The optimization of polymer use in water and wastewater treatment processes remains a challenge, leading to high recurring expenses and sub-optimal process performance. This presentation emphasizes the critical role of polymer activation and its direct impact on process efficiency. By selecting suitable polymer and employing appropriate mixing technologies, polymer activation can reduce polymer usage and enhance the downstream separation process, resulting in improved overall performance and substantial annual cost savings. The presentation focuses on the science of polymer activation, offering insights into the fundamental principles of polymer mixing. It showcases the advantages of adopting a two-stage mixing approach, characterized by high initial mixing energy followed by low and uniform mixing energy. Theoretical considerations and practical test data provide tangible evidence of the benefits of this approach for both emulsion and dry polymers. Additionally, a comparative analysis of mechanical and hydraulic mixing technologies will be presented to aid in equipment selection for specific applications. Through a series of compelling case studies, the presentation not only highlights the impact of polymer savings but also demonstrates the effect on the process downstream. Comparisons between different mixing technologies will provide insights for decision-making processes when optimizing polymer activation. Additionally, the discussion will include design considerations and valuable lessons learned, offering practical guidance for implementing effective polymer activation solutions.

The City of Rio Rancho currently disposes of its dewatered solids to a private landfill that has several challenges both for its current operations and viability of its long-term operations. These include the risk of the hauled away solids being turned away from the disposal site under wet weather conditions jeopardizing the daily operations for the City. With the combination of aging infrastructure, increasing tipping fees, and lack of availability of other reliable solids disposal options, the City commissioned a study to investigate sustainable and cost-effective disposal options. The City owns three wastewater treatment facilities that produce dewatered sludge using belt filter press with an average concentration of 14 percent solids. The project team evaluated a variety of disposal options that will provide the client with long-term practical solutions to provide reliability and offer a sustainable solids management plan. The team's goal was to evaluate a range of alternatives that consider both economic (capital investment and operational costs) and non-economic factors (ease of access, ease of overall operation and maintenance (O&M) and independence from other entities). The three main disposal options considered were surface disposal, composting, and landfilling. These options directly align with the National Pollutant Discharge Elimination System (NPDES) regulations that prescribe the various methods Rio Rancho can employ to dispose of their dewatered solids. These regulations categorize the requirements into three different elements. Element 1 (Land Application) and Element 2 (Surface Disposal) are regulated under EPA 40 CFR 503 Parts B and C. These two elements require stabilization of the sludge to Class A or Class B standards. Since the City does not currently stabilize their solids, the team did not prioritize land application or surface disposal as feasible alternatives due to stabilization requirements under Elements 1 and 2. Element 3 (Municipal Solid Waste Landfill Disposal) does not require stabilization, making landfill disposal of the dewatered solids the most desired choice for the City under the current operational scheme of things. The team analyzed seven different disposal alternatives and determined a final recommendation by performing a 20-year net present worth (NPW) using the following criteria: tipping fees, distance of the disposal location from the plants generating the solids, number of truck loads required per day, and the labor and maintenance costs associated with landfill disposal. The selected option was another landfill located a few further miles away compared to the current private landfill facility. However, being a county (government) operated landfill, the facility not only provided reliability and peace of mind but also offered a lower tipping fee than the current option under a government-to-government rate structure. So even with the longer hauling distance involved, the county landfill facility proved to be a better option in terms of overall costs of disposal under a NPW analysis. The second part of the project focused on evaluating alternatives to optimize operations. The team evaluated four alternatives for enhancing dewatering that could produce a higher concentration of solids and potentially stabilizing the solids along with the dewatering process. The options include: 1. Optimize the existing process and focus on operational efficiencies by changing the type of polymer and the polymer dose used to achieve a solids concentration of 16%. This 'low hanging fruit' approach could decrease overall disposal costs even by marginally increasing the dewatering performance for little to no major capital investment. 2. Replace the City's 25-year-old belt filter press equipment in a 'like for like' replacement to increase solids concentration and improve reliability. This would entail a slight capital cost but provide an opportunity to work with new equipment that has higher efficiency and reliability. 3. Add an electro-dewatering system after the belt filter press that could produce up to 35% solids. This would have a reasonable capital cost and higher O&M but produce a dewatered sludge (not stabilized) that has much higher solids, thereby significantly reducing disposal costs. 4. Add a thermal dryer following the belt filter press that could increase solids concentration up to 90%. This option has the highest capital and O&M expenses but also produces a Class A product with minimal disposal costs and provides the opportunity to harness a value-added product and create a revenue stream. This option also provides the best solution to address future regulatory issues related to emerging contaminants and Per- and polyfluoroalkyl substances (PFAS), if needed. Lastly, a combination of a belt filter press, electro-dewatering, and thermal dryer could further optimize the selection of the system. This combination option allows for maximum long-range planning and operational flexibility depending on the desired end goals - disposal of dewatered solids at the minimize costs, regulatory and/or sustainability drivers or production of a value-added product and can be implemented in a phased manner to manage capital spend and outlay. Considerations while evaluating and implementing new and innovative technologies include public perception, sustainability drivers, challenges such as finding the skills to operate and maintain these systems and the desire to prepare for a changing and evolving regulatory landscape. Additionally, site conditions and space availability can impact equipment sizing and access for O&M. The team completed a 20-year NPW analysis as part of the evaluation. Figure 1 provides a summary of this analysis and compares the quantity of solids offset per year and the associated number of truckloads for 14%, 16%, 35%, and 90% solids for 2024 (current year) and 2043 (20-year outlook). The number of truckloads of dewatered solids and overall quantity of solids can significantly decrease with increasing solids concentration and potentially provide the City with significant cost savings. Figure 1. Note: One truckload is based on ten cubic yards and 2043 projections are based on a 2% population increase. Overall, the team recommends that the City consider implementing a project that will not only provide a cost effective and reliable disposal option in the near and long term but also reduce the total quantity of solids produced thereby providing a more comprehensive, holistic, and sustainable approach to solids management. This will not only help improve operations in the long run but also offer independence and control over the solids handling and management process with less reliance on external stakeholders.

Objectives Hydrothermal liquefaction (HTL) is a promising technology which has many distinct advantages over existing wastewater sludge treatment processes (i.e., anaerobic digestion, composting, etc.) and other thermal treatment processes including lower reactor temperatures than pyrolysis, all while avoiding the need to dewater the feedstock.[1,2] This developing technology has the potential to completely eliminate the need for land application/landfilling of biosolids, while producing a new renewable energy stream while allowing for the recovery of essential plant nutrients (nitrogen and phosphorous) from the HTL aqueous and hydrochar phases. Despite the promise of HTL, little is known about the fate and partitioning of contaminants of emerging concern (CECs) during HTL. This includes the aqueous phase (i.e., remaining water which requires further treatment), and the biocrude/hydrochar streams. About 80% of the total sludge volume entering the HTL process exits in this aqueous stream which must be further treated at the wastewater treatment facility where CECs can potentially re-enter the process. Therefore, the objective of this study was to examine the fate and transport of multiple CECs through an HTL process to investigate their partitioning between phases and/or their removal. Methodology Wastewater sludge was obtained from a municipal secondary wastewater treatment facility in BC, Canada. Mixed primary (55%) and secondary (45%) v/v sludge was dewatered by centrifugation to 20% total solids (TS) without polymer addition. Five CECs, (including azithromycin (AZM), bezafibrate (BZF), carbamazepine (CBZ), diclofenac (DCF), and mefenamic acid (MFA)) were studied. Six runs total were performed at six different experimental conditions. The dewatered sludge was either not spiked (i.e., only environmental CEC levels were present), or was spiked, as shown in Fig. 1. A low and high level of spike, corresponding to concentrations of 200 and 500 µg of CEC/g TS, were selected. The dewatered sludge was then added to a 1-L Parr reactor vessel. The vessel was continuously mixed and heated to either 332°C (630°F) and held at temperature for 17 minutes or it was heated to 350°C (662°F) and held at temperature for 15 minutes. The pressure increased to 170 bar (2465 psi) during operation due to volatilization within the fixed-volume vessel. After cooling, the produced gas, liquid 'aqueous phase,' and the remaining solid phase (consisting of hydrochar and biocrude) was collected. The two components of the solid phase were analyzed together to eliminate the possibility of the CECs being lost to the extraction solvent. Isotope dilution CEC extraction and analysis methods (adapted from US EPA 1694 and another HTL study), were used to extract CECs from all matrices. [3,4,5] After extraction, CECs were analyzed via liquid chromatography with tandem mass spectrometry (LC-MS/MS). CEC concentrations prior to HTL in mixed sludge, dewatered sludge, and the resulting sludge dewatering centrate, along with HTL effluent solid and aqueous phases were analyzed to monitor CEC flux through the HTL process. Process influent and effluent was used to simulate a CEC mass balance across a model full-scale HTL train and for comparison to existing thermophilic anaerobic digestion processes. Findings The average yields of the HTL aqueous and solid products were 80% and 20% of the total mass, respectively, from the six runs. In past experiments within our group, the average output of the HTL process at these two reaction conditions (332°C/17 min and 350°C/15 min) yielded 82% aqueous, 3% hydrochar and 9% biocrude and 2% gas by mass. The amount of each CEC that would be recycled through the process back to the headworks in the mixed sludge dewatering liquids (prior to HTL) was determined based on the mass balance calculations of a full-scale system model. This represents the environmental CEC levels present. The mass balance showed that 24% of AZM, 40% of CBZ, 21% of DCF and 8% of MFA partitioned to the centrate during sludge dewatering. No BZF was returned as none was detected in the initial dewatered sludge. After HTL, except for trace (< 0.5 ppb) levels of AZM in four of the six scenarios, there were no detectable CECs in any of the HTL aqueous stream samples as shown in Figure 2. This indicates that any CECs remaining after HTL treatment are either destroyed or did not partition into the aqueous phase. Similar to the aqueous stream, the biocrude/hydrochar stream had lower levels of CECs remaining after the HTL process, as shown in Figure 3. Across the six scenarios, the three CECs (AZM, BZF and CBZ) were found to be <4 ppb. AZM was <0.3 ppb in each scenario indicating almost complete removal. BZF was only detected in the low spike scenarios, at 1.8 ppb for the 332°C condition and at 3 ppb for the 350°C condition. This again indicates an almost complete removal from the system. CBZ was detected in all six scenarios, although at very low (<1.5 ppb) concentrations. Based on these results, the percent removal was determined from the CECs concentration in the feedstock, the dewatered sludge. In the aqueous fraction, 100% removals can be seen for all five compounds investigated in all scenarios, except for the BZF in the 'No Spike' trials because there was none present in the input dewatered sludge (Figure 2). In the solid fraction, there was 100% removal for all three investigated compounds for the low and high spike treatments (Figure 3). However, in the 'No Spike' scenario, as in the aqueous, there was no BZF in the input dewatered sludge. Also, there was only a 65-70% removal for CBZ in that treatment. This is likely because of the low input concentration and the amount of noise inherent in this matrix during quantification. The combined results from the aqueous and solid fractions of the HTL products indicate the HTL process thermochemically converted almost all the environmentally present compounds in the sample matrix, as well as the externally spiked compounds to other end products. A fraction (8-40% depending on the CECs) of the CECs from the initial sludge are recycled as dewatering centrate to the headworks prior to HTL, for another cycle through the wastewater facility for further removal. The remaining portion that enters the HTL would achieve a nearly complete (>99.9%) removal. This suggests that incorporating an HTL process into a wastewater treatment facility will likely result in far lower levels of CECs discharged to the environment compared to an anaerobic digestion process which had limited success against refractory CECs investigated in a previous study.[6] Conclusions - This study indicates that HTL is an effective method for removing the studied recalcitrant pharmaceuticals from dewatered wastewater sludge. - In the aqueous product stream of the HTL process, trace amounts of AZM (<0.5 ppb) were detected in the three of the six scenarios. In the other scenarios, no AZM was detected, nor the other CECs examined. - In the HTL solids stream, the three CECs studied were detected in at least one scenario. However, the compounds were detected at low concentrations of <4 ppb. Learning Objectives 1.Hydrothermal liquefaction technology has the potential to remove contaminants of emerging concern from municipal wastewater sludge, reducing pollution in the environment. 2.In addition to removing trace contaminants, this process simultaneously converts wastewater sludge into a valuable renewable energy source. The remaining hydrochar reduces the volume of solid material for ultimate disposal by ≥ 97%.

In the past few years the concerns of the presence of PFAS compounds and how they may impact potential state and federal regulatory actions have dominated the narrative in the water industry. With the actions of Maine and more recently Connecticut, the threat of a ban on biosolids land application has prompted many municipalities to re-examine their biosolids management strategy. Many states have begun to collect data regarding the levels of PFAS in biosolids. Other such as Michigan has established a tiered standards based on extensive data collection to limit biosolids land application based on PFAS concentration. The majority of states are however, waiting for the results of the EPA risk assessment and pending actions before acting. In 2020 in anticipation of the above stated challenges, Pinellas County determined that they should become less dependent on using biosolids on land even though they have a successful history of marketing the thermally dried biosolids since 2013. The county has also set a goal to reduce the amount of wastes going to the landfill. With their waste to energy facility the volume of solid wastes to be landfilled have substantially been reduced. However, yard wastes and wastes tires continued to present challenges at times. There is also a desire to divert more organics from the landfill, thus the consideration of food wastes, and FOG wastes that cannot be handled by co-digestion at the South Cross Bayou Advanced Water Reclamation Facility (SCBAWRF) and the private haulers, also become part of the resource recovery targets. A concept to integrate resource recovery of these waste streams began to emerge. Furthermore, ten other wastewater facilities owned by various cities throughout Pinellas County still rely heavily on land application of biosolids and are facing similar challenges. Thus there is a desire to develop this into a regional facility. A request for proposal was subsequently issued to engage an engineering consultant to further develop this concept. CDM Smith was brought under contract in late 2022 to begin developing the regional resource recovery facility (RRRF) concept. The RRRF will accept a variety of feedstocks including FOG and yard wastes along with biosolids. The intent is that biosolids from Pinellas County, and several other local municipalities (estimated at 42 dry tons per day) will be transported to the RRRF for additional treatment and processing to produce a variety of market ready products such as biogas, biochar, compost, or others. Processing options to be considered include those of FOG and yard wastes for co-processing with biosolids or can synergistically contribute to efficient biosolids processing. After establishing the basic project information such as biosolids and other waste quantities, a number of treatment technologies were first reviewed and screened for applicability at the RRRF. Tables 1 and 2 provide a summary of the biosolids and other organic wastes streams available from Pinellas County and potential partners. The screened technologies are then utilized to develop processing alternatives at the proposed RRRF for evaluation. The screening and evaluation processes resulted in five treatment trains to be further evaluated. These shortlisted process alternatives include anaerobic digestion with potential pretreatment with thermal hydrolysis, thermal processes including drying, both thermal and solar, pyrolysis and gasification. FOG and food wastes codigestion are considered, with energy recovery through biogas generation. The woody portion of yard wastes are being considered as an alternative energy source to support the processes such as solar drying and thermal drying as well as power generation. One of the challenging aspects of the technology evaluation involves identifying technologies that can effectively eliminate PFAS, with a product that can be utilized independent of land application. Without a firm regulatory position, it is not known if complete destruction of PFAS compounds will be required, and whether it is even achievable with available technologies. While thermal technologies such as pyrolysis and gasification as well as advanced technologies such as supercritical water oxidation and hydrothermal liquefaction have been touted as technologies that can effectively destroy PFAS compounds, actual experience that can be pointed to are extremely limited, especially at the scale of the project being considered. Another challenging aspect of these technologies is the lack of available technical information. Since these technologies are mostly proprietary, technology providers are hesitant in sharing information. With little full-scale experience, basic engineering information such as general layout drawings, mass balance, energy balance, equipment costs, operating and maintenance requirements and costs are unavailable or difficult to come by. In order to overcome these challenges, CDM Smith spent much time reaching out to various technology providers and working with them closely to develop these details as part of our evaluation. Through the process, it became clear that most of these technologies are not deployment ready for the scale of facility we are considering. As such, we develop some alternative process trains that would allow us to use established technologies for the proposed facilities but at the same time accommodate some of these technologies at an acceptable scale. Figures 1 and 2 show two process trains with this concept. The final evaluation of these process trains includes the development of capital and operational and maintenance costs for each process train. This is followed by a business case analysis to establish the cost impacts to each municipality under each alternative. The County and partners are currently reviewing these cost impacts. The presentation will focus on the approach taken to develop a strategy that can address potential PFAS impacts as well as reducing the associated risks with new technologies.

OBJECTIVE: The increasing emphasis on circular economies has led wastewater treatment in recent years to become a renewable source for energy, heat, water, fertilizers, carbon products, and soil amendments. Despite these advancements, one significant and potential resource that remains unrealized is biogenic CO2, which can be used for geological sequestration or other manufacturing. Given the arising climate change policies and markets for biogenic, or green CO2, there will be greater financial incentives in the future for WRRFs to implement bioenergy programs with carbon capture, utilization, and sequestration (BECCUS) strategies. This paper will explore a market assessment for biogenic CO2 end-uses, funding mechanisms and economic incentives, regulations and policies, technological solutions, and a techno-economic analysis (TEA) of a case study for carbon capture at a WRRF. CURRENT CO2 MARKET In 2022, commodity CO2 demand in the United States was estimated at 10.3 million MT per year with over 64% of that sourced from fossil fuel derivatives (Figure 1). About 25 percent of CO2 are mined, with the remaining demand supplied as a byproduct from chemical manufacturing processes (ammonia, ethanol, hydrogen, and natural gas processing). While most of the CO2 is used in enhanced oil recovery (EOR), which is the process of injecting CO2 into the oil reservoir to increase the mobility of the oil, the second most common use of CO2 is for the food/beverage industry (approximately 30% of all CO2 demand). THE VALUE OF BIOGENIC CO2 AND THE FUTURE CO2 MARKET CO2 can be categorized by its sourcing as traditional CO2 or green CO2. Traditional CO2 mainly comes from the burning of fossil fuels and results in an accumulation of CO2 in the atmosphere. As climate-driven initiatives and regulations become more pressing, the CO2 market will need to evolve to more sustainable alternatives. Green CO2 is a sustainable type of CO2 as it is sourced from the natural carbon cycle making it effectively carbon neutral. The two main sources of green CO2 are direct air capture (DAC) CO2 and biogenic CO2. DAC is a technology that separates CO2 from the atmosphere through chemical reactions and is not limited to point of emission locations. However, DAC is both an expensive and energy intensive method of capturing CO2, as it requires concentrating the dilute stream of CO2 from the atmosphere (Figure 2). Biogenic CO2 is a favorable alternative as it comes from the degradation (digestion/fermentation), combustion, or mineralization of organic matter, and tends to result in a higher concentrated CO2 stream. Currently, ethanol plants provide up to one quarter of the existing biogenic CO2 market's supply in the U.S., but its production is limited to the midwest region. For WRRFs, biogenic CO2 is a natural byproduct of both anaerobic digestion and from the combustion of biogas in combined heat and power systems (CHP), making it a prime point of emission location. Over 1,300 WRRFs are equipped with anaerobic digestion systems, and many are located in urban centers. OPPORTUNITIES AND CHALLENGES FOR BIOGENIC CO2 WRRFs can utilize two pathways for biogenic CO2: carbon capture and utilization (CCU) or carbon capture and storage (CCS). Figure 3 shows a general diagram of the two paths. A national survey was performed to examine the prospects for captured biogenic CO2 from WRRFs to be utilized in the food/beverage, e-fuels, or sold to a distributor. Partial details of the survey are included below; full details will be included in the paper: -E-Fuels -- also known as 'electrofuels', are a class of synthetic fuels that are produced from combining the carbon in CO2 with green or blue hydrogen. Twelve, a carbon transformation company and E-Jet fuel supplier, stated that they source their biogenic CO2 for $20-100 per ton from the ethanol industry. - E-Chemistry -- similar to e-fuels, e-chemicals use electrosynthesis to produce chemicals through more sustainable avenues. This sector is still developing but may become a major user of CO2 in the future. Biogenic CO2 would be highly compatible with this end-use. - Cement manufacturing -- biogenic CO2 can be used as a direct replacement for traditional CO2 which is used for the manufacturing of concrete. Scale and size may limit acceptance. CCS is the process in which captured CO2 is compressed and injected in underground geologic formations for permanent storage or sequestration. WRRF would partner or contract with a regional or local CCS service provider, and the credits can be used to offset a utility's emissions or sold in the voluntary or compliance carbon market. FUNDING MECHANISMS AND ECONOMIC INCENTIVES The Inflation Reduction Act (IRA) was passed in 2022 and provided over $369 billion dollars in climate-related funding for domestic clean energy production, decarbonization technologies, climate change mitigation, and resiliency programs. Within Section 45Q of the IRA, provisions for CCU and CCS provide the financial incentives for utilities with bioenergy programs to invest in CO2 capture technologies (Table 1). TECHNOLOGICAL SOLUTIONS The biogas upgrading to RNG process includes cleaning and separation to remove CO2, H2S, siloxanes, VOCs, and moisture, resulting in RNG and a CO2-rich tail gas that contains 93 to 99.9 percent CO2. This tail gas can be further processed to recover biogenic CO2 rather than vented to atmosphere. Each of these technologies have varying levels of compatibility with CO2 recovery in the tail gas as shown in Table 2. TECHNO-ECONOMIC ANALYSIS A TEA was developed to evaluate the financial feasibility of two different CO2 capture program sizes with and without IRA eligibility. This TEA only considered the CO2 capture program as an add on and not a full CO2 and RNG program which may change the economics. Interviews with various CO2 capture equipment manufacturers, CO2 commodity suppliers and distributors, and CO2 end-users provided economic information for this TEA. The key assumptions that drove the economic model are summarized in Table 3. The results of the TEA illustrates that a 'no distributor model' with IRA funding reflected a positive NPV. The other modelled scenarios are illustrated in Figure 5. Note that the current IRA 45Q guidelines provides credits for only 12 years and that CO2 pricing, transportation costs are highly region dependent and may change the economics (Smith et al. 2021). CONCLUSIONS Capturing CO2 from municipal bioenergy programs is a significant opportunity for resource recovery and carbon management and stands out for its practicality and effectiveness. One advantage of CO2 capture from biogas is its high concentration in the airstream, with purity typically ranging from 30-50% and up to 99.9% from biogas upgrading to RNG. There are several end-uses for biogenic CO2 in the CCS (sequestering and selling credits to the voluntary or compliance carbon market) and CCU market (i.e. food/beverage, industrial uses, e-fuels). However, a limitation for WRRFs-sourced biogenic CO2 is its scale and size as many require a production of a minimum of 30,000 to 50,000 tons of CO2 per year for partnership. We anticipate that the competition for green CO2 sources will drive these end-users to seek WRRFs in the future. The future paper and presentation will explore additional sources of CO2 from WRRFs such as from post-combustion capture, and aeration tanks.

Introduction and Background The Sand Island Wastewater Treatment Plant (Sand Island) is located on the idyllic shores of Oahu with deep blue waters laying before it, lush green mountain of jungle vegetation behind it, Pearl Harbor to its left, and the bustling high-rises of downtown Honolulu and Waikiki to its right. Sand Island is owned and operated by the City and County of Honolulu (CCH). Sand Island is currently a 90 MGD primary treatment with UV disinfection and biosolids treatment plant with ocean discharge for its treated effluent and thermally dried pellets for its biosolids distribution. CCH is under a federal mandate to upgrade Sand Island to meet full secondary treatment water quality standards by 2035. Sand Island is undergoing its upgrade in two phases. Phase 1 is under construction to build ~20 MGD of Membrane Bioreactors (MBR) capacity and additional mesophilic anaerobic digestion capacity to handle the waste activated sludge (WAS) along with the projected increase in primary sludge due to the continued population growth within the CCH service area through 2035. Phase 2 is in progress transition into the detailed design phase and will complete the full secondary treatment capacity to 90 MGD including wet weather storage to carry Sand Island through a 2045 planning horizon. The selected secondary treatment process for Phase 2 is Aerobic Granular Sludge (AGS) and the combination of Primary sludge, MBR WAS and AGS WAS, a never-before-seen sludge cocktail in our industry and a unique blend to consistently process on a small island with limited space and options for biosolids product distribution. This is the backdrop for a one-of-a-kind solids alternatives analysis in paradise. The existing solids handling treatment at Sand Island involves conventional mesophilic digestion, dewatering, and drying. The existing solids handling system will require additional treatment capacity to process the increased solids load when full secondary treatment is in service. With this task at hand we set to work on pitting tried and true biosolids processing strategies for Sand Island against new effective options adaptable to the Hawaii market to produce sustainable biosolids and energy to fuel Sand Island. This will also lower the utilities' impact of the Island of Oahu and its limited and imported natural resources. Solids Treatment Alternatives Four distinct alternatives for the solids treatment upgrades were identified as potentially viable solutions and were evaluated on their merits to economically enhance process performance, redundancy and reliability. - Alternative 1: Conventional mesophilic anaerobic digestion (AD) + Thermal Drying (TD) - This alternative is the baseline case and uses the existing solids treatment process philosophy of mesophilic anaerobic digestion at a 20-day solids retention time (SRT) followed by rotary drum drying, producing Class A dried pellets for beneficial reuse (Figure 1) expanded to the new Primary Sludge + WAS solids projections through 2045. - Alternative 2: Thermal Hydrolysis Process (THP) + AD + TD - This alternative modifies the existing treatment process to include sludge pre-conditioning for THP followed by mesophilic anaerobic digestion, producing Class A biosolids and reducing the volume of solids undergoing digestion, followed by dewatering, rotary drum drying, and producing Class A biosolids for beneficial reuse (Figure 2). - Alternative 3: THP + AD + Combined Heat & Power (CHP) (No Dryer) - This alternative modifies Alternative 2 to eliminate the drying operation. THP produces Class A biosolids cake that can be land applied. However, the land application market for Class A dewatered cake in Oahu requires further analysis. Dewatered cake can also be accepted at H-POWER (Covanta Honolulu Resource Recovery Venture) to produce power. By eliminating thermal drying a surplus of biogas becomes available for heat and power generation through a CHP system with a very favorable return on investment (ROI) of 5 years due to the resource limitations of Hawaii (Figure 3). - Alternative 4: Thermophilic Anaerobic Digestion (TPAD) + CHP (No Dryer) - This alternative would modify and augment the anaerobic digestion process currently under construction at Sand Island with batch thermophilic anaerobic digestion at 55°C (131 °F) followed by mesophilic anaerobic digestion at 35 °C (95 °F) (TPAD) to produce a low odor Class A biosolids cake eliminating the need for thermal drying to achieve Class A Biosolids. However, the land application market for Class A dewatered cake in Oahu requires further analysis. Dewatered cake can also be accepted at H-POWER (Covanta Honolulu Resource Recovery Venture) to produce power (Figure 4). Capital, Operations and Maintenance (O&M) Costs Class 5 Opinion of Probable Construction Cost (OPCC) estimates include the costs associated with construction, engineering, administration, and contingency were performed. The total capital cost with high and low range sensitivity analysis estimates for Alternatives 1, 2, and 3 is depicted in Figure 5. Alternative 4 is still under evaluation and will be complete by the time of presentation. O&M costs include the costs associated with energy and consumables use, labor, and the maintenance for the improvements identified and detailed in each alternative. Figure 6 depicts the annual O&M costs associated with Alternatives 1, 2 and 3. Alternative 4 is still under evaluation and will be complete by the time of presentation. Net Present Value Analysis NPV analysis was performed to evaluate life cycle costs over a 20-year horizon which includes the cumulative capital and O&M costs associated with each alternative (Figure 7). Key Takeaways This presentation will provide insights on - Impacts of each alternative on the existing solids treatment train - Mass and Energy Balance analysis summary associated with different alternatives - Life cycle cost analysis for each alternative over 20-year planning horizon - Comparison of alternatives based on the following: -- Economic Criteria: Capital and O&M Cost -- Non-Economic Criteria: O&M Complexity, Technology Maturity/Reliability, Health & Safety, Product Application, and Footprint. - Furthermore, driving factors associated with higher costs in noncontiguous state such as Hawaii in comparison to Mainland states will be discussed.

It has been accepted wisdom in the wastewater industry for many years that primary treatment combined with anaerobic digestion becomes more cost-effective the larger the size of the water reclamation facility, whereas at smaller facilities waste activated sludge (WAS) only systems are more commonly used. Primary treatment reduces the organic load on secondary processes, leading to aeration savings, and anaerobic digestion provides opportunities for beneficial use of biogas. However, for facilities with nutrient removal requirements, diverting carbon to anaerobic digestion can lead to a deficit of carbon for nutrient removal needs, and lead to costly addition of supplemental carbon. Meanwhile, treatment technology is constantly improving and changes in technology and green initiatives can have a significant impact on the optimum solution for carbon diversion. Several considerations are outlined below. ...Enhanced primary treatment (e.g. primary filtration): leads to higher carbon diversion to digestion and less carbon to secondary processes, reducing aeration basin volume and aeration costs, but potentially leading to higher supplemental carbon needs if nutrient removal is required. ...Primary sludge fermentation: can be used to solubilize some of the carbon in primary sludge for diversion back to liquid stream processes to meet nutrient removal needs, while also minimizing aeration basin volume that would otherwise be driven by additional aeration basin influent solids without primary treatment. Sidestream Enhanced Biological Phosphorus Removal (S2EBPR): provides the opportunity to ferment return activated sludge (RAS) or mixed liquor to drive biological phosphorus removal via carbon in the RAS/mixed liquor, reducing reliance on influent carbon or supplemental carbon. ...Partial denitrification anammox (PdNA): is an emerging process that has been proven at full scale and which has significant potential to reduce carbon needs for denitrification and also reduces aeration demand. Both S2EBPR and PdNA offer the potential to reduce supplemental carbon needs for nutrient removal, freeing up more carbon for diversion to anaerobic digesters. ...Renewable Identification Numbers (RINs): are green trading credits applied to the production of renewable fuel that incentivize the production of renewable natural gas (RNG) from biogas at wastewater facilities with anaerobic digesters. In addition to the current RIN system that incentivizes RNG, a pathway for electrical RINs (eRINs) may soon be available that could incentivize production of electricity (e.g. via combined heat and power systems) This paper will provide an economic analysis evaluating the impact of various factors on the decision of whether or not to implement primary treatment and anaerobic digestion at water reclamation facilities. Factors to be evaluated will include the following: 1.Facility size 2.Efficiency of primary treatment carbon capture (conventional versus enhanced primary treatment) 3.Nitrification only facilities compared to those with nutrient removal requirements for nitrogen and phosphorus 4.Implementation of primary sludge fermentation to provide more carbon to meet nutrient removal needs 5.Implementation of S2EBPR for more efficient use of carbon for P removal 6.Implementation of PdNA to reduce carbon needs for total nitrogen removal 7.Cost sensitivity to green incentives (e.g. RINs) for biogas upgrading To provide an example of the type of analysis that will be included in the paper, a preliminary life cycle cost analysis has been conducted for various sizes of facilities for the simplest scenario where only nitrification is required (no nutrient removal requirements). The full paper will expand on this analysis to develop life cycle costs to evaluate the factors outlined above. The following approach was taken: 1.Process unit sizing was developed for a range of facility sizes from 5MGD to 100MGD 2.Two scenarios were evaluated for each facility size, one with primary clarification and anaerobic digestion and the other with no primary clarification. 3.Capital, operating and life cycle costs were developed for each size of facility for each scenario. Details of the scope of capital costs included for each scenario are provided in Table 1. In general, the scope of capital and operating cost development was limited to items that would differ between the two scenarios being investigated. Details of the scope of operating costs included and key assumptions are provided in Table 2. It is acknowledged that the assumptions made inevitably impact the outcome of the evaluation and sensitivity to a range of assumptions will be included in the final paper. Net present costs were developed using a 2% inflation-adjusted rate over 20 years. Results are shown in Figure 3 and Figure 4. Key take-aways from this preliminary analysis are as follows: 1.Capital cost for the scenarios utilizing primary clarification and digestion were higher than those with WAS only activated sludge 2.Operating costs for the WAS only activated sludge scenarios were higher than those with primary clarification and digestion 3.As expected, economies of scale led to primary treatment and anaerobic digestion becoming more cost-effective as facility size increases The full paper will elaborate extensively on this analysis, providing utilities with useful insights to help understand under what conditions primary treatment and anaerobic digestion is favorable compared to WAS only activated sludge.

PROBLEM STATEMENT/PURPOSE: This paper and presentation will detail the typical lifecycle of a municipal RNG project from the facilities planning phase through post startup operation in order to inform those considering such a project. It will delve into the common key decisions that are made along the way as well as specific details about these types of projects. The lifecycle will be broken down into the following major phases: 1.Planning 2.Design 3.Construction 4.Operation Historically municipalities would choose to anaerobically digest their wastewater sludge to reduce the volume produced to lower hauling and landfill costs compared to other stabilization methods. The biogas produced would mostly be flared with some potentially beneficially used to heat the digestion process. Over time methods have evolved to get increasing higher value out of the biogas that would otherwise be flared. These include electrical power production, combined heat and power systems, and heat recovery steam generation to name a few. In recent years a more lucrative biogas use has grown out of the renewable fuel standard (RFS). Under the RFS gasoline and diesel producers and importers (obligated parties) are required to purchase a certain amount of renewable fuel every year to offset transportation related greenhouse gas emissions and limit reliance on foreign energy. This has driven the value of biogas (in the form of renewable natural gas or RNG for short) to higher than the equivalent amount of natural gas and therefore many municipalities considering upgrades to their biosolids processes today are including anaerobic digestion with a method of selling their biogas (Figure 1 - RIN prices by category over time). RNG value lies largely with the renewable identification number (RIN) trading that occurs between producers and obligated parties. Figure 1 - RIN prices by category over time. RNG PROJECT LIFECYCLE Experience from the following municipal biogas RNG projects will inform the project lifecycle insight provided in this presentation. These projects are in varying stages of the 4 main project phases outlined in this presentation. - Thereasa St. WRRF, Lincoln, NE - Columbia Blvd, WTP, Portland, OR - Papillion Creek WWTP, Omaha, NE - Piscataway WWTP, Accokeek, MD - Cedar Rapids WPCF, Cedar Rapids, IA - Des Moines STP, Des Moines, IA - Arlington WPCP, Arlington, VA PLANNING The first step in an RNG project lifecycle is in the facility planning phase. This phase is usually kicked off when a municipality is looking to either implement an overall biosolids process improvement or wants to beneficially use biogas from an existing digestion process. Biogas beneficial use options at this phase will typically include combined heat and power, electricity generation, thermal drying, and pipeline injection. In most cases if there is a natural gas utility or transportation end user located within a reasonable distance of the plant RNG production will win out over the other alternatives. The strongest argument for RNG is financial but it also has environmental and social advantages over the alternatives which will be detailed (Figure 2 - Example of greenhouse gas (GHG) emissions for design alternatives). When producing and selling RNG is identified as a feasible path forward the highest priority becomes reaching out to potential receivers; either a natural gas utility or a vehicle fleet operator. The receiver must both be receptive to accepting RNG and provide details that will guide the design. These details include gas quality requirements, interconnection design, custody transfer, site location, payment and funding split. DESIGN The next major phase of an RNG project is final design. During this phase many key decisions are made. Many RNG projects have very similar key design decision points. The following are some of the design decisions that will be discussed: - Should there be gas utilization options in addition to RNG (Figure 3) - Biogas design flow and peaking factors - Whether or not to upgrade peaks in biogas production - Should there be gas storage? - Levels of redundancy (flare, compression, upgrading, etc.) - CO2 removal technology and tail-gas treatment - Design H2S, VOC, and siloxane concentrations and how to treat. - Gas conveyance (wet vs. dry) to upgrading system. Other important design details that will be discussed are examples of process control description, commissioning plan, and performance testing plan development. Figure 3 - Example of a process with many gas utilization alternatives. CONSTRUCTION After design the next major phase is construction. During construction coordination with the gas receiving entity continues and this presentation will give examples of the ongoing coordination that can be expected (including potential involvement of a RIN broker). Figure 4 shows an example of initial RNG acceptance coordination with the gas utility during startup. The period of commissioning, functional testing and performance testing is the most operationally intensive phase of construction. This presentation will give examples of how to prepare for a successful commissioning phase that involves all stakeholders. Specific detail will focus on team collaboration and process driven decision making. Figure 4 - Example of RNG acceptance coordination with gas utility. OPERATION The last lifecycle phase that will be covered is operation of an RNG production system. It will give details on what to expect in terms of revenue generation, operation and maintenance, uptime, and potential contingency scenarios (down time). Figure 5 shows maintenance of one of the most common H2S removal technologies, iron sponge adsorption. Figure 5 - Photo of iron sponge H2S removal media change - Courtesy of MV Tech

Conventional thickening processes use gravitational forces or mechanical methods such as centrifuges or belt filter presses for solids separation. Although these methods have proven to be efficient, gravity based thickening methods require large footprint and mechanical thickening processes can be energy intensive. Recently, several innovative technologies have been introduced that aim to enhance energy efficiency of thickening process while reducing the footprint. Dissolved Air Flotation (DAF) process has been around for over a century and initially used in the early 1900s, primarily in the pulp and paper industry to remove fibers and other solids from water. Interest in DAF resurged in the 1960s for wastewater treatment applications and since then DAF has been used as one of the main thickening processes. DAF introduces air into the wastewater solids, and creates tiny bubbles. Then these bubbles attach to the sludge particles, causing them to float to the surface, where they form a thickened sludge layer. This layer is then skimmed off, leaving clearer water below. However, DAF has shown to be energy intensive since it requires recirculation pumps, compressors. Lately, a new thickening technology called Suspended Air Flotation (SAF) was introduced into the wastewater industry. SAF operates similar to DAF by using air to float sludge. However, there is a key difference: SAF employs charged particles for bubble flotation. SAF also aims to float the particles but without the use of dissolved air. Therefore, thickening performance is not limited by changing conditions such as gas solubility, pressure, and temperature. The flotation occurs by the application of froth made from an anionic surfactant, water, and air instead of air bubbles for flotation. Similar to DAF, SAF mixes feed sludge with a conditioning polymer before it enters the flotation tank. Froth, composed of charged microbubbles called aphrons, is then introduced downstream of the polymer injection. The micron-sized air bubbles, ranging from 7 to 50 µm, in water to attain a volumetric air content of 40 to 50%. These bubbles are coated with a thin layer of soap film derived from an electrically charged anionic or cationic surfactant. The charged bubbles offer a substantial interfacial area for the adsorption of oppositely charged flocculated wastewater solids. In practice, suspensions of charged bubbles are introduced into the flotation tank to interact with wastewater solids. The solids then ascend to the surface and are skimmed off. The clarified effluent is recirculated to the headworks. SAF enhances traditional thickening methods like Dissolved Air Flotation (DAF) by eliminating the need for dissolved air, thus obviating the requirement for pressurization systems, recirculation pumps, compressors, and airlines, leading to considerable energy savings. SAF's capability to manage high solids loads also results in substantial footprint and power savings, high solids recovery (up to 98%), and a high solids loading rate (up to 40 lb/ft2/hr). Moreover, no polymer is needed to thicken sludge to 4% solids. Owing to these benefits, adopting SAF technology can lead to a reduction in greenhouse gas emissions by more than 60-70% and energy savings of up to 90% compared to its conventional counterparts, such as DAF. In a recent project funded by California Energy Commission (CEC), this innovative thickening process was selected to be tested at demonstration scale. The demonstration facility is located at Linda County California, north of Sacramento. The project includes several advanced treatment processes for biosolids. Another innovative technology Supercritical water oxidation (SCWO) is also included after SAF to replace anaerobic digesters. Figure 1 shows the process flow diagram at demonstration facility. SAF process have already shown promising results for their low energy consumption. Recent findings indicated over 90% savings in energy use by switching from DAF to SAF. Table 1 compares SAF process with conventional thickening processes. The cost savings for SAF process was also evaluated with other conventional thickening processes including Rotary Drum Thickener (RDT) and also DAF. Table 2 summarizes the 30 year net present value comparison of SAF process. This presentation will evaluate this novel technology, discuss the critical design criteria for this process and assess its performance focusing on energy savings.

The City of Orlando, Florida is home to 312,000 people and is one of the fastest growing cities in the U.S. The City is recognized as a progressive, sustainability minded community and has a Water Reclamation Division of the Public Works Department that provides wastewater collection and treatment services to the City's businesses and residents. The Water Reclamation System has historically been divided into the easterly and westerly subsystems. The easterly subsystem is served by the Iron Bridge Water Reclamation Facility, a 40 million gallon per day ('MGD') plant, and the Conserv I Water Reclamation Facility, a 7.5 MGD plant. The westerly subsystem is served by the Conserv II Water Reclamation Facility, a 25 MGD plant. Currently, biosolids from each of the plants are dewatered, stabilized and hauled to land application sites or landfills for disposal. Due to concerns of nutrient contamination of both surface and groundwaters, regulations established by SB 712 restrict this practice during wet weather. Presently, biosolids cannot be applied to land when groundwater is within 2 feet of the surface, and landfills are often hesitant to accept biosolids during these periods. Considering Florida's seasonal pattern of thunderstorm activity and exposure to tropical weather, this happens with regularity, necessitating on-site dewatering and storage of sludge-a practice the City aims to minimize through the adoption of technologies that can reduce sludge volumes and eliminate reliance on land application. As a proactive measure, the City is also seeking solutions to address contamination issues, specifically concerning per- and polyfluoroalkyl substances (PFAS), to safeguard water sources potentially impacted by biosolid disposal. After evaluating various management strategies, including composting, incineration, and drying, the City identified supercritical water oxidation (SCWO) as an innovative and cost-effective solution for both biosolids volume reduction and contaminant elimination. With support from the Bipartisan Infrastructure Law emerging contaminant funding, the City received a grant from the Florida Department of Environmental Protection (FDEP) through the Clean Water State Revolving Fund to pilot test a SCWO system capable of processing 6 wet tons of biosolids per day developed by the technology provider 374Water. If the pilot test proves to be successful, FDEP has committed to provide an additional grant to the City for the purchase and installation of a 30 ton per day unit at the City's Conserv I plant. SCWO is a waste treatment technique that converts organic-rich waste into clean vent gas and liquid effluent composed solely of water, inert inorganics and minerals. During the SCWO process, waste is heated and pressurized above the critical point of water (374°C, 221 bar), allowing it to enter a supercritical state. In this state, organics become highly soluble, facilitating the mineralization of persistent compounds like PFAS. The oxidation of organic matter generates energy in the form of heat, which is recycled within the process. The outcome is a treatment technology that transforms biosolids into a contaminant-free, mineral-rich effluent and clean vent gas. 374Water's AirSCWO system utilizes ambient air to supply oxygen, enhancing oxidation efficiency while reducing costs and risks associated with the handling of compressed gases such as pure oxygen or hydrogen peroxide. Its innovative reactor design promotes high velocity to prevent clogging, enhances corrosion protection, and allows for a more compact system. Additionally, the modular, containerized design fits within a 40-foot shipping container, ensuring safety and ease of transport and installation. Pilot-scale demonstrations and numerous lab-scale studies have confirmed AirSCWO's capability to eliminate emerging contaminants like PFAS with over 99.9% efficiency, generating no harmful by-products in the liquid effluent or vent gas. These advancements provide confidence that 374Water's technology is well-suited to meet the biosolids management goals of Orlando's Iron Bridge Water Reclamation Facility. The overarching project goal was to install, commission, and test one of 374Water's AirSCWO 6 units at the City of Orlando's Iron Bridge Water Reclamation Facility. The measures of success for the project included (1) ensuring the timely preparation of the site and delivery/installation of the AirSCWO 6 unit, (2) passing functional tests, and (3) continuously processing biosolids that meet volume and organics/PFAS reduction targets. To do so, samples were collected prior to influent wastewater screening, between the end of sludge handling and the AirSCWO 6 inlet, at the effluent of the AirSCWO 6 unit, and at the effluent of the wastewater treatment process (see Figure 1). At each sampling point, relevant parameters including flowrate, chemical oxygen demand, and PFAS (via EPA Method 1633) were assessed and used to evaluate the performance. The extensive sampling plan (Table 1) included baseline testing, system startup testing, and monthly testing. This presentation will explore the opportunities and challenges of conducting an on-site demonstration of an emerging technology, using the implementation of 374Water's AirSCWO 6 at the City of Orlando's Iron Bridge Water Reclamation Facility as a case-study. The discussion will outline the project's background, the City's motivations and planning processes, as well as expectations, risk analysis/mitigation strategies, timelines, and budgeting. 374Water will provide updates on progress toward meeting project goals, address past, present, and upcoming risks, and offer insights on navigating flexible timelines to ensure the successful commercialization of new technologies.

Introduction: While some sectors can be fully decarbonized through the implementation of renewable energy sources, the decarbonization pathways for the wastewater sector are more complex. Resource recovery through sludge management can be an option to reduce GHG emissions in water resource recovery facilities (WRRFs). Of all the sludge produced in the U.S., 22% is being landfilled, 16% is being incinerated, and 52% is being land applied (with 80% of the sludge being digested before land application).[1] New regulations and concerns about emerging contaminants such as per- and polyfluoroalkyl substances are creating challenges and increasing costs for land application, the most used disposal strategy. Thus, it is critical to implement new processes to maximize resource recovery and remove emerging contaminants without increasing overall costs and GHG emissions. HTL is a promising technology that can reduce sludge volume by 90%, recover phosphorous, remove emerging contaminants, and convert 65% of the energy content in the sludge into biocrude oil, a precursor for aviation fuel.[2,3] A large-scale adaption of HTL for WRRFs requires an evaluation of the economic, environmental and social impacts of HTL. Here we premier the first evaluation of technical feasibility and assessment of economic, environmental and social impacts related to the implementation of HTL in the WRRF of the City of Detroit (GLWA), which operates one of the largest WRRF in the nation. The feasibility study consisted of three tasks. Task 1 assessed the availability and detailed characterization of waste streams. Task 2 conducted community engagement (hearing from the community and professional stakeholders). Task 3 involved Economic and environmental analysis. GLWA generates 320 dry ton of sludge per day. 240 dry ton/day of sludge is being converted in class A-EQ biosolids for land application through a thermal process and the rest (80 dry ton/day), is incinerated. Our feasibility assessment focused on identifying three promising scenarios for replacing incineration at GLWA with HTL. Furthermore, one of the scenarios was compared from an environmental and economic perspective with two other sludge management options (current GLWA sludge management practices and the replacement of the incinerator with AD). Current GLWA sludge management practices GLWA generates 320 dry ton of sludge per day. 240 dry ton/day of sludge is being converted in class A-EQ biosolids for land application through a thermal process and the rest (80 dry ton/day), is incinerated. Our feasibility assessment focuses on replacing the incinerator with HTL. Task 1: Availability and detailed characterization of waste streams The number of multiple types of organic wastes was quantified in the City of Detroit and its surroundings (Table 1). Samples of different types of wastes were characterized by Pacific Northwest National Laboratory (PNNL) to evaluate them as a substrate for HTL. For each waste PNNL evaluated its pumpability and the solids and ash percentage. Furthermore, Proximate, FAMES and ICP analyses were conducted on the different wastes collected. This data was used for subsequent tasks related to HTL modeling, and economic and environmental assessment. Task 2: Community engagement (hearing from the community and professional stakeholders) We performed two separate workshops: (1) a community workshop with neighbors from Detroit and (2) a professional workshop with personnel from wastewater utilities and refineries, consultants and waste haulers. These workshops collected relevant data for our environmental and economic analysis. The community workshop identified sustainability metrics that were relevant for the neighbors of the WRRF in Detroit. The workshop also revealed the community's perspective on the HTL co-substrates. For example, the community groups preferred food waste to be diverted to composting instead of HTL, which was taken into consideration when determining the three best scenarios to implement HTL. Furthermore, a survey was sent to the neighbors in Delray (neighborhood close to WRRF) to know their opinion about resource recovery from wastes. Overall, the survey showed that neighbors have a positive perception about resource recovery and HTL (Figure 1). The professional stakeholders expressed benefits and risks HTL can have for their type of industry. The benefits are related to economic incentives of biocrude, the reduction of solids and the potential to destroy emerging contaminants. The risks they expressed were related to the willingness of refineries to accept the crude and the safety and operation of high temperature and pressure systems. Specially, having personnel able to work with such systems are not abundant in WRRFs. Task 3: Economic and environmental analysis Task 3.1: Three most optimal waste-to-energy scenarios involving HTL Based on wet waste resources and logistic analyses in the Detroit area, communication with project team, community groups and stakeholders, and economic and environmental analyses, three blending scenarios made through our selection of optimal waste-to-energy scenarios (see Table 2). Table 3 and Figure 2 show the economic and environmental indicators for the three blending scenarios. As per the GREET model, the potential avoided emissions for food waste and sludge are 1238 and 735 kg CO2e/dry ton, respectively. In the LCOD calculation of scenarios involving food waste, a $36/wet ton tipping fee is assumed for food waste along with the transportation costs associated of delivering food waste to the HTL plant gate. In Scenario 3, 35 dry tons per day of food waste are mixed with 110 dry tons of sludge to generate biocrude. Increasing the utilization of food waste leads to enhancements in environmental indicators like GHG, WI, NRRU, and SW, albeit at the expense of a higher LCOD. Task 3.2: Comparison among current practices, AD and HTL For this task we compared scenario 1 from task 3.1 with GLWA current practices and with a scenario where GLWA replaces the incineration with AD. Table 4 and 5 show the life cycle inventories and the sustainability indicator values, respectively. Compared to AD alternatives, HTL offers better energy efficiency and production, as well as lower levelized disposal costs and water intensity. However, the AD scenario has the lowest greenhouse gas (GHG) emissions among the three scenarios because part of the generated biogas is assumed to heat the digesters, eliminating the need for additional natural gas in the AD process.

Energy recovery and sustainability projects at water resource recovery facilities (WRRF) are typically discretionary and require an attractive return on investment to justify the capital expense. The Inflation Reduction Act (IRA), which provides federal funding for projects that produce renewable energy, dramatically changed financial considerations for energy projects. The certainty of the IRA to provide up to a 50% rebate on qualified capital expenditures means WRRF bioenergy projects that otherwise would not have been attractive have moved forward across the United States. To qualify, construction had to begin before December 31, 2024, creating increased urgency to accelerate project schedules that is novel to our industry. Many WRRFs pursued eligibility by implementing biogas fueled cogeneration (also known as combined heat and power, or CHP) systems to produce renewable electricity and heat on-site. With greater urgency in project schedule comes greater potential for overlooking big picture and fine details that are critical to a successful cogeneration system. Even with IRA rebate, cogeneration can be a big capital investment that hinges on the upside of its O&M benefit, so when they are not designed properly, the consequences can be severe for the owner. This is key to our industry's future, because interest in beneficial use of biogas is surging nationally as more utilities and municipalities implement voluntary climate action plans to reduce near-term greenhouse gas (GHG) emissions. We will see more facilities pursuing energy recovery technologies like cogeneration. OBJECTIVE This manuscript will summarize: 1.The cogeneration system sizing approach recently taken by a large WRRF that all stakeholders can learn from, including: owners, consultants, and plant staff. 2.Evidence for why it's important to size cogeneration systems properly. 3.The array of site-specific factors that drive the sizing and configuration of a cogeneration system. The intent is to give the audience an idea of what questions one should ask if interested in adding cogeneration to their facility. The session will use an evaluation done for the City of Columbus, Ohio (City) Southerly WWTP (SWWTP) Bioenergy Project that includes: 6 MG of digestion, fats oils grease (FOG) receiving facility for co-digestion, and 6 MW cogeneration system, as a case study showcasing the influence of IRA funding on cogeneration system alternatives development. Drivers that are client site-specific include: 1.The City has a climate action plan with aggressive goals to slash GHGs. 2.City staff have familiarity owning and operating a cogeneration system because their sister plant recently installed engines. 3.Life cycle economics are significantly better over the status quo. 4.Adding cogeneration to the Bioenergy Project makes it eligible for IRA Credit. To determine how to best leverage IRA funding, the City considered biogas conditioning and biogas upgrading paired with internal combustion engine or turbine technology (also referred to as 'prime mover'). Although very uncommon, pairing biogas upgrading to renewable natural gas quality with cogeneration was investigated to evaluate the reduced O&M requirements of the engines or turbines and simplification of fuel blending. SIZING APPROACH Goals and objectives must be established, and understanding how they differ helps to manage expectations and decision making as the design progresses. Goals serve as long term aspirations while objectives are requirements that must be met for the system to be deemed functional. Objectives SHOULD be weighted heavier, and oftentimes these aren't identified until the project team drills down into what's required to achieve goals. For the City it was more important that the system had high uptime, but it wasn't a necessary to keep the prime mover loaded 100% 24/7. The City wanted turndown for startup through year 20 biogas production which includes ramping up the FOG program - but they could tolerate some flaring. The heat recovery performance was weighted heavy because this will have a large impact on reducing the natural gas bill and meeting City climate action plan goals. The manuscript and presentation will do a deep dive into the details of matching the cogeneration system's size to the facility's biogas production and heat demands, which include: - Know Your Gas: having a firm handle on biogas production is going to bracket the cogeneration system's operation. The design biogas flow is estimated to be nearly 2,000 SCFM, while the startup minimum flow could be as low as 650 SCFM. - Utilize Your Gas, Big Picture: establish the universe of prime mover size alternatives that could fit the amount of biogas produced (Figure 1). Smaller sizes will be fully loaded early in the design life but may be overtaken by peak biogas flows in future years. Larger sizes can utilize all biogas flows through the design year, but the impacts of turn-down limitations need to be carefully considered. - Dynamic Conditions: understand the distribution, or bell curve, of biogas production, so that we can be confident of how much and how frequently the cogeneration system is loaded. When biogas production falls within the 'gaps' of the cogeneration system's operating bands, this biogas may need to be flared (Figure 2). - Natural Gas Blending: natural gas can be blended with biogas to keep the prime mover loaded in its acceptable operating range, but its not necessarily a 'silver bullet'. Owners that seek to reduce GHGs may not tolerate elevated natural gas consumption. - Heat Recovery: consider how the prime mover heat recovery fits the needs of the facility. Primer mover heat recovery performance can fluctuate throughout the year due to changes in climatic conditions impacting efficiency. EXPORT POWER? Cogeneration systems cannot be sized solely based on estimate biogas production. It needs to be coupled with the facility's electrical demand to capture the full picture of possible restrictions on the cogeneration system's daily operation and overall output. Depending on the frequency and magnitude of electrical demand fluctuations, there can be periods where surplus power is produced, therefore its critical to engage the power utility very early in the design to understand the implications of sending power back to the utility grid. Power utilities may require electromechanical safeguards that increase project cost and complexity. Permits required to export power can be logistically burdensome on the owner and are known to take years for approval. CONCLUSION AND KEY TAKEAWAYS The manuscript and presentation will tell the story of Columbus's cogeneration system sizing approach. Facilities of this size implementing cogeneration are limited, consequently there are invaluable lessons learned and considerations that all stakeholders can learn from. Carefully consider how your digester gas production lines up with the turn-down of the prime mover: this is going to drive operating costs and its especially important if utilizing all produced biogas is a must. The manuscript will include simulated 20-year biogas variability using daily biogas flow data from the SWWTP and similar size facilities to reflect the dynamic operating conditions and turn-down requirements of the cogeneration system. For some owners the recoverable heat can be more valuable than the electricity. For ALL owners, meeting the heat demands of your process IS the first priority. The manuscript will include an analysis that illustrates how SWWTP's heat demands vary season to season and compare prime mover technology heat recovery performance. For the plant-wide electrical system: the devil is in the details. The manuscript will include a deep dive into SWWTP's electrical data (Figure 3) and highlight key considerations of the plant-wide electrical infrastructure that are often overlooked during design. The ultimate outcome is confidence the cogeneration system design provides the City the maximum benefit. For the audience, an inside look at a sizing approach framework that can help our industry pursue successful energy recovery projects.