 2050. Legislation approved in 2021 requires natural gas and electric utilities (i.e. Xcel) to reduce the use of natural gas by consumers. Xcel could purchase RNG from Metro to decrease the reliance on natural gas. While a cap-and-trade program introduced this year was vetoed by the Governor, the Public Utility Council is currently reviewing a means of implementation for the legislation which could include an avenue for RNG. Alternatively, Metro could decide to pursue this type of program on a voluntary basis with other states or utilities that have existing programs. While the State has evaluated different types of RNG legislation and potentially creating their own LCFS program, nothing has materialized that would influence Metro's decision on which biogas alternative to move forward with. Variability of Utility Costs Electricity and natural gas costs are large operating expenses for Metro's annual budget. Pricing volatility for electricity and natural gas could impact either of the biogas alternatives. The EIA forecasts that increasing renewable energy capacity will result in a slight decrease of electrical rates through 2050. However, regional differences will occur based on the level of renewable energy in the regional electric utility's portfolio. According to the EIA, natural gas pricing fluctuates based on weather, economic growth, market competition, gasoline prices, and availability. Figure 3 illustrates the yearly average Henry Hub natural gas spot pricing. Sensitivity Evaluations Sensitivity analyses were developed to capture the financial viability of both alternatives based on the changing future conditions described above. Figure 4 presents the range of life cycle costs for the cogeneration alternative, with consideration of changing electricity prices and renewable electricity credit value. Figure 5 presents the range of life cycle costs for the pipeline injection alternative, with consideration of RIN pricing, voluntary market, and natural gas market volatility. Based on the sensitivity evaluations, the pipeline injection alternative in almost all cases provides a positive financial return to Metro when compared to the cogeneration alternative. The pipeline injection alternative has a simple payback of 3 to 10 years depending on the revenue model. When comparing the base case alternatives, pipeline injection has a 20-year net present value that is $205 million higher than the cogeneration alternative. Based on the recommendations of this study, Metro is planning to proceed with preliminary design and development of a biogas upgrading and pipeline injection system.

This paper was presented at the WEF Residuals and Biosolids Conference in Columbus, Ohio, May 24-27, 2022.

SpeakerLuna, Becky

Presentation time

8:30:00

9:00:00

Session time

8:30:00

11:45:00

Session number08

Session locationGreater Columbus Convention Center, Columbus, Ohio

TopicBiosolids, Finance, Renewable Natural Gas

Author(s)