Sierra, Natalie

Natalie Sierra is Brown and Caldwells National Practice Lead for Solids and Energy, based out of Andover, Massachusetts. She has over 20 years of...

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About Sierra, Natalie

Natalie Sierra is Brown and Caldwells National Practice Lead for Solids and Energy, based out of Andover, Massachusetts. She has over 20 years of experience in the industry with expertise in biosolids management, biosolids markets and regulations, and emerging contaminants. Her work nationally focuses on long-term solids treatment planning and supporting utilities in developing biosolids programs.

Sierra, Natalie

Titles from this speaker

Are Your Digesters Up to the Task? Aligning Resource Recovery Planning with Reality

Abstract

Abstract Anaerobic digestion serves as the linchpin for much of the wastewater solids treatment in the United States. In many major metropolitan areas, digesters were constructed between the 1950s and 1970s, and are reaching the end of their useful life. As utilities seek to increase resource recovery and intensify digestion, these older vintage digesters may not be able to accommodate simple upgrades that allow for higher temperature or higher total solids operation. Introduction Anerobic digestion sits at the nexus between traditional wastewater treatment and modern utility climate goals, including greenhouse gas (GHG) reduction, landfill diversion, and green energy generation. Utilities performing solids and energy planning around these goals are typically relying heavily upon their anaerobic digesters to be efficient and high performing, often seeking to intensify digestion so as to accommodate imported feedstocks (e.g. fats, oil and grease, food waste, outside sludge, etc.) or simply to provide capacity for future flows and loads within the same tankage. In many major metropolitan areas, digesters were constructed between the 1950s and 1970s, and are reaching the end of their useful life. As utilities seek to increase resource recovery and intensify digestion, these older vintage digesters may not be able to accommodate simple upgrades that allow for higher temperature or higher total solids operation. Results and Discussion When seeking to achieve higher loading rates (either due to increased population in the service area or a desire to import high strength wastes), it is typical for utilities to start the planning process by assessing the potential of existing anaerobic digestion tankage. Intensifying digestion via established processes such as thermophilic digestion or thermal hydrolysis can be an appealing way to expand capacity (see Figure) with a seemingly incremental investment (e.g. heat exchangers, thermal hydrolysis skid). The ability to intensify digestion can be especially important in older cities where sites may be constrained and expansion of a digester complex is not possible. Despite these advantages, however, digestion infrastructure may not be capable of realizing the full potential of intensification due to either structural inadequacy or suboptimal configuration. As a general industry practice, digester tanks are expected to remain in service for 50 to 75 years, with the associated mechanical equipment having a shorter service life of approximately 20 years. Factors that can affect this service life include freeze/thaw cycles, which can weaken concrete, and seismic activity. In addition, many older digesters were constructed with floating covers, and cover integrity, as well as interior and exterior coating integrity, can expose the digester structure to wear inducing conditions. While not a hard trigger, replacement of the digesters prior to reaching 75 years of life serves as a sound rule of thumb. Very few comparable facilities have digester structures of this age operational, although a small number remain in service with plans to replace prior to 2030 (e.g., San Francisco's Southeast Water Pollution Control Plant). In addition, considerations about capacity, given that older digesters were simply not designed to perform at the higher loading rates needed for codigestion applications, amplify the need for eventual replacement of these structures. Other unknowns, including structural vulnerabilities, could accelerate this replacement timeline. Operating conditions associated with higher rate digestion that can be problematic for older digestion infrastructure include higher gas production rates, biogas entrainment, and changes to viscosity. Older gas mixing systems, for example, are likely inadequate for realizing the full active volume of a digester generally, a condition that is exacerbated by sludges of higher total solids content. Changes to viscosity associated with higher total solids content (thicker sludge) and/or inclusion of food waste can, in addition to impacting mixing performance, can entrain biogas, contributing to acute operational issues such as digester foaming. Changes to sludge rheology will also impact ancillary systems, such as pumps and heat exchangers, which should be assessed for upgrades. Higher digester loading limits could potentially be realized if existing digesters are upgraded with features such as improved mixing and surface withdrawal, both of which will help realize the full active volume of the digester and minimize gas and foam entrainment (see Figure). Such upgrades can be included in existing digesters, assuming the structural integrity of the tank is intact. A detailed condition and structural assessment is recommended prior to implementing digester enhancements intended to accommodate higher rate digestion. Conclusions When assessing the capability of existing digesters to process higher organic loads, a thorough assessment must be undertaken. This includes a robust condition assessment, as well as an evaluation of retrofits that can maximize the benefits of intensification. Full costs of such upgrades should be compared against the cost and feasibility of construction of new, modern digesters to help utilities realize their full plans for resource recovery.

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

SpeakerSierra, Natalie

Presentation time

10:45:00

11:05:00

Session time

10:45:00

11:45:00

SessionPractical Considerations in Digestion

Session number4

Session locationBaltimore Convention Center, Baltimore, Maryland, USA

TopicAnaerobic co-digestion, Biomethane, Lipids/proteins/carbohydrates ratio, TWAS, Manure, SSO, Anaerobic Digestion, Asset Management, Biomethane Potential Test, Condition Assessment, Corrosion, Intensification, Resource Recovery, Struvite

Author(s)

Sierra, Natalie, Muller, Christopher

Author(s)N. Sierra1, C. Muller1

Author affiliation(s)Brown and Caldwell, 1Brown and Caldwell, 1

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date May 2025

DOI10.2175/193864718825159777

Volume / Issue

Content sourceResiduals and Biosolids Conference

Word count14

Developing a Regional Biosolids Master Plan for the North Shore Water Reclamation District

Abstract

In 2023, the North Shore Water Reclamation District (NSWRD) developed a comprehensive Biosolids Master Plan (BMP) to leverage opportunities for the regionalization of solids handling facilities that were in need of renewal and modernization. The BMP addressed operational and maintenance challenges, optimized resource recovery, and made plans for current and future regulations, within the framework of stakeholder goals and values. The NSWRD BMP planning process is complete, and a discussion of the planning approach, considerations, and the selected alternative will be presented. This approach to biosolids master planning could be implemented by any water resource reclamation facility seeking to take a holistic approach to their biosolids management program, solids handling technology, and the operational requirements of their solids processing. The NSWRD serves around 300,000 residents north of Chicago and processes a total average of 63 million gallons and 7,785 dry tons of Class A Exceptional Quality (EQ) biosolids per day. The NSWRD is composed of three water reclamation facilities (WRFs), Gurnee WRF, Waukegan WRF, and Clavey Road WRF, and a regional biosolids drying facility (Figure 1). The drivers for completing this BMP included the following: Capacity constraints , aging assets, operational challenges associated with the drying and marketing of unstabilized solids, and other regulatory considerations. At the onset of the planning effort, a collaborative effort was undertaken by the NSWRD and the Brown and Caldwell team to develop a set of guiding principles to keep the plan aligned with the long-term goals of the NSWRD's. Those program goals and objectives are listed below:

*Modernize NSWRD's aging solids handling assets in a cost-effective manner that balances program goals with stakeholders' financial interests.

*Create solids handling solutions that can incorporate innovation and are operation and maintenance (O&M) friendly/easy to own.

*Improve regulatory and market resiliency by creating solutions that lend themselves to program flexibility and redundancy.

*Set a course that supports environmental stewardship, including reduction or recovery of energy, and the creation of marketable biosolids products.

*Create an adaptable plan that can be implemented to leverage current assets and address near-term challenges, while prioritizing those projects that address the NSWRD's goals for the future. The preferred alternative was selected through a two-phase planning process, with numerous collaborative and iterative rounds of analysis and screening. In Phase I of the planning process, the planning team established the operational, economic, and environmental baseline for the existing biosolids management program at NSWRD and performed a regulatory and market assessment of the current biosolids land application landscape. In Phase II, the team performed a biosolids stabilization and biogas management technology pre-screening and an intensive three-round alternatives analysis, Each round of the analysis provided some clear trends. An outline of the number of alternatives, the objective of each round, and a summary of those takeaways are presented in Figures 2-5. The selection of the preferred alternative was made through a multi-criteria decision-making process in which the alternatives from round 3 were compared on cost and relative benefit. This process facilitates the selection of the program that provides the best value to the District by considering a variety of specific factors that the District's staff weigh in order of importance. A dashboard of these results is shown in Figure 6. The preferred alternative implements an advanced regionalized digestion and drying program that generates renewable energy and a high-quality Class A EQ product. It also consolidates solids management at the Gurnee WRF over the next 20 years. The regionalized thermophilic anaerobic digestion (TAD) and belt drying program will be located at the Gurnee WRF, with pipeline injection of the upgraded biogas or renewable natural gas (RNG). At full implementation, solids from Waukegan WRF and Clavey Road WRF would be conveyed via tanker or forcemain to Gurnee WRF for fully regionalized digestion, dewatering, and drying, with the option to convert to a Class A temperature-phased anaerobic digestion system in the future

In 2023, the North Shore Water Reclamation District in Illinois developed a Biosolids Master Plan (BMP) to layout the next twenty years of upgrades to their solids handling program. The BMP addressed operational and maintenance challenges, optimized resource recovery, and accommodated current and future regulations, all while incorporating stakeholder goals and values.

SpeakerMarino, Joe

Presentation time

16:00:00

16:30:00

Session time

15:30:00

17:00:00

SessionManaging Biosolids for Tomorrow: Infinite Resources, Finite Uses

Session number218

Session locationRoom 253

TopicBiosolids and Residuals, Circular Water Economy, Energy Production, Conservation, and Management, Intermediate Level, Public Communication and Outreach

Author(s)

Marino, Joe, Ma, Persephone, Sierra, Natalie, Waters, Steve, Vodnik, Travis, Prentice, Emily, Le, Trung

Author(s)J. Marino1, P. Ma1, N.V. Sierra2, S. Waters3, T. Vodnik3, E. Prentice3, T. Le4

Author affiliation(s)1Brown and Caldwell, IL, 2Brown and Caldwell, MA, 3North Shore Water Reclamation District, IL, 4Brown and Caldwell, VA

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2024

DOI10.2175/193864718825159644

Volume / Issue

Content sourceWEFTEC

Word count14

Description: Developing a Regional Biosolids Master Plan for the North Shore Water Reclamation...

Developing a Regional Biosolids Master Plan for the North Shore Water Reclamation District

Abstract

In 2023, the North Shore Water Reclamation District (NSWRD) developed a comprehensive Biosolids Master Plan (BMP) to leverage opportunities for the regionalization of solids handling facilities that were in need of renewal and modernization. The BMP addressed operational and maintenance challenges, optimized resource recovery, and made plans for current and future regulations, within the framework of stakeholder goals and values. The NSWRD BMP planning process is complete, and a discussion of the planning approach, considerations, and the selected alternative will be presented. This approach to biosolids master planning could be implemented by any water resource reclamation facility seeking to take a holistic approach to their biosolids management program, solids handling technology, and the operational requirements of their solids processing. The NSWRD serves around 300,000 residents north of Chicago and processes a total average of 63 million gallons and 7,785 dry tons of Class A Exceptional Quality (EQ) biosolids per day. The NSWRD is composed of three water reclamation facilities (WRFs), Gurnee WRF, Waukegan WRF, and Clavey Road WRF, and a regional biosolids drying facility (Figure 1). The drivers for completing this BMP included the following: Capacity constraints , aging assets, operational challenges associated with the drying and marketing of unstabilized solids, and other regulatory considerations. At the onset of the planning effort, a collaborative effort was undertaken by the NSWRD and the Brown and Caldwell team to develop a set of guiding principles to keep the plan aligned with the long-term goals of the NSWRD's. Those program goals and objectives are listed below: - Modernize NSWRD's aging solids handling assets in a cost-effective manner that balances program goals with stakeholders' financial interests. - Create solids handling solutions that can incorporate innovation and are operation and maintenance (O&M) friendly/easy to own. - Improve regulatory and market resiliency by creating solutions that lend themselves to program flexibility and redundancy. - Set a course that supports environmental stewardship, including reduction or recovery of energy, and the creation of marketable biosolids products. - Create an adaptable plan that can be implemented to leverage current assets and address near-term challenges, while prioritizing those projects that address the NSWRD's goals for the future. The preferred alternative was selected through a two-phase planning process, with numerous collaborative and iterative rounds of analysis and screening. In Phase I of the planning process, the planning team established the operational, economic, and environmental baseline for the existing biosolids management program at NSWRD and performed a regulatory and market assessment of the current biosolids land application landscape. In Phase II, the team performed a biosolids stabilization and biogas management technology pre-screening and an intensive three-round alternatives analysis, Each round of the analysis provided some clear trends. An outline of the number of alternatives, the objective of each round, and a summary of those takeaways are presented in Figures 2-5. The selection of the preferred alternative was made through a multi-criteria decision-making process in which the alternatives from round 3 were compared on cost and relative benefit. This process facilitates the selection of the program that provides the best value to the District by considering a variety of specific factors that the District's staff weigh in order of importance. A dashboard of these results is shown in Figure 6. The preferred alternative implements an advanced regionalized digestion and drying program that generates renewable energy and a high-quality Class A EQ product. It also consolidates solids management at the Gurnee WRF over the next 20 years. The regionalized thermophilic anaerobic digestion (TAD) and belt drying program will be located at the Gurnee WRF, with pipeline injection of the upgraded biogas or renewable natural gas (RNG). At full implementation, solids from Waukegan WRF and Clavey Road WRF would be conveyed via tanker or forcemain to Gurnee WRF for fully regionalized digestion, dewatering, and drying, with the option to convert to a Class A temperature-phased anaerobic digestion system in the future. A process flow diagram of the preferred alternative is shown in Figure 7. The preferred alternative maximizes operational resiliency and resource recovery while reducing costs through consolidating solids processing and utilizing existing assets. After the selection of the preferred alternative, an implementation plan was developed for the biosolids program by dividing the BMP into sub-projects to distribute construction costs across the twenty-year planning time frame. During the BMP process, the NSWRD staff identified several concerns that could arise from regulatory changes, community impacts, and market conditions. The team prepared conditional projects in response to those concerns. They are not part of the core BMP, but were identified, discussed, modeled, and cost estimates were prepared. The intent was to give NSWRD some insight into what changes may need to occur to mitigate the risks of those future challenges. The preferred alternative and conditional projects for the BMP are summarized in Table 1. The NSWRD selected a new biosolids management program that addresses the drivers and issues as well as meets the stated goals by reducing solids, providing resiliency, adding redundancy, and creating renewable energy. Results and takeaways from throughout the planning process will be presented.

This paper was presented at the WEF Residuals and Biosolids Conference, June 18-21, 2024.

SpeakerMarino, Joe

Presentation time

09:00:00

09:30:00

Session time

08:30:00

11:15:00

SessionCase Studies & Lessons Learned

Session number27

Session locationOklahoma City Convention Center, Oklahoma City, Oklahoma

TopicAnaerobic Digestion, Biosolids Management Planning, Thermal Processes

Author(s)

Marino, Joe

Author(s)J. Marino1, P. Ma1, S. Waters2, N. Sierra1, T. Vodnik2, E. Silver2

Author affiliation(s)Brown and Caldwell 1; Brown and Caldwell 1; North Shore Water Reclamation District 2; Brown and Caldwell 1; North Shore Water Reclamation District 2; North Shore Water Reclamation District 2;

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Jun 2024

DOI10.2175/193864718825159433

Volume / Issue

Content sourceResiduals and Biosolids Conference

Word count14

Description: Employee Network Groups as Engines for Change: How Candid Conversations Around...

Employee Network Groups as Engines for Change: How Candid Conversations Around Gender Create an Authentic and Empowered Workforce

Abstract

Women’s representation has increased significantly in the workforce, yet diversity and true inclusion, including opportunities to advance, remains an issue. In addition to addressing barriers to advancement, the global COVID-19 pandemic has caused many women to leave the workforce, unable to juggle competing demands over the duration of the pandemic. One tool for overcoming the challenges that women face in the workplace is an Employee Networking Group (ENG). The focus of an ENG is to work on the ‘how’ of improving inclusion rather than the ‘what’ of diversity so that as diversity of hiring pools improves, employees feel a sense of belonging, and choose to stay in a given workplace. This paper discusses the founding of the first ENG at our company and lessons learned along the way.

“Employee Network Groups as Engines for Change: How Candid Conversations Around Gender Create an Authentic and Empowered Workforce.” This paper discusses one tool in overcoming challenges that women and minorities face in the workplace – Employee Networking Groups (ENGs). The focus of an ENG is to work on improving inclusion so that as diversity of hiring pools improves, employees feel a sense of belonging and choose to stay in a given workplace. Our paper discusses the founding of our Women’s ENG at our company, the positive changes that have resulted, and lessons learned along the way.

SpeakerSierra, Natalie

Presentation time

11:30:00

11:45:00

Session time

11:00:00

12:30:00

SessionProactive Leveraging of Workplace Diversity, Equity, and Inclusion in Utility and Private Organizations

Session number208

TopicPolicy and Regulation, Research and Innovation, Utility Management and Leadership

Author(s)

Natalie Sierra

Author(s)N. Sierra1; N. Laughlin2;

Author affiliation(s)Brown and Caldwell, Boston, MA 1Brown and Caldwell, Lakewood, CO2

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2021

DOI10.2175/193864718825158043

Volume / Issue

Content sourceWEFTEC

Word count19

Managing Biosolids in Maine: Challenges and Potential Solutions

Abstract

Background Portland Water District (PWD) has four wastewater treatment facilities (WWTFs) with a capacity of more than 25 million gallons per day. Two of the four facilities - East End and Westbrook - process most of the solids in the system and were the focus of PWD's comprehensive approach to assess the current solids system and develop a strategic plan that outlines the necessary upgrades, process modifications, and state-of-good-repair projects that PWD should undertake during the next 20-year planning period. PWD began contemplating this planning effort not only due to aging infrastructure, but rather due to increasing concern over lack of biosolids management options and rising public concern around per- and polyfluoroalkyl substances (PFAS) in biosolids. Throughout New England, decreased biosolids management capacity has been a rising concern. Much of the region relies upon landfills and regional incinerators, but beneficial use (land application) has served as a reliable, sustainable option for a number of utilities. In Maine, land application had been an accepted practice, with good market understanding of the benefits of biosolids, including biosolids based compost and thermally dried products. Concerns over PFAS in wastewater residuals, or solids, prompted legislative action to prohibit land application of treated wastewater solids (biosolids) and products containing biosolids in Maine (LD 1911 [An Act to Prohibit the Contamination of Clean Soils with So-Called Forever Chemicals]). The Governor signed this bill in April 2022, and it is currently in effect as Public Law 2021 Chapter 641. This law leaves Maine wastewater utilities with landfill as the only option for solids management within the state-and few, costly options outside the state. Instate wastewater solids landfilling became more challenging with the passing of solid waste bill, LD 1639 (An Act To Protect the Health and Welfare of Maine Communities and Reduce Harmful Solid Waste) in April 2022, and enacted February 1, 2023. This bill restricts the importation of out-of-state solid waste for processing in the state of Maine. Dewatered wastewater solids cake is considered a 'wet waste' by landfill operators and is typically mixed with bulking agents at landfills to avoid stability issues. Out-of-state solid waste (e.g., oversized bulky waste and construction and demolition debris) was one of the main sources of bulking agents for stabilizing wastewater solids. When the availability of these bulking agents decreased, the landfill operators handling most of the biosolids disposal in the state reported they needed to consequently reduce the amount of wastewater solids they accept. This left many utilities scrambling for alternatives, including costly long-distance hauling to Canada. Despite a two-year reprieve to LD 1639 (via LD 718, An Act to Facilitate the Management of Wastewater Treatment Plant Sludge at the State-owned Juniper Ridge Landfill), wastewater utilities in Maine, including Portland Water District (PWD), are still restricted to landfilling instate in the short-term, and following the two-year reprieve will face severe challenges in the long-term. Methodology This project was completed to define the technical, economic, and programmatic considerations for implementing a regional anaerobic digestion, drying, and thermal treatment biosolids processing facility. These technologies were selected for consideration for their following attributes: - Anaerobic Digestion. Anaerobic digestion biologically degrades solids, reducing their mass by 40-50 percent and generating energy-rich biogas. Anaerobic digestion can process a wide variety of liquid organic wastes, including food and beverage processing wastes and fats, oils, and grease waste. Anaerobic digestion and biogas utilization offer substantial opportunities for greenhouse gas reduction at a WWTF and for the region when processing imported organic waste. Anaerobic digestion can also treat solids to United States Environmental Protection Agency (USEPA) requirements for Class B or A stabilization and improves downstream processing by improving and homogenizing solids quantities and quality. - Thermal Drying. Thermal drying removes nearly all the entrained water in dewatered solids, reducing solids mass by 4 to 5 times. This reduces the amount of solids needing to be hauled and can remedy capacity and structural limitations associated with landfilling of dewatered solids. Thermal drying can also meet USEPA Class A stabilization requirements, which provides nearly unrestricted beneficial reuse opportunities in other states. - High Temperature Thermal Processing. Thermal processing submits solids to high temperatures for further mass reduction and treatment of emerging contaminants such as PFAS. This has traditionally been performed by sewage sludge incineration (SSI), which oxidizes all solids to an ash. However, SSI air permitting regulations have become especially onerous and make SSI adoption in New England unlikely today. Pyrolysis and gasification are emerging, non-incineration thermal processes that employ high temperatures at oxygen free or starved conditions to generate a carbon-dense beneficial reuse product called biochar and a gas stream with an appreciable energy value. The technology is still in a developmental stage with one commercial biosolids pyrolysis facility in operation in the US at Silicon Valley, CA. In 2020, the USEPA found the Silicon Valley pyrolysis system removed PFAS from biochar to below reportable levels (Thoma et al., 2021). BC, with Silicon Valley Clean Water and the Water Environment Federation are scheduled to perform a PFAS air emissions test early 2024 to evaluate PFAS destruction in the gas phase. The Silicon Valley pyrolysis system uses a thermal oxidizer for emissions control and heat recovery and previous work by the USEPA demonstrated thermal oxidation as suitable for designation as a Best Available Control Technology for PFAS and capable of meeting permitted PFAS destruction criteria (Barr, 2022; Beahm, 2019; Focus Environmental Inc., 2020). While pyrolysis and gasification require solids be dewatered and dried for processing, a new class of thermal processes is also emerging called hydrothermal treatment, that treat solids in a liquid, slurry form at high temperatures. Super critical water oxidation is one example where all organics (including organoflourines such as PFAS) are intended for oxidation within a flow-through reactor. Hydrothermal carbonization and hydrothermal liquefaction use heat without an oxidant to refine the solids into solid and liquid biofuels, respectively. Conclusions The BC and PWD team completed the following outreach and assessment tasks to identify and compare current market offerings for the solids processing technologies mentioned above. The investigation included assessment of commercially available equipment and overall project delivery and operation under the following tasks. - Request for Information (RFI): BC developed and issued an RFI digestion, drying, and thermal processing system suppliers. The goal of issuing this RFI was to identify interested technology and/or solution providers and to compare current commercial offerings based on lifecycle cost and key non-economic criteria. - Technology Summit: Responders to the RFI could participate in a two-day in-person and virtual technology summit, in which each participant had 20 minutes to present information about their technology. These presentations were recorded and are available on the PWD website. - RFI Submission Review: Each submission was evaluated based upon set criteria, established in the RFI document. Table 1 summarizes the scores for the highest ranked submissions. - Alternative Evaluation: Based on the top three ranked system supplier offerings/technologies, facility concept level designs were developed for a business case evaluation (BCE). The Alternatives BCE evaluated three onsite and three regional technology alternatives. These alternatives are summarized along with their BCEs in Table 2. - Recommendations: The RFI submissions and BCEs enabled the PWD and BC team to identify a potential phased path forward for PWD. The purpose of this report is to summarize and describe the methodology BC employed, as well as the economic and noneconomic findings, from the evaluation of a regional, offsite biosolids processing facility. Ultimately, the goal is to characterize the economic viability and noneconomic attributes to assist PWD in determining a path forward to manage

This paper was presented at the WEF Residuals and Biosolids Conference, June 18-21, 2024.

SpeakerBrower, William

Presentation time

14:00:00

14:30:00

Session time

13:30:00

15:00:00

SessionOutreach Updates: From State to Regional Solutions

Session number07

Session locationOklahoma City Convention Center, Oklahoma City, Oklahoma

TopicBiosolids Management Planning, business case evaluation, Regionalization

Author(s)

Firmin, Scott

Author(s)S. Firmin1, W. Brower2, T. Chouinard2, J. Ross2, N. Sierra2

Author affiliation(s)Portland Water District 1; Brown and Caldwell 2; Brown and Caldwell 2; Brown and Caldwell 2; Brown and Caldwell 2;

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Jun 2024

DOI10.2175/193864718825159464

Volume / Issue

Content sourceResiduals and Biosolids Conference

Word count9

Description: Master Planning When the Ground Keeps Shifting: Portland (Maine) Water District's...

Master Planning When the Ground Keeps Shifting: Portland (Maine) Water District's Biosolids Master Planning Experience in the Age of PFAS

Abstract

Background Portland Water District (PWD) has four wastewater treatment facilities (WWTFs) with a capacity of more than 25 million gallons per day. Two of the four facilities - East End and Westbrook process most of the solids in the system and were the focus of PWD's comprehensive approach to assess the current solids system and develop a strategic plan that outlines the necessary upgrades, process modifications, and state-of-good-repair projects that PWD should undertake during the next 20-year planning period. PWD began contemplating this planning effort not only due to aging infrastructure, but rather due to increasing concern over lack of biosolids management options and rising public concern around per- and polyfluoroalkyl substances (PFAS) in biosolids. Throughout New England, decreased biosolids management capacity has been a rising concern. Much of the region relies upon landfills and regional incinerators, but beneficial use (land application) has served as a reliable, sustainable option for a number of utilities. In Maine, land application had been an accepted practice, with good market understanding of the benefits of biosolids, including biosolids based compost and thermally dried products. In 2019, however, PFAS contamination was discovered at a Maine dairy farm that had historically land applied both biosolids and short paper fibers. This led the Maine Department of Environmental Protection (DEP) to promulgate soil screening standards for two PFAS - perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS). These screening standards were used to limit biosolids land application rates based on the concentrations of these two compounds, and the understanding that PWD might be able to land apply in the future served as an initial assumption of the study. Shortly after study initiation, the Maine legislature passed LD 1911, which prohibits the land application or sale of biosolids and biosolids-derived products in the state of Maine. While options were already limited before this new law, the only option for biosolids management in Maine is now landfill disposal. The passage of LD 1911 thus focused the biosolids master plan on technologies that significantly reduce volume and/or employ thermal destruction. Methodology The goal of this project is to create a 20-year system-wide implementable plan, including near- and long-term improvements that improve the reliability of PWD's solids handling assets while meeting the project goals of mitigating emerging contaminants risks, enhancing reliability and regulatory resiliency, and increasing the public's confidence in PWD's environmental stewardship. PWD worked with its consultant to create a master plan that has both near- and long-term improvements to improve the reliability of PWD's solids handling. Alternatives were evaluated based on regulatory, financial, social, and environmental goals and objectives. An overview of the master planning process is shown in Figure 1. Custom solids and energy models were created to reflect the operation of East End and Westbrook, which were used to determine alternatives for solids handling. The consultant team also provided PWD with estimated operational and capital costs, solids production, and energy requirements based on actual PWD unit costs. Throughout this process, the PWD and consultant team developed and evaluated seven alternatives at six workshops. The outcome of these workshops was a roadmap with several triggers rather than a final solution due to the uncertainty and expected changes in Maine's regulatory framework. Alternatives were evaluated using a mass and energy balance model that supported evaluation of both technical and operational performance. When combined with the capital investment required for each alternative, the model produces a net present cost (NPC) lifecycle cost of each alternative that, when compared to the baseline process condition, determines its financial viability. For this study, it was assumed that the planning horizon for the project would be 20 years. The alternatives evaluated are: -Alternative 0: Status quo. No operational or capital improvements. -Alternative 1: Modified baseline. Baseline operation with new dewatering and sludge storage. This alternative considers the possibility of sending dewatered solids to a merchant facility or to a landfill. -Alternative 2: Thin film Dryer. Westbrook dewatered solids hauled to East End, and the combined solids are dried in a thin film dryer and then disposed of at a landfill. -Alternative 3: PS AD + thermal dryer. Westbrook dewatered solids hauled to East End. East End primary sludge (PS) only mesophilic anaerobic digestion (AD) with thermal drying of all East End and Westbrook sludge. Landfill disposal with possible beneficial end use options in the future. -Alternative 4: Regional Pyrolysis. Westbrook and East End dewatered solids hauled to a PWD-owned regional pyrolysis facility, with either biodrying or thermal drying. Biochar is beneficially used. -Alternative 5: Regional Solar Drying. Westbrook and East End dewatered solids hauled to a PWD-owned regional solar drying facility. Landfill disposal with possible beneficial end use options in the future. Table 1 presents the results of the NPC analysis for these alternatives at a range of solids management costs, which are the largest contributors to the annual solids handling and processing costs. Note: Pyrolysis alternatives do not increase with rising tip fees, as it was assumed PWD had an agreement with the vendor to take the biochar at no cost. Sludge pyrolysis has not been demonstrated at PWD's size, so PWD decided the uncertainty with this technology was too significant at this high capital cost; therefore, PWD decided to continue to monitor the technology before making a final decision. The remaining alternatives were then evaluated based on non-cost factors including de-risking PWD on end use, sustainability, cost predictability, and improved reliability. Table 2 shows a summary of the goal factors for each of the alternatives. The modified baseline, which centers around improved dewatering, was found to be advantageous under current tip fees, and helps de-risk PWD as tip fee volatility increases. This was considered a 'no regrets' project as it both replaces aging infrastructure, and saves PWD money over the long term. With respect to the other alternatives, external factors, particularly the manner in which Maine DEP does or does not permit certain technologies, will affect which alternative should be implemented. As a result, a roadmap was made with key regulatory, market, and other implementation triggers to help guide PWD's actions in the next five years. The roadmap is presented as Figure 2, with the 'no regrets' project serving as the starting point (e.g. will be implemented). Key triggers will cause PWD to go on a certain path of the map, while additional triggers will further refine the likely or viable options. The final two branches (red and orange) of the roadmap are highly unlikely but could still be an outcome. The three key triggers are tip fees continue to rise, landfills reject biosolids, and tip fees stabilize or drop. This adaptable model allows PWD to make immediate improvements that will result in cost savings (dewatering upgrades and thickened sludge storage), while allowing for planning in the face of continuing regulatory flux. It is anticipated that over the next few years, Maine's regulatory approach will stabilize, clarifying the appropriate path forward. Conclusions While state and federal biosolids regulations are still uncertain, PWD can take the following actions recommended by the master plan: -Engage with regional partners now. Should support exist (both from Maine DEP and peer utilities) for regionalization, PWD and its potential partners would have time to determine challenging aspects of partnership such as governance. -Continue to engage with service providers as they explore merchant regional solutions. The master plan established a range of tip fees at which it could be advantageous for PWD to secure long-term management capacity. -Conduct a preliminary design project for the no-regrets projects at East End and Westbrook. This project would provide PWD with a basis of design report (BODR) in which dewatering technology and location would be selected as well as selection of size and location for sludge storage tanks at East End. The BODR would also include evaluation of conveyance of cake, automation of the screw press, and polymer changes at Westbrook. -Continue to engage Maine DEP on technology updates and data updates on PFAS mitigation. -Explore funding mechanisms and continue discussions with vendors on viable solutions. -Visit dryer and other vendor installations.

This paper was presented at the WEF/IWA Residuals and Biosolids Conference, May 16-19, 2023.

SpeakerSierra, Natalie

Presentation time

11:15:00

11:45:00

Session time

8:30:00

11:45:00

SessionSession 10: PFAS Challenges and Treatment

Session number10

Session locationCharlotte Convention Center, Charlotte, North Carolina, USA

TopicEmerging Issues (PFAS, Microplastics, Covid, etc.)

Author(s)

N. Sierra

Author(s)D. Price1, N. Sierra2, S. Firmin3, T. Chouinard4,

Author affiliation(s)Brown and Caldwell1; Portland Water District2

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date May 2023

DOI10.2175/193864718825158820

Volume / Issue

Content sourceResiduals and Biosolids

Word count21

Description: Thermal Drying Economics: Integrating Market Analysis and Lifecycle Costs to Assess...

Thermal Drying Economics: Integrating Market Analysis and Lifecycle Costs to Assess Thermal Drying Feasibility

Abstract

Introduction In recent years, several regions of the country have experienced skyrocketing biosolids management costs. Though the triggers may be unique to each region, management capacity constraints are at the heart of these trends. Additional factors, such as concerns over PFAS in states like New Hampshire and Maine, have placed additional pressures on an already tight market. As utilities in regions like New England, Metro Atlanta, and the New York-New Jersey metro area are experiencing increases of 50-100% in biosolids management costs, the option of thermal drying may be a logical solution with respect to volume reduction and improved product quality. In several recent projects, Brown and Caldwell has integrated local market analysis, particularly trends in biosolids management costs, with traditional life cycle cost analysis in order to assist utilities in determining whether thermal drying could be a solution to mitigate risk around biosolids management. While no single answer applies, there are markets for which drying simply for volume reduction can curb rapid cost increases today, while other markets (particularly where natural gas costs are high and end use costs are not rising at as rapidly) would not necessarily trigger the need for such an upgrade. We will present an overview of the factors that go into such an analysis, as well as two recently completed case studies with different outcomes. Methodology The analysis begins with the end in mind, by assessing the regional market pricing trends for biosolids management. Opportunities for use of thermally dried products were also assessed at this point, to understand whether market capacity exists regionally for product acceptance. When coupled with costs associated with the current operation, this constitutes the baseline and provides some boundary conditions for a sensitivity analysis around end use costs. Alternatives were then built to incorporate both capital and life cycle costs including additional labor, chemicals, natural gas, and end use costs. Sensitivity analyses were then run live in a workshop setting around areas of risk, including end use and energy costs. Results and Discussion In the first case study, the cost of continued landfill disposal of unstabilized solids was compared against installation of a thermal dryer. Given regional market volatility and shrinking landfill capacity, landfill disposal cost projections were escalated at current (10%) and historic (5%) annual trends. A conceptual dryer design was developed to identify realistic capital and annual operating and maintenance expenditures and assessed over a range of end use scenarios from landfill disposal, contracted land application, sale to specialty markets, and onsite dried product pyrolysis. The lifecycle cost assessment, displayed in Figure 1, demonstrated that (1) thermal drying provided a strong economic benefit at the current rate of landfill disposal cost escalation, (2) thermal drying was economically viable even if landfill tipping fees returned to more steady, historic escalation rates and (3) the resulting volume of dried product did not provide the cost differential required to justify the additional capital expenditure for pyrolysis or added operational and maintenance complexity for pelletizing and bagging operations to sell to specialty markets. In the second case study, solids are already digested to Class B, and management costs are approximately $50/wet ton. When compared against other Class A alternatives, thermal drying was the preferred alternative on a life cycle cost basis. However, with multiple capital upgrades necessary, this utility wanted to assess when the best time — purely from a cost standpoint — would be to upgrade to Class A. Market analysis was used to predict possible cost trends for biosolids management over the next twenty years. Looking at a range of scenarios, shown in Figure 2, the BC team assessed the possibility of constructing a thermal dryer near term, 10 years out, or 20 years out. Given the anticipated rate of change of end use management fees, it was determined that building the project immediately was not necessary. Given the great degree of fluctuation in the regional biosolids market, it was preferred to monitor market trends and plan for a thermal drying facility as tip fees approached $150/wet ton. While it is anticipated that tip fees will rise that high within the 20 year planning period, it is unlikely to occur within the next 10 years, thus allowing this utility to prioritize other necessary projects. Conclusions The economic justification for installation and operation of a dryer is based on its resulting cost differential in residuals management. Emerging trends such as potential PFAS regulations and shrinking disposal outlets bring uncertainty to planning projections, but economic assessment tools that incorporate market fluctuations can be used to characterize a targeted set of future scenarios to provide a transparent and defensible basis for dryer feasibility. In comparing thermal drying against multiple scenarios for landfill tipping fee escalation, the utility in the first case study developed a clear understanding of the dryer's economic viability and the relative value of additional investments (e.g. pelletizer or pyrolysis). Market assessment can also bring greater certainty to economic evaluations by identifying target markets for dried product distribution and future trends within those markets. The second case study highlighted that understanding the market's anticipated rate of change can help pinpoint when installation of a dryer will be most effective in achieving cost control compared to alternative management options to assist with capital planning. Given that biosolids management costs are expected to continue to pose a threat to multiple US geographies, these case studies provide a valuable framework for the utilities assessing thermal drying to deploy the most viable solution given their local conditions.

The following conference paper was presented at Residuals and Biosolids 2021: A Virtual Event, May 11-13, 2021.

SpeakerSierra, Natalie

Presentation time

15:45:00

16:00:00

Session time

15:00:00

16:15:00

SessionInnovative Biosolids Process Enhancements

Session number2

Session locationSimu-Live

Topicbusiness case evaluation

Author(s)

N. SierraJ. Ross

Author(s)N. Sierra1; J. Ross2

Author affiliation(s)Brown and Caldwell 1; Brown and Caldwell 2;

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date May 2021

DOI10.2175/193864718825157949

Volume / Issue

Content sourceResiduals and Biosolids Conference

Word count15

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