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.

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.

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%.

Background: The paper will present a case study on thickening impacts when implementing biological nutrient removal (BNR) at the Salt Lake City Water Reclamation Facility (SLCWRF) as part of a $750+ million-dollar plant upgrade. The 48 MGD trickling filter / activated sludge plant is being upgraded to a BNR facility using the Westbank process. The new facility is being constructed in the area that previously housed the sludge drying beds (Figure 1). The upgrade will include new primary sludge thickeners that will be operated as fermenters to provide volatile fatty acids (VFA's) to the BNR facility. The existing rotary drum thickeners (RDT) will continue to be used for waste activated sludge (WAS) thickening. Primary Sludge Thickening: SLCWRF currently uses gravity thickening for primary sludge, but the existing thickeners do not meet current seismic codes and are not sized appropriately to be operated as fermenters. The existing gravity thickeners are also not located in an ideal location at the site in comparison to where the new BNR facility will be located. For initial construction two 67-foot-diameter primary sludge thickeners will be used, designed for the maximum month total suspended solids load. This is based on requiring one in service for the annual average condition, and two for the maximum month condition. Under average conditions, the solids retention time (SRT) will be 6 days with two primary sludge thickeners in operation and 3 days with one out of service. These SRTs are considered adequate for volatile fatty acid generation for the biological phosphorus removal process. The site layout also accounts for space for two future gravity thickeners to allow for future plant expansion. The new gravity thickeners are under construction as shown in Figure 2. WAS Thickening Four existing RDTs, as shown in Figure 3, were installed in the last ten years and will continue to be used to thicken the WAS from the new BNR process. Each RDT is rated for 400 gpm and the building includes space to add a fifth RDT to allow for future expansion. The RDTs are used to increase the WAS concentration from an average of 0.5 percent total solids (TS) to approximately 5 percent TS. RDT filtrate will be pumped to the new WAS gravity thickener supernatant pump station, using the existing filtrate pumps. After being combined, the two supernatant streams will be pumped to the primary clarifiers. The RDT sludge will be pumped to the existing digesters for stabilization, using the four existing sludge pumps. Reusing the existing WAS thickening, however, resulted in several challenges for the new BNR facility. These challenges were due to existing issues with the rotary drum thickeners as well as challenges integrating it with the new BNR facility. A first challenge related to the original design intent to implement surface wasting from the BNR which would result in very thin WAS and a high volume that would exceed the capacity of the RDTs. The low TS in the WAS (less than 0.5%) would also derate the capacity of the RDT further exacerbating the capacity issue. Options such as gravity pre-thickening of the WAS were considered initially but was ultimately ruled out since WAS doesn't settle well; this would add additional cost and the gravity pre-thickening may also promote phosphorus release. A second challenge related to the first challenge was meeting design throughput of the existing RDTs (400 gpm) with the current dry polymer set up. When using dry polymer, the RDT's could only run at less than half of the design capacity. Testing with emulsion polymer, however, showed that the design capacity of 400 gpm could be achieved, but this would result in much higher polymer costs. At current WAS loads, the capacity of the RDTs operating with the lower cost dry polymer at less than half design capacity was sufficient for operations, but this would not provide sufficient capacity for design future loadings. A third challenge was maintenance issues with the existing rotary drum thickeners. This included uneven wear on trunnion ultra-high molecular weight polyethylene roller bearings that caused pre-mature failures. After initially replacing only the failed bearings it was found that this would result in other bearing failures. Now when one bearing fails, all are replaced. Several RDTs experienced catastrophic failures involving horizontal cracking in drums at trunnion rollers. The repairs to the RDTs included upgraded materials for stabilizer rollers, sprockets, chain, and base tensioner. Because of these challenges, it is desired to have future unit(s) with bearings outside of wetted parts. Because of the capacity and maintenance challenges, several additional thickening alternatives were considered. This included replacing all of the existing RDTs with a different manufacturer, adding a 5th RDT of a different manufacturer, replacing RDTs with Volute Presses and replacing RDTs with DAFs. The results of the evaluation found that adding a fifth RDT would be the lowest cost option, and that design future capacity could be met with the RDTs if polymer was switched from dry to emulsion polymer. To better evaluate alternatives, SLCWRF pilot tested an alternative RDT and a volute thickener. This pilot testing showed similar performance results as existing RDTs with emulsion polymer. The pilot test also found that capacity was derated when operating with dry polymer but data with dry polymer was limited. After completing the study and pilot testing, several recommendations were developed for future WAS thickening. First, SLCWRF will integrate use of emulsion polymer to increase capacity when needed. Second, a fifth RDT will be added for capacity, when needed, likely with an alternative RDT manufacturer. Finally, SLCWRF will re-evaluate thickening technology when the existing RDTs reach the end of their useful life. Conclusion The experience from Salt Lake City shows the importance of thickening when considering advanced treatment such as BNR. The impacts on technology selection or using existing assets will be important for other utilities which may be considering similar process upgrades.

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.

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

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.

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.

Introduction South Platte Renew (SPR) is the third largest Water Resource Recovery Facility (WRRF) in Colorado, utilizing advanced treatment processes, including Dissolved Air Flotation Tanks (DAFTs). The ongoing DAFT Optimization Study aims to evaluate the feasibility of eliminating polymer dosing to the DAFTs, potentially leading to significant cost savings. Expected to conclude in December 2024, this study could save SPR up to $85,000 annually in chemical expenses. The research is being conducted by SPR staff using internal resources. Main Objectives 1.Evaluate the modifications implemented in DAFT Operations to achieve the elimination of polymer usage. 2.Provide a framework for other WRRFs to use insights from this study, facilitating the operation of DAFTS without the need for polymer. DAFT Background DAFTs are a technology that are used in a WRRF to thicken solids, effectively reducing the volume of water sent to digesters and, subsequently, to centrifuges. By minimizing the water content in the solids before they reach the dewatering stage, DAFTs create a more energy efficient process for dewatering, ultimately producing drier solids that are suitable for agricultural applications. DAFTs operate through a process called dissolved air floatation: air is dissolved in water under high pressure and then released at atmospheric pressure, forming tiny bubbles. These bubbles attach to particles, causing them to rise and form a sludge layer, known as the float blanket, which is skimmed off and sent to the digesters. Remaining solids sink to the bottom and are either recycled back into the DAFTs for additional floatation attempts or send back to the plant headworks. Study Timeline Project Kickoff: September 1, 2024 Phase 1: October 2 -- November 6, 2024 Phase 2: November 6 -- December 4, 2024 Phase 3: Dependent on outcome of Phase 2 Methodology SPR has three DAFTs on the facility, but typically, only one DAFT is in operation at a time. In Phase 1 of the Study, an additional DAFT was brought online to facilitate a comparative analysis. DAFT 4, the control, continues to operate with polymer dosing, while DAFT 3 operates without polymer. This approach limits the impact of operational changes by confining them to only half of the flow, reducing risks to downstream processes. The initial design criteria is shown in Table 1. While the design criteria served as the initial baseline, parameters were adjusted throughout the study to optimize the performance of DAFT 3 without polymer. Phase 1 is currently showing promising results, so the project team has decided to move forward with Phase 2 of the study. In Phase 2, both DAFTs will continue to operate, but neither will receive polymer. This phase will continue to explore the ideal configurations for both DAFTs as they operate without polymer. This phase will also explore the ideal configuration for wasting and recirculating the bottom blanket. Depending on Phase 2 results, Phase 3 may be pursued. This final phase would involve running a single DAFT (as SPR typically operates) without polymer to test the operational limits of the DAFTs. For all three phases of the study, a mass balance will be conducted to track solids flow, as well as an energy balance to assess any changes in energy consumption. Results Throughout Phase 1, the project team has been closely monitoring subnatant total suspended solids (TSS) and float blanket total solids (TS) to assess the effectiveness of the Study. Table 2 provides the TSS and TS values for DAFTs 3 and 4 throughout the duration of Phase 1. The data shows a decreasing trend in subnantant TSS as the Study progresses, indicating that the solids concentration in the subnantant is reducing -- a positive outcome for the Study. This decrease in TSS is attributed to operational changes that have optimized the process. Details of these changes and their direct impacts will be described in detail during the presentation. DAFT 4 demonstrates typical DAFT performance at SPR, while DAFT 3 is showing slightly lower efficiency compared to operations that use polymer. For Float TS, the ideal operation is around 6%, with DAFT 3 averaging about 5.2%, which, while slightly lower than ideal, remains within the acceptable range of 5-6%. Further operational adjustments are planned to bring DAFT 3 performance closer to that of DAFT 4/ normal operation performance. A full analysis of the data and lessons learned from all the phases of the study will be shared during the presentation, offering valuable insight into optimizing DAFT operations without polymer. These findings have the potential to reduce chemical and energy costs and provide a model for other WRRFs to adopt similar practices.

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.

Introduction Anaerobic digestion (AD) is employed for municipal wastewater solids stabilization and industrial and agricultural wastewater treatment generating methane-rich biogas that can be used for renewable energy (Speece, 2008). Specific methanogenic activity (SMA) values (mL CH4/gVSS-d) are often measured to assess the health of methanogenic biomass and one way to increase biogas production is to increase the utilization rates of key substrates and intermediates. Rates are often modelled using the Monod kinetic expressions (Metcalf & Eddy, 2014), and the constants of that expression, the maximum specific substrate utilization rate (km) (mg COD/mg CODx-d), half saturation coefficient (Ks) (mg COD/L), and active biomass fraction (X) (mg CODx/L) are required for each substrate and intermediate in models such as AD Model Number 1 (ADM1) (Batstone et al., 2002). Currently, no practical methods are described in the literature and none are consistently used in the field to measure km, Ks and X (Benn et al., 2024); therefore, default values have been suggested for each substrate or intermediate in ADM1 (Batstone et al., 2006). Alternatively, the values that give the best fit between observed and predicted model output are determined during model calibration and employed (Batstone et al., 2006). However, determining the constant values de novo for a specific anaerobic biomass or determining the range of typical values for a given anaerobic process configuration would be beneficial when attempting to improve process performance or ADM1 modeling (Benn et al., 2023). Furthermore, some constant values vary greatly from one specific biomass source to another (Benn et al., 2024). Therefore, it is hypothesized that kinetic constant values may be correlated with microbial community composition (Venkiteshwaran et al., 2016). The exact identity and number of taxa in an anaerobic digester may dictate, in part, the value of kinetic constants. In this study, values of acetate SMA (SMAac), km (km,ac), Ks (Ks,ac) and X (Xac) were determined for a suite of different methanogenic, anaerobic biomass samples having significantly different microbial communities from different reactor configurations. One goal was to determine appropriate ranges of the constant values to use in modelling. A second goal was to correlate the km,ac, Ks,ac and Xac values with the identity and abundance of acetoclastic methanogens present in the samples and identify potential biomass characteristics (taxa identity, taxa abundance values, biomass source, biomass type, digester type) that associate with high values of km,ac and Xac. Material and Methods Anaerobic biomass samples were collected from seven different full-scale anaerobic digesters including different biomass sources (digesters fed with municipal sludge, beverage wastewater, dairy wastewater, and paper mill wastewater), digester types (complete mix stirred tank reactors, upflow anaerobic sludge blanket, and anaerobic lagoons), and biomass types (granular and flocculent). To measure km,ac, Ks,ac and Xac values, activity tests were performed at 35 °C in triplicate using three subsequent doses of acetate substrate (2 g COD/L each dose) and cumulative methane production over time was measured using an automated respirometer system (Benn et al., 2023). Samples were collected before substrate addition and after each substrate dose for microbial community analysis using partial 16S rRNA gene amplicon sequencing. The km,ac, Ks,ac and Xac values were calculated using the approach described elsewhere (Benn et al., 2024) and SMAac values were calculated using km,ac and Xac values. The Spearman correlation coefficient was computed between km,ac, Ks,ac and Xac values and the relative abundance of acetoclastic methanogens. Results and Discussion The results for km,ac and Ks,ac are within the literature range recommended by ADM1 (Batstone et al., 2002) but the parameters high coefficient of variation values (CV) (km,ac CV = 78.1%; Ks,ac CV = 66.2%; Xac CV = 49.5%; SMAac CV = 90.6%) suggest that specific kinetic parameters vary greatly from one biomass to another and, therefore, it would be helpful to determine them for different anaerobic biomasses (Table 1). Granular biomass km,ac values were significantly higher than those of flocculant samples. Therefore, there are ostensibly fundamental differences between flocculant and granular biomass processes, such as direct interspecies electron transfer, that warrant further investigation. The average granular biomass km,ac value was 29.3 ± 13.6 mg COD/mg CODx-d, 3.4 times higher than the average flocculent biomass km,ac value (p = 7.72E-16). The Ks,ac and Xac values were also higher for granular versus flocculent biomass (p- Ks,ac = 0.003; p- Xac = 0.035). Granular biomass also demonstrated significantly higher SMAac values compared to flocculent biomass (p = 6.14E-12). The average SMAac values for granular and flocculent biomass samples were, respectively, 180 ± 95.8 mL CH4/g VSS-d and 45.6 ± 31.2 mL CH4/g VSS-d. These values are within the SMA range reported in the literature for granular and flocculent biomass samples (Hussain & Dubey, 2017; van Haandel & Lettinga, 1994). A positive relationship was observed between km,ac values and the relative abundance of acetoclastic methanogens in the samples (r = 0.70; p = 1.43E-10) (Figure 1). Weaker relationships were observed for Xac (r = 0.35; p = 4.91E-03) and Ks,ac (r = 0.40; p = 1.05E-03) values and acetoclastic methanogen relative abundance. This may be because relative abundance may be a poor indicator of total methanogen mass and correlation with absolute abundance determined via qPCR or other methods may be more appropriate. The biomass type (granular vs flocculent) was strongly associated with the abundance of acetoclastic methanogens (p = 2.05E-07); for this, granular biomass had significantly higher relative abundance of acetoclastic methanogens (2.42 ± 0.96 %; range of 0.47 -- 4.62 %) than flocculent biomass (1.18 ± 0.52 %; range of 0.36 -- 2.39 %). Strong relationships were observed between SMAac and km,ac values under different Xac conditions (Figure 2), showing that SMAac and km,ac values increase in granular biomass regardless of the active biomass fraction, whereas all the flocculant biomass km,ac values were approximately 8 mg COD/mgCODx-d. Therefore, the identity and acetate utilization rates of different acetoclastic methanogens present (Figure 1) may be more important than Xac to achieve high methane production rates. Conclusion The SMAac and constants (km,ac, Ks,ac and Xac) values using anaerobic biomass samples from seven full-scale digesters determined in this study can inform AD modelling, design, operation, and control. The km,ac, Ks,ac and Xac and SMAac values were significantly higher in granular compared to flocculent biomass. The fundamental kinetic and microbial community differences between flocculant and granular biomass processes warrant further investigation. A positive relationship was observed between km,ac values and the relative abundance of acetoclastic methanogens. This correlation can be used to assess AD function and increase substrate utilization rate and methane production in AD systems. The SMA values reported herein can be used as benchmark values to assess the performance of other flocculant and granular AD systems. Additionally, the range of Monod kinetic constant values reported herein can inform value selection when calibrating ADM1. Acknowledgment The authors thank Mr. Ethan Yen of Black & Veatch for reviewing the draft abstract and for providing comments that helped the authors improve the abstract.