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Due to the possibility of increasing methane yields, anaerobic co-digestion of fats, oils, and grease (FOG) and municipal solids has become an attractive option to employ at water resource recovery facilities (WRRFs). For many practitioners in the industry, however, the risks associated with anaerobic co-digestion of FOG have overshadowed the many benefits. In recent years, much effort has been given to understanding the chemical and microbial aspects of achieving stable co-digestion of FOG. To date, no full-scale studies have been conducted to understand how current lab-scale research on the topic correlates to FOG co-digestion at scale. To fill this gap within the literature, two 1.36-million-gallon digesters (AD#1 and AD#3) receiving primary solids, thickened waste activated sludge, and FOG were sampled for 10 months. COD and volatile solids (VS) concentrations were measured weekly for influent and effluent streams. Concentrations of short-chain fatty acids were measured weekly within each digester, and concentrations of long-chain fatty acids were measured weekly within each digester and in the FOG holding tank. The methane content of biogas was measured once per week. qPCR targeting the genus Syntrophomonas and 16S rRNA gene sequencing were performed on digester biomass twice per month and once per month, respectively. FOG loading averaged 10.3 and 13.8 % of VS and COD loading, respectively, and reached as high as 24.5 and 35 % of VS and COD loading, respectively. The concentration of short-chain fatty acids, pH, alkalinity, and methane content of the biogas all stayed within ranges that indicate stable and healthy anaerobic digestion. LCFA concentrations within the digester were below inhibitory levels throughout the study despite fluctuations within the mass rate of LCFAs delivered to the digesters. A strong positive correlation was found between % VS destroyed and kg of FOG VS fed per day (Figure 1), indicating that FOG was a relatively easily degradable substrate and enhanced overall % VS destruction. This trend suggests that the co-digestion of FOG could help municipalities meet 503c VS reduction requirements on top of added methane production. Microbial analysis revealed that specific bacterial and archaeal genera shifted based on the concentration of LCFA within the digesters and the mass rate of LCFA fed to the digesters. Relative abundance of Methanospirillum and Smithella were enriched when LCFA concentrations within the digesters increased but remained low during high LCFA loading (Figure 2). Previous studies have identified these genera as important in facilitating stable FOG co-digestion, but this study suggests they are more important in lowering elevated intermediate product concentrations. Increases in the concentration of LCFA within the digesters caused sharp changes to 16S rRNA gene copies of Syntrophomonas (Figure 3). In contrast, increases in LCFA mass rate resulted in slower response times for Syntrophomonas abundance. Fully characterizing major intermediates within the anaerobic food web, especially LCFAs, was pivotal in interpreting microbial ecology data.

Charlotte Water (CLT Water) is the largest public water and wastewater utility in the Carolinas, serving more than a million customers in the City of Charlotte and greater Mecklenburg County. Charlotte Water currently owns and operates five major wastewater treatment plants (WWTPs), treating an average of 78.1 million gallons per day (MGD) of wastewater and is in design for a six plant, the Stowe Regional Water Resource Recovery Facility (WRRF) that will treat flows from the western portion of Mecklenburg County and will also accept and treat flow from two neighboring towns in a bordering county. Charlotte Water oversees one of the largest class B biosolids programs in the Southeastern United States, operating with 17,000 acres of permitted agricultural land in both North and South Carolina and producing over 100,000 wet tons of biosolids annually. In 2013, Charlotte Water working with CDM Smith completed a Biosolids and Residuals Master Plan that consisted of a comprehensive review and evaluation of biosolids and residuals management alternatives and treatment technologies for all CLT Water's Water Treatment Plants (WTPs) and WWTPs (including the future Stowe Regional WRRF). This Biosolids and Residuals Master Plan presented a balanced life-cycle cost-based, environmentally sound, and publicly acceptable approach to meet Charlotte Water's short- and long-term residuals processing needs. The plan revealed several limitations to the Utility's program, including Charlotte Water's need -to transition a major portion of the biosolids program to a Class A product in order to diversify disposal outlet options -to centralize and optimize solids operations to the most extent possible in order to explore and engage more in Nutrient and Resource Recovery efforts The Master Plan identified implementation of a thermal hydrolysis process (THP) coupled with continued operation of existing anaerobic digesters and future thermal drying as the best treatment methods to achieve the desires of Charlotte Water. A 20-year life cycle cost analysis was prepared to compare the implementation of various alternatives for solids treatment and associated end-product management. Regionalization of solids coupled with the implementation of pre-digestion THP showed a lower 20-year life cycle cost by ~$10M. Implementing THP also affords other avenues for revenue generation including possible marketing of the end-product as well as increasing and consolidating biogas production at one facility to allow consideration of selling the gas for offsite uses. The project will be implemented as a phased program aimed at consolidating biosolids treatment at the McAlpine Creek Wastewater Management Facility (WWMF) and will include infrastructure that will convey biosolids from the Stowe Regional WRRF to the McAlpine Creek WWMF for treatment. Planned future phases include extension of the pipeline from Stowe RWRRF to the Irwin Creek WWTP and conveyance of combined Stowe and Irwin solids from the Irwin Creek WWTP to the McAlpine Creek WWMF. Upon completion of the project solids from four of CLT Water's six major WWTPs will be treated at McAlpine to produce a Class A product. This presentation will review and detail the current implementation of the Biosolids Program which will ultimately create a biosolids treatment system at Charlotte Water's largest Water Resource Recovery Facility, the McAlpine Creek WWMF, capable of processing upwards of 175 dry tons/day which is a significant increase compared to current capacity. Much of this capacity will be used to regionalize solids from three of Charlotte Waters other treatment facilities the Irwin Creek, Sugar Creek, and Stowe treatment facilities but will also leave some excess capacity for partnerships with other utilities as well as freeing up the older 4 digesters for other uses including possible future solids treatment capacity expansions.

Introduction As markets and regulations change, so must our approach to biosolids resource recovery. Loudoun Water's Broad Run Water Reclamation Facility (BRWRF), located in Ashburn, VA was first constructed in 2008 and has a total current capacity of 11 million gallons per day. Loudoun Water is currently constructing an expansion of the liquids treatment process to a design flow of 16.5 mgd. The BRWRF sets a new world-wide technology standard for environmental protection and water reclamation. Waste activated sludge is centrifuge thickened, combined with primary sludge for stabilization in anaerobic digesters, and centrifuge dewatered prior to land application as a Class B biosolid product. To anticipate future growth, regulatory changes regarding PFAS, and a shift in appetite from Class B to Class A products, the BRWRF has undertaken planning efforts to expand several treatment processes. As part of the evaluation, Loudoun Water determined that a thermal rotary drum drying system will best prepare the BRWRF for flexibility in future expansion and upgrades as well as provide short-term solids treatment capacity. The approach for identifying and evaluating treatment processes and technologies for the BRWRF involved: -Defining the near-term and long-term boundary conditions -Exploring the world of options relevant to biosolids treatment processes -Evaluating integrated technology solutions that can serve Loudoun Water's near- and long-term needs -Converging on a selected path forward As illustrated in Figure 1, the overall approach is analogous to a sieve analysis whereby each step facilitates convergence towards integrated alternatives that are most applicable to the BRWRF. Boundary Conditions Hazen established boundary conditions to ensure project decisions meet the near-term and long-term needs of the BRWRF for the following criteria: -Environmental discharge -Flexibility for future end use -Biosolids -Energy -Reliability -Resource recovery -Treatment capacity Hazen developed the near-term (up to 2040) and long-term (2040 to 2070) boundary conditions with input from Loudoun Water to ensure that decisions align with the BRWRF-specific vision, and position Loudoun Water for a flexible future. Figure 2 is a graphical depiction of the near-term boundary conditions, and Figure 3 is a graphical depiction of the long-term boundary conditions that the BRWRF will maintain flexibility for in the future. Viability Screening Hazen developed a world-of-options of innovative to established biosolids treatment technologies. The list was narrowed down to technologies viable for BRWRF through a multi-criteria evaluation that scored the technologies on six overarching themes. The biosolids treatment overarching themes included: appetite for innovation, product marketability, sidestream impacts, biosolids/energy co-management approach, long term applicability, and reliability/redundancy. Figure 4 and Figure 5 show the results of the multi-criteria evaluation at this screening stage. Applicability Screening Following the viability screening phase, Hazen evaluated the technologies further for applicability to the BRWRF using the criteria shown in Table 1. Among the screened stabilization technologies, thermal hydrolysis (THP) was initially recommended for sludge pretreatment. THP increases the production of digester gas, reduces the final mass of biosolids for disposal, reduce digester volume and footprint, increase the dewaterability of biosolids, produce a Class A biosolids, and will support the long-term vision for resource recovery and movement towards energy neutrality. During piloting, it was found that the biosolids pretreatment process released high concentrations of nitrogen, phosphorus and COD to the return stream in forms that were not bioavailable for removal in the liquid treatment train, increasing final recalcitrant nutrient concentrations in the effluent. At that time, the project team came to the consensus that THP was not a technology to be evaluated further due to the stringent effluent limits imposed on BRWRF. The screened advanced biosolids treatment technologies were evaluated based on anticipated regulatory requirements regarding emerging contaminants and final product management. Loudoun Water required biosolids treatment to produce Class B biosolids at a minimum; however, flexibility for PFAS destruction in the future was an important consideration. As PFAS is a concern that is developing globally, technologies for PFAS destruction are still undergoing research, and Loudoun Water had a preference to implement technologies that are established in the industry. SCWO was eliminated due to the lack of case studies in which the technology has been implemented successfully. Advanced thermal processing has been implemented in several locations for the purpose of reducing biosolids volume; however, the success of each technology in PFAS destruction is still undergoing R&D. Current results show several data points where PFAS is non-detect in the biochar product. Research is on-going to validate destruction of PFAS in the gas emissions following the thermal oxidation of the produced syngas. Nutrient reclamation was a consideration that was driven by end product marketability. Biosolids fertilizer pellets was considered because it is an enhancement to BRWRF efforts in increased resource recovery. Ultimately, this processing approach was eliminated as the end product did not appear to provide significant economic benefits as compared to the cost required to implement the technology. The two technologies that scored the highest the applicability screening phase include conventional mesophilic digestion and thermal drying. As shown in Table 1, conventional mesophilic digestion is a technology with which the staff are familiar with operation and maintenance. It can be used in conjunction with downstream advanced biosolids treatment technologies to produce a higher than Class B quality end product. Thermal drying was determined to be the most reliable technology that exceeds the near-term minimum boundary condition (production of Class B biosolids) and has potential for expanded beneficial reuse alternatives. Thermal drying can also serve as a prerequisite step to advanced thermal processing. Advanced thermal processing is an enhancement that was determined to be non-critical for implementation as part of the near-term planning. However, it may be considered in the future as a viable long-term technology. Benefit to Cost Ratio Evaluation Hazen performed a benefit-to-cost ratio evaluation on the final two alternatives that were being considered for implementation. The first alternative, in which the entire solids load is digested, is described schematically in Figure 6. The second alternative, including thermal drying, is described schematically in Figure 7. Loudoun Water assigned a level of importance to each criterion shown in Table 2. The most important criteria were ease of operations and maintenance, future flexibility, and regulatory compliance. Figure 8 shows the weighted scoring for the two alternatives evaluated. Although the baseline alternative scores highest in ease of operations and maintenance, the PS only digestion + thermal drying alternative offers greater regulatory compliance and future flexibility than the baseline alternative, which ultimately gives the PS only digestion + thermal drying alternative the highest weighted MCE score. After determining the weighted scores, Hazen calculated the benefit-to-cost ratio for the two alternatives. The benefit-to-cost ratio is the total weighted MCE score (shown in Figure 8) divided by the 20-year net present value. A higher benefit-to-cost ratio reflects a better alternative because more value will be provided for a lower cost. The PS only digestion + thermal drying option was found to have a higher benefit-to-cost ratio compared to the baseline option. Converge The evaluation of technologies converged on a near-term solution that addresses the issue of insufficient capacity, satisfies the near-term (and many of the long term) boundary conditions for BRWRF, and allows for future implementation of long-term solutions. Detailed design will proceed with the near-term solution of digesting only primary solids at a 12-day SRT (minimum), including an excess primary solids bypass only to be used under peak conditions, and constructing a thermal drying system. Because Class A biosolids are achieved in the proposed design, Loudoun Water can defer the decision of how to manage primary sludge digestion beyond the capacity of the existing digesters to a future stage of improvements. Consideration of long-term solutions will advance when regulations and R&D for emerging contaminants develop further.

The need for a circular economy and organic waste diversion regulations aimed at reducing carbon footprint is driving cities and utilities to adopt a holistic resource recovery approach for organic waste streams typically disposed in landfills. These waste streams can range from organic fraction of the municipal solid waste (MSW), pre-consumer waste streams such as those produced by food processing facilities, packaged food and beverages, biosolids produced by water resource and recovery facilities (WRRFs), and organic wastes produced by other City public service departments. States and cities across North America are developing plans and strategies to reduce greenhouse gas (GHG) emissions for climate change adaption and develop a circular (green) economy. The plans typically identify WRRFs as a strategic solution provider for sustainable organic waste management and resource recovery, and to produce value added products such as biogas, renewable natural gas (RNG) and/or compost. WRRFs are typically located in urban environments, in proximity to pre-consumer and post-consumer food waste generation, fats, oil and grease (FOG) waste streams, and have the treatment infrastructure to efficiently process and manage these waste streams. A 2012 Water Research Foundation (WRF) Study concluded that hauling of food waste to municipal WRRFs and utilizing it beneficially for resource recovery through anaerobic digestion (AD) results in reduction of carbon footprint of food waste management, when compared with other commonly adopted industry practices such as landfills and composting. Although the benefits of co-processing of organics waste streams with wastewater solids are uncontested, the adoption of this approach by utilities has been slow. This is primarily due to limited understanding of managing this feedstock, especially pretreatment/conditioning required to make these feedstocks more amenable to process in anaerobic digestion, system design considerations, permitting requirements and plantwide operational impacts. Using case studies summarized below, the authors will share their experience and lessons learned assisting early North American adopters with planning, design, construction, commissioning, and operation of organic resource recovery and co-digestion facilities. 1)Case Study 1 - Oneida County WPCP Energy Independence, Utica, New York: Beginning January 1, 2022, the New York State Food Donation and Food Scraps Recycling Law went into effect. This law prohibits large generators of food waste that produce more than 2 tons per week from disposing of that food waste as solid waste. To help meet the requirements of the recycling law and reduce greenhouse gas emissions, the Onieda-Herkimer Solid Waste Authority partnered with the Oneida County WPCP to process source separated organic food waste slurry in the new anaerobic digesters at the Oneida County WPCP. The Oneida County Solid Waste Facility is located adjacent to the Oneida County WPCP. Under the County's Food2Energy Initiative, the Solid Waste Authority has been able to divert food waste, which makes up approximately 22 percent of the waste stream, away from the Regional Landfill. The co-digestion of food waste slurry with wastewater solids has allowed the WPCP to enhance biogas production and electricity generation onsite. To fully utilize the biogas and eliminate flaring, the County plans to expand its cogeneration facility by installing two new 200 kW microturbines, in addition to three (3) existing 200 kW microturbines. The case study will provide the attendees an understanding of the successful partnership between the Solid Waste Authority and the WPCP, and the benefits to the WPCP to advance its energy independence and reduce its GHG footprint. Exhibit 1 Process Flow Diagram for Oneida County's SSO Pre-treatment and Conveyance 2)Case Study 2 - Central Marin Sanitation Agency Organic Waste Acceptance and Power Generation Program, San Rafael, California The State of California has promulgated several regulations to reduce GHG emissions; most notably SB 1383 promulgated to achieve 75 percent reduction in landfilled organic waste by 2025 and reduce short-lived climate pollutants in California. Beginning 2014, the Central Marin Sanitation Agency (CMSA) entered into a public-private-partnership with Marin Sanitary Service (MSS), a private solid waste service provider, to accept pre-consumer food waste. The pre-consumer food waste is co-digested together with wastewater solids produced by CMSA's WWTP and fats, oil and grease (FOG) collected from the service area. Biogas produced by co-digestion is conditioned and used as fuel in an existing internal combustion engine based cogeneration system for electricity generation. The Organic Waste Receiving Facility (OWRF) has been successfully operational for many years now. Lessons learned through years of experience include high strength waste (HSW, a mixture of pre-processed food waste and FOG) storage limitation at the WWTP, pumping and handling challenges due to high solids content and corrosive nature of the HSW stream, and shredded inorganics in the HSW slurry resulting in operating and maintenance nuisances and high operating costs. The authors are in the process of making improvements to the OWSF to provide dedicated fine screening and storage for FOG to address storage and HSW slurry quality challenges. The case study will provide the attendees an understanding of lessons learned, operational and maintenance challenges, and improvements CMSA plans to make. The other purpose of the improvements is to enhance utilization of available anaerobic digestion capacity to increase biogas production and operate the cogeneration system 24 x 7. The most unpredictable failure has been with hose breakdown for the peristaltic hose pumps. CMSA has averaged approximately six (6) hose replacements per year for the pumps. The following graphic is a process flow diagram of the upgraded OWSF. Exhibit 2 Process Flow Diagram of CMSA's Organic Waste Receiving Facility after Improvements. 3)Case Study 3 - Rialto Bioenergy Facility, California, United States: The Rialto Bioenergy Facility (RBF) processes approximately 700 tons per day (tpd) of organics/food waste recovered from solid waste through anaerobic digestion and 300 tpd of biosolids from external WRRFs into renewable electricity, renewable natural gas (RNG), and fertilizer products. Dewatered cake from external WRRFs and anaerobically digested biosolids is dried in two belt dryer units. The dried biosolids will be processed in a pyrolysis system and converted into syngas, bio-oil and a nutrient-rich biochar. The pyrolysis process is expected to become operational by Q1 2023. The produced syngas would be used to run the dryers, along with the waste heat from the cogeneration system. The pyrolysis oil will be recirculated in the anaerobic digesters to enhance biogas production. This case study will provide the attendees an understanding of how various innovative technologies can be combined to enhance energy recovery and reduce GHG footprint, and preliminary operating data will be presented. The Facility initially became operational in 2020. Exhibit 3 Aerial Image of the Rialto Bioenergy Facility

1) Introduction & Objectives The City of Raleigh, NC (Raleigh) is currently constructing new anaerobic digestion facilities including pre-digestion thermal hydrolysis process (THP) at its Neuse River Resource Recovery Facility. Raleigh has run a successful Class A limed cake program and land applied aerobically digested Class B liquid solids, but the new Class A THP biosolids cake will be a significantly different product. To inform their marketing plans, Raleigh wanted to gain insight from the four existing THP facilities in the U.S. The objectives of this paper are to: Determine the current status of marketing and product development efforts, and lessons learned, -Better understand the characteristics of their products, -Estimate heavy metal and nutrient concentrations for Raleigh THP cake. 2) Methods Details of the four water resource recovery facilities (WRRFs) in the U.S. with operating THP units are shown in Table 1. Telephone interviews were conducted with key staff from each utility covering a range of questions about biosolids treatment and end-use management before and after installing THP. Survey respondents were asked about changes in product characteristics that are attributed to THP, regulatory approvals, odors, additional cake processing, branding and marketing efforts. Utilities also submitted corresponding biosolids lab data. [Table 1. Existing THP Facilities] 3) Results A) Marketing efforts Raleigh is expecting the vast majority of its THP material to be distributed to agriculture initially. While Raleigh has experience marketing limed Class A material, THP cake will be a significantly new product in their region. Market familiarity exists with other Class A biosolids (e.g., compost, pellets) but Raleigh will need to educate former and potential future users on the benefits of applying Class A cake. To inform their marketing approach, Raleigh wanted to have a better understanding of the marketing efforts of facilities with similar material. These are summarized in Table 2. Of note, Medina does not plan to market its material due to the low cost of its land application program (~$15/wet ton), making it difficult to realize a return on investment through marketing. By contrast, DC Water has a well-established marketing program, currently consisting of 5-6 FTEs. [Table 2. Marketing Efforts of Existing THP Facilities] B) Product development efforts Raleigh is exploring options for post-dewatering processing to manufacture products with higher market value and a longer period of use than agricultural land application. The additional processing steps for Class A dewatered cake that have been presented previously are: 1) soil blending, 2) curing, 3) partial drying, 4) composting (Brower, 2018; Smoot, 2021). Blending and curing are generating the most interest among current and future THP facilities. In addition to blending performed on-site by staff, DC Water sells Bloom to soil blenders in the area, which incorporate the material into their blends. HRSD has on-going research looking at blending water treatment residuals with THP cake, with a particular aim to immobilize and/or dilute PFAS, and in the past completed market research pertaining to THP cake and soil blends. The curing process was developed at DC Water, with the assistance of R. Alexander Associates, Inc. (Brower, 2018). Dewatered cake is laid out in long piles and turned periodically, similar to windrow composting. Over the course of several weeks, if protected from precipitation, the less stable organic matter in the biosolids decomposes and the material dries out, creating a product that is easier to handle and is lower odor and more stable when incorporated in soil. HRSD has an on-going curing pilot and is looking to upgrade existing facilities to facilitate on-site curing. C) Heavy metals The heavy metal data obtained from the existing THP facilities before and after installing THP is shown in Table 3. The DC Water data is most illustrative of a change, similar to Raleigh, of a facility going from no anaerobic digestion to THP with anaerobic digestion with the same solids. [Table 3. Heavy metal concentration in biosolids before and after installing THP (mg/kg, dry)] Many of the metals in the DC Water cake increased around 150%, meaning a 2.5-times increase. Table 4 shows the average and maximum concentrations for Raleigh solids from a period in 2020-2021, and those values with a 150% increase. These values are compared to federal and state Exceptional Quality limits. Even the maximum heavy metal values when more than doubled are still no more than 51% of the EQ limit, so Raleigh should not be at risk of exceeding EQ standards. [Table 4. Raleigh Dewatered Cake Part 503 Heavy Metal Concentrations, Apr '20 - Mar '21 (mg/kg)] D) Nutrients Data from other THP plants were used to estimate likely nutrient values in Raleigh cake. Table 5 summarizes previously published nutrient data from WWRFs in Europe, along with data gathered from the existing U.S. installations. [Table 5. Typical properties of thermally hydrolyzed digested biosolids cake from municipal water resource recovery facilities] Based on these data, a range of likely characteristics were estimated for the Raleigh cake (last line of Table 5). HRSD and Oakland County were used to estimate TKN and ammonia as these plants have the most similar treatment to Raleigh. 4) Lessons Learned Marketing Based on the experience of the four existing THP facilities, markets exist for THP biosolids, particularly in agriculture. While cost savings and revenue are possible, resources must be dedicated to marketing efforts and related market conditions must be considered. DC Water is saving well over $1M per year (compared with contracted land application) but estimates 5-6 FTEs support this effort. Medina County is seeing competition for their THP solids, but since they contract their biosolids management they are not able to obtain value reflecting that demand. Product Development Class A designation opens up opportunities for THP solids, including soil blending. DC Water has expanded its blending facility and HRSD is conducting research on blends. DC Water has also found a market for Bloom as a feedstock for external soil blenders. Curing, which Raleigh is exploring, produces a product with the highest market value. Most outlets for Cured Bloom are in bulk, but it is a testament to the quality of the material that it is able to be bagged and has a retail price higher than other bagged amendments. Heavy Metals While the effect of THP on heavy metals through digestion is unclear, the experience of the existing facilities show that heavy metals will not typically concentrate more than would be expected from the conversion of solid organic matter to biogas. Nutrients Existing THP facilities, in the U.S. and Europe, provide a useful guide for typical nutrient levels in THP biosolids; however, each facility is different and nutrient interactions are complex so the true levels will not be known until the digesters reach steady state. Raleigh's cake is estimated to have an NPK of 1.5-2-0 on a wet-weight basis. 5) Conclusions The uncertainty in nutrient levels (a range of +/- 0.5% for nitrogen on a wet-weight basis) can have a dramatic impact in the field. A dewatered cake with a nitrogen concentration of 1% would be applied at a significantly higher application rate than a cake with a nitrogen concentration of 2%. These values are not absolute even for existing facilities. For instance, for Medina cake in 2021 the total Kjeldahl nitrogen and ammonia concentrations varied 40% and 230%, respectively. From a preliminary analysis, it does not appear Raleigh will have an issue meeting Exceptional Quality requirements. The Water Environment Federation (WEF) has a Research and Innovation Committee (RIC) focus group on Improving Pre-digestion Hydrolysis with a sub-group on End-Product Considerations. In initial discussions, this group has expressed interest in exploring the effect of THP on product characteristics, nutrients and heavy metals in more detail. The preliminary results in this abstract could be the starting point for a more detailed analysis of more extensive data from these utilities before and after installing THP to refine these results. Based on the experience of the four existing THP facilities, markets exist for THP biosolids, particularly in agriculture. While cost savings and revenue are possible, resources must be dedicated to marketing efforts. Additional processing, such as curing, can increase market value and open up additional outlets to support broader diversification of end uses.

Introduction Nowadays, there is an increase interest in recovering value-added products, such as volatile fatty acids (VFA), nutrients, and biomethane from the wastewater. Anaerobic digestion (AD) is a promising technology to reclaim energy from organic matter. Generally, methane produced from the last phase of AD is the main beneficial product. However, by excluding the methane-forming stage, valuable organic acids such as VFAs can be produced by anaerobic fermentation (hydrolysis and acidogenesis). However, relatively long hydraulic retention time (HRT) and low VFA yield are the main challenges associated with fermentation technology. pre-treatment technology with fermentation can be one of the solutions. Hydrothermal pre-treatment (HTP) has attracted industry attention as it accelerates the hydrolysis step, removes pathogens, reduces the viscosity of the sludge, facilitates smoother operation, improves dewatering, and improves the quality of biosolids in terms of odor (Taboada-Santos et al., 2019). Also, to increase organic loading rates without compromising biogas production and organics destruction, recuperative thickening, which involves solid separation of the digestate and solids recirculation to the digester, has been used to increase reactor capacity (Cobbledick et al., 2016a, 2016b; Li et al., 2020). On the other hand, other techniques such as vacuum evaporation is used for sludge dewatering (Yan et al., 2009) and it has been also employed for ammonia and volatile recovery (Nguyen et al., 2011) and hydrogen recovery from yeast fermentation broth (Sonnleitner et al., 2012). Applying a vacuum to the fermenter and or digester allows the decoupling of HRT from solid retention time (SRT) and can facilitate the separation and recovery of resources such as ammonia and VFA, while simultaneously enhancing sludge thickening. However, this technology is limited by low VFA production yield and rate. Therefore, the integration of HTP and vacuum fermentation is proposed and investigated. Integration of the HTP and vacuum fermentation is expected to enhance the degree of solubilization and increase the solids reduction. Furthermore, the effects of vacuum on the interaction of hydrolytic bacteria, fermentative bacteria, and acetogenic bacteria are largely unknown and therefore this study evaluates the microbial community changes in a vacuum and conventional fermentation systems and the integration of the HTP system. Materials and Methods Mixed sludge and anaerobically digested sludge from Ashbridge's wastewater plant were used to run four semi-continuous systems. Fours systems shown in Figure 1 include System (1) conventional fermentation fed with raw TWAS and PS; System (2) Vacuum fermentation fed with raw sludge; System (3) Conventional fermentation fed by pretreated TWAS + raw PS; System (4) Novel vacuum fermentation fed by pretreated TWAS + raw PS. Vacuumed high-grade VFAs and fermentate produced from these systems were further tested for biological nutrient removal (BNR) and AD, respectively. The optimum HTP condition obtained from our previous studies was used to pre-treat TWAS only (temperature: 170 °C, holding time: 30 min, pressure 6 bar) (Kakar et al., 2019). Fermentation tests were set up under thermophilic conditions, in a 3 L reactor. Conventional fermenters operated with HRT=SRT=3 days and vacuum-fermentation with SRT of 3 days and HRT of 1.5 days. Genomic DNA was extracted from the biomass using the PowerSoil DNA isolation kit (MoBio Laboratories Inc.). The DNA samples were sent to the Genome Quebec Research and Testing Laboratory in Montréal, Québec for 16S rRNA gene sequencing (Illumina MiSeq). The DNA samples were amplified using PCR for amplicon preparations. The GenPipes version 4.0.0 (Bourgey et al., 2019) amplicon-seq pipeline was used to perform microbial community analyses. All the water quality analysis were measured according to the standard methods. Results Results revealed that hydrothermal pre-treatment integration with vacuum fermentation significantly improves the overall sludge hydrolysis (p>0.005), while its impact on fermentation was not significant. Figure 2 reports the average COD solubilization for all four systems. The figure shows that both vacuum fermentation systems, either fed by raw or pretreated sludge, had almost similar COD solubilization of 29% and 31% solubilization due to fermentation only. On the other hand, vacuum fermentation demonstrated about 30% improvement in COD solubilization compared to the conventional fermentation (24% vs 31%). As shown in Figure 3, pretreated feed demonstrates higher VFA yield for both cases (vacuum and conventional fermenters). Furthermore, feeding raw sludge exhibited superior results for vacuum fermenter compared to the conventional fermenter (See Figure 3). The average VFA yields in conventional reactors for raw and pretreated feed were 0.12 and 0.21 g COD/g VSS added, respectively, accounting for about 47% improvement due to HTP. The application of the vacuum led to a much higher VFA yield in fermentate compared to condensate. The average VFA yield in the steady-state phase for fermentate, condensate, and overall (fermentate + condensate) were 0.22, 0.011, and 0.23 g COD/g VSS added, respectively. Whereas, in the conventional reactor, the average VFA produced (0.125 g COD/g VSS added) was about 45% lower than the overall (fermentate + condensate) in vacuum fermenter. The microbial community results showed that the most abundant type of bacteria was Coprothermobacteraeota, followed by Synergistetes, Thermotogae, and Firmicutes which are mainly anaerobic bacteria growing in thermophilic conditions (55 „ƒ- 70 „ƒ). The vacuum application showed a great impact on the alpha diversity while for all the sample points the ASV for the vacuum reactors was lower than the conventional reactor by 15-20% (See Figure 4). Considering the steady-state data, the average ASV value for the vacuum and conventional reactors of 14 and 16, respectively, it was evidnced that the hydrothermal pre-treatment impacted the diversity of the microbial communities significantly. The dominant type of bacteria found for pretreated samples from both conventional and vacuum fermenters and raw for the vacuum system were Coprothermobacteraeota and Synergistetes, while on the other hand, Thermotogae and Synergestetes were the most abundant phyla for raw-conventional samples. The effluents of four different fermentation systems were tested to be used as a potential carbon source for denitrification. According to specific denitrification rate (SDNR) results using four effluents, the nitrite accumulation spike was lowest with the HTP vacuum condensate treatment, which indicates that the nitrite reduction (denitrification) started early in the bioreactor fed with HTP vacuum condensate. This is consistent with the above-mentioned finding where overall solubilized COD accumulation was highest in the HTP vacuum bioreactor. Nitrite accumulation was relatively fast with the raw vacuum fermentate (which indicates possibly nitrate removal rate was fast in this reactor). Furthermore, results revealed that condensate of the vacuum fermenters with and without pretreatment has the highest SDNR of 7.6 and 7.2 mg NO3-N/g VSS.h, compared to all other samples, and control (acetate, 6.8 mg NO3-N/g VSS.h), respectively. The results from the biochemical methane potential (BMP) tests of the fermentates that were produced from the four fermenters revealed that the integrated HTP and vacuum fermentation promotes hydrolysis and considerably enhance the methane production yield. The results showed that raw conventional fermented samples and raw vacuum fermented exhibited 28% and 36% increases in methane yield compared to raw (non-fermented sample). Additionally, integrating the HTP and vacuum fermentation increased the methane yields by 53% compared to raw (non-fermented sample). Conclusions Integration of vacuum in the fermentation reactor led to increasing the VFA yields by about 40% compared to the conventional fermentation, and it controlled the acid accumulation due to the continuous extraction of VFA from the system. While the integration of HTP with vacuum fermentation led to reducing the required HRT by 50% (from 3 days to 1.5 days), increasing the VFA yields to 330 mg COD/g VSS compared to 210 mg COD/g VSS for conventional (HTP) reactor, a higher degree of solubilization (45%), and enrichment of the thermophilic microbial communities such as Coprothermobacteraeota and Synergistetes phyla.

Raleigh Water has made a significant investment in a Bioenergy Recovery Project at the 75-mgd Neuse River Resource Recovery Facility (NRRRF) to transform management of the City's biosolids. The Project is delivering a new system that will produce a high quality Class A biosolid product for beneficial use as a soil conditioner and renewable natural gas to offset fuel usage in the City's bus fleet. The new process will include sludge thickening, sludge screening, pre-dewatering, thermal hydrolysis, sludge cooling, anaerobic digestion, final dewatering, steam boilers, upgrading of digester gas to produce renewable natural gas (RNG), a sidestream deammonification system and potential future plans to accommodate potential receiving of fats, oils and grease in future. This presentation will focus on the following aspects of the project: - Design phase decision making related to selection of core technology -Maintenance of plant operations during construction -Planning for start-up and commissioning of the new system Design While the core process selection involving advanced digestion with thermal hydrolysis was made early in the project, several other key decisions needed to be made during the design phase to find the best-fit technical solutions to meet Raleigh Water's needs. Some of these key decisions are summarized in Table 1. The full paper will provide details regarding how these key decisions were made to ensure selection of cost-effective and efficient solutions to meet Raleigh Water's goals. Maintenance of Plant Operations (MOPO) During Construction The existing solids process and end use strategy at NRRRF included aerobic digestion of waste activated sludge (WAS) for liquid class B land application, lime stabilization of blended undigested sludge to produce a Class A product and third party composting of primary/WAS dewatered cake. It was vitally important that Raleigh Water maintained the ability to reliably process residuals during the construction period. A detailed MOPO planning exercise was undertaken to overcome various challenges associated with construction phasing and plant operation. Key 'pinch points' included: -The need to continue to process WAS while rehabbing the existing gravity belt thickener building -Continuing the ability to load out dewatered cake despite moving and re-purposing two cake bins to their new location for pre-THP cake storage -The need for continued final dewatering while rehabbing the belt filter press building -Conflicts between the existing lime stabilization system and plans for temporary dewatering Planning to overcome all of these challenges was achieved by the whole team including Raleigh Water staff, the design team of Hazen / B&V and the CMAR contractor, Crowder Construction. Schematics were prepared showing both the existing and new process with each step clearly marked up to show the solids processing route and key modifications to the process. This approach ensured that the whole team understood and was able to consider risks associated with the proposed approach. An example showing moving of the cake bins is provided in Figure 1. The full paper will provide details of the full strategy and key considerations for MOPO during construction, as well as lessons learned through the process. Proactive Planning for Commissioning and Operations Planning for commissioning of the Bioenergy Recovery Project has been a collaborative ongoing effort with monthly commissioning meetings held between the Raleigh Water O&M staff, the design team and the CMAR contractor. A key consideration has been the method for seeding and startup of the digesters and THP process. Because THP heats the feed sludge to a high temperature (killing off microorganisms in the sludge), seed sludge is required. To ensure that the digesters quickly meet Class A requirements, the plans included trucking of seed sludge from the existing THP digestion facility at Hampton Roads Sanitation District. Seeding with both liquid sludge and re-wetted cake were considered as viable options. Ultimately the team selected seeding with 1.0 MG of liquid sludge into Digester 2, to avoid the need for re-wetting of the sludge and the addition of alkalinity lost during dewatering at HRSD. The seeding approach involves the following steps: -Filling Digester 2 to 25 % full with disinfected reuse water -Heating the digester contents using steam injection into the recirculation line -Seeding with 1.0 MG of Class A liquid digested sludge from HRSD -Gradually ramping up feed from THP, based on a target volatile solids organic loading rate (lb of VS added per day per lb of VS in the digester) -Transferring 50% of the sludge in Digester 2 to Digester 1 when Digester 2 becomes full -Continuing to ramp up based on loading rate Projections showing the feed solids and digester levels are provided in Figure 2 and Figure 3 respectively. The final paper will provide an update on plant status based on activities completed in early 2023. Another key aspect of the proactive planning process has been to plan for additional staffing requirements and training needs for the facility, given the increased complexity of the new system in contrast to previous operations. The final paper will outline this transition process and planned staffing and training for the new facility.

Spartanburg Water, through the Spartanburg Sanitary Sewer District (SSSD), owns and operates eight wastewater treatment facilities (WWTFs) throughout Spartanburg County. Sludge generated by the seven smaller facilities are typically hauled to the A. Manning Lynch WWTF (AM Lynch), where it is blended with grease trap waste (GTW) that is also hauled in from around the County, then centrifugally dewatered. The dewatered cake is then hauled to two local landfills. SSSD wanted to take a fresh look at their biosolids management strategy due to: -Rising landfill tip fees and the risk landfills can stop accepting sludge with little notice -Regulatory uncertainty, especially around per- and polyfluoroalkyl substances (PFAS) -Changing biosolids treatment technology landscape A Biosolids Master Plan and Roadmap was developed that compares the current biosolids management approach to a range of potential new technologies and beneficial end uses. The master plan approach first evaluated the local market for biosolids derived products, which informed potential management strategies and technology selections. A detailed evaluation was conducted of SSSD's current and preferred sludge management practices and critical existing processes to customize the alternatives to SSSD's on the ground realities. A large list of alternatives was screened incrementally down to the five most attractive strategies, which then received a cost and non-cost analysis. BC developed an implementation plan that immediately reduces costs and risks to SSSD's sludge management program, while providing flexibility to respond to regulations and market conditions that may further alter the sludge management landscape in the coming years. The result is a Biosolids Master Plan that identifies near-, mid-, and long-term options for biosolids management that are informed by the existing and projected regulations and market demand for biosolids, and customized to SSSD's size, operating budget, and preferences. The plan includes a dynamic roadmap for implementing the selected biosolids management strategies, with timing of selected near-, mid- and long-term strategies informed by various triggers. Biosolids Market Study The biosolids market study shed light on actual demand for different biosolids derived products (compost, dried Class A biosolids, Class B Cake, and biochar) in SSSD's local market. This helped inform the attractiveness of different biosolids management strategies and technologies. Evaluating actual local market conditions first reduced risk and uncertainty around making capital investments to access different biosolids end use markets. In addition to identifying markets for beneficial reuse, the team also evaluated alternative disposal options for SSSD's sludge and separate processing of GTW to improve dewatering operations. Regionalization Considerations Detailed evaluation was conducted to determine sludge production and projections at all plants, and trucking logistics to bring thickened sludge to the centralized solids processing facility at AM Lynch WWTF. The sludge projections and AM Lynch mass balance indicate that the sludge storage tank is running out of capacity to effectively equalize, blend, and decant SSSD's sludge and GTW prior to centrifugal dewatering. By 2025, there will not be enough capacity to equalize average week sludge loads and maintain decant operations. If decant abilities were completely lost, SSSD would have to increase centrifuge weekly run time by 55%, and would experience reduced centrifuge performance (e.g., lower cake solids concentrations), both of which will increase operational costs. Table 1 outlines options to increase sludge storage to allow for reliable decanting in the future and to provide peak week equalization to limit required processing capacity of downstream equipment. Technology Screening Fifteen (15) technologies were identified as being attractive for SSSD. Eight (8) technologies remained after a pre-screening effort, which eliminated any technologies that: -Could not achieve Class A Biosolids -Increased the volume of biosolids to manage -Were embryonic (did not have a successful full-scale municipal sludge installation in the US) Conceptual designs (equipment sizing and site plans), along with pros and cons were presented for the eight (8) prescreened options in the Initial Screening Workshop. At the workshop, the team came to consensus on the five (5) alternatives to advance for detailed evaluation; the alternatives and their reason for selection are summarized in Table 2. Long-Term Alternatives Analysis Lifecycle cost and non-cost analyses were conducted for the five (5) alternatives. Sensitivity analyses were performed on landfill tipping fees, chemical prices, land application cost. Off-site composting by a third party had the best non-cost rating, lowest capital costs, and lowest operating costs of all the options being considered. The biosolids market study determined that compost also had the greatest local market demand. There is also strong interest from two experienced and successful large-scale composters to build a new facility and have SSSD as their main client. For all these reasons, BC recommended moving forward with off-site composting immediately, as it will reduce risk and should reduce biosolids management costs on day one. BC is currently assisted SSSD in releasing an RFP for off-site 3rd party processing services. A summary of considerations for each alternative will be discussed in the manuscript. Biosolids Road Map BC developed an implementation plan that immediately reduces costs and risks to SSSD's sludge management program, while providing flexibility to respond to regulations and market conditions that may further alter the sludge management landscape in the coming years. Near-Term Recommendations (2022-2025): SSSD should focus on diversifying their solids management, improving sludge storage and dewatering at AM Lynch, and monitoring regulations on PFAS. This includes: -Letting an RFP for off-site third-party processing of the majority of SSSD's dewatered cake. -Evaluate third party processing of the GTW accepted and stored at AM Lynch, as well as evaluating centrifuge optimization options. -Build a redundant sludge storage tank to provide required volume for equalizing peak week loads and to continue decanting operations. SSSD is currently moving forward with all of these recommendations. Mid-Term Recommendations (2026-2035): SSSD should re-evaluate this biosolids master plan and make capital improvements necessary for aging equipment. This includes: -A master plan update that evaluates how satisfied SSSD is with the off-site third-party composting contract, provides an updated regulatory landscape regarding PFAS's impact on biosolids beneficial reuse, quantifies the increased costs and risks of trucking sludge (which will inform both sludge hauling to AM Lynch, and trucking of dewatered cake from AM Lynch), as well as an updated evaluation of landfill access/fees and the local biosolids market. -A condition assessment of critical equipment should be included prior to or as part of this master plan update. -Replace the two older centrifuges and their ancillary systems, as well as any other capital improvements identified as part of the condition assessment and master plan update. Long-Term Recommendations (2036-2045): Given the current regulatory uncertainty, and the luxury of pursuing off-site third-party composting to reduce risks and control sludge management costs over the next decade, no significant investments that would alter the sludge handling process at AM Lynch are recommended. The recommendations reduce risks and control costs in the near- to mid-term and buys SSSD time to see how PFAS regulations will unfold, how expensive and restrictive landfill disposal of sludge becomes, and how the many new advanced sludge destruction technologies perform at full scale municipal WWTFs in the US. The long-term recommendations will be decided in the biosolids master plan update schedule for 2029-2030, which will be based on the outcome of the above variables, as well as results of the condition assessment. Capital Improvements Planning: To facilitate CIP planning, three alternative budgets of solids management capital investments were developed associated with these recommendations: 1.Recommended budget assumes off-site composting by a third-party remains the long-term biosolids management strategy for SSSD 2.This alternative budget represents investments needed if market triggers result in SSSD adding a thermal belt dryer at AM Lynch to reduce costs and risks. 3.This alternative budget represents investments needed if regulatory triggers result in SSSD adding a sludge destruction technology at AM Lynch to reduce costs and risks.

INTRODUCTION Water resource recovery facilities (WRRF) have become more and more efficient within their system limits over time. With increasing degree of energy efficiency, further optimization measures are becoming more challenging, especially if the WRRF is understood as an autarkic energy system. Multiple WRRF have already achieved a positive energy balance. Further optimization possibilities consist of smoothing load profiles in order to avoid feeding electricity into the public grid or actively taking part on energy markets. The main option to actively manage loads on WRRF is the combined heat and power plant including the gas storage. It offers good opportunities to decouple energy consumption and energy production, especially since the effects on the waste water treatment performance of the WRRF remains largely unaffected. Nevertheless, gas storage capacities are limited. Especially with increasing size of the WRRF, the storage capacity is only sufficient for a few hours. Fig 1 shows the ratio of gas storage capacity and daily biogas yield for WRRF with different sizes. Energy rich co-substrates with high biological degradability can compensate small gas storage capacities if they are dosed with foresight. In this study different feeding strategies were evaluated and their effects on process stability and dewaterability. MATERIAL AND METHODS Semi-technical investigations were carried out in four identical digesters (37 °C) with a capacity of 20 liters. The feed consisted of municipal sewage sludge (mixture of primary (PS) and surplus sludge, SS) and flotation sludge (FS) from the dairy industry. All digesters were operated with a hydraulic retention time (HRT) of 19.5 d over a period of 2 months. 41 days were evaluated within this study. Fig. 2 shows the experimental set up of the 4 reactors. D4 was solely fed with sewage sludge continuously with an interval of 2 hours. D1 was continuously fed with sewage sludge and additionally once a day with a charge of flotation sludge. D3 was also fed continuously with sewage sludge, flotation sludge was given twice a week. D4 was fed intermittently with sewage sludge and flotation sludge. Operating parameters can be taken from Tab.1. Analysis were conducted according to the analytical methods specified by the German Institute for Standardization. Additionally, dewatering tests were conducted with a filter press, including sludge conditioning with polymers (Kemira) with an amount of 10 mg active substance per g TS. RESULTS and DISCUSSION The share of flotation sludge on the total feed was around 20 w-% for D1 to D3 over the observation time. As the COD content was twice as high in the co-substrate (95,100 mg/l compared to 52,500 mg/l in the raw sludge) and its high degradability the share of the flotation sludge on the total methane gas produced amounted to 35 - 40 %. In D1 gas production rate can be elevated by 81 % within 6 hours or even 112 % within 2 hours (cf. Fig. 2). In D2 gas production rates were elevated by 80 % within 20 hours or 130 % within 4 hours. Maximum rates were reached after 1 - 2 hours after feeding. In Fig. 4 a COD balance over a period of 41 days is displayed. The balance shows the measured values of the COD loads. The degraded COD (COD-deg) was determined by the difference between the COD in the feed (COD-input) and the COD in the output stream (COD-output). To cross check the results, the biogas content was also converted into a COD-load (COD-biogas) using the conversion factor of 0.35 m ³ CH4/kg COD ). D1 and D2 showed the same degradation rates despite having different organic loading rates (OLR) per feeding events (1.5 and 4 g COD/(m ³ d)) due to different feeding intervals and flotation sludge amounts per feed. Overall degradation rate was 66 % respectively 69 % for both reactors. Specific methane production was almost identical. D3 showed a higher specific methane production. Thus, the dry matter content increased in this reactor steadily with this kind of feeding pattern. All reactors were fed with the same moderate loading rate related to the entire observation time. It is known, that famine phases have a major impact on the biocenosis and can stimulate biogas yield which could be an explanation for the higher specific methane production in D3. All digesters were stable regarding the volatile fatty acids (VFA) concentration. Fig. 3 is showing the course of organic acids after feeding the flotation sludge. Depending on the amount of flotation sludge fed a steep increase in the concentration is observed and depending on the amount of flotation sludge fed the maximum gas production rate is reached. Most importantly all reactors reached low concentration after 6 to 12 hours prior to the next flotation sludge feed. Dewatering test showed similar values for D1 and D2, cf. Fig. 5. D3 showed significant lower dewatering properties. CONCLUSION Flotation sludge have a high energy density which is a multiple of the energy density of biogas. It can be used in order to compensate small gas storage capacities when used with foresight. They are able to increase gas production rates within a relatively short time after feeding. Maximum turnover rates are reached for highly degradable substrates after 0.5 - 1.5 hour. Implementing unknown substrates afford a tight monitoring at the beginning to understand kinetics regarding VFA accumulation. Highly degradable substrates will show steep increase in VFA for a defined time. Accordingly, minimum feeding intervals can be defined in order to avoid VFA accumulation. Dewaterability will detoriate using co-substrates especially protein and lipid rich substrates as used in this case. Thus, gains from the additional biogas yield must be weighed against the losses from sludge disposal. Nevertheless, as long as sludge is fed continuously feeding intervals seem to have a minor impact on the dewaterability properties of the digested sludge. In the following the results are going to be set into context of a full scale plant by evaluating data from a WRRF of 350.000 PE (cf. Fig. 6 and Fig. 7).

The State of North Carolina, with its rich diversity, inviting climate, growing population, and substantial natural resources to protect, has been one of the fastest growing states in the Southeastern U.S. in the 21st century. A byproduct of that growth is an increasing volume of residuals and biosolids that are produced, in addition to the other organic by-products of North Carolina's economic activity such as food processing, forestry, farming, and other industries. The paper and presentation will review North Carolina's trends in biosolids management over the last two decades and discuss the emerging trends of energy and resource recovery, which are currently developing in many of the state's metropolitan areas such as Charlotte, Raleigh, Fayetteville, Greensboro, Winston-Salem, Asheville, and Hickory. Lesser known and smaller, but equally innovative projects and local initiatives in the state related to biosolids and organics management will also be discussed. The paper will summarize and compare data from the 1st (2004 data year) and 2nd (2018 data year) National Surveys of Biosolids Regulation, Quality, End Use and Disposal in the U.S., also known as the National Biosolids Data Project (NBDP). Information from the Environmental Protection Agency (EPA), the North Carolina Department of Environment and Natural Resources (NC-DENR), and North Carolina State University (NCSU), among other sources, will also be used to provide an overview of biosolids management for protecting the state's natural resources. A case will be made that biosolids will become greater economic drivers in the future as traditional, fossil sources of fuels and fertilizers continue to increase in cost. See Figure 1. North Carolina reported approximately 123,00 dry metric tons (DMT) of biosolids produced in 2004, increasing to approximately 130,000 DMT in 2018. Over the same period, the amount of biosolids treated to Class A pathogen-reduction standards increased by about 15%, while the amount of Class B biosolids beneficially used on land increased by about 50%. During the same 14-year period, the amount of biosolids incinerated in North Carolina decreased by about 15%, and the amount of biosolids landfilled decreased by almost 60%. Probable reasons and drivers behind these trends will be discussed in the paper and presentation. See Tables 1 and 2. Biosolids land application and composting programs have had a long and largely successful history in North Carolina spanning at least 50 years. Other biosolids processing technologies have entered the picture over the last 20 to 30 years, such as thermal drying, advanced digestion processes (both aerobic and anaerobic), and energy recovery systems. Specifically, the amount of biosolids being thermally dried and marketed in North Carolina has increased substantially during the last two decades, so the thermal drying facilities in North Carolina will be highlighted and discussed. The production and handling of fats, oils & grease (FOG), and septage have also grown substantially during the 21st century. About 75% of FOG and septage produced in North Carolina is land applied on permitted sites, while the remaining 25% is accepted and treated at water resource recovery facilities (WRRFs). The proportion of FOG and septage that is accepted at WRRFs, as opposed to being land applied, continues to increase as North Carolina's cities and water utilities build and expand trucked-waste receiving facilities at their WRRFs. The paper and presentation will also address the regulatory environment and public-acceptance challenges of biosolids and residuals management in North Carolina. Organized groups that voice opposition to the beneficial-use practices continue to remain active in the state. Several water utilities have stepped up their public information programs to proactively counter the opposition groups. The City of Raleigh and Charlotte Water will be cited and described as examples of utilities that have increased their public information and involvement efforts as part of their Environment Management Systems and related programs. Anticipated, future trends that will be discussed in the paper and presentation include: -Increased production of Class A biosolids to create market outlets besides agriculture -More focus on industrial pretreatment to remove micro-pollutants, including microplastics -Development of systems to reduce or eliminate per and polyfluorinated compounds (PFAS) from biosolids -More energy recovery from solids to reduce GHG emissions and net energy use at WRRF's, including production of biochars with little or no measurable micro-pollutants.

BACKGROUND
The Oakland-Macomb Interceptor Drain (OMID) is the main wastewater interceptor that serves nearly 850,000 customers in 25 municipalities in Oakland and Macomb Counties north of Detroit, MI, USA. The Oakland-Macomb Interceptor Drain Drainage District (OMIDDD) operates the approximately 22-mile (35.4-km) unreinforced concrete interceptor that includes piping from 3 feet (0.3 meters) to 12.75 feet (3.9 meters) in diameter, 10 metering facilities receiving flow from contributing community sewers, and the 273-MGD (1,033-MLD) rated capacity Northeast Sewage Pumping Station (NESPS). Upstream of the NESPS, the OMID also receives flow from the Macomb Interceptor Drain (MID) that collects flow from suburbs to the east and is operated by the Macomb Interceptor Drain Drainage District (MIDDD). The MID portion includes about 26 miles (41.8 km) of large-diameter unreinforced concrete interceptor piping, 23 metering facilities, and 2 pump stations. There is corrosion in some locations of the OMID due to sulfuric acid (H2SO4) formed from hydrogen sulfide (H2S). The H2S released from the sewer also results in recurring odor complaints. Hydrogen sulfide release is greatest at turbulent vertical drop manholes where community sewers at higher elevations discharge into the deeper OMID and when control gates are operated during the OMID's unique 'storage and release' practice of flow control. Odor and corrosion issues extend back to the 1970s when the OMID was constructed. Since 2011, the OMIDDD has taken steps to study these issues and initiate mitigative improvements on behalf of ratepayers.

OBJECTIVES
Through both comprehensive studies and mitigation strategies, the OMIDDD seeks to accomplish the following key objectives for the interceptor: -Reduce the rates of corrosion -Cost-effectively extend its operating life -Minimize odor complaints throughout the system Though this paper focuses on the efforts of the OMIDDD, the MIDDD maintains similar objectives with their interceptor. Together, both Districts are working toward complete odor and corrosion control coverage of their combined systems. The Districts currently have active interceptor grouting and lining operations; however, the size of the interceptors makes Contractor mobilization, access, and liner installation a costly effort. With appropriate odor and corrosion control, these lining operations could potentially be limited to specific problematic segments and result in a significant cost savings.

METHODOLOGY
Characterizing the impact of sulfide generation, H2S release, and sewer corrosion required a comprehensive approach. This included reviewing past studies and completing field sampling, sewer process modeling, air dispersion modeling, and fan testing. The extensive data collection program at 17 locations throughout the OMID included liquid-phase dissolved sulfide grab samples and about four weeks of continuous monitoring of sewer differential pressure and vapor-phase H2S concentration using digital monitors. The same sampling effort was completed at 19 locations in the MID; thus, allowing for complete characterization of the large diameter tunnel network. Field sampling, wastewater quality, and hydraulic modeling data were used to develop and calibrate a complete system sewer process model. With this model, multiple conditions that might influence odor generation and sewer corrosion were evaluated: -Dry weather (low flow), -Wet weather from inflow and infiltration (high flow), -'Storage and release' operations -Future phased rehabilitation (e.g., adjusting gate operation frequency/duration for routine Contractor access) -OMID realignment Rates of concrete corrosion predicted by the sewer process model were correlated to prior condition assessments completed using the Pipeline Assessment Certification Program (PACP) ratings and used to approximate remaining pipe life based on the long-term operating strategy of the system up to a maximum allowable concrete loss of 1 inch (25 mm). Concrete loss plots (see example, Figure 1) for the various conditions were created to identify locations along the interceptor alignment most susceptible to deterioration. Process modeling also accounted for 'storage and release' operation, where wastewater is stored in the OMID using flow control (gate) structures. Storing wastewater either for flow management or downstream maintenance access increases detention time, thus generating sulfide. When released either by raising the low-flow sluice gates or overtopping the divider walls in the flow control structures turbulence results in H2S stripping (Figure 2). This pressurizes the H2S-containing odorous air in the interceptor headspace, often leading to off-gassing through ground-level manhole cover pick holes. Sensitivity of ground-level receptors to sewer off-gassing under average dry weather flow and at drop connection manholes was evaluated through air dispersion modeling. The OMID system has relatively few venting locations. Manholes along the interceptors that are spaced relatively far apart (about 1,000 feet, or 300 m) result in low natural ventilation rates. Assuming that the ambient odor impact criteria should be at or below a 7-D/T for 1-hour of community impact 99.5% of the time, air dispersion modeling results characterized the likelihood that an odor control strategy would affect ground-level impacts through management of sewer pressure, H2S, or both. Finally, once the most appropriate odor and corrosion mitigation locations and vapor-phase treatment technologies were identified, field fan testing with sewer pressure monitoring was completed to right-size the future odor control system (Figure 3).

RESULTS AND CONCLUSIONS
This comprehensive approach to evaluating OMID-specific operating conditions enabled the design team to identify the most effective locations and methods to address odor and corrosion. Both liquid-phase and vapor-phase technologies were evaluated through sewer process modeling. Three locations for activated carbon vapor-phase odor control systems were identified. Two systems one actively ventilated and the other passively will be located at flow control gate structures. The third system will be actively ventilated and located at the drop manhole downstream of a community sewer metering facility. Together these systems are expected to address odors and corrosion across most of the OMID. During storage conditions, the vapor-phase systems will not provide continuous control due to headspace constrictions. Likewise, the sizes of the recommended vapor-phase devices will not be large enough to depressurize the sewers for some storage and release events when the release rates are relatively fast and the stored wastewater volumes are relatively high. Process modeling showed that if storage and release events were to be conducted frequently-such as every day-the pipe life could be significantly reduced. However, under normal dry weather conditions, these systems will effectively depressurize the sewers and odors will be effectively mitigated. Corrosion will also be greatly reduced in the main interceptor but may persist at some locations lacking continuously wetted surfaces. These areas may be appropriate candidates for lining. Design has begun at each location, providing unique challenges related to aesthetics, visibility, and site constraints for which unique solutions are being pursued. For example, the community metering station is surrounded by residential homes, therefore requiring concealment that closely reflects the neighborhood (Figure 4). Facility designs will be completed in 2023.

Background The Broad Run Water Reclamation Facility (BRWRF) is owned and operated by Loudoun Water (LW). The BRWRF has a design flow of 11 million gallons per day (mgd) and is an advanced treatment facility that complies with very stringent effluent standards, including monthly average effluent chemical Oxygen Demand (COD), Total Kjeldahl Nitrogen (TKN), Total Nitrogen (TN) and Total Phosphorus (TP) limits of 10 mg/L, 1.0 mg/L, 4.0 mg/L and 0.1 mg/L, respectively at current flows and loads. Currently, liquids treatment at the BRWRF employs primary clarification, 5-stage biological reactor basins and membrane filtration (MBRs) for biological nutrient removal. Granular activated carbon contactors are used as a final polishing step for organic carbon, nitrogen, and phosphorus removal. Solid stream treatment employs anaerobic digestion (AD) for stabilization of primary sludge and thickened waste activated sludge. Stabilized solids are then dewatered via centrifugation. Dewatering and thickening centrate are returned to the liquid stream process without further treatment. Figure 1 shows a schematic diagram of the treatment process at the BRWRF. Motivation As part of planning efforts to increase solids treatment expansion, sludge pre-treatment via thermal hydrolysis (TH) was identified as one of the alternatives that could help Loudoun Water meet solids treatment capacity needs at the BRWRF. TH has the potential to provide the BRWRF with a class A biosolids product while reducing digester volume requirement for solids stabilization. However, evaluating the impact of increased production of potentially non-readily biodegradable organic compounds in the combined THP-MAD process on COD, TKN, TN and TP concentrations in the mainstream as well as the plant discharge was critical, given the stringent discharge requirements. This pilot study was therefore aimed at benchmarking digester and solids process performance with upstream THP, as well as understanding the potential impacts of THP pretreatment on the effluent discharge from the BRWRF. The pilot study was performed over a 15-month period, from February 2021 through May 2022. Set-up and Methods The pilot treatment process included pre-dewatering of blended primary sludge (PS) and thickened waste activated sludge (WAS), followed by TH, AD and post-dewatering to produce the final cake solids. Pre-dewatered solids were diluted to a TS concentration of 10 12% total solids (TS) before batch treatment in a TH pilot unit provided by Cambi ® (shown in Figure 2). Digestion was performed using semi-continuous benchtop anaerobic digesters with a 5-liter working volume (Figure 3), while THP was accomplished using a pilot unit. Pre-dewatering was performed with a pilot-scale screw press, while post-dewatering was performed by a combination of centrifugation and filtration. Digester operation was performed in three phases: -Phase 1 involved digester operation without TH pretreatment, at a 23-day solids retention time (SRT). The digesters were fed with a blend of primary sludge and thickened waste activated sludge (TWAS) at a solids concentration of 4.5%, in line with current, full-scale operations. -Phase 2 involved digester operation with TH pretreatment, at a 23-day SRT. Three TH temperatures were tested in this phase, 135 ºC, 150 ºC, and 165 ºC. The digesters were gradually acclimated to TH over a period of four months. -Phase 3 involved digester operation with TH pretreatment, at a 15-day SRT. This phase mimicked projected full-scale operation with TH at the BRWRF. Similar to Phase 2, three TH temperatures were tested in this phase, 135 ºC, 150 ºC, and 165 ºC. To achieve the target retention time, digester SRT was shortened by half a day on a daily basis, over a one-month period to prevent shock changes to operating conditions. During each phase, digester operation and performance were closely monitored by analyzing pH, alkalinity, volatile fatty acid concentrations (VFA) as well as COD and nutrient species concentrations in samples of the digestate, as well as the post-dewatering centrate. Additionally, biodegradability assays were performed on the centrate to quantify the non-biodegradable fractions of COD, nitrogen, and phosphorus in the centrate recycle. These results helped inform the impacts of the centrate recycle on final effluent COD and nutrient concentrations. Summary of Results Impacts to Anaerobic Digestion Increased solids loading to the digesters (by a factor of 2 or 3 over current loading) was able to achieve same digester SRT with 50 66% lower digester volume in operation. The pilot digesters were able to acclimate to a solids feed treated using TH over a period of 3 4 months through a gradual ramping up of solids and organic loading to ensure that key indicators of digester health (such as pH, VFA, Alkalinity, gas production and solids destruction) continued to remain in optimal ranges. Overall, greater solids destruction and gas production were observed across the combined TH and AD process relative to AD without TH pretreatment. A fundamental shift was observed in digester operational parameters and digestate characteristics. The higher solids and organic loading to the digesters, coupled with increased solubilization of carbon and nutrients in the TH process led to increased concentrations of sCOD and nutrient species in the digesters. The higher solids loading also resulted in higher TS content in the digested solids, increasing from approximately 2.5% to 4.5% TS. TH pretreatment was found to result in the production of increased COD and nutrient species in the centrate, especially soluble COD, TKN and ammonia. Impacts to Centrate Characteristics Concentrations of dissolved organic nitrogen and phosphorus (DON and DOP) in the centrate were also found to be significantly higher with TH pretreatment versus without TH. In addition to an increase in DON, DOP and sCOD, the non-biodegradable fractions of the constituents (i.e., nbDON, nbDOP and nbsCOD) were also higher in the centrate when TH pretreatment was applied. Table 1 shows the difference in post-dewatering centrate characteristics with and without TH pretreatment. €ƒ Impacts on Plant Effluent and Mainstream Data from pilot testing indicated that implementing TH could potentially increase final effluent sCOD concentrations to be in the range of 8 to 12 mg/L. This would trigger a need for additional treatment to meet the monthly average permit limit for COD. Final effluent TKN was estimated to increase to between 0.50 and 0.75 mg/L, which is within 20% of the monthly TKN limit. However, in order to meet TN of 2 mg/L and lower at future flows and loads (i.e., TKN< 0.5 mg/L and TIN < 1.2 mg/L), Loudoun Water may need to implement additional treatment. Final effluent TP was estimated to increase to between 0.02 and 0.05 mg/L. This encroaches upon LW's safety buffer for the monthly TP limit. However, in order to meet effluent TP concentrations of 0.05 mg/L and lower at future flows and loads (i.e., Orthophosphate < 0.02 mg/L and DOP < 0.02 mg/L), Loudoun Water may need to implement additional treatment. Cumulatively, these results suggest that the increases in sCOD, TKN and TP that may result from implementation of TH at BRWRF may present a challenge for meeting current and future permit limits at the BRWRF. Consequently, implementation of TH at BRWRF would likely trigger the implementation of additional treatment for nutrients onsite or diversion of centrate to an offsite facility for treatment or disposal.