Schaich, Laurel

Laurel Schaich is an environmental engineer and project technical leader with experience working on some of the industry’s most...

Titles from this speaker

Alternative Approach to Accelerate Beneficial Biogas Utilization and RNG Production

Abstract

Charlotte Water (CLT Water) is the largest public water and wastewater utility in the Carolinas, serving more than one million customers in the City of Charlotte and greater Mecklenburg County. Charlotte Water currently owns and operates five major water reclamation facilities (WRFs), treating an average of 325 million liters per day (ML/d) or 86 million gallons per day (MGD) of wastewater and is in design for a sixth plant, the Stowe Regional Water Resource Recovery Facility (WRRF). Stowe Regional WRRF will treat flows from the western portion of Mecklenburg County and will also accept and treat flow from two neighboring towns in a bordering county. The Stowe Facility will have the capacity to process 68 ML/d or 15 MGD of wastewater, which will eventually grow to 114 ML/d or 25 MGD. CLT Water has a phased regionalization program in place for consolidation of biosolids treatment at McAlpine Creek Wastewater Management Facility (McAlpine Creek WWMF) as shown in Figure 1, which includes solids conveyance projects and the design and construction of a thermal hydrolysis process (THP) system for pre-treatment of solids prior to anaerobic digestion. CLT Water completed a Biogas Production and Utilization Study for the McAlpine Creek WWMF in September 2020. This study projected expected biogas production at McAlpine Creek WWMF taking into account the regionalization of solids treatment and the installation of THP. The combined regionalization and digestion improvements are anticipated to increase biogas production to approximately 1,930 normal cubic meters per hour (Nm3/h) or 1,200 standard cubic feet per minute (scfm). These projected biogas production values were used to generate a bioenergy model to evaluate multiple alternatives for beneficial biogas utilization including Combined Heater and Power, Steam Generation for THP, Compressed Natural Gas (CNG) fueling, and Renewable Natural Gas (RNG) pipeline injection. The bioenergy model, shown in Figure 2, considered capital and lifecycle costs of each alternative and produced dynamic comparisons of the different alternatives based on varying assumptions and user inputs. A non-economic evaluation was also used to compare the biogas utilization options, including safety, risk and O&M considerations, bioenergy utilization, private development opportunity, and public relations. The outcome of the study was a recommendation to implement RNG pipeline injection as this would allow for the largest percent utilization (99%) of the biogas and the most flexibility to operations, while aligning closely with the City of Charlotte's Strategic Energy Action Plan (SEAP). Following completion of the Study, CLT Water proceeded with a competitive sale process, viewing the biogas as a personal property to be sold as a commodity to a buyer to be converted to RNG and soliciting sealed bids from project teams to implement the RNG strategy. As a condition of the sale, the potential buyer was required to provide a 'turn-key' solution for the utilization of the biogas by providing the buyer's own capital, facilities, design, construction, operation, management, and permitting services necessary to convert the biogas into RNG. The buyer will perform conditioning of the biogas and resell the resulting product gas as RNG, which will create Renewable Identification Numbers (RINs) that can be monetized via the federal RIN market as well as state level credit markets. The buyer will have the rights to all environmental credits/attributes such as renewable energy certificates, low carbon fuel standard credits, and other similar entitlements associated with the RNG. Figure 3 shows an arrangement of the proposed biogas utilization program. CLT Water conducted the following two solicitation steps in order to enter into an agreement for the sale: 1)Request for Proposals (RFP): Utilized to short-list qualified companies taking into consideration vendor qualifications and experience, demonstration of safe RNG operation practices, quality, delivery, workmanship, and any applicable environmentally preferable attributes associated with the company's proposed solution for RNG. The short-listed companies were qualified to receive an Invitation to Bid. 2)Invitation to Bid (ITB): sealed bid sale where short listed companies have an opportunity to provide CLT Water their best price for the purchase of unconditioned biogas within a defined cost framework. This procurement approach encouraged competition in the determination of the biogas value and efficiency of proposed solutions. CLT Water has completed the RFP and ITB stages, selected the highest responsive, responsible bidder, and are currently undergoing final contract negotiations which include a land license for the facility construction inside CLT Water property and an offtake agreement for the delivery of biogas. Design of the facility is expected to commence in Spring 2025 and is anticipated to be sized for 1,930 Nm3/h (1,200 scfm). The system will be capable of removing hydrogen sulfide (H2S), volatile organic compounds (VOCs), siloxanes, and carbon dioxide (CO2) to meet pipeline specifications. The presentation will summarize the history of the biogas utilization study, development of the RNG implementation approach, and highlights of design efforts completed at the time of the conference.

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

SpeakerPortiolli, Giovanna

Presentation time

10:15:00

10:35:00

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)

Portiolli, Giovanna, Schaich, Laurel

Author(s)G. Portiolli1, L. Schaich2

Author affiliation(s)Charlotte Water, 1CDM Smith, 2

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date May 2025

DOI10.2175/193864718825159801

Volume / Issue

Content sourceResiduals and Biosolids Conference

Word count11

Description: Fort Wayne's Journey Towards Resilience and Clean Energy - Implementation of a...

Fort Wayne's Journey Towards Resilience and Clean Energy - Implementation of a Microgrid Program and RNG Injection

Abstract

In the era of climate change and extreme weather events, utility resilience has become increasingly important. Water facilities face multiple energy-related challenges as they strive to avoid power outages and decarbonize their operations. As a result, many are exploring microgrids for diversified on-site energy management. Microgrids are beneficial for reducing a facility's carbon footprint, improving resiliency of energy availability, minimizing disruption due to a utility outage, and reducing electric utility costs. Currently, microgrids provide less than 0.3 % of U.S. electricity, but their capacity has grown by almost 11% in the past four years, highlighting the growing interest and demand in this area.

Fort Wayne City Utilities (FWCU) provides water, wastewater, and stormwater services for approximately 300,000 people in city and surrounding areas. Over the past 20 years, FWCU has invested in energy resiliency by installing emergency power at its 72-mgd drinking water facility and a biogas-fueled combined heat and power (CHP) system at its 100-mgd wastewater treatment facility. Recently, FWCU has implemented a $24M Microgrid Program at its facilities for sustainable and renewable energy generation, to improve resiliency of energy use, and to move towards the circular water economy. In parallel, a biogas to renewable natural gas (RNG) project is in development at FWCU's wastewater facility. This presentation will encompass both the Microgrid Program and the RNG project, where drivers, successes, and lessons learned will be described. Combined, these two projects will allow FWCU to generate over 11.5 MW of renewable energy from solar and biogas, enough to power nearly 5,000 homes.

Microgrid Program
The Microgrid Program encompasses three of Fort Wayne's water facilities — the wastewater plant, the drinking water plant, and a wet weather retention facility. These three facilities are interconnected electrically to function as a single utility. The Microgrid Program includes solar, a backup battery system, biogas & natural gas-fueled generators as energy sources, and emergency backup generators. The 6.5 MW floating solar array is installed on an existing stormwater retention pond (Figure 1) and is coupled to a 1 MWh battery energy storage system to enhance operational flexibility. The master Microgrid Controller manages the system based on actual consumption from the three facilities and power generation from the energy sources. Renewable sources, such as the solar and biogas powered systems, are preferentially used to limit operational costs and greenhouse gas emissions. A single electric utility connection at one of the facilities is maintained for continuous use.

Energy generation capabilities of the microgrid were balanced against environmental and operational considerations. FWCU prioritized leveraging existing assets and adaptability during the planning stages of the program. Figure 2 shows an example energy demand and supply curve based on a 24-hour period. Solar energy is generated during daylight hours, peaking in the early afternoon, and is supplemented by biogas CHP. During the night, standby generators are used to minimize electric utility consumption.

Based on our results, operation of the Microgrid Program reduces the overall electric utility consumption by 80%, resulting in annual power savings of over $1.5M. Currently, the Microgrid Program is being commissioned, with generating assets being brought online sequentially. The presentation will include operational data and lessons learned from the Microgrid Program.

RNG Project
Fort Wayne operates a successful hauled waste program for co-digestion of outside organic waste, resulting in significantly more biogas than would be generated from the wastewater residuals alone. Biogas produced by the anaerobic digesters at the wastewater plant can be beneficially used continuously in the CHP system as part of the Microgrid Program. If additional digester heating is needed, it can be supplied by biogas-fueled boilers, otherwise excess biogas is flared.

A Bioenergy Model (Figure 3) was developed to evaluate the economics of expansion of the CHP system compared to producing renewable natural gas (RNG). The model accounted for organic waste loading to the digesters, operations and maintenance (O&M) costs, potential RNG value through the sale of Renewable Identification Number (RIN) credits, and the overall heat balance of the digesters. Sensitivity analyses were performed with varying amounts of outside organic waste and economic factors (such as RIN value) to further evaluate the biogas utilization scenarios. Results showed that upgrading most or all of the biogas to RNG was found to be most economically favorable due to the sale of RIN credits.

A biogas upgrading system is currently in design for production of pipeline-quality RNG for injection into the local natural gas distribution system. The RNG equipment consists of a 450-standard cubic feet per minute (scfm) three-stage membrane scrubbing system with hydrogen sulfide (H2S) and siloxane pre-treatment. To minimize construction schedule delays due to long equipment lead times, the equipment was pre-purchased at the 30% design stage. Lessons learned from the project will be described, including the importance of sensitivity analysis to the financial model, allowing for flexibility in biogas utilization operations, and planning for future growth.

This paper was presented at WEFTEC 2025, held September 27-October 1, 2025 in Chicago, Illinois.

Presentation time

08:30:00

08:45:00

Session time

08:30:00

10:00:00

SessionAdvancing Resilience through Innovative Sustainable Practices

Session locationMcCormick Place, Chicago, Illinois, USA

TopicEffective Utility Management

Author(s)

Schaich, Laurel, Schortgen, Zachary

Author(s)L. Schaich1, Z. Schortgen2

Author affiliation(s)CDM Smith1, City of Fort Wayne Planning & Design Services2, , , , , ,

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Sep 2025

DOI10.2175/193864718825159906

Volume / Issue

Content sourceWEFTEC

Word count18

Monte Carlo Modeling Approach for Anaerobic Digestion and Biogas Utilization

Abstract

Background and Objectives: Methods to recover energy at Water Reclamation Facilities (WRFs) are becoming increasingly studied and implemented. One source of recovered energy from wastewater is biogas generated from anaerobic digestion. This bioenergy is commonly used for digester heating at WRFs in boilers or combined heat and power (CHP) systems. Upgrading biogas to renewable natural gas (RNG) for pipeline injection and use in vehicle fuel is an alternative with additional opportunity due to federal and state incentive programs. To elucidate economic and energy tradeoffs between CHP and RNG systems, a Bioenergy Model was developed to compare biogas utilization in a CHP system versus an RNG system for 2,270 cubic meters per day (500,000 gallons per day) of anaerobic digester feed. The Bioenergy Model accounts for distributions in digester feed, digestion kinetics, utility costs, renewable identification number (RIN) values, and biogas utilization system parameters to evaluate uncertainty and sensitivity of project financials and energy utilization. Methodology: Ten projects evaluating biogas utilization in CHP and/or RNG were used to establish the range of inputs applicable to CHP and RNG systems. The previous EPA analysis informed additional system input assumptions of CHP (2017). CHP and RNG scenarios were modeled to determine equipment sizing and costs, capital costs, operating expenses, and financial benefits. For CHP, financial benefits were evaluated based on power and heat produced that the plant could beneficially use. For RNG, financial benefits included revenue from the wholesale gas and sale of D3 RINs through the Renewable Fuel Standard (RFS). A Monte Carlo analysis with 10,000 simulations was applied to understand the uncertainty of the inputs used in the model, and Spearman's correlation coefficients were determined to assess the sensitivity of outputs to inputs. For each Monte Carlo simulation, anaerobic digestion kinetic parameters outputted biogas flows and energy available. The resulting average biogas production was approximately 1,400 normal cubic meters per hour (Nm3/hr), or 900 standard cubic feet per minute (scfm). Historical D3 RIN values were used for analysis, assuming a constant value for each simulation based on weekly D3 prices since 2015 (Figure 1). Historical RIN Prices are presented, sorted by D-code (D3 and D5). Note that $1 per RIN is equivalent to $0.04 per kWh ($11.727 per MMBtu) (U.S. Environmental Protection Agency, 2021). External economic factors (e.g., future predictions of RIN values) were not incorporated. The model accounted for a range of methane recovery and parasitic load in RNG systems, including membrane systems, liquid scrubbing systems, and pressure swing adsorption. Net present value was determined by discounting project capital expenses for the analysis period (i.e., 20 years). Findings: Results of the analysis show generally positive economic benefits for both CHP and RNG, with median Year 1 values of $3,300,000 for RNG projects and $990,000 for CHP. The CHP net annual values were typically lower than RNG net annual values and had a tighter range. The net value of RNG projects was highly varied due to the range of RIN values ($0.48 to $3.24 per RIN) and the associated RIN revenue. However, despite the high revenue potential of RNG projects, in approximately one-percent of the evaluated scenarios, the net RNG value was negative (i.e., RNG operations costs outweighed the financial benefit). Year 20 values were also determined for CHP and RNG projects and compared to Year 1 values (Figure 2). Net present values for CHP projects and RNG projects are presented for Year 1 and Year 20 of the analysis period. The standard box and whiskers chart from Microsoft Excel was used, which presents the median (as the middle line), the average (as the 'x'), the range from median of the first quartile to median of the third quartile (as the box), local minima and maxima (as the whiskers), and outliers (as dots). Spearman's rank correlation coefficients were determined to evaluate the inputs with the most impact, both positive and negative, on the results. Based on the Spearman's evaluation, parameters with significant impact on project financials included plant power cost ($/kwh), RIN values, and digester feed (Figure 3). Spearman's rank coefficients were determined for Year 1 net values of CHP and RNG projects. The red line represents the Spearman's value correlated to a P value of 0.05, signifying variables of significance. To further understand sensitivity of critical variables, plant power cost and RIN values were further evaluated to compare a ratio of RNG to CHP Year 1 values (Figure 4), with a value of 1 representing equal value between RNG and CHP, values above 1 favoring RNG scenarios, and values below 1 favoring CHP scenarios. Results from the Monte Carlo analysis were plotted in a contour plot and smoothed with a Loess smoothing function (sampling proportion of 0.1, polynomial degree of 1.0). The contour plot is presented as a logarithmic scale, where the Value Ratio is given by: Value Ratio=10^(RNG Value-CHP Value)/|RNG Value|. A value ratio of 1.0 represents that the RNG and CHP values are equal. If the value ratio is greater than 1.0, RNG is more financially viable; likewise, a value ratio of less than 1.0 represents a scenario where CHP is more economical. The black line plotted represents a value ratio of 1.0. In addition to a financial analysis, the Bioenergy Model was also used to compare net energy produced for CHP and RNG scenarios (Figure 5). Net energy from CHP and RNG projects were compared and plotted in box and whisker plots. Net energy is expressed as MMBtu/day (1 MMBtu/day = 12.2 kW) and as a percentage of the inlet biogas energy. For CHP, net energy represented the total energy produced from heat and power in a reciprocating engine; for RNG, net energy was evaluated based on the methane recovery and parasitic load of the gas upgrading system. Net energy from RNG represented an average of 91-percent of the inlet biogas energy, compared to an average of 78-percent for CHP projects. Significance: Ultimately, the Bioenergy Model is a tool that can be used for the financial evaluation of biogas utilization scenarios and modified to suit a specific plant's needs. All parameters are designed to be adjustable, allowing for variations in the analysis based on digester feed flows, anaerobic digestion kinetics, plant utility costs, and RNG offtake values. Specifically, the Bioenergy Model was designed to evaluate D3 RIN values compared to CHP via a reciprocating engine; the model can be revised to account for specific digester kinetic factors, varying RIN values (e.g., co-digestion of outside sludges for D5 RIN production), additional environmental credit programs (e.g., California low carbon fuel standard, Oregon clean fuels program), greenhouse gas emissions comparison, carbon intensity evaluation, additional sensitivity analysis on inputs, or other cogenerating technologies for detailed biogas utilization analysis.

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

SpeakerSchaich, Laurel

Presentation time

9:00:00

9:30:00

Session time

8:30:00

11:45:00

Session number08

Session locationGreater Columbus Convention Center, Columbus, Ohio

TopicBiogas, Cogeneration, Renewable Natural Gas

Author(s)

L. Schaich

Author(s)L. Schaich1; J. Hutchison2

Author affiliation(s)CDM Smith; 1University of Kansas; 2

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date May, 2022

DOI10.2175/193864718825158396

Volume / Issue

Content sourceResiduals and Biosolids

Word count11

Seeding, Startup, and Commissioning of THP Systems at Three WRRFs

Abstract

Implementation of thermal hydrolysis process (THP) systems is becoming increasingly common at water resource recovery facilities (WRRFs). These systems reduce required anaerobic digester volume (for both rehabilitation and new construction), increase biogas production, improve dewaterability, and can produce Class A biosolids. Because THP systems involve coordination amongst several unit processes, startup and commissioning of these systems is complex and requires significant coordination between the owner, engineer, and contractor. CDM Smith designed and participated in the startup and commissioning of three THP facilities ranging in size from 16 to 189 mgd or 11 to 200 dtpd. All facilities installed Cambi THP systems, including the B-2, B-6 and B-12 skids as well as pre-dewatering, anaerobic digesters, and all required ancillary systems. This presentation will provide guidance and lessons learned on the initial digester seeding, sequential startup and operation of the system, and troubleshooting and operational data analysis.

-Digester Seeding-
Digester seeding can be achieved by using onsite sludge and slowly cultivating the correct microorganisms or by using seed sludge from an existing facility. Since THP was new to the US when the first of these systems was commissioned, there were no options for THP seed and limited options for quality seed sludge, all of which required hauling large amounts of sludge long distances. An innovative solution was developed to utilize liquid class A pasteurized sludge at the first plant then dewatered Class A THP digested cake, rather than liquid sludge, as the seed source at the other plants. By using dewatered cake hauling costs were reduced and rapid startup of the digesters was achieved. Figure 1 shows a schematic of a typical seeding flow diagram using this method. A series of frac tanks were provided for dilution and mixing of the seed cake prior to feeding to the digesters. Numerous points were included for alkalinity adjustment. The seed sludge was heated to mesophilic temperatures using hot water in the heat exchangers (which typically operate for cooling instead of heating). Lessons learned and considerations for digester seeding will be discussed, including regulations for seed material, transportation, alkalinity adjustment, and on-site handling procedures.

-Sequential Startup-
While digesters are being seeded, equipment and subsystems must be started to provide feed and maintain the digesters. These subsystems include pre-dewatering, THP, digester cooling, boilers, and digester gas conditioning. Overall, solids processing at each facility was carefully sequenced with the equipment startup to ensure appropriate timing of THP commissioning with upstream processes. This allowed for processing solids through the system and ultimately to the digesters without the need for temporary piping, bypassing equipment, or shutdowns. Figure 2 provides an example flow schematic from one facility and outlines seven distinct modules for commissioning: 1) plant effluent water pumping (not shown), 2) WAS storage facilities, 3) pre-dewatering centrifuges, 4) Digester 1 and digester seeding, 5) THP and biogas utilization equipment, 6) Digester 2, and 7) post-dewatering equipment. The three facilities' startup sequencing and solids handling will be compared to illustrate the general approach as well as the site-specific complexities for startup and commissioning.

-Troubleshooting and Operational Data-
It is typical for commissioning teams to have to overcome numerous challenges during the initial months of operations, especially on complex systems. Foremost among these challenges during THP commissioning is maintaining digester stability while also troubleshooting equipment startup. Any issues which are not resolved quickly may result in a digester upset delaying full capacity by weeks or months. It is imperative that digester operating data is monitored and trended continuously to ensure digester health and inform the commissioning team for next steps. A detailed data analysis of key digester operating parameters for the three plants will be presented and a simulated experience of the day-to-day decision-making process required to startup a THP and digester system will be provided. As an example, Figure 3 shows a comparison of digester feeding (kg VS fed/kg TS) and VSR in the digesters during the first 120 days after startup. Additional data, including biogas production, VFAs, alkalinity, pH, etc. will also be presented. Other issues resolved during the startup and commissioning phase which will be discussed include sludge viscosity differences between design and reality, potential digester foaming, and feed sludge quality.

-Conclusions-
As more facilities in the US implement THP systems, lessons learned and shared experiences from the startup and commissioning of these facilities can provide valuable insight for designers, constructors, and operators of similar biosolids processing facilities. Digester seeding methodology is an important first step for THP system startup as it directly impacts the commissioning duration and the ability to meet Class A requirements. Sequential startup and operation of new THP system equipment to simplify solids handling during startup and maintain digester stability is key. Operational issues are inevitable to any startup; however, monitoring digester operating data can help troubleshoot issues and develop quick resolutions.

This paper was presented at WEFTEC 2025, held September 27-October 1, 2025 in Chicago, Illinois.

Presentation time

11:00:00

11:15:00

Session time

10:30:00

12:00:00

SessionLessons from Biosolids Project Startups

Session locationMcCormick Place, Chicago, Illinois, USA

TopicBiosolids & Residuals

Author(s)

Schaich, Laurel, Bond, Daniel, Sadatiyan Abkenar, Seyed Mohsen

Author(s)L. Schaich1, D. Bond1, S. Sadatiyan Abkenar1

Author affiliation(s)CDM Smith1, Stantec Inc.2

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2025

DOI10.2175/193864718825160033

Volume / Issue

Content sourceWEFTEC

Word count11