Background Biosolids management in the United States is driven by evolving federal and state regulations which shape, not only wastewater solids processing technologies, but also the marketing, distribution, and overall cost to manage the processed biosolids product. In recent years, the impetus of revisions to federal and state regulations has been environmental stressors such as climate change and the presence of Contaminants of Emerging Concern (CECs) in biosolids. In particular, a group of CEC's known as per- and polyfluoroalkyl substances (PFAS), has been the primary focus of the USEPA and has already begun to shape the landscape surrounding biosolids beneficial use and disposal across the country. The USEPA is in the process of finalizing the Biosolids Risk Assessment for PFOS and PFOA in biosolids. The Risk Assessment is part of a multi-stage process to evaluate the need for regulatory guidance surrounding the compound's presence in biosolids. The USEPA is expected to provide draft results for the Assessment before the end of 2024, an unprecedented tactic that does not follow the formal Risk Assessment Process. This analysis will review the draft results, what they mean, and how they are impacting the formulation of new state regulations across the country. In anticipation of USEPA guidance on PFAS in biosolids, a few key states have adopted unique policy changes which have had tremendous impact across the country. This analysis will also review recent changes to state regulations in Michigan, California, Maine, and New York which have each implemented changes in the regulatory framework which guides beneficial use and disposal of biosolids in their respective states and influenced state policy across their regions. The changes to regulations in each state have presented unique opportunities and challenges to utilities as they develop long-term strategies for the management of wastewater solids generated at their respective facilities. As utilities respond to changes in regulations, the landscape surrounding beneficial use and disposal of the end product has and will continue to shift. Objective The USEPA Risk Assessment process will be analyzed to provide context for the draft results to be released ahead of the conference, with a focus on the following objectives: 1.Review the standard Risk Assessment process used by the USEPA to develop Part 503 guidance for the beneficial use of biosolids. 2.Analyze the draft results provided by the USEPA for PFOA and PFOS, adding context to the results by reviewing the risk ratio used to develop the results. 3.Provide a review of the next steps in the Risk Assessment process. Several states have enacted policy updates and changes ahead of USEPA's release of the biosolids Risk Assessment, this presentation will evaluate those changes and show trends on how biosolids management has been impacted focusing on the following objectives: 1.Review which states have implemented PFAS reduction strategies which require sampling and/or provide limits for PFAS in biosolids. 2.Review the process of implementing PFAS reduction strategies in key states such as Maine, Michigan, California, and New York. 3.Compare and analyze the initial draft results of the USEPA Risk Assessment with the existing state regulations surrounding PFAS in biosolids. Methodology In depth research was conducted on the USEPA Risk Assessment process to develop a Risk Assessment Factsheet for WEF. The research conducted will be used to show the historical use of the Risk Assessment process in the formulation of regulatory guidelines surrounding beneficial use of biosolids as well as the existing process used for the evaluation of PFAS in biosolids. Detailed reviews of state regulations surrounding the beneficial use and disposal of biosolids was conducted for key states across the country. Research was analyzed and confirmed by completing surveys with regulators across each state, providing updates to recent regulatory efforts and potential impacts for the beneficial use and disposal of biosolids. Findings and Current Status An analysis of the USEPA Risk Assessment process is used to compare and contract historical applications of the Assessment with the existing process being used to evaluate PFOA and PFOS in biosolids. A summary of key insights follows: 1.High-level review of the USEPA's Risk Assessment shows changes to the process of evaluating results and the need for regulatory changes. The traditional Risk Assessment Process utilizes a Risk Management analysis ahead of releasing draft results of the Risk Assessment. The Risk Management analysis is used to determine the cost-benefit of regulatory changes compared to the risk of exposure to the analyzed chemicals. 2.Reviewing how the draft results were developed based upon USEPA's approach to the Risk Assessment. The USEPA used a deterministic approach to evaluating the risk of PFOA and PFOS in biosolids, a process which produces a single risk value. The risk ratio used during the process focused on risk relative to the farm family. This ratio, paired with the deterministic approach used by the USEPA, will result in draft results showcasing a single value worst-case scenario which may not be representative of typical conditions. 3.Review of Draft Results and Next Steps. Draft results released by USEPA will be reviewed using the research provided in the earlier stages to add context to the results and what the next steps will be for determining the need for PFOA and PFOS limits in biosolids. Regulatory Assessments for each state reveal unique opportunities and challenges associated with beneficial use and disposal of biosolids products driven by historic, recent, and potential future state specific regulations. The guidelines issued by Maine, California, Michigan, and New York each represent unique ways of managing PFAS in biosolids ahead of direction from the USEPA. Each state's approach will be compared and contrasted to the draft results provided by the USEPA. California has focused on source control PFAS and mandated monitoring for PFOA and PFOS in biosolids to show the real-time reduction of PFAS compounds in biosolids as key regulatory efforts are implemented focused on source control. The average concentration of PFAS compounds in biosolids will be compared to the draft numbers provided by USEPA. Michigan set the precedent for PFAS monitoring and limits in the United States, developing the Michigan Model which has received praise from USEPA and influenced surrounding states. The process used to develop and implement the model will be reviewed and compared to other state regulatory efforts such as New York and Maine.

Abstract: There is growing concern related to the potential health impacts of continued application of biosolids, produced during wastewater treatment, to land. These relate to a variety of micro-contaminants such as perfluorinated compounds (PFAS etc), microplastics and other xenobiotic compounds. This has led to a trend in the use of advanced thermal processes such as pyrolysis and gasification, and renewed interest in incineration in a bid to diverge away from land application. However, these processes are energy intensive as they require drying upstream. This paper looks at how thermal hydrolysis, both with and without digestion can make these processes sustainable by reducing energy demands due to fundamental improvements in dewaterability and presents results from research where the technologies have been combined to optimize destruction of micro-contaminants. KEYWORDS Thermal hydrolysis; pyrolysis; micro-contaminants; energy demand; drying INTRODUCTION Thermal hydrolysis (TH), a popular pre-treatment to digestion with approximately 130 facilities worldwide including several in North America, has typically been associated with producing a high-quality biosolids product for land application. In combination with improved digestion performance, elevated dewatering (typically over 30% dry solids) results in less than half the biosolids cake compared to standard digestion. However, less well known is that thermal hydrolysis was initially conceived as a dewatering aid prior to thermal processing. Although thermally-hydrolysed digested cake dewaters well compared to other process trains, previous work has shown that having digestion downstream of thermal hydrolysis actually deteriorates the dewaterability potential of the hydrolysed cake. This can be by as much as 20% points. This has been shown to be due to the reproduction of extracellular polymers as a consequence of biological metabolism. The dewaterability improvements afforded by thermal hydrolysis become of interest with advanced thermal processing. Systems such as pyrolysis and gasification are limited as they are fundamentally dependent on requiring a dried feedstock, typically over 85% solids. Drying of sludge is extremely energy (and subsequently carbon) intensive. Driers usually require 900 -- 1,100 kWhr energy per metric tonne water evaporated. Even with extreme energy recovery this is still orders of magnitude higher than the energy needs of aeration which are considered high and account for half of the energy needs of wastewater treatment. The aim of this work is to highlight the influence thermal hydrolysis has on downstream energy requirements of thermal processing systems with respect to reducing the large energy demands of drying prior to thermal destruction. The work will show the impact of hydrolysis both with and also without digestion on these thermal systems and will look at research work into the impacts of hydrolysis on outputs of pyrolysis. This work is based on a variety of aspects. A study was set up to determine the influence of thermal hydrolysis and operating conditions, with and without digestion on dewaterability and ultimately on drying and advanced thermal processing. The study was a combination of theoretical determinations based on site-data, data collection from multiple sites and analysis, investigation of full-scale operating plants which combined thermal hydrolysis with thermal processing, and a review of literature on combining thermal hydrolysis with advanced thermal processing looking at the impacts of thermal hydrolysis on pyrolysis. As an example of a full-scale facility, thermal hydrolysis was installed on half of the produced waste activated sludge at Psyttalia in Athens, Greece as part of a project to become more energy efficient. Prior to thermal hydrolysis installation, sludge was digested and dried in 4 drum driers to 93% dry solids. Biogas produced from the site was diverted to the drying plant to meet its energy demand. Following a combination of dewatering optimization with thermal hydrolysis, dewatering improved from 21% to 31% dry solids. The influence of this on the energy demands of the drying plant is shown in Figure 1. Prior to the improvements, almost 75% of the biogas was consumed by drying, and the energy demand reduced by 40%. In combination with more biogas generated via digestion, almost three times additional energy was available for non-drying purposes such as the generation of renewable energy. In this instance the energy required for steam to run thermal hydrolysis, was available via high-grade heat recovered from co-generation. Figure 2 expands that data to look at different hydrolysis configurations combined with hydrolysis without digestion. It is based on the potential impacts on dewaterability as shown in Figure 3. Surplus energy is shown as the energy left after accommodating the energy needs of both drying and thermal hydrolysis. In this instance, thermal hydrolysis placed after digestion -- to redestroy the extracellular polymers, provides the greatest overall energy benefit. In this example, thermal hydrolysis without digestion is assumed to have no biogas benefit. However, other data, at both full- and lab-scale show separate digestion of the liquid fraction of the dewatered cake. Here, cake is at 50% dry solids or above, and biogas is produced from the liquid. Laboratory work has looked specifically at energy recovery from waste activated sludge (WAS) with/without thermal hydrolysis and compared this with energy recovered from separate liquid and solid fractions immediately following thermal hydrolysis combined with dewatering (i.e. with no downstream digestion of the sludge). The results showed approximately 30% increase in methane production from 11 litres to 15 litres produced/litre WAS processed with standard thermal hydrolysis followed by digestion. However, when the WAS was directly dewatered and the liquid and solid fractions were separated, almost as much biogas was produced from the liquid fraction with a further 40% from the solids. In combination this resulted in over 60% more energy recovered compared to absence of thermal hydrolysis. The work then studied at the solid dewatered fraction with respect to combining it with drying and downstream pyrolysis. This work investigated the influence of various operating parameters on the production of char and its energy content. Whilst thermal hydrolysis has been associated with the production of a high-quality biosolids agricultural product, its influence on sludge reduction, and more importantly dewaterability, make it complementary to thermal processes. Better dewatering fundamentally reduces energy needs of drying, and is dependent on the configuration of thermal hydrolysis. Combining thermal hydrolysis, either with or without digestion, with thermal processing can help with the large energy requirements of advanced thermal processing facilities.

Introduction Biosolids management in North America is significantly focused on beneficial use. As reported by the National Biosolids Data Project 2018 (NBDP, 2018), in the United States (U.S.), approximately 5.8 million dry metric tons of biosolids was generated in 2018 by Publicly Owned Treatment Plants (Water Resource Recovery Facilities or WRRFs), of which 53% was beneficially used (see Figure 1). The biosolids comprising Class B, Class A and exceptional quality EPA 503 designations are primarily used for agricultural applications. PFAS and other contaminants of emerging concern in biosolids are an issue that could impact the future of beneficial use as we know it. With existing (Maine, Connecticut) and other states considering potential of land applications bans, Biosolids Managers are considering alternatives to remove PFAS from biosolids. To date, thermal treatment has been identified as a promising pathway for removing PFAS from biosolids. Research has indicated that thermal oxidation (incineration), pyrolysis and gasification show high potential for removing PFAS from the solids. Other technologies, such as hydrothermal liquefaction, deep well injection and supercritical water oxidation (SCWO) are also in the early stages of development. Thermal oxidation has demonstrated that PFAS is removed from the residual and ash (Winchell, 2024). On-going research is evaluating the fate of PFAS in the gaseous phase. Similarly, pyrolysis and gasification can produce a biochar free from measurable PFAS and on-going research is evaluating the fate of PFAS in the gaseous phase (Williams, 2023). The other emerging technologies are thought to destroy PFAS, but research is required to verify this. Thermal oxidation is an established technology with an estimated 80 facilities in operation. In the U.S., thermal oxidation has traditionally been used to process unstabilized solids, specifically as a disposal method, with a few facilities employing external energy recovery, e.g. to produce electricity. Pyrolysis and gasification are well established in other industries with large facilities that use relatively dry feedstocks with large throughputs. However, pyrolysis and gasification are emerging technologies for biosolids management, because of the relatively lower throughput capacities required and the unique physical and chemical characteristics of biosolids causing heat balance and material handling issues. There are a few vendors around the world that are developing systems right-sized for biosolids management. Development of emerging technologies can take 10 to 20 years to reach commercialization. While industry develops and commercializes these technologies, there is a potential gap that needs to be filled to provide alternatives for existing facilities that have invested in technologies to stabilize biosolids for beneficial uses. Thermal oxidation is one such developed technology that can be added to existing technologies to produce a safe end product. Methodology This paper will present three biosolids stabilization technology process trains based on existing case studies (See Figure 2 for an example) that include thermal oxidation and using heat and material balances, demonstrate process viability, as well as compare economics and environmental factors. Process trains (see Figures 3,4 and 5) will include: - Class B mesophilic anaerobic digestion (MAD), dewatering and thermal oxidation - Class B MAD using WAS only THP, dewatering and thermal oxidation - Class A advanced MAD using thermal hydrolysis upstream of AD, dewatering and thermal oxidation Each of the process trains include state-of-the-art fluidized bed (FB) technology with energy recovery and air pollution control equipment that will meet New Source Performance Standards. Economic factors will include capital investment, operating and maintenance costs and life cycle costs. Environmental factors will include Part 503 Regulations, Part 60, Subpart LLLL regulations and greenhouse gas (GHG) emissions. Discussion The discussion will focus on the thermal oxidation technology that is required for the Class B and Class A AD process trains (see Figures 6 and 7), with an emphasis of meeting MACT emission regulations, as well as the results of the heat and material balances. The impact of the energy requirements for adding thermal oxidation will be presented. AD and advanced AD provide the most energy efficient way of converting biomass into recoverable energy through biogas utilization. So, the addition of thermal oxidation will focus on autogenous operation with a dewatered cake that has reduced volatile solids content due to AD and advanced AD. The impact on GHG emissions the biosolids management alternatives by adding thermal oxidation compared to agricultural land application will be reviewed. Specifically, the generation of nitrous oxide (N2O) by FB technology will be discussed and operational methods to reduce emissions will be presented. Closing This paper will be useful to Biosolids Managers, Water Resource Recovery Facility Managers and Consulting Engineers in understanding the immediate future role that thermal oxidation can fill for utilities that operate anaerobic and advanced anaerobic digesters facilities in providing a beneficial end-use for biosolids if land application is not available.

Intensicarb® is a vacuum-based sludge concentration technology, that when installed to intensify anaerobic digestion at a Water Resource Recovery Facility (WRRF) could decrease hydraulic retention times (HRT) while maintaining solids retention times (SRT), providing various benefits towards process intensification. Previous work has demonstrated Intensicarb® feasibility for fermentation intensification (Okoye et al. 2022) and digestion intensification (Khadir et al. 2024) at lab scale as well as its economic feasibility for use as fermentation intensification for onsite WRRF supplemental carbon production (Armenta et al. 2023). This study presents a techno-economic analysis (TEA) of the Intensicarb® process when used to intensify mesophilic anaerobic digestion (MAD) at WRRFs of multiple sizes (10 million gallons per day (MGD), 50 MGD, and 250 MGD of influent flow). Significant reductions of overall lifecycle costs, including reductions in process volume and facility footprint were seen for all 3 facility sizes analyzed. Methodology Three facility sizes were evaluated, based on 10, 50, and 250 MGD influent flows, representing small, medium, and large facilities. This was correlated to digester solids loadings of 11,000, 54,000, and 270,000 lb/day respectively. Four scenarios of increasing intensification were developed and evaluated for each facility size. These scenarios were based on the decoupling of HRT and SRT provided by the IntensiCarb® technology. Average operating SRT was assumed to be 30 days for all scenarios, and the HRT was changed from 30 days (conventional MAD), to 15, 7.5, and 5 days with IntensiCarb®. These were designated as intensification factors (IFs) 1, 2, 4, and 6. Simplified process diagrams showing the conventional MAD process and MAD with IntensiCarb® are shown in Figures 1 and 2, respectively. Flows and loads used in each scenario were developed in Excel (Microsoft), with the assumption that volatile solids destruction was constant over the range of intensification studied (Khadir et al. 2024). Further assumptions are shown in Tables 1 and 2. These parameters were then used to develop the TEA, using a Net Present Cost approach and assuming a 30-year project lifespan. A nominal discount rate of 6% and an escalation rate of 3% were assumed (Construction Cost Index 2019-2022 2022; Guidelines and Discount Rates for Benefit-Cost Analysis of Federal Programs 2023). Costs associated with this TEA were developed based on vendor budgetary estimates for vacuum evaporators from PRAB and IWE, and AD tank mixers from Anaergia. Other equipment estimates, including conventional concrete AD tanks and associated pumps were developed based on previous Brown and Caldwell designs. Operational costs outside of labor, including electrical energy costs for pumping and mixing, sludge heating energy costs, and rehabilitation and replacement costs were developed based on the process modeling outputs and the budgetary estimates outlined above. A sensitivity analysis based on several key unit costs was developed to better estimate lifecycle costs for sites in North America with different operating costs. To simplify the analysis and provide a more conservative estimate of IntensiCarb®'s potential cost savings, two key potential benefits of the IntensiCarb® process were not included in this analysis. These were biogas recovery enhancement, and reduction of nitrogen levels in the sludge (Muller et al. 2024). Additionally, vendor estimates were used to develop physical layouts for all scenarios, which were compared on a volume and footprint basis to determine any physical space savings provided by the Intensicarb® technology. Results and Discussion The results of the TEA indicated significant reductions in process volume and footprint, particularly in larger facilities, leading to potential cost savings. These results are shown in Figure 3. The economic analysis showed that higher intensification factors generally result in lower life cycle costs, with the most substantial savings observed at intensification factors of 4 and 6. However, the benefits diminish at higher intensification levels for midsize plants due to the discrete sizes of evaporator equipment available. Life cycle costs for the 50 MGD facility are shown in Figure 4. The study concludes that IntensiCarb® technology is viable at small, medium, and large scales, with the largest savings seen at IF 6 for all sizes (27%, 26%, 16% NPC savings over conventional MAD seen at IF 6 for the small, medium, and large facilities respectively). Through a sensitivity analysis, key factors driving life cycle costs were identified, with natural gas, electricity prices, and IntensiCarb® facility construction costs causing the most impact on NPC. The baseline values for these costs, as well as their identified upper and lower bounds, are shown in Table 3. Future work should focus on empirical testing and theoretical analysis to refine cost assumptions and explore additional benefits like biogas quality improvement and nutrient recovery.

The City of South Sioux City (SSC), Nebraska, faced a pivotal challenge in wastewater management when the Sioux City, IA Wastewater Treatment Plant (SCWWTP) announced its decision to cease acceptance of wastewater from local heavy industries (e.g., meat packing) . This was compounded by significant flooding in 2019 that damaged local infrastructure, prompted the city to accelerate plans for constructing its own wastewater treatment facility (WWTF). Anaerobic treatment is an ideal fit for high strength wastewaters, and with anaerobic systems comes the need for biogas handling. The City of SSC planned to utilize this resource beneficially, however sulfur quickly became a problem. The City of SSC embarked on constructing a covered anaerobic lagoon (CAL) system integrated with Nebraska's first Aerobic Granular Sludge (AGS) system to effectively manage its industrial wastewater. A site layout illustrated in (Figure 1). The lagoons where to provide pretreatment to the high strength wastewater. Lagoon discharge would then be collected in a wet well and pumped to an aerobic granular sludge system for final treatment, UV disinfection, then finally sent to the Missouri River. The anaerobic pretreatment would generate biogas that could be used beneficially in the WWTF boilers, with future plans to augment the City's natural gas by cleaning the biogas to a renewable natural gas level for injection. During the startup phase of the anaerobic lagoon, biogas was generated with unexpectedly high levels of hydrogen sulfide (H2S), reaching concentrations as high as 2.5% by volume, shown in (Figure 2). These elevated H2S levels overwhelmed the biogas H2S removal system, which utilized a proprietary activated carbon vessel designed to manage lower concentrations. The initial biogas management strategy intended for this gas was to supplement natural gas in a boiler system for heating the anaerobic lagoons, but the challenges presented by the high H2S levels made the biogas unusable in the boilers without a removal system capable of treatment. This led to the question of 'where is the sulfur coming from?'. The background water quality in the area was known to have a high sulfate concentration, and the industries were known to discharge elevated sulfur, however these two sources could only account for approximately 50% of the Sulfur coming into the facility. A sulfur balance was performed, and modeling was done to estimate the fate of the sulfur once it entered the WWTF. A simplified figure shows this balance in (Figure 3). The results lead to discussions with local industries, and the discovery of increased sulfuric acid usage at the industries on site pretreatment to meet the Cities new WWTF's influent FOG limits. HDR worked with the City, the industry, and the Nebraska Department of Environment and Energy to implement a pilot study at the industries pretreatment system. The intent was to reduce sulfuric acid usage to find a reasonable balance between acid usage and FOG discharge limits. Although the results of the pilot study succeeded in reducing sulfur to the WWTF it consequently generated colloidal none settling solids. These colloidal solids were not removed in either the anaerobic or AGS system and cause strain on both the WWTF's UV disinfection system, by reducing UVT, and effluent TSS limits. photos of the settleability testing and Reduced UVT effluent quality are shown in (Figure 4) and (Figure 5). The pilot study was immediately ceased, and the industry agreed to explore alternative acid sources in the future. In response to these challenges, SSC implemented immediate operational adjustments while exploring the economic feasibility of on-site sulfur management strategies. Both liquid phase and gas phase sulfur management strategies were evaluated, resulting in the decision to pursue installation of a more robust biogas chemical scrubber system. This planned upgrade aims not only to improve biogas quality but also to enhance the economic viability of the biogas produced. Future plans include integrating the upgraded biogas treatment system with a third-party renewable natural gas (RNG) facility, enabling further purification and injection into the natural gas grid. This strategic pivot highlights SSC's commitment to sustainability and innovation in its wastewater management practices. This presentation will delve into the technical specifications of the anaerobic lagoon design, the challenges encountered during the startup phase, and the innovative strategies employed to manage biogas quality effectively. It will also provide insights into the operational adjustments made to mitigate the high H2S levels. Additionally, facility operating data is being used to help develop and calibrate a desktop model of the overall sulfur balance around the facility including gas and liquid phase dynamics with variable loadings and operating conditions. This work will contribute to the broader discourse on effective sustainable biogas and sulfur management practices and innovative approaches in wastewater treatment facilities dealing with similar challenges. This study serves as a case study for other treatment facilities aiming to optimize their biogas management strategies while ensuring compliance with environmental standards and promoting sustainable practices in wastewater treatment.

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.

Abstract: Anaerobic digestion of sewage has been practiced over 150 years and results in the production of a methane enriched biogas which is considered a renewable energy source. After processing, biogas can be used directly to produce electricity via a co-generation plant, or following removal of the carbon dioxide within it, be used as a substitute to natural gas, or after compression, vehicle fuel. By displacing fossil-fuels, use of this biogas can help Water Utilities with their quest to become carbon-neutral. However, to make biogas, sludge needs to be anaerobically digested, the biogas cleaned, and the nutrients released to the digestate need to be destroyed. Furthermore, there are direct methane emissions from storage, leaks and incomplete processing. This paper looks to quantify these to determine the carbon impact of using biogas produced from municipal digestion of sewage sludge. KEYWORDS Anaerobic digestion; biogas; biomethane; carbon footprint INTRODUCTION There is increasing concern over the impacts of anthropogenic activities on the climate. This is leading to growing interest in renewable energy as an alternative to fossil-fuels. Biogas, a by-product generated from sewage treatment, is a valuable source of renewable energy. It can be used to generate electricity from engines which displaces energy made elsewhere at a power station resulting in a reduction in carbon footprint. However, to make biogas, sludge has to be anaerobically digested, and both the gas and liquid streams need to be processed (summarized in Figure 1). This processing generates a carbon impact in the form of electricity consumption (for example to mix digesters and to run conveying systems), chemical use (polymers for dewatering and carbon for nutrient removal) and direct methane losses (from storage, incomplete use or processing of the gas). However, the benefits of producing and using biogas are potentially becoming less clear. Globally, a shift towards cleaner forms of energy is making the displacement of energy using electricity derived from biogas less beneficial. Greater reductions of carbon were possible before when 'dirtier' forms of energy, such as coal were being displaced. Now, with cleaner energy mixes, these benefits are eroding. Despite this, direct losses of methane are still being seen. The wastewater sector is a major source of methane emission, contributing to 5--8% of global anthropogenic emissions (Ocko et al, 2021) and traditionally in the UK, open secondary digestion was common to provide additional destruction of pathogens from the wastewater. Recent measurements in the USA showing far greater losses of methane than previously believed (Vasquez, 2023). Methane has a global warming potential of 25 times that of carbon dioxide over a hundred-year period, but there has been emphasis in the industry to use a more realistic 20-year horizon, in which case it is 86 times worse. This means that leaks do not have to be large to offset the benefit of using the biogas in the first instance. For example, the digestion of sewage sludge can typically yield 350 m3 biogas/tonne solids fed to a digester. This is on average 65% methane, and based on its inherent energy, the biogas will have an energy content of 2,400 kWhr. After losses, a third of this energy could be used in an engine to offset fossil-fuel, i.e. 720 kWhr. This would displace 570 kg carbon equivalents of coal. A 1% loss of biogas, i.e. 3.5 m3 would contain 2.3 m3 of methane with a weight of approximately 4.6 kg. Using a 20-year horizon for methane, this has a carbon footprint of 396 kg. For a displacement of 570 kg carbon, therefore a loss of (576/396 =) 1.45% of the biogas would cancel the benefit of using the biogas. Figure 2 shows the contributing factors towards carbon footprint for the various stages on the carbon footprint of biogas used in co-generation, on the grid or as a displacement fuel for gasoline or diesel. This is only referring to the loss of methane. As mentioned, the sludge, biogas and liquid streams derived from biogas generation need processing and these also carry an environmental impact. This paper will go into detail into the processing impacts of biogas production and use, and compare that to the alternatives where digestion is absent, or organic materials are not digested but rather diverted to landfills, in order to provide a greater insight into the influence of anaerobic digestion on reducing carbon pollution. REFERENCES Ocko I. B.; Sun T.; Shindell D.; Oppenheimer M.; Hristov A. N.; Pacala S. W.; Mauzerall D. L.; Xu Y.; Hamburg S. P. 2021 Acting rapidly to deploy readily available methane mitigation measures by sector can immediately slow global warming. Environmental Research Letters, 16 (5). Vasquez, K. (2023) Wastewater treatment releases nearly double the methane that was previously thought, Chemical & Engineering News.

Cambi developed the Thermal Hydrolysis Process (THP) during the 1990's, based on ideas from Professor Halvard Ødegaard (Norwegian University of Science and Technology) and experiences reported from the Zimpro and Porteous processes developed decades prior. The Zimpro and the Porteous processes are sometimes referred to as Hydro-Thermal Carbonization (HTC) and were installed mainly to enhance dewatering. Unfortunately, these processes suffered from both design and operational challenges such as scaling in heat exchangers, odor release and reliability issues. Furthermore, the long holding times at high temperatures resulted in high concentrations of refractory compounds which are formed through caramelization of sugars and Maillard reactions. These reactions caused elevated concentrations of refractory Chemical Oxygen Demand (COD) and refractory Dissolved Organic Nitrogen (DON), and this became increasingly problematic with more stringent water emission requirements. Cambi developed its THP to operate at lower temperatures in order to form less refractory compounds. Most Cambi THP plants operate in the range from 140-165 °C and with 20 to 30 minutes retention time. HTC processes typically have somewhat longer retention times compared to THP and typically operate at or above 180 °C. The goal with the present work was to identify process conditions and develop a process design to improve dewatering properties while keeping formation or refractory compounds at low levels. All experiments carried out in the present work was on thermophilically digested mixed sludge which was treated in a lab-scale THP-pilot at temperatures between 140 and 200 °C for 30 or 60 minutes. Pre-AD-THP has now been widely adopted in several countries and many new plants have been successfully commissioned in North America. The main drivers are often intensification of the digestion process, improved dewaterability, increased biogas production and high-quality Class A biosolids with low odor. On average, the pre-AD-THP improves dewaterability by approximately 8 percentage points compared to conventional digestion. Full scale and laboratory studies shows that post-AD-THP improves dewaterability to a greater extent compared to pre-AD-THP. With post-AD-THP, the increased conversion of Volatile Solids (VS) into biogas and improved dewaterability can reduce the final cake volume by more than 60% compared to conventional digestion. Cambi´s post-AD-THP solution, Cambi SolidStream®, has been demonstrated both in lab scale and in full scale in Germany. The amounts of VS solubilized to soluble COD (sCOD) depends on the type of sludge and treatment conditions. In the present work, solubilization measurements, presented in Figure 2, shows that about 10 to 40 % of VS was solubilized. Previous dewatering experiments carried out by Cambi with a Bucher laboratory scale dewatering setup on sludge from the same plant shows that a final cake dryness in the range from 46 to 57 %DS was achieved after treatment at temperatures within the range from 140 to 212 °C and retention times between 30 and 120 minutes. The highest dryness levels were achieved with the most severe conditions. In SolidStream, most of the sCOD and some of the particulate COD (pCOD) will enter the centrate or filtrate which is returned to the anaerobic digester as shown in Figure 1. Refractory compounds formed through caramelization and Maillard reactions are difficult to degrade in biological processes and typically produce a yellow or brown color. The amounts of refractory compounds formed depends on the type of feedstock and increases with temperature and retention time. Some of the practical consequences for a WWTP are that refractory compounds are not converted into biogas, it may deteriorate the efficiency of UV-disinfection, reduce side stream nitrogen removal efficiency, and such compounds may end up in the final effluent if not removed. There is a link between the extent of formation of refractory compounds and color. In this work, color has been measured as APHA color of filtrate (0.45 µm) as shown in Figure 3. It should be highlighted that this work was carried out on digested sludge. Other work carried out on raw sludge typically shows a relatively larger increase in color already at lower temperatures. This could possibly be explained by the relatively higher concentrations of sugars and proteins in raw compared to digested sludges. While increased biogas production from centrate or filtrate returned to anaerobic digestion is a benefit with post-AD-THP, the main driver is typically improved dewaterability. Capillary Suction Time (CST) is a common measurement which to some extent can give indications on dewatering characteristics. Figure 4 shows the CST values measured on sludge treated at different process conditions. Measured CST decreased with more severe treatment conditions. As shown in Fig.3, color formation is somewhat limited at or below 165 °C and 30 minutes retention time, which are conditions typically used for THP while, it is more pronounced at typical HTC conditions which are at or above 180 °C and 30 min retention time. Furthermore, retention time has a somewhat limited influence on color formation below approximately 160 °C while the influence on CST, as shown in Fig.4, is large. This finding is relevant for the THP system shown in Figure 5. This system includes two energy recovery steps where temperature in the warmest pre-heating step and pressure reduction step is sufficiently high for desired reactions to take place. Cambi is currently delivering one post-AD-THP system in Norway which will be equipped with two energy recovery steps, and which is designed with flexibility for operating with reactor temperatures from about 140 up to 180 °C. Laboratory experiments on sludge from this plant shows that adding retention time in the warm pulper and flashtank helps to decrease polymer demand for final dewatering by around 70% compared to operation with only 40 minutes retention time at 180 °C and no holding time in pre-heating and pressure reduction steps. Results from this work shows that formation of colored compounds can be kept low at conditions typical for THP and that retention time has a large influence on dewatering properties when operating at low temperatures. A possible explanation for the relatively low color formation measured in the present work could be that sugar and protein concentrations are lower in digested compared to raw sludges. Cambi has developed a novel THP design which includes a cold pulper, hot pulper, reactors, hot flashtank and a cold flashtank. The additional retention time in the hot pulper and hot flashtank appears to provide substantial benefits with regards to dewaterability and polymer consumption while the impact on color formation appears to be limited in a post-AD-THP configuration.

As municipalities and utilities chart a sustainable wastewater future through the development of a master plan, they need to evaluate their current and future biosolids and energy management practices amid rising costs and changing regulations and available end use outlets. A detailed evaluation of their short- and longer-term strategies and drivers inform potential pathways forward, which can be a significant undertaking to create a master plan that answers the following questions: 1. What is a sustainable path forward? 2.What are the goals for the utility? How can we meet these goals? 3.What are the current regulatory drivers? What are potential regulatory changes? 4. What are current end use drivers? What are potential future end use drivers? 5. Will the path forward meet these goals and drivers, and does it have flexibility to deal with potential future changes in regulations and/or end use drivers? Regional, state, and local drivers are key considerations and will impact the outcome of a master plan. A solution for a utility in Maine is not the same for a utility in the Carolinas. Similarly, a solution in the Carolinas may not work in Florida. Each region has different drivers. There are regional differences in reaction to market disruptors such as the current concerns with PFAS and other contaminants of concern. Additionally, there is a backdrop of uncertainty across the country as there have been examples of sudden events that have had significant impact on biosolids practices in those regions. In 2022, Maine passed LD-1911 which bans land application or any use of biosolids. A recent lawsuit in Texas filed against one the nation's largest biosolids management companies has cast uncertainty for the future of land application in that state with long range implications unknown. The passage of LD-1911 in Maine had an immediate and lasting effect on biosolids management in Maine and New England. New England has historically had a precarious balance between capacity of biosolids outlets and the supply of biosolids with land application a significant end use for regional biosolids. With the ban on land application utilities are sending solids to a landfill or hauling greater distances to places outside of Maine such as Canada. Within the last four months, tip fees have significantly increased and sometimes, contracts are being cancelled. On the other side of the country, California has its own concerns. California has some of the most stringent air regulations and has enacted a food waste diversion law (SB-1383). Utilities especially those in major cities have significant footprint and truck traffic constraints. Many of these utilities have greenhouse gas reduction and renewable energy goals. Additionally, the State has financial incentives for utilities to produce renewable energy. As there are biosolids outlet options, the long-term focus seems to be on achieving these other goals and looking beyond just producing a Class A or B product. Solids handling tends to be more about diversifying end use options. In the Southeast, like California there are outlets for biosolids. But the availability varies by state. In Florida, the Florida department of environmental protection (FDEP) made revisions to biosolids regulations in response to the passing of Senate Bill 712 (SB-712). This bill aimed to reduce the impacts to Florida's water resources caused by nutrient loading. This resulted in a reduction of Class B and A land application, driving biosolids to landfills, out of state, or production of Class AA biosolids. Historically, North Carolina landfilled biosolids, but now has moved to more beneficial reuse, while, South Carolina continues to have a significant portion of its biosolids going to landfill (National Biosolids Data Project 2018). However, with increasing landfill tip fees and other constraints, there is a driver for land application. This manuscript will review various regulatory and economic drivers that would affect a utility's master plan, strategies to address those drivers and maintain flexibility to reduce long term risk due to potential future market disruptors. It will also include specific examples from recently completed master plans including plans containing the following pictorially depicted roadmaps as shown in Figures 1 and 2.

Introduction The problem of food waste accumulation, combined with the pollution of petroleum-based plastic, presents a significant environmental challenge (Atiwesh et al., 2021, Paritosh et al., 2017). Converting food waste into bioplastics offers a potential solution to these issues by reducing landfilled food waste and replacing traditional plastics with biodegradable alternatives. Haloferax mediterranei (HM), a halophilic microorganism, is notable for its ability to produce the bioplastic poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) while thriving in high-salinity environments, which inherently reduces contamination risks (Meereboer et al., 2020). Previous studies have demonstrated that HM can produce PHBV from food waste in single-batch reactors, yet these systems are inefficient for large-scale industrialization (Wang and Zhang, 2021). The sequencing batch reactor (SBR) system addresses these limitations by enabling semi-continuous production, thereby enhancing economic feasibility and scalability (Allman, 2024). Despite these advantages, research on the long-term stability and operational optimization of SBRs for PHBV production remains limited. This study aims to fill this knowledge gap by investigating the effects of cycle time and volume exchange ratio (VER) of SBR on PHBV production performance. This work presents an opportunity to address both food waste management and plastic pollution challenges in one approach, contributing to a more sustainable and environmentally friendly future. Materials and Methods The food waste used as a substrate in the experiment was processed into digestate through arrested anaerobic digestion, which breaks down complex molecules into simpler, more digestible forms. The digestate was prepared with controlled composition, including organic acids and other nutrient sources, and was diluted to minimize substrate inhibition. The arrested anaerobic digestion was conducted at 35°C with a hydraulic retention time of 12 days and maintained a consistent organic loading rate of 2.5 g volatile solids (VS)/L-day. The PHBV production process was conducted in a 500 mL SBR, with a working volume of 400 mL (Figure 1). Each cycle included phases of feeding, reaction, and discharging, with the cycle time and VER as key variables. The SBR operated at 37°C with aeration and maintained high salinity (156 g/L NaCl) to support HM's growth while minimizing contamination risks. The cycle time was systematically increased from 1 to 12 days in the initial phase, while the VER remained constant at 0.5 (Figure 2). In the subsequent phase, the VER was adjusted from 0.3 to 0.5, with the cycle time determined by HM growth. The experiment included a 450-day continuous operation, making it one of the longest durations reported for HM fermentation. To assess HM growth, total organic carbon (TOC) reduction, and PHBV production, samples were collected at regular intervals and analyzed using various analytical techniques. Cell density was monitored with OD600nm, and PHBV content was measured using gas chromatography following a series of extraction and purification steps. Results 1.Optimal Dilution and TOC Utilization: HM demonstrated substrate inhibition with undiluted food waste digestate, showing no growth or PHBV production. A dilution factor of 2, with an initial TOC concentration of 7 g/L, achieved optimal PHBV yield, maintaining approximately 70% PHBV content and 6% 3-hydroxyvalerate (HV) fraction in the cellular biomass. This condition was chosen for subsequent SBR operations. 2.Growth and Substrate Utilization: Stable HM growth was observed over the 450 days, with optimal cell concentrations achieved at low VERs due to higher retention of HM cells in the reactor (Figure 3A). Substrate utilization showed a direct correlation with cell growth; however, around 2 g/L TOC remained unutilized, which was hypothesized to be linked to product inhibition (Figure 3B). 3.\PHBV production performance: PHBV cellular content stabilized at around 65% for over 450 days without contamination (Figure 4A). The HV fraction in PHBV remained consistently near 15%, aligning with commercial application standards. PHBV titer followed the same trend as HM growth (Figure 4B). PHBV yield declined as VER decreased, likely due to product inhibition (Figure 4C). PHBV productivity followed organic loading rate (OLR) trends, demonstrating that higher OLR increases PHBV production rate (Figure 4D). Discussion The study demonstrates that SBRs provide a viable solution for long-term PHBV production from food waste, maintaining stable production and minimizing contamination risks due to HM's halophilic nature. However, substrate inhibition from food waste digestate and product inhibition in the SBR pose limitations to production titer and yield. The relationship between PHBV productivity and OLR suggests that increasing OLR can enhance productivity, while controlling VER can mitigate inhibitor accumulation, optimizing yield and titer. These findings underscore the importance of managing cycle time and VER to balance microbial growth, product accumulation, and inhibitory effects. This research offers insights into scaling PHBV production sustainably, aligning with industry goals to reduce reliance on petroleum-based plastics. Conclusion This study successfully demonstrates the feasibility of long-term, stable PHBV production by HM using food waste digestate in SBRs over 450 days. By optimizing operational parameters such as cycle time and VER, the study presents a scalable approach for converting food waste into bioplastics, addressing environmental concerns associated with food waste and plastic pollution. Future research should focus on mitigating substrate and product inhibition to enhance industrial applications of this bioplastic production method, contributing to more sustainable waste management and plastic reduction efforts.

WSSC Water recently purchased an Optical Gas Imaging camera to help identify fugitive methane leaks around their facilities on an on-going basis. They are the first wastewater utility to purchase their own OGI camera. This presentation will discuss how they made the business case for purchasing the camera and how they plan to use it on a regular basis. Upgrading biogas to RNG quality for pipeline injection has become an excellent complement to the water reclamation portfolio of renewable products providing an additional, non-rate based, source of utility revenue while simultaneously reducing carbon emissions. While many utilities utilize digester biogas for cogeneration and thermal demands, many continue to flare excess biogas representing a significant waste of a renewable resource. For many decades, Pima County relied on cogeneration CHP while flared excess biogas as needed. That all changed in 2021 when a biogas upgrading facility was installed at the Tres Rios WRF. The 3-stage membrane separation process produces RNG and saleable environmental attributes while achieving greenhouse gas (GHG) emission reductions and generating annual revenues in excess of $5,000,000 for the utility. However, the installation of any new process always presents new challenges. The Tres Rios WRF has instituted a rigorous leak detection program for fugitive methane emissions to address facility worker safety. Reducing fugitive emissions not only ensures worker safety, but also helps prevents loss of potential revenues. To help achieve these goals, Tres Rios utilizes a variety of means for monitoring fugitive emissions including open path LIDAR for outdoor monitoring, acoustic leak detection for pressurized, piping networks, and optical gas imaging cameras for routine inspection of digesters covers and hatches, pressure relief valves and condensate drains and traps.