Introduction Metro Water Recovery, based in Denver, Colorado, serves 2.2 million population equivalents through the Robert W. Hite Treatment Facility (RWHTF) and the Northern Treatment Plant. RWHTF has a design capacity of 220 MGD and treats an average daily flow of 130 MGD. The facility's solids handling complex includes gravity thickening, grease processing, dissolved air flotation thickening of waste activated sludge, two-phase mesophilic anaerobic digestion, centrifuge dewatering, phosphorus recovery, and biosolids management for storage, hauling, and land application. In 2016, Metro piloted the MagPrex post-digestion phosphorus recovery system (PREX) to address challenges posed by enhanced biological phosphorus removal (EBPR). EBPR results in high concentrations of soluble phosphorus in the digesters, which combines with magnesium and ammonia to form nuisance struvite, causing scaling in equipment, lowering dewatering efficiency, and upcycling phosphorus through the treatment process. In response to stricter effluent TP limits imposed by the Colorado Department of Public Health and Environment (CDPHE), Metro commissioned the world's largest PREX reactor in October 2020. This system allows RWHTF to reliably meet a TP target of 0.7 mg/L, with fewer operational disruptions associated with nuisance struvite formation. Phosphorus Recovery System Overview The PREX reactor is a completely mixed system receiving 600-800 GPM of digester effluent with orthophosphate (OP) concentrations between 350-450 mg/L. PREX quickly transforms OP into struvite by adding magnesium chloride and raising pH through air stripping via coarse air bubble diffusers . The reactor can harvest struvite as a reusable product, with large crystals settling in the reactor cone for separation, Figure 1. Since startup, the reactor has achieved >90% OP conversion, enabling Metro to maintain effluent TP concentrations below 0.4 mg/L. Optimization Objectives While the PREX system has successfully achieved the required OP conversion, opportunities for further optimization quickly became apparent. Initially, only 2% of the struvite formed in the PREX reactor was captured for reuse, and maintenance costs to address nuisance struvite downstream remain high (Figure 2), estimated at over $9,000 per month in labor alone. This study aims to enhance the system design and assess the downstream impacts on centrifuge dewatering, struvite scaling in PREX effluent, and centrate piping. The optimization efforts are guided by three key objectives: 1. Maximize Struvite Recovery: Increase recovery beyond the initial average of 300 lbs/day to meet the reactor's estimated potential of 2,000 lbs/day. This effort investigates changes to process operation and configuration to increase struvite recovery. 2. Minimize Downstream Struvite Accumulation: Address scaling in the PREX effluent and centrate system. Although anerobic digestors have observed a reduction of nuisance struvite, portions of PREX effluent system require a high pressure cleaning every three weeks to remove struvite accumulation. 3. Optimize Residual Magnesium for Dewatering: Evaluation of residual magnesium from the PREX reactor to improve dewatering efficiency by reducing polymer demand and lowering chemical costs. Methods The PREX reactor was operated under various conditions, including adjustments to hydraulic retention time (HRT), pH, and Mg:OP ratios. A 3D multi-phase turbulent model was developed to refine operational settings and predict particle settling efficiency. To assess struvite scaling, ion mass balances were performed on centrate samples collected at two points: upstream at the centrifuge discharge and downstream at the outlet to the sidestream deammonification reactor. These samples were analyzed for OP, TP, magnesium (Mg), and pH. Additionally, soluble and total magnesium concentrations were measured in the PREX effluent and centrate. The relationship between these concentrations, polymer demand, and dewatering performance was explored. Conductivity and zeta potential measurements were collected as potential proxies for cation concentrations, enabling real-time monitoring of dewatering performance. Results 1.Struvite Recovery Optimization The 3D CFD model revealed that only 10% of struvite crystals under 250 μm in size could be captured under typical airflow conditions (Figure 3). Particles with a diameter >700 um had an average recovery rate of 80%. However, over 50% of the struvite produced by PREX was less than 250 μm, significantly limiting recovery. Improvements included adjusting classifier operation such as classifier bed height , introducing dilution water, and recycling classifier overflow. These changes increased struvite recovery from 300 to 1,200 lbs/day. 2.Minimizing Downstream Struvite Accumulation While the PREX system significantly reduced nuisance struvite formation in the digesters, accumulation persisted in the PREX effluent piping due to the presence of small struvite crystals and turbulent flow, which caused localized pH shifts and the precipitation of residual OP, Mg, and NH4. Polyvinylidene fluoride (PVDF) liners are being installed in the effluent lines to reduce turbulence and mitigate scaling. Ongoing ion mass balance sampling will provide further insights, with results to be presented at the conference. 3.Residual Magnesium and Dewatering Performance Maintaining residual magnesium concentrations of 50-60 mg/L reduced normalized dewatering polymer usage per flow by 39%, resulting in chemical cost savings of $800,000 annually (from $2.9 million to $2.1 million) (Figure 4). Conductivity and zeta potential measurements strongly correlated with cation concentrations, indicating their potential use for real-time monitoring and future optimization. Conclusions The optimization of Metro's PREX system demonstrates the potential for substantial improvements in phosphorus recovery and operational reliability. Struvite recovery increased fourfold, highlighting the importance of fine-tuning operational parameters and integrating recycling strategies. Addressing scaling in effluent lines through material upgrades and improved chemistry management will further enhance long-term system reliability. Optimizing magnesium levels improved dewatering performance and delivered substantial chemical cost savings. Potential real-time monitoring using conductivity and zeta potential as proxies for cation concentrations offers an innovative approach to operational control and performance optimization. As phosphorus regulations become more stringent, these advancements position Metro as a leader in sustainable resource recovery. These findings provide valuable insights for other utilities aiming to enhance phosphorus recovery, minimize operational disruptions, and reduce chemical usage, advancing the next generation of phosphorus management for water resource recovery facilities.

Introduction A commercial-scale short-term demonstration of biosolids pyrolysis will be conducted at the Synagro Drying Facility at the City of Baltimore Back River WWTP i, Maryland. The pyrolysis process is designed and supplied by CHAR Technologies, of Toronto, CA. This project aligns with current environmental priorities, particularly the need for PFAS (per- and polyfluoroalkyl substances) mitigation in waste streams. The proposed objectives for this temporary pyrolysis demonstration unit will be: a. Verify the PFAS (synthetic, per- and polyfluoroalkyl substances) characteristics of the biosolids, the Syngas and the Biochar confirming the anticipated PFAS destruction in the pyrolysis process. b. Demonstrate the viability of converting biosolids pellets into valuable by-products: syngas for potential energy recovery and biochar for agricultural or environmental applications.. c. Verify the performance of the pyrolysis process on biosolids continuously for at least six months. d. Verify the resultant Syngas characteristics, and the opportunities and requirements for reusing within the dryer system or upgrading to renewable energy. e. Verify the resultant Biochar characteristics, and suitability for its use as a soil amendment. This six-month demonstration, scheduled from January 2025 to July 2025, aims to provide valuable insights into the operational sustainability and environmental benefits of pyrolysis in biosolids management. Process Description The Pyrolysis Demonstration Unit from Char Technologies uses a pyrolysis process to thermally decompose biosolids pellets in the absence of oxygen; the absence of oxygen prevents incineration from occurring. This pyrolysis process occurs within a rotary kiln chamber with an external burner that after starting-up with propane, burns the Syngas generated during the pyrolysis process. The Char Technologies pyrolysis demonstration unit will process over 8 tons per day of dried biosolids pellets and is projected to produce approximately 143 standard cubic feet per minute of high heating value Syngas containing dust, steam, hydrogen, carbon monoxide, carbon dioxide and methane. The Pyrolysis Demonstration Unit includes Syngas scrubbers that convert the Syngas for internal use in the pyrolysis unit. The excess Syngas that is not used in the pyrolysis process will be combusted, in a thermal oxidizer unit before being discharged at the Demonstration Unit Stack. An isometric of the facility being constructed is presented in Figure 1. A photo of the pyrolysis kiln is provided in Figure 2. A process flow diagram is presented in Figure 3. Sampling and Analytical Methodology Comprehensive sampling and analysis will be performed throughout the six-month demonstration period, with multiple data points collected from key stages of the process. These sampling points are presented in red in Figure 3. Parameters measured include: - Feedstock and Biochar: Elemental and proximate analysis, metals, nutrients, PFAS - Wastewater Analysis: BOD/COD, nutrients, pH - Raw pyrogas, clean syngas, and exhaust gas analysis: hydrocarbons and VOCs, particulates and metals, acid gas, NOx and Sox, PFAS US EPA Method 1633 will be followed to test for all PFAS compounds. Sampling will be conducted at regular intervals to capture variability in process performance. Quality assurance measures, including duplicate and blank samples, will be implemented for data validation. The test methods used for analysis are outlined in Table 1. Results and Discussion We expect to have interim analytical results available by April 2025 for presentation at RBC. Primary discussion will include fate and transformation of PFAS compounds, but will also discuss biochar characteristics, syngas quality and lessons learned in operating and maintaining the pyrolysis unit.

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

Introduction Background: The solids retention time (SRT) or sludge age is one of the most fundamental design parameters in the design of AS systems. As the sludge age of the AS system increases, the active fraction of the biomass decreases due to endogenous cell decay leaving cell residues or debris termed endogenous products [1], [2]. Various studies examining the biodegradability of waste activated sludge (WAS) concluded that endogenous products generated in the AS system are believed to be inert unbiodegradable particulate matter under both aerobic and anaerobic conditions [3], [4]. However, under starvation conditions, microorganisms can produce lytic enzymes that can degrade cell walls as a survival response [5]. Modelling the impact of thermal hydrolysis pretreatment (THP) has not been widely investigated, especially the impact of THP on the degradation kinetics or hydrolysis rates of different feedstocks, including mixtures of primary sludge (PS) and WAS. Additionally, due to the prevalence of sidestream treatment processes development for nutrient removal, the capacity of mainstream processes in handling thermal hydrolysis dewatering liquors has been largely ignored. Objectives: In this study, the impact of the aerobic sludge on the biosolids' composition and the performance of thermal hydrolysis is evaluated. The degradation kinetics of wastewater biosolids (i.e., PS and WAS) pre- and post-thermal hydrolysis are identified. This study also assesses the impact of thermal hydrolysis dewatering liquors on mainstream wastewater processes without sidestream treatment on effluent nitrogen concentrations and fractionation. Methodology BioWin 6.2 (EnviroSim Associates Ltd, Canada), was used to perform 18 scenarios of 3 full-scale plants at different sludge ages (i.e., 5, 10, 15, 20, 30, and 60 d), emulating the changes in the biosolids' characteristics at different sludge ages, the various THP induced conversions, their impact on downstream processes., and the impact of their conversion on methane production and biodegradability. Plant Configurations Figures 1--3 depict the schematic process of the models adopted throughout the study. Detailed influent wastewater characteristics are summarized in Table 1. Model Calibration Thermal Hydrolysis Unit Figure 4 depicts the conversion ratios of the different components of the pretreated biosolids. Kinetics For the 60-d sludge age models, an endogenous products decay rate of 0.012 d-1 was adopted from Lubello et al. [6] and Ramdani et al. [7] and integrated into the local kinetic model of the bioreactors to emulate the aerobic degradation of endogenous products at prolonged sludge ages (i.e., > 30 d). The hydrolysis rate for WAS of 0.21 d-1 was adopted from Abubakar et al. [13]. The hydrolysis rate for thermally pretreated WAS of 1.5 d-1 was adopted from Phothilangka et al. [9]. The hydrolysis rates of the raw and pretreated mixture of WAS and PS was identified through a series of simulations using the models depicted in Figures 1--3. Results and Discussion Simulations carried out on the mixed biosolids at higher aerobic sludge ages than 5 days using the hydrolysis rate attained from the baseline simulation (i.e., 0.73 d-1) were unsuccessful due to the model's reliance on the active biomass in the WAS for hydrolysis. Hence, as the active fraction of the biomass decreased, hydrolysis was hindered, and the biodegradability of the raw biosolids was grossly underestimated. The biodegradability of the PS and WAS had to be predicted separately to attain representative results. However, since an overexaggerated hydrolysis rate was required to predict the actual biodegradability of PS, the biodegradability of the PS was estimated from steady-state mesophilic AD data of Ikumi et al. [10] at SRTs of 10, 18, 25, 40, and 60 d by interpolation, and fixed to 39% at a 15 d SRT. The biodegradability of the biosolids mixture was calculated based on the weighted average biodegradability of the PS and the WAS, which depended on the sludge age of the AS system. The calculated biodegradability of the PS and WAS mixture was then matched with model simulations with hydrolysis rates ranging from 0.73 d-1 to 1.25 d-1. Changes in Characteristics The biosolids produced and processed by the plants decreased by 65% as the sludge age of the AS system increased from 5 d to 60 d. The production of endogenous products increased by 147% from 554 to 1371 kg COD/d due to cell decay. The impact of THP is reflected in the increase in the sCOD fractions from almost 0.2% to a range of 27% to 34%. The solubilization efficiencies and VSR in the MLE/MLE-MBR configurations decreased from 32% to 27% as the sludge age increased from 5 d to 60 d. However, the reduction in solubilization efficiencies was not as significant as that of the Carrousel configuration, which decreased from 37% to 28%. Methane Production, Yields, and Biodegradability Methane yields are depicted in Figure 5. The increase in the sludge age decreased methane production potential and the yields of the raw biosolids as the available biodegradable material decreased. The biodegradability of the raw biosolids mixture decreased from 50% to 32% as the sludge age increased from 5 d to 60 d, and from 18% to 12% as the sludge age of the Carrousel configuration increased from 20 d to 60 d. At the 5-d sludge age, the impact of THP was the lowest, increasing the methane yield by only 14%. At sludge ages 10 d and 15 d, the yield increase was 41% and 67%, respectively. Methane yields increased over twofold at the longer sludge ages, with increases of 65%, 62%, and 59% and 155%, 156%, and 186% at sludge ages of 20, 30, and 60 d. In the MLE-MBR and Carrousel configurations, respectively. The increase in methane yields in the Carrousel configuration resonates with the findings of Pinnekamp [11] who reported a 270% increase in the methane yield of anaerobically digested biosolids with THP at 180 °C at an SRT of 10 d. Recycled Nitrogen Table 2 summarizes the recycled nitrogen loads to the wastewater treatment plant and effluent nitrogen concentrations with and without THP. The recycled nitrogen loads decreased with the increase in sludge age, primarily due to the lower WAS:PS ratio. In the MLE configuration, the nitrogen loads recycled to the wastewater stream increased by 42% to 110%, with the least percentage increase at the 5-d sludge age, corresponding to the least improvement in biodegradability. At sludge ages of 15--30 d, the increase in the recycled nitrogen was relatively consistent at 108% to 110%, decreasing to 98% at 60 d, consistent with the improvements in anaerobic biodegradability, despite the reduction of the WAS fraction from 38% to 22% owing to the conversion of a larger fraction of endogenous products. In the Carrousel configuration, the increases in the recycled nitrogen loads were the highest across all scenarios ranging from 117% to 125%, despite the total COD being 47% to 65% less than the base model of a 5-d sludge age, due to the nature of the protein content of the WAS, making it susceptible to ammonification after thermal hydrolysis and AD [12], [13], which explains the higher nitrogen load at low sludge ages. Despite the significant increases in the recycled nitrogen loads, increases in effluent nitrogen concentrations ranged only from 6.9% to 13%, while maintaining the same effluent ammonia concentrations, demonstrating that conventional nitrogen removal systems are effectively capable of reducing recycled nitrogen loads without dedicated sidestream ammonia removal [14], agreeing with Lacroix et al. [15] who reported stable mainstream nitrogen removal as the recycled nitrogen load increased to 15% of the influent load at the Truckee Meadows Water Reclamation Facility in Reno, NV. Conclusions The increased biodegradability and enhanced methane production rate associated with THP stem directly from the conversion of endogenous products to simpler compounds favourable for microbial consumption, the fraction of which depends on the sludge age of the wastewater treatment system. Simulations demonstrated that AS systems operating at sludge ages of less than 10 d showed the least improvements in anaerobic biodegradability (i.e., 14%) due to the relatively high biodegradability of the raw biosolids. Even at sludge ages of 60 d where the biosolids might be considered aerobically stabilized, improvements in anaerobic biodegradability with thermal hydrolysis ranged from 59% and 186%.The improvements in methane yields were relatively constant at sludge ages > 10 d, despite the variation in the fractionation of the pretreated biosolids. Mainstream wastewater treatment can successfully handle the incremental nitrogen load from thermal hydrolysis without sidestream treatment and without compromising effluent ammonia requirements, as it constitutes only 2% to 13% of the influent nitrogen load.

Introduction Advanced Primary Treatment (APT) is a process in which filtration or micro-screening technology is used to replace or supplement Conventional Primary Treatment (CPT). In this project, the Cloth Disc Primary Filter (CDPF) and Proteus Primary Filter (Proteus PF) have been demonstrated for 3 and 1.5 years, respectively. Significantly higher treatment performance values (i.e., 40 to 50 % higher) were observed with both primary filtration (PF) technologies compared to CPT. PF increases capacities of primary and secondary treatment systems minimizing (or sometimes even eliminating) expansion requirements for existing installations or reduce the required footprint for new installations. Primary filtration is also the most effective carbon diversion strategy at Water Resource Recovery Facilities (WRRFs). Carbon diversion involves reducing the organic load on secondary systems by redirecting more biochemical oxygen demand towards the solids line at the primary treatment stage, which reduces the aeration requirements for aerobic biological processes downstream. Resultant benefits of PF are: (1) savings in aeration energy costs, (2) increase in digester gas energy production, and (3) reduction in primary and secondary treatment footprint and volume requirements. Significant CAPEX and OPEX savings are realized because of these benefits. One important design and operational challenge for PF is the high primary sludge volume produced during backwash operation. Sludge produced from PF backwash is also thinner (i.e., 0.2 to 0.4 %) compared to CPT sludge. Thickening is an essential process component of PF systems and its design conditions are quite different due to high sludge volumes, low solids concentrations, and significant differences in sludge characteristics. Optimization of PF systems to minimize backwash sludge volumes and still achieving high treatment efficiencies is one of the main objectives of this on-going technology research and demonstration project. Methodology Funded by California Energy Commission, the focus of this project is to evaluate the treatment and hydraulic performance of several PF technologies at Linda County Water District's (Linda) WRRF located in Olivehurst, CA (Fig. 1). General information for the Proteus PF and CDPF systems are provided in Table 1. The Proteus PF and CDPF units are shown in Figs. 2 and 3, respectively. CDPF unit has been in operation since January 2022 and Proteus PF has been in operation since July 2023. The specific objectives of the project include: (1) Evaluate the performance of PF technologies; (2) Improve the treatment and hydraulic performances; (3) Optimize the design & operational criteria including sludge treatment system, and (4) Evaluate impacts on downstream secondary process. Inline turbidity/TSS sensors and flow meters have been installed at each PF system and sensor data are synchronized to provide real-time monitoring of treatment performance. Inline sensor data are complemented by lab analysis of 24-h composite samples from influent and effluent channels of each unit. Overall, the evaluation is based on hydraulic and treatment performances. The hydraulic performance was assessed using solids loading rate (SLR), hydraulic loading rate (HLR), and backwash reject ratios (BRR) of both PF systems. High HLR, low BRR, and high SLR typically correlate to lower capital and operational costs. The key parameters impacting BRR include: HLR, SLR, pressure build-up rate, backwash flowrate, and backwash frequency and duration. The treatment performance was evaluated based on total COD (tCOD), soluble COD (sCOD), total BOD (tBOD), soluble BOD (sBOD), TSS and total Kjeldahl nitrogen (TKN) removal. Treatment Performance of APT systems The performance of the Proteus Filter and Cloth Disk Primary Filter are reported and compared to conventional primary sedimentation. Proteus Filter: The TSS and COD removal performances of the Proteus Filter are shown in Fig. 4 and Fig. 5, respectively. Results were obtained based on 24-hr composite samples collected between July 2023 and September 2024. More than 100 samples were used to evaluate the removal performances. As shown in Fig. 4, influent and effluent TSS concentrations averaged at 471 and 100 mg/L, respectively, when the unit was operated between its average and peak flow design conditions. Influent and effluent COD, as reported in Fig. 5, averaged 981 and 419 mg/L, respectively. Cloth Disk Primary Filter: The TSS and COD removal performances of the full-scale CDPF system are shown in Fig. 6 and 7, respectively. Results were obtained based on 24-hr composite samples collected between May 2022 and September 2024. More than 150 samples were used to evaluate the removal performances. As shown in Fig. 6, influent and effluent TSS concentrations averaged at 421 and 56 mg/L, respectively. It should be noted that even though influent wastewater TSS concentrations varied significantly, a relatively stable effluent TSS between 50 to 70 mg/L was observed. Influent and effluent COD, as reported in Fig. 7, averaged 805 and 335 mg/L, respectively. Overall, the CDPF performance has been observed to be similar to the results obtained from previous demonstrations where 75-85% and 50-60% removal for TSS and COD were observed, respectively (Caliskaner et al., 2018, 2019, 2020, 2021, 2022). Performance Comparison versus Primary Sedimentation: Both PF systems were operated in parallel with the existing primary clarifiers at the Linda WRRF, and performance comparisons were conducted using samples taken during the same 24-hr sampling intervals. As seen in Fig. 8, primary clarifier (PC) achieved average removals of 38% for COD and 66% for TSS. As seen in Fig. 8, the Proteus PF unit achieved average removals of 65% for COD and 85% for TSS when operated at 2 gpm/ft2, which are 40 to 50 % higher compared to PC removal efficiencies. Similar high treatment performances were also obtained with the CDPF system when compared to primary clarifier. Average removals of 56% for COD and 85% for TSS were achieved with the CDPF system. Hydraulic Performance of APT systems The optimum design and operational conditions are investigated in this project considering HLR, SLR, headloss development (across the filter media), and BRR ratios. Summary of hydraulic values observed for both PF systems are presented in Table 2. PF backwash is triggered by preset filtration time or maximum headloss development , whichever comes first. Headloss development is measured by pressure transducers. Headloss development rates were observed to change with changes in HLRs. Proteus PF: As illustrated in Fig. 9, headloss development increases as the HLR increases resulting in higher BRRs. The daily average headloss development under HLR of 2 gpm/ft2 and 6 gpm/ft2 were 5.2 and 6.2 psig, respectively. The increased flowrate and HLR caused increased accumulation of particulate material within the filter media resulting in larger headloss values and hence higher BRR values. The HLR and BRR values with respect to time are summarized in Fig. 10. The Proteus PF system has been operated between 2 and 9 gpm/ft2 most of the demonstration resulting in an average BRR of 9.4%. Daily average HLR and SLR for the Proteus PF System during the demonstration is shown on Fig. 11. Based on an analysis of HLR and BRR values, HLR ranging from 2 to 2.5 gpm/ft2 are considered for optimum average flow design conditions and 5 to 6 gpm/ft2 are considered for peak flow design conditions. Cloth Disk Primary Filter: The volumes of filtered effluent, backwash reject, and sludge wasting are all monitored along with HLR and SLR values. Recorded HLR and BRR values are shown in Fig. 12. Similar to Proteus PF system, headloss development and BRR increase as the HLR increases. Average daily BRR values were observed to be approximately 10 percent under average design flow/loading conditions. Based on an analysis of HLR and BRR values, HLR value of approximately 2 gpm/ft2 is considered for optimum average flow design conditions and 4 to 4.5 gpm/ft2 are considered for peak flow design conditions. Impact of Primary Filtration Systems on Energy Consumption and Recovery One major project objective is to demonstrate the energy and capacity impacts of PF on WRRFs. Specifically, impacts of PF on MLE process and three Advanced Secondary Treatment technologies including Microvi, AGS and MABR were evaluated. Energy savings and footprint reductions are measured directly in addition to the process modeling studies to further investigate the impacts on BNR kinetics. The impacts of PF on secondary treatment and anaerobic digestion were predicted with SUMO process modeling using the obtained PF demonstration data. PF results in 25% in aeration energy savings and 35% increase in digester gas production (Fig. 13).

INTRODUCTION/BACKGROUND Land application of biosolids provides benefits via recycling nutrients and carbon to soil. However, Per- and polyfluoroalkyl substances (PFAS) are becoming a main hindrance to land application of biosolids with increasingly stringent regulations (McNamara, 2023). PFAS are found ubiquitously in many industrial and consumer products due to their unique chemical properties. These same properties also make them highly persistent and potentially toxic to ecosystems and humans (Holmquist, 2020). New restrictions around land application coupled with a reduction in potential landfill sites for biosolids has led many WRRFs to investigate thermal processes for biosolids management (Winchell, 2022). Incineration provides the benefit of reducing residual solids loads to be managed. Pyrolysis and gasification are emerging thermal process alternatives that also reduce residual solids loads. Moreover, these two processes offer benefits of lower concerns for exhaust gas emissions and the ability to sequester carbon in the solid residuals (Winchell, 2022). Of particular interest now to WRRFs is that these thermal processes can remove and/or transform PFAS (Winchell, 2022; McNamara, 2023). While PFAS are part of the biosolids management decision tree, they are not the only important thing. Any process implemented today still needs to make sense in two decades even if PFAS are no longer a primary concern. Additionally, the relative importance of PFAS in light of other critical environmental concerns like global warming and eutrophication have not been widely studied. While facing a seemingly pivotal moment in biosolids management history, it is critical to understand management options and the relative importance of PFAS. For this research we combined PFAS fate data from our own experiments and from literature through thermal processes. These results were then included in the LCA as their own impact category and as an input to toxicity. To the knowledge of the authors, this is the first LCA on solids handling alternatives to date that has incorporated PFAS toxicity in this way and compared impacts to conventional LCA components. In short, LCA was used to compare thermal drying, incineration, pyrolysis, and gasification holistically with regards to their impacts on humans and the environment. APPROACH PFAS Fate Through Thermal Processes Lab-scale pyrolysis and gasification experiments were conducted as part of WRF Project 5211. Targeted analysis of PFAS was completed by Eurofins on influent biosolids and effluent solids (char), liquid (py-liquid), and gas (py-gas or gasification gas). These data were used to assess removal and release of PFAS in the effluent phases. Incineration data from Winchell, 2023 was used for incineration PFAS removal performance as a reference scenario. LCA Structure 1)Five biosolids treatment scenarios for a 'typical' WRRF were compared, distinguishing between different thermal processes: thermal drying only, pyrolysis at low (500 degrees C) and high temperature (800 degrees C), gasification, and incineration. See Table 1 for a description of each scenario's treatment train. 2)Mass and energy balances across the treatment trains for each scenario were conducted, as well as a global warming potential (GWP) evaluation, using the BEAM*2022 tool (NEBRA et al., 2022). 3)PFAS emissions were first characterized alone in an impact category called 'PFAS potential,' representing total mass of PFAS emitted in each scenario as fluoride equivalents. 4)PFAS emissions were then also characterized within the toxicity impact category using the modified USEtox PFAS framework from Holmquist et. al. 2020. 5)These results were than used as an input to the LCA to compare the five thermal process scenarios with five main impact categories: i) GWP, ii) eutrophication potential, iii) freshwater ecotoxicity potential, iv) human cancerous and noncancerous toxicity potential, v) and PFAS potential. RESULTS/DISCUSSION Global Warming Comparison The incineration scenario had the highest GWP, driven mainly by scope 1 emissions (Figure 1). The scenarios with a fertilizer offset credit applied had negative scope 3 emissions. This was particularly significant for thermal drying only, because the biosolids had the highest nitrogen content, which largely drove the GWP fertilizer credit. The pyrolysis scenarios were determined to have the lowest GWPs, largely driven by lower scope 1 emissions through carbon sequestration credits achieved by the stability of the biochar product. Eutrophication Comparison The thermal drying only scenario had the highest eutrophication impact, driven by the increased hauling of the wet biosolid compared to other scenarios (Figure 2). All land applied scenarios had a beneficial fertilizer offset credit as well. This credit was largely similar between these scenarios, as the phosphorus content of the solid drove eutrophication impact for fertilizer credit and was assumed to be similar between scenarios. The lowest eutrophication potential was in the pyrolysis scenario. Toxicity Comparison Little difference was observed in freshwater ecotoxicity and human cancerous toxicity, largely due to the dominance of heavy metals, making up at least 99.5% and 96.2% in these two categories across scenarios. Heavy metal loads in the end product were assumed to be similar across all thermal processes, as only a small portion of the heavy metals would volatize, and the majority would remain in the solid residuals. In terms of PFAS potential, pyrolysis did not appear to remove much PFAS, but instead transform them into different PFAS species. Incineration and gasification were the lowest in PFAS potential, due to their high PFAS removal performance. This led also to lower human noncancerous toxicity potentials (Figure 3). Overall, heavy metals had the highest impact in human noncancerous toxicity for each scenario, but PFAS were still impactful. It should be noted that two effect factors were presented for noncancerous toxicity in Holmquist's modified USETOX model (based on epidemiological vs. rodent data). To be conservative, the higher of the two was used. Relative Impacts of Inputs Figure 4 shows the relative contribution of each input to the relevant impact categories, focusing on the thermal drying only scenario for simplicity. Most notably, it can be seen that the impact of heavy metals makes up between 93.2-99.5% of each toxicity potential category for thermal drying only. PFAS emissions comparatively only made up to 6.7% of the toxicity emissions (for human noncancerous toxicity). Eutrophication is mainly impacted by electricity use, while GWP is mainly impacted by scope 1 emissions. The PFAS potential impact category was not shown in the figure. This is because there is only one input to the PFAS potential broken up by the effluent phase the PFAS are emitted to in each scenario. CONCLUSION/SIGNIFICANCE This analysis highlights the importance of PFAS when taken into context with other known and regulated toxicants in biosolids such as heavy metals. Heavy metals made up at least 99.5% and 96.2% of freshwater ecotoxicity and human cancerous toxicity impacts across all scenarios. Even when a conservative assumption for PFAS toxicity was used for human noncancerous toxicity, heavy metals made up the largest portion of this impact as well. This analysis also highlights two biosolids alternatives, gasification and pyrolysis. Gasification was observed to be a relatively low impact alternative in most of the LCA categories that also safeguards against uncertainty around PFAS toxicity and future regulations in biosolids. This option provides not just transformation, but potentially good removal of PFAS species. Pyrolysis however was observed to be the best option in this analysis when considering the relatively low impact of PFAS on the toxicity potential impact categories, and that pyrolysis had the lowest impact in the other critical LCA impart categories. The key impact of this work is the reframing of PFAS as not the only consideration, but one of many aspects to be included for holistic biosolids management.

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

SUSTAINABLE SLUDGE MANAGEMENT BY CONTROL OF MICROBIAL POPULATION DYNAMICS Rob Whiteman, Ph.D. Technical Director, ABS Inc. For 100+ years engineering technology has employed capital intensive processes for biological wastewater treatment (WWT) using the approach of in-situ growth to control the development of biology under aeration, to flocculate in the clarifier to meet Water Quality Standards. Issues of filamentous bulking and poor settleability result in less concentrated biosolids meaning larger volumes to handle along with poor dewatering characteristics meaning more polymer and expense for dewatering. The increased use of cleaners, antibiotics and hand sanitizers has led to deterioration in the microbial populations for good floc structure and settleability, while reducing viability. The handling and disposal of these biosolids residuals represents a significant cost to Utilities, which employ a range of equipment to reduce the volume and mass: digesters, presses, pelletization or incineration. With increasing environmental pressures for sustainable disposal methods driven there is a need for innovative 'point source reduction' (PSR) technologies and a method or process which improves settleability, allowing an increase in the mean cell residence time (MCRT), hence reduction in wastage and new ways to meet Class A pathogen reduction standards inexpensively. However, now with the discovery of microplastics in drinking water and biosolids, there is even greater demand for a point source reduction technology. Advances in biotechnology and understanding the role of microbial population dynamics in wastewater treatment have led to the investigation of PSR technology, a new approach using an ex-situ growth process to grow and routinely inject probiotics which controls the biology in the treatment system. This resulted in unprecedented beneficial results discovered over the past decade, which improved settleability allowing an increase in the mean cell residence time (MCRT) and hence reduction in wastage. With this reduction in biosolids residual, it was possible to extend the holding times to further reduce the mass of biosolids while improving the quality to make a Class A biosolids residual and in some cases Class AA, which is a breakthrough providing a sustainable, low-cost, affordable method of treatment and disposal. Side Stream Reactor: Biofermentation is a process and method for growing single cell microorganisms in a standalone side stream reactor. The process allows cultivation of specific microbes which are injected from the side stream reactor and have not been exposed to the selection pressures experienced by the wastewater treatment plant. The cultures are grown overnight and injected daily as a 'probiotic' allowing complete control of the microbial population for the first time in 115 years, since development of activated sludge in 1910. Improving Settleability: Settleability is the limiting factor for environmental engineers designing smaller, more compact activated sludge systems. Filamentous bulking is a common occurrence in municipal wastewater treatment, which causes poor settleability by bridging and preventing water escaping from between the flocs as the sludge concentrates in the clarifier. Several of these microorganisms are often associated with high loads of fats, oils and grease, such as Microthrix parvicella and others with long MCRT's of greater than 20 days, such as 0041 and 0675. While the concept of ageing was supposed to encourage flocculation, few systems can operate beyond 25 days without experiencing bulking. Through the introduction of selected microbes using the Biofermentation process, it has been possible to improve settleability substantially allowing the mixed liquor suspended solids (MLSS) to be increased by increasing the MCRT. . The process has been applied at one plant for 3.5 years during which time the MLSS has been raised from 3-4,000 to 9-10,000 with improved settleability and clarity. The improvement in floc structure is seen in Figure 1, while the settleometers are shown in Figure 2. This extended aeration plant now operates with an estimated MCRT in excess of 70 days. REDUCING BIOSOLIDS PRODUCTION: With the ability to improve settleability and hence increase MCRT comes less mass wasted. In part of another 5 year 'Cause and Effect Study', the biosolids production versus food to microorganism ratio (F:M) was compared as shown in Figure 3. The data shows a reduction in the amount of biosolids produced irrespective of F:M when treated with the probiotics. More importantly the R2 in the untreated is only 0.458, while 0.968 in the treated, which demonstrates a more stable, predictable biomass. Overall, the process showed typically a 60+% reduction in biosolids production in the aeration basin. Reducing biosolids production by this amount significantly reduces downstream handling and processing not to mention disposal. 'ADVANCED DIGESTION': Advanced digestion was used which involved injecting probiotics, which compensate for the long MCRT. Figure 4 shows the results in the lbs of biosolids produced per lb of BOD reduced over 10+ years comparing hauling to a chemical process (BCR) and probiotics with and without Advanced Digestion. When only using probiotics in the wastewater treatment system there is a 54-70% reduction in the amount of biosolids produced depending on whether comparing hauling or the chemical process. When coupled with the Advanced Digestion process this plant has experienced in excess of 90% reduction with no biosolids hauled from the facility since April 2017 through 2022. The digester was allowed to digest biosolids without addition of new biosolids for over 60-days. A geometric mean for fecals was taken, which showed that the biosolids met Class A standards (See Figure 5). Metals were also measured which indicate the residuals meet a Class AA under Florida Law. Mass reduction occurred as previously discussed, which is more paramount with new legislation on microplastics and other biosolids contaminants. This facility continues to lead the way in using Biotechnology to resolve biological challenges. In summary, the addition of probiotics has now been proven and even validated with respect to improving settleability by control of population dynamics, providing the operator more control to increase MCRT, while reducing biosolids production 60% economically. This has the ensuing benefits of opening up space downstream for Advanced Digestion, which further reduces biosolids production of up to 90% with the potential to create a Class A or AA residual or economically dispose of the final biosolids because of the substantial reduction in mass and volume.

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 The Microbial Hydrolysis Process (MHP), developed to enhance anaerobic digestion (AD) performance, uses the hyper-thermophilic bacterium Caldicellulosiruptor bescii (C. bescii) in a post-digestion hydrolysis process. Unlike pre-digestion methods (Hansen et al, 2021), MHP feeds AD digestate to a 75°C hydrolysis tank populated with C. bescii for a hydraulic retention time of two days (Parry et al. 2022). Here, C. bescii and its enzymes hydrolyse cellulose and complex carbohydrates and convert them to volatile fatty acids (VFAs) in an anaerobic, neutral-pH reactor. The VFAs are then returned to the AD, where methanogens convert them into biogas. Figure 1 illustrates the microbial activity AD with MHP. The performance of AD with MHP has been tested at lab- and pilot-scale with consistent results; the addition of MHP increases volatile solids reduction (VSR) to greater than 75%. Figure 2 shows the results of MHP studies on solids from 4 different water resource recovery facilities (WRRFs) with well-performing existing AD systems. Encouraged by pilot results, VandCenter Syd (VCS) in Denmark is now designing MHP implementation at its Ejby Mølle WRRF, and conceptual and preliminary designs have been developed for several WRRFs in the US. An ongoing pilot at North Davis Sewer District (NDSD) in Syracuse, UT has operated at steady-state since July 2024. Data from this pilot and prior studies are used to refine a process model (Sumo) to predict AD performance with MHP based on feed characteristics. The results of the pilot study, the model and preliminary design, and analytical results for pathogens, microbial populations, sludge dewaterability, and sludge characterization will be presented. Material and Methods AD with MHP has been studied using solids from several facilities at both lab and pilot scales. Most recently, pilot-scale testing has been conducted at North Davis Sewer District in Syracuse, UT. The pilot-scale system consists two 325-gallon anaerobic digesters and one 140-gallon MHP reactor. Pictures of the pilot trailer located at NDSD and the pilot trailer process room are shown in Figure 3. The NDSD pilot system is operated to simulate proposed process changes to achieve Class A biosolids, boost VSR, and increase biogas production, using a staged AD with batch intermediate MHP and heat recovery. A simplified process flow diagram of the pilot MHP system is presented in Figure 4 and a process flow diagram of the proposed full-scale system with heat recovery is presented in Figure 5. Pilot Anaerobic Digester 1 (AD1) was fed digested sludge once per day from the full-scale digested sludge transfer pumps. Sludge from AD1 was automatically fed 4 times per day to the MHP tank, and hydrolysed sludge from the MHP tank was fed 4 times per day to Pilot Anaerobic Digester 2 (AD2). Characteristics of the full-scale system feed and digestate as well as the contents of AD1, the MHP tank, and AD2 were measured using standard methods. Routine analyses to monitor performance and stability include volatile and total solids, total acids, alkalinity, and pH, while additional sludge analysis assesses pathogen reduction, microbial populations, sludge dewaterability, carbohydrate composition, and VFA fractionation. The VSR of the digestion process with MHP, calculated using the volatile and total solids measurements, was the key indicator of performance. Results of this pilot study are used to calibrate a process (Sumo) model to predict digestion performance for facilities with different feed characteristics and will be discussed in the final paper. Findings Previous studies have proven significant improvement in digester performance with the addition of MHP, as indicated by the increase in VSR to 75 and higher. These findings were corroborated by the results of the pilot at NDSD, shown in Figure 6. The existing AD system at NDSD achieves 63.8 percent VSR on average, and the addition of MHP improved performance to 75 percent once steady state was achieved. Table 1 presents the comparison the proposed staged AD with batch intermediate MHP to baseline AD performance. The increased VSR and improved dewaterability result in a 38% decrease in wet tons of biosolids produced per year, and an estimated 18% increase in biogas production assuming the biogas yield is unchanged. Further, laboratory analyses confirm that batch MHP reduces the concentration of fecal coliform below detectable levels, meeting the EPA criteria for pathogen reduction in Class A biosolids. The operational data and results of routine analyses, microbial population analysis, and sludge characterization from the pilot study at NDSD have informed the continued development of a model to simulate the impact of MHP based on influent sludge characterization. With this model, performance of AD with MHP at other facilities can be predicted. Significance MHP represents a significant advancement in AD technology and offers the highest achievable VSR for municipal WRRF AD systems to date. By allowing the digestion of cellulose and other recalcitrant organics, MHP maximizes AD efficiency, thus increasing biogas yield and reducing biosolid production. These improvements result in substantial cost savings on biosolids management -- a major interest for WRRFs. These benefits position MHP as a scalable, innovative solution to enhance AD performance globally.

Aries Clean Technologies (Aries) is a gasification technology provider and patent holder that uses its gasification systems to dispose of waste. Aries retained Stantec to quantify annual Scope 1, 2, and 3 operational greenhouse gas (GHG) emissions for their existing and potential future (Generation 2) biosolids gasification facilities as a step to achieving their goal of a carbon neutral biosolids gasification facility. These facilities feature extensive heat recovery, electricity generation, and emissions control systems, necessitating the use of multiple calculation sources and a unique inventory approach to ensure accuracy and to avoid double-counting of emissions.

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.