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.

Problem Statement: Wastewater treatment plants (WWTPs) are increasingly challenged to manage biosolids efficiently while meeting stringent regulations, especially for emerging contaminants like PFAS (per- and polyfluoroalkyl substances). Traditional biosolids disposal methods, such as landfill and land application, face restrictions due to environmental concerns. Rising energy costs further compel WWTPs to adopt treatment solutions that maximize energy recovery, reduce emissions, and align with regulatory standards. This study provides a mass and energy balance evaluation of six biosolids treatment technologies-drying, incineration, mesophilic anaerobic digestion (MAD) with post-digestion drying, thermal hydrolysis pretreatment (THP) followed by MAD and drying, and drying prior to pyrolysis or gasification-focusing on energy efficiency, life cycle costs, carbon sequestration, environmental impacts, and PFAS removal potential. Drying of biosolids from 20% to 90% total solids (TS) achieves a 90% reduction in mass, improving biosolids handling and transport for downstream processes. However, drying is energy-intensive, requiring approximately 1,000--1,200 BTU per pound of water removed, totaling around 1.76 MMBTU per ton of biosolids (Kreuger et al., 2020). Incineration does not require pre-drying and provides high energy recovery of around 6--8 MMBTU per ton of wet biosolids (Samolada & Zabaniotou, 2014). Operating at temperatures above 800°C, incineration shows promise for PFAS breakdown, though studies are ongoing regarding PFAS fate in ash and emissions. Incineration achieves 90% mass reduction with ash as the final residue. MAD operates with biosolids at 20--30% TS, producing approximately 7.9 MMBTU per ton in biogas energy (Zhou et al., 2019). Post-digestion drying requires an additional 1.76 MMBTU per ton, resulting in a net energy output of around 6.14 MMBTU per ton. While MAD is effective for moderate energy recovery and carbon sequestration, it has minimal impact on PFAS, making it less suited for facilities with strict PFAS requirements. THP + MAD enhances biogas production to approximately 9.0 MMBTU per ton by pre-treating biosolids with high-temperature thermal hydrolysis, which partially breaks down organic matter (Carrere et al., 2016). Combined, THP + MAD yields a net energy output of around 6.54 MMBTU per ton and reduces final digestate mass by 85%. Both pyrolysis and gasification require drying upto 90% TS. Pyrolysis decomposes biosolids into biochar, bio-oil, and syngas, providing stable carbon storage but resulting in a net negative energy balance due to drying (Winchell et al., 2022). Gasification, producing primarily syngas and ash, yields 0.8--1.0 MMBTU per ton and a 90% mass reduction. The ongoing studies need to be finalized to assess and understand the fate of PFAS byproducts in pyrolysis and gasification. Findings and Implications: MAD and THP+MAD are effective for facilities prioritizing moderate energy recovery and carbon sequestration. Incineration offers high energy output with significant emissions control costs. Pyrolysis and gasification, while energy-intensive, provide carbon sequestration and emerging PFAS removal capabilities. This analysis supports WWTPs in selecting biosolids treatment technologies aligned with regulatory, environmental, and energy objectives. Additional Insights on Life Cycle Costs, Environmental Impacts, PFAS Removal, and Carbon Sequestration Potential 1. PFAS Removal Potential - Incineration: Operating at temperatures above 800°C, incineration shows promise for PFAS breakdown. Studies are ongoing to assess the fate of PFAS and resulting compounds in ash and emissions (Samolada & Zabaniotou, 2014). - Pyrolysis and Gasification: High temperatures in pyrolysis and gasification may break down PFAS, but research is investigating the environmental fate of resulting byproducts in biochar (Winchell et al., 2022). 2. Life Cycle Cost Analysis - Drying: High operational cost due to drying energy demand (1.76 MMBTU/ton). Costs can be reduced with heat recovery systems (Kreuger et al., 2020). - Incineration: High initial capital and emissions control costs, but the significant energy output can provide a return on investment in high-throughput facilities (Samolada & Zabaniotou, 2014). - MAD + Drying: Moderate capital and operational costs; biogas revenue can offset drying energy costs (Zhou et al., 2019). - THP + MAD: Higher initial costs with THP, which improves biogas yield, making it favorable for facilities facing stricter regulations (Carrere et al., 2016). - Pyrolysis/Gasification: High operational costs for drying and emissions control, with net negative energy due to drying demands. Suited for facilities prioritizing PFAS destruction and carbon sequestration. 3. Environmental Considerations and Carbon Sequestration Potential - Carbon Sequestration: Pyrolysis produces biochar, offering stable carbon storage for soil. MAD and THP+MAD provide moderate carbon sequestration through digestate land application (Winchell et al., 2022). - Emissions Control: Incineration and gasification generate emissions requiring control systems, while gasification and pyrolysis emit lower greenhouse gases due to reduced oxidation (Samolada & Zabaniotou, 2014).

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 Greenhouse gas (GHG), such as methane (CH4), nitrous oxide (N2O) and hydrofluorocarbons (HFCs), emissions are considered a major contributor to global climate change which has a substantial impact on the public and environmental health (Hopwood et al., 2008; Gautam et al., 2021). Multiple sources, including the Intergovernmental Panel on Climate Change (IPCC), highlighted that global temperatures have increased between 0.3 - 0.74 degrees Celsius in the past century due to the natural and anthropogenic sources including the GHG emissions (Solomon et al, 2010; Liu et al., 2019). Methane as a GHG has been reported to have 27-29 times higher global warming potential compared to carbon dioxide. According to EPA's 2022 report, the wastewater sector is the fifth largest methane source. For example, the methane emissions from domestic sewage in WWTPs can reach up to 25 Tg-CH4/yr (Wallington et al. 2019). Such estimations were developed based on top-down approaches where average emission factor is used to estimate such emissions. However, a major contributor to such emissions is direct process and fugitive methane emissions such as anaerobic digesters and waste gas burners. Such emissions may vary significantly according to operational conditions and infrastructure integrity. Moreover, there might be additional unexpected sources of GHG emissions that may contribute to the overall emissions from WWTPs. Therefore, the application of sensing technologies can aid in accurate quantification of the methane emissions from the WWTPs where these emissions can be correlated to specific treatment processes. Objectives In the current study, the main objectives are to: (1) utilize a multi-platform sensor approach to detect and quantify the fugitive methane emissions from a WWTP using drone and Optical Gas Imaging (OGI) sensing; (2) identify the hotspots of methane emissions within the wastewater treatment facility based on these different sensing technologies; and (3) determine the overall methane emissions from the treatment facility. Methods and Materials A drone and OGI sensing campaigns were carried out in a local WWTP in Ontario, Canada during the Summer of 2024. The WWTP contains the typical treatment processes including the primary treatment, secondary treatment, anaerobic digesters, biosolids loading facilities, and sludge settling tanks. Worth noting, this WWTP receives high organic loading rates which can significantly increase the methane emissions from the WWTP. During the campaign, the drone was flown to isolate each treatment process through creating flight paths upwind and downwind each process and building. These flight paths are known as the wind curtains where they are selected to be perpendicular on the wind direction at different altitudes around the potential process sources. To effectively capture the methane plumes from emission sources, the wind curtains were flown between 30 to 150 ft upwind and downwind the potential sources and treatment processes. The drone sensing approach generally features a quantification sensor (i.e., open-path laser spectrometer (OPLS)) that can detect methane levels as low as 10 parts per billion (ppb). In general, the flight conditions of the drone require a wind speed range of 4 and 20 mph while maintaining a consistent drone speed approximately 3.0 to 4.0 mph for optimal performance. In addition, an OGI camera was mounted on the drone for detecting the potential leakage within the treatment processes. A hand-held OGI camera comprising a cooled infrared sensor was used to access the areas that cannot be assessed using the drone including the indoor spaces and chambers. The OGI camera detects the methane using three factors: the infrared absorption of the gas aligning with the camera's spectral response, the temperature difference between the gas and background, and the gas concentration meeting the camera's sensitivity threshold. The OGI camera is connected with a gimbal which enables the OGI camera to rotate freely without restrictions. Results According to the outcomes of the drone and OGI campaigns, it was found that there are multiple hotspots for methane emissions within the WWTP. For example, the primary treatment process emitted approximately 8.0 kg-CH4/hr. This can be referred to the high organic loads received in such a treatment plant and mixing primary sludge with thickened waste activated sludge. In addition, the anaerobic digesters, gas burner facility, and sludge handling facilities yielded high emissions that ranged from 2.0 to 19.8 kg-CH4/hr. based on the sludge treatment stages and wind characteristics. For example, the anaerobic digesters had an emission rate of approximately 8.9 kg-CH4/hr. (Fig. 1a). Interestingly, considerable methane emissions were observed around the aeration tanks where the methane emission rate was approximately 3.8 kg-CH4/hr. (Fig. 1b). The activated sludge process in this plant does not entail any anoxic or anaerobic zones. Hence, the high emissions from the aeration basins can be attributed to unideal aeration and mixing conditions (coarse bubble aeration used for mixing and aeration), and/or the circulation of the centrate which is anticipated to be saturated with dissolved methane. A major methane emission spot was found to be the sludge holding tanks. Methane concentrations from such tanks reached more than 60 ppm, highlighting a major fugitive methane emission in the facility. However, there were some challenges in estimating the actual methane emission rates due to low wind speed at this area which ranged between 0.7 to 2.0 m/s that were lower than the recommended values of wind speed for accurate quantification of methane emissions using drone-based sensing techniques. In general, these hotspots were also surveilled using either the drone-based or hand-held OGI camera where the methane plumes were detected and recognized (Fig. 2). Conclusions and summary The current study aimed to accurately quantify the methane emissions from a WWTP using drone-based sensing approach to assist in calculating the methane emissions rates from various treatment processes. The methane emission quantification campaign at the WWTP demonstrated the efficacy of drone-based sensing combined with OGI cameras for detecting and measuring fugitive methane emissions where it provided important insights into the interplay between the treatment processes and methane emissions. The results showed significant methane hotspots near the primary tanks, aeration basins, sludge processing and anaerobic digestion units. This encompasses both anticipated and unexpected emissions sources which can enhance our understanding about the sources of fugitive methane emissions in WWTPs. The advantages of the aerial drone, coupled with the OGI camera, allowed for rapid and comprehensive coverage of the facility, providing accurate spatial emission data. Overall, the campaign underscored the potential of drone and OGI technology as a powerful tool for enhancing fugitive methane monitoring and supporting emission reduction strategies in wastewater operations.

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 Amid the accelerating impacts of climate change, the urgent need to reduce greenhouse gas (GHG) emissions is more critical than ever, yielding commitments from developing countries aimed at achieving net-zero emissions by 2050. While energy sector decarbonization is underway, less attention has been given to direct GHG emissions from essential infrastructure. To this end, the wastewater sector alone contributes approximately 5% of global non-CO2‚ GHG emissions, largely in the form of methane (CH) and nitrous oxide (N2O), which have global warming potentials of 28 and 298 times higher than CO2, respectively [1]. As a prerequisite to mitigation, there has been growing academic and industrial interest in the quantification of the direct, or scope 1, emissions from wastewater treatment plants (WWTPs) -- emissions generated through bioprocesses [2]. The standard method for estimating emissions relies on the current Intergovernmental Panel on Climate Change (IPCC) guidelines, which use a simplified global emission factor (EF). However, this approach lacks the granularity required to capture the actual dynamics of GHG emissions from WWTPs [3]. Recent studies document substantial discrepancies, with observed CH emissions reaching up to 100 times the IPCC's estimated EF [4], and N2O emissions varying over six orders of magnitude [5]. These findings underscore the critical need for site-specific investigations to better understand emissions behavior, identify the factors driving variability, and pinpoint the specific sources contributing to these emissions. Therefore, in this research, we present findings from an ongoing Canadian project monitoring greenhouse gas (GHG) emissions from three full-scale wastewater treatment plants (WWTPs) across Canada. Our multi-level approach combines various advanced measurement techniques, including gas/liquid sensors, optical gas imaging, drone-based sensing, aircraft imaging, and satellite imaging. While previous studies have largely examined emissions variability in relation to treatment technology [5] and plant's size [4], this research attempts to link plant's GHG emissions with influent characteristics, compliance limits, and operational patterns. Treatment plant description and measurements campaign The Canadian wastewater treatment plant featured in this study operates with a typical treatment configuration. The plant comprises primary treatment, followed by the activated sludge (AS) process and, finally, disinfection. Given that there are no nitrogen compliance requirements, the AS process does not incorporate anaerobic and anoxic zones. Secondary sludge undergoes thickening, which is then combined with primary sludge for anaerobic digestion. The digested sludge is subsequently dewatered, and the centrate is returned to the AS process. To enhance settling efficiency, thickened waste activated sludge (TWAS) is mixed with primary sludge (PS) before digestion. To monitor nitrous oxide, two Unisense® sensors were used and located strategically to capture possible variation across the aeration tank. Methane (CH) emissions are quantified using 16 ground-based sensors, complemented by a 3-day intensive measurement campaign employing drone-based and optical gas imaging techniques. Results and discussion For over six months, liquid N2O concentrations were monitored at two locations in the aeration basin: the first and third quarters. As illustrated in Figure 1, median daily N2O emissions were recorded at 2.22 KgN-N2O/day and 2.91 KgN-N2O/day, with only occasional instances exceeding 10 KgN-N2O/day. This corresponds to an N2O emission factor (EF) of 0.005±0.0012 kg N2O-N per kg TN which is substantially lower than the IPCC EF of 0.016 kg N2O-N per kg. This can be referred to the limited nitrogen removal in the plant, Figure 1. This is because the plant does not have ammonia or total nitrogen compliance limit. While prior studies reported higher N2O emissions with incomplete nitrification [6], the present plant was operated at sludge age (3.34±0.65 day) close to the washout of nitrifying biomass which resulted in lower EF. Results of the methane emissions quantification are shown in Figure 2. The average methane emissions from the plant equal to 1293±807 kgCH4/day. This is equivalent to 3.5-4% of gCH4/m3 treated and 2.9-3.1% of the influent COD load. These values are relatively high but are within the typical range reported in literature [4]. Yet, emissions distribution within the plant is interesting. As seen in Figure 2, the highest contributors to methane emissions are the aeration tanks and primary clarifiers which combined contributed to almost 60% of total plant's methane emissions, whereas Digesters and gas burners contributed only 25% of such emissions. The low emissions from the digesters were confirmed by the handheld OGI camera which indicated no detected leakage either from covers or structural cracks. The high emissions from aeration tanks can be referred to several potential reasons. One possible reason can be unideal aeration and mixing, given that coarse bubble aeration is used to do both. This is supported by the low DO levels observed at the first quarter of the tank (below 0.5 mg/L). Another potential source is the centrate return after digesters which can contain high dissolved methane concentrations. Similar observation were reported in prior studies [7]. The high emissions from the primary clarifiers can be potentially explained by (i) high methane concentrations in the received influent, (ii) high TSS concentrations in the influent, (iii) the return of the TWAS and associated high sludge blankets in the primary sludge. The resulting total daily GHG emissions of the plant are estimated to be equivalent to 43.57 metric tonne of CO2. Interestingly, as shown in Figure 3, methane constituted more than 80% of the plant's emission. This is opposing the typical results in the literature where N2O contributes to more than 50% of plant's GHG emissions [3,8]. This is due to (i) compliance limits that do not mandate ammonia removal, (ii) operational decisions such as centrate return, operating at short sludge age washing out nitrifiers, TWAS return, and (iii) received influent that contained high dissolved methane concentrations and high TSS concentrations. Conclusion In conclusion, this study highlights how influent characteristics, operational patterns, and compliance limits can influence GHG emissions from wastewater treatment plant processes. Methane accounted for over 80% of the total emissions, contrasting with typical findings where Nâ‚‚O dominates. These findings emphasize the need for site-specific GHG monitoring and targeted mitigation strategies in wastewater treatment.

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.