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.

LEARNING OBJECTIVE: Pima County's Tres Rios Water Reclamation Facility (TRWRF) recently evaluated process benefits and cost effectiveness of including PONDUS into their process, ultimately deciding to proceed with the design and construction based on several advantages. Participants of this presentation will learn the findings of the evaluation including present-value and life-cycle costs of implementing the new process, positive impacts to digestion capacity, biogas production and sales, and solids loading rates at dewatering and the future Class A biosolids solar dryer system. INTRODUCTION | BACKGROUND The TRWRF, owned by The Pima County Regional Wastewater Reclamation Department (County), serves as the centralized solids handling and treatment system for the entire county, offering a treatment capacity of 50 MGD. The TRWRF currently produces approximately 180 wet tons per day (WTPD) of Class B biosolids at approximately 18-20% total solids content. With the goals to reduce TRWRF energy requirements, lower solids disposal costs, and address future biosolids disposal regulations the County is planning for a solar dryer to produce Class A biosolids. An opportunity to maximize these goals is to introduce a hydrolysis process that can further reduce biosolids volumes and reduce the size of the solar dryer. In addition, a hydrolysis process would create additional needed digester capacity, increase biogas production, and create a dryer cake going into the solar dryer amongst other potential TRWRF benefits. The thermochemical hydrolysis process PONDUS was specifically targeted based on limited additional operational requirements and small footprint. METHODOLOGY The PONDUS system is a thermal/alkaline hydrolysis process designed for breaking down bacteria cell walls from thickened waste activated sludge (TWAS). The cell membrane breakdown releases organic acids into the downstream anaerobic digester that ultimately feed methanogens to produce greater methane production. Note that this process is not designed to treat primary sludge (PS) that also goes into the anaerobic digester, as that material does not contain a high fraction of bacteria for lysing. The process combines the TWAS at around 6% TS with caustic soda (NaOH) to a pH of approximately 10. The TWAS is then heated to between 140o F and 160o F for 30 minutes for the reaction to take place. The system is offered from a single manufacturer Centrisys-CNP as a package which includes the chemical storage and delivery system, TWAS recirculation pumping and heat exchange, and instrumentation and controls. A preliminary mass balance and process flow diagram of the system is represented in Figure 1 below. Figure 1 PONDUS Mass Balance and Process Flow Diagram Potential Benefits The PONDUS system creates operational savings with increased biogas production and reduced total solids needing to be processed, which is the primary driver for using the system. Other benefits of PONDUS include the following: - Lower Viscosity: The hydrolyzed sludge reduces the digester feed sludge viscosity by over 50%. The biosolids can be pumped, mixed, and heated with lower energy requirements and allows for a higher TS loading rate into the digesters. A higher loading rate allows for reduced total digester volume required to meet minimum solids retention times (15 days), greater storage capacity, and allows greater flexibility for a digester to be taken offline. Additionally, the higher total solids feed rate to the digesters reduces the water heating requirement, and therefore reduces natural gas heating water needs on the digester boilers at an anticipated savings of approximately $80,000/year. The lower digester viscosity could also reduce energy demands on pumping and mixing systems. - Achieving Class A Biosolids: The PONDUS thermal/alkaline hydrolysis process will result in higher volatile destruction, resulting in more biogas and less sludge to manage. A secondary benefit to the volatile solids destruction is a further reduction in fecal coliform, salmonella, enteric viruses, and viable helminth ova in the biosolids exiting digestion. This further reduction will increase the ability for the Solar Dryer to achieve Class A biosolids under the 503 Regulations at a lower total solids concentration. The lower total solids exiting the future solar dryer will reduce dust production and create a better working environment. - Total Solids Cake Dryness: With a breakdown and reduction in volatile solids, a dryer dewatered cake total solids concentration can be assumed. Manufacturer data and an independent study of 17 different samples shows that the total solids of cake will increase between 3% and 6%. The independent study data from KBKopp Sludge Analytics is provided in Table 1. - Polymer Demand: Manufacturer data shows that a 20% decrease in polymer can be expected when using PONDUS. Table 1 implies that primary sludge subjected to PONDUS has a marginal polymer demand increase. Given the high WAS:PS fraction at TRWRF, and the nature of PONDUS breaking down volatile solids it can be assumed polymer demand will be reduced. - Dewatered/Dried Biosolids Odors: The PONDUS biosolids cake is reported to have a lower odor concentration than traditional anaerobically digested sludge. This is due to the greater volatile solids reduction. The benefits include reduced odor concentrations to treat, increased biofilter bed-life, and reduced risk of odor complaints. Operations and Maintenance Considerations The largest direct operational costs of the PONDUS system is caustic soda consumption. Daily caustic soda use is expected to be 155 gallons resulting as high as $280,000 yearly cost. Heating the TWAS in the PONDUS Lysing Reactor adds minimal cost from an overall perspective, as the heat energy required to heat the TWAS from 140o F to 160o F is eventually used in the downstream anaerobic digester process. Table 1 PONDUS Independent Study: Sludge Effect on PONDUS (Dr Julia Kopp, 2022) DISCUSSION Revised Mass Balance Estimate With a PONDUS system, the increase in biogas is expected to be 22% higher than the existing TRWRF anaerobic digester system. The daily biogas production would increase by 91 million BTU (MMBTU). The sell back value of those 91 MMBTU, with the EPA value of 11.7 Renewable Identification Numbers (RINs) per MMBTU and at $2.30 per RIN results in an additional $2,463 in biogas sales per day, or $899,000 in biogas sale per year. The expected increase in biogas production also reduces the total solids needing to be dewatered, dried through the solar dryer, and hauled away. Coupled with an expected dryer cake, the current 180 WTPD of solids through the existing plant processes ending at dewatering would be reduced to 124 WTPD of solids after dewatering. This is a 53 WTPD total solids reduction, or about two hauling trucks per day of reduction. At current costs per wet ton disposal of $27.20, this results in a potential savings of $526,000 per year. Implementation Risk The PONDUS process includes risks that must be recognized and managed to the extent possible. Key implementation risks include the following: - Full-Scale Implementation: The primary risk of the process is that PONDUS has limited installations to use as proofs and lessons learned. There are over 20 installations in Germany, with one fully operational facility in the US. While the thermal/alkaline process is well understood and proven, the unknowns of full-scale may reduce the estimated savings. To mitigate against this uncertainty, the County and its design team conduct a site visits and spend time at the existing US facility to help understand full-scale operations, maintenance, and data comprehension of the process. - The lysing process creates an opportunity for a lower centrate/pressate capture rate of solids downstream of dewatering due to the high volatile solids destruction rate. This can be addressed by using total solids metering on centrate/pressate to identify and fix under performance. - Increased nutrient ratios within the centrate/pressate from PONDUS is expected. Table 1 shows a 28% chemical oxygen demand (COD) increase, an 18% ammonia increase, and a 26% orthophosphate increase. Updated BIOWIN modeling may be necessary to to confirm impacts on centrate/pressate deammonifiaction and secondary treatment processes. RESULTS & STATUS Installation of PONDUS is anticipated to create an operational savings of $1,060,000 per year and a system payback in under 10-years. The County determined these savings opportunities along with added digester capacity and future solar dryer benefits justifies continuing with the project. The new PONDUS facility is now in design at TRWRF with a construction start date of 2025.

Introduction In 2024, WSSC Water, the largest water/wastewater utility in Maryland, commissioned a centralized biosolids processing facility (Bioenergy Facility), which utilizes a thermal hydrolysis pretreatment (THP)-enhanced anaerobic digester (AD) process. The Bioenergy Facility will receive biosolids from six regional Water Resource Recovery Facilities (WRRFs), which have a combined treatment capacity of 100 MGD. The filtrate from the Bioenergy Facility's dewatering process is treated using the AnitaMox deammonification process before being returned to the headworks of the 30 MGD Piscataway WRRF. Bench-scale evaluations estimated that the total nitrogen (TN) in Piscataway's effluent could increase by up to 1 mg/L due to the production of recalcitrant dissolved organic nitrogen (rDON) via the Maillard reaction resulting from the THP process as detailed in our previous study [1]. The anticipated increase in rDON loading will place the Piscataway WRRF at risk of exceeding the stringent TN effluent limit of 3.25 mg/L. In addition, operational changes at two of the biosolids source WRRFs, which plan to shift to biological phosphorous removal, are expected to result in higher orthophosphate (ortho-P) presence is in the Bioenergy Facility's AD effluent and dewatering filtrate, potentially causing struvite formation in downstream equipment. To address these issues, a temporary, easy-to-implement approach, that can be applied at this and other WRRFs operating a THP-AD process, was tested in pilot-scale to control rDON and ortho-P. A previous study reported that rDON mainly contains negatively-charged molecules, which have a remarkable coagulation capacity with many metallic ions, such as ferric chloride (FeCl3) [2, 3]. Phase 1 of this study evaluated the influence of FeCl3 addition during dewatering of AD effluent on filtrate rDON and ortho-P concentrations at lab scale. Results from these lab-scale experiments reported herein demonstrate the strong potential of FeCl3 for reducing rDON and ortho-P concentrations in AD filtrate. Phase 2 of the study will focus on validating these lab-scale results by conducting a second round of testing at full-scale. A comparison of the lab-scale and full-scale results will be reported, alongside an assessment of the practicality and effectiveness of FeCl3 addition for rDON and ortho-P control at this centralized biosolids processing facility. Materials and Methods The process flow diagram of the study is shown in Figure 1. Samples of dewatered mixed sludge cake with an approximately 22% total solids (TS) content were collected from WSSC Water's four largest WRRFs (Piscataway, Western Branch, Seneca, and Parkway) with a blending ratio (wet mass) of 4.3 : 3.3 : 2.4 : 1 that is based on an estimated future biosolids production. The blended cake samples were diluted to around 16% TS followed by processing through a pilot-scale Cambi THP unit (Cambi, Asker, Norway) operated at 6 bar steam pressure (equivalent to 165 °C) for 30 minutes. The pretreated sludge was then mixed with AD inoculum collected from a full-scale THP-AD system at a local WRRF and anaerobically incubated at 36.5 °C until the cumulative biogas production reached a plateau. After digestion, the optimal polymer dose (OPD) of the digested sludge was determined based on capillary suction time (CST) [4]. The lab-scale dewatering protocol, developed by VT-CAWRI, includes shearing of the sludge-polymer mixture and piston compression of the solids, which has been calibrated to a full-scale belt filter press installation according to methods detailed in a previous study [5]. Two variables were investigated in this study: FeCl3 dose and polymer dose. Briefly, FeCl3 solutions were added to the digested sludge during dewatering at doses of 0.5%, 1.0%, 2.0%, 2.7%, and 5.5% Fe (g Fe3+/g DS) along with polymer dosing at either OPD or 1/2 OPD. The intent for varying polymer dose is to understand whether FeCl3 can compensate part of the role played by polymer during dewatering, ultimately saving the cost of polymer consumption. Samples of dewatering filtrate were collected for characterization and recalcitrant species tests. The recalcitrant species test, developed by VT-CAWRI, consisted of ammonia (TAN) stripping to minimize background noise when calculating DON = sTN - NOx - TAN and subsequent aerobic incubation to eliminate biodegradable DON, with the remainder treated as rDON which ultimately contributes to Piscataway WRRF's effluent. Results and Discussion Effects on rDON removal Without FeCl3 addition, around 24.1% and 9.4% of rDON were removed as part of the biosolids during dewatering with OPD and 1/2 OPD after accounting for polymer dilution of the sludge, leaving nearly 76% and 91% of rDON in the filtrate, respectively (Figure 2a). As the FeCl3 dose increases, a linear reduction in filtrate rDON was observed, with a nearly 60% removal at a 5.5% FeCl3 dose alongside 1/2 OPD (Figure 2b). Previous studies have reported that rDON produced from the THP process mainly consists of melanoidin molecules, which are negatively charged nitrogen-containing byproducts of the Maillard reaction that have shown remarkable binding capacity with metallic ions [6]. Therefore, the removal mechanism of rDON in this tested approach was believed to be precipitation or coagulation by ferric ions and cationic polymer. Although both polymer and FeCl3 demonstrated rDON removal capability according to Figure 2a, the contribution from FeCl3 was greater since polymer alone could only achieve a maximum removal of 24.1% at the OPD. Effect on ortho-P removal Unlike rDON removal, the removal of ortho-P without any FeCl3 addition was minimal. Only less than 5% of ortho-P was removed from the liquid phase at OPD, and even no change was observed with 1/2 OPD of polymer during dewatering (Figure 3a). However, it is notable that even the lowest dose of FeCl3 (i.e., 0.5% Fe) combined with 1/2 OPD of polymer achieved an over 85% removal of ortho-P from the filtrate, while dosing 2% Fe resulted in nearly complete elimination (Figure 3a). This exponential reduction of ortho-P in Figure 3b indicates that FeCl3 dosing during dewatering is more efficient for ortho-P removal than for rDON removal, making rDON levels in the filtrate likely the determining factor for appropriate FeCl3 dose selection. Moreover, the effective removal of ortho-P from the dewatering filtrate essentially eliminated the risk of struvite formation in downstream equipment. Effect on sludge dewatering and cation overdosing It is our hypothesis that the addition of metallic coagulants during dewatering along with the optimal dose of polymer may lead to cation overdosing, which disrupts charge neutralization and ultimately results in worse cake dryness. To test this, cake dryness at full and half OPD, with and without coagulant addition, was analyzed. Without any FeCl3 addition, results in Figure 4 showed exceptional cake dryness of 33.1% TS at OPD and a deteriorated cake dryness of 25.3% TS at 1/2 OPD due to underdosing of cations. Adding 5.5% Fe on top of OPD substantially aggravated cake dryness to less than 25% TS (Figure 4). However, in addition to 1/2 OPD, dosing 1% Fe could recover the cake dryness to as high as 31.6% TS from the 25.3% TS at 1/2 OPD only (Figure 4). The results suggest that the deterioration in cake dryness as a result of overdosing of cations during dewatering can be solved by cutting back polymer usage while not sacrificing the superiority in the removal of rDON and ortho-P by FeCl3. Effect on pH and alkalinity It is our concern that the drop in pH and alkalinity at high FeCl3 doses may negatively impact the anammox-based sidestream deammonification process in full-scale operation. As shown in Figure 5, consistent decreases in filtrate pH and alkalinity as a result of FeCl3 dosing during dewatering was observed due to hydrogen ion release from the formation of metal-hydroxide complexes [7]. Without extra alkalinity supplementation, the tradeoff between effective rDON removal and decreases in pH and alkalinity becomes a crucial consideration for selecting FeCl3 doses in full-scale operations. It is important to ensure a sufficient alkalinity for deammonification and a suitable pH range of 6.5 to 7.5 for AOB and anammox bacterial activities [8, 9]. Conclusions and Ongoing Work The results from this pilot study revealed that FeCl3 dosing along with polymer during digestate dewatering can (1) reduce rDON by nearly 60% at 5.5% Fe, (2) achieve nearly 100% ortho-P at 2% Fe, and (3) maintain excellent cake dryness while reducing polymer dosing by 50%. These promising findings provide strong proof of concept, which is currently being validated in full-scale operations at the Bioenergy Facility through early 2025. Potential side effects, such as decreased pH and alkalinity will also be verified and addressed.

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.

Purpose: Common phosphate minerals in wastewater treatment plants, such as struvite/magnesium ammonium phosphate (MAP, MgNH4PO4- 6H2O), calcium phosphates such as amorphous calcium phosphate (ACP, Ca3(PO4)2), and iron salt precipitates such as vivianite (Fe3(PO4)2 8H2O), are known for their tendency to scale and deposit within anaerobic digesters, pipe bends, and dewatering equipment downstream of anaerobic digesters. These deposits pose maintenance and operational challenges. Precipitation of these minerals occurs when the concentrations of ionic constituents exceed the solubility product (Ksp) of the solid, measured as scaling tendency (ST) or saturation index (SI). The solubility of these precipitates depends on factors such as pH, temperature, competing ions, and nucleation sites. Chemical thermodynamic modeling can evaluate the parameters contributing to scaling and, thereby, safeguard process equipment from scaling-induced damage, improve treatment efficiency, and regulate phosphorus sequestration to produce nutrient-rich biosolids. This modeling work could benefit the wastewater treatment industry by providing rapid optioneering for solutions limiting and targeting scaling mineral deposition and assessing various process optimizations for new pilot technologies. In this study, two chemical thermodynamic models were evaluated: (i) Visual MINTEQ Version 4.0 and (ii) OLI Studio. Model inputs were gathered from a pilot-scale experimental setup at Hampton Roads Sanitation District's (HRSD) Atlantic Treatment Plant (ATP), in Virginia Beach, VA. The pilot evaluated the impact of aeration, mixing, and chemical addition on the scaling tendency of thermally hydrolyzed, pretreated, anaerobically digested solids. Critical parameters such as pH, temperature, alkalinity, orthophosphate (OP), ammonia (NH3), and major cations and anions concentrations were measured as model inputs. The solids formed during these evaluations were characterized by: X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM)/Energy Dispersive X-Ray Spectroscopy (EDS), and Raman Spectroscopy analysis to validate predictions of the two models. Methods: The pilot setup at ATP consisted of four tanks (Figure 1), each 11 feet tall and capable of holding about 45 gallons of digestate. These tanks operated as daily batch fed continuously stirred tank reactors, maintained by pump recirculation at a 3-day solids retention time (SRT). Aeration was provided using fine bubble diffuser membranes, operated either at a constant airflow rate or via a dissolved oxygen (DO) set point. The effects of chemical injection of magnesium hydroxide [Mg(OH)2] and calcium hydroxide [Ca(OH)2] were also studied at various Ca+Mg:OP ratios of 0 (control), 0.25:1, 0.5:1, and 1:1. The modeling process was based on pilot operational conditions: anaerobic digestate (pilot influent), aerated anaerobic digestate constantly at 5 LPM, and aerated anaerobic digestate on a DO setpoint of 0.2 mg/L. Inputs for these operational conditions were collected during pilot tests and averaged for model insertion. For each model run, pH and temperature sensitivity analyses were conducted from pH 7-9, and temperatures 20 - 40°C to determine effects on precipitate formation according to Visual MINTEQ and OLI Studio. Experiments with Mg(OH)2 and Ca(OH)2 were conducted in both models for the aerated cases to simulate chemical injection and evaluate the effectiveness of each chemical in OP removal, as well as the accuracy of each model in predicting mineral formation. Results: Both Visual MINTEQ and OLI Studio effectively predicted mineral formation in anaerobic digestate under varying conditions. Initially, both models predicted the formation of metal phosphates (Mg, Ca, Fe) in anaerobic digestate. Upon aeration at 5 LPM, both models identified struvite as the dominant mineral formed in the pH sensitivity analysis, though they differed in predicting other compounds. Visual MINTEQ predicted the formation of calcite and vivianite, while OLI Studio predicted tricalcium phosphates, calcite, and siderite. In the temperature sensitivity analysis, both models yielded consistent results for calcite and struvite formation, suggesting that temperature has a less significant impact on mineral precipitation than pH. In the aerated run targeting a DO setpoint of 0.2 mg/L with Mg(OH)2, both models accurately predicted struvite as the dominant mineral, with its formation increasing alongside the chemical dose, as depicted in Figures 2 and 3. Table 1 compares the OP removal predicted by each model to the measured pilot results for the same test. Both models closely aligned with the measured OP removal via struvite formation, and solid-phase characterization confirmed struvite as the major compound, as indicated by XRD pattern peaks. The presentation will showcase the outcomes derived from each model, offering insights into their respective abilities to predict the potential for the precipitation of controlling solids. The precipitate characterization analysis will also be compared to determine the validity of results and to further optimize both modeling software. The results of this study will enhance our understanding regarding scaling minerals likely to form within anaerobic digestion pretreated with a thermal hydrolysis process, post anaerobic digestion, and on downstream equipment, as well as in a potential post aerobic digestion setup. A validated model could then be used to predict scaling potential and characterize minerals formed at other WRRFs to better treat these nuisance scaling minerals and determine their potential for harvesting/sequestration as a nutrient rich product.

Purpose: Struvite (MgNH4PO4 · 6H2O) and other common precipitates have long posed persistent maintenance and operational challenges at wastewater treatment plants. These precipitates can be enhanced at plants that utilize biological phosphorus removal and can precipitate within anaerobic digesters and on final dewatering equipment which causes damage and decreases treatment efficiency. Struvite can be sequestered as nutrient rich biosolids if properly controlled to remain in the cake. In a digested solids storage tank (DSST) that is in between anaerobic digestion and final dewatering, precipitation can be controlled by manipulating variables such as mixing, aeration of digestate to achieve a low solids retention time (SRT) post aerobic digestion (PAD) and by chemical addition. Optimizing this via pilot testing can control nuisance struvite formation, increase phosphorus in the cake and achieve additional volatile solids reduction (VSR). This research will review findings from pilot scale tests and discuss the nature of these precipitates. Objectives include determining the mechanisms that provide optimal phosphorus removal, ammonia removal, solids removal, and analyzing the precipitated solids of interest. The presentation will discuss results and lessons learned at the pilot scale and how they might translate to full scale plant upgrades. Motivation and Background: The Atlantic Treatment Plant (ATP) in Virginia Beach, VA, operated by Hampton Roads Sanitation District (HRSD) is a high-rate facility with an A/O process configuration. In solids handling, a Thermal Hydrolysis Process (THP) is utilized prior to anaerobic digestion. ATP is actively engaged in efforts to control formation of scaling precipitates and nuisance struvite for optimal operational efficiency. Precipitate formation is determined predominantly by the solids solubility product (Ksp) and the saturation in solution and can be controlled by pH [1]. Manipulation of pH via CO2 stripping from agitation and aeration has successfully been shown to control solubility reactions [2, 3]. Increasing the saturation index via chemical addition can also control precipitation reactions and improve cake dryness with an SRT of a few hours [4]. Likewise, PAD has been shown to achieve ammonia removal and additional VSR at a 5-6 day SRT [5]. Based on these findings, a pilot scale set up (Figure 1) was operated at an SRT of 3 days to provide some benefits from PAD such as ammonia removal, but with a longer reaction time that may be more beneficial for phosphorus mineral sequestration. Mixing, aeration rates, and chemical addition were manipulated to determine the optimal operation conditions on phosphorus sequestration in the Class A biosolids. Pilot Design and Operation: The pilot setup at ATP consisted of four tanks. Each tank had a volume of about 45 gallons. Simulating the DSST, the tanks were operated as daily batch fed continuously stirred tank reactors maintained by pump recirculation with a 3-day SRT. The tanks were aerated with fine bubble diffuser membranes which were operated at either constant air flow rates, or via Dissolved Oxygen (DO) or pH set points. Results: Six pilot campaigns were conducted to test the effects of aeration at a constant flow rate of 5 LPM, at a DO setpoint of 0.2 mg/L, and at pH setpoints of 7.5, 8, 8.5, and 9. Mg(OH)2 and Ca(OH)2 were injected at various Ca2++Mg2+:P ratios of 0 (control), 0.25:1, 0.5:1, 1:1, 1.3:1 and 1.6:1, and the effects of mixing was studied. Pilot results indicated aeration on a DO setpoint provided more stability to pH and DO measurements than constant aeration, which had a direct improvement on OP-P removal, NH3-N removal, the formation of precipitates, and alkalinity removal. Both Mg(OH)2 and Ca(OH)2 addition effectively removed OP-P, with improved efficiency as the Ca2++Mg2+:P ratio increased. At the higher 1:1 dosage, the performance of these two chemicals and aeration settings converged, showing no statistically significant difference in their phosphorus removal efficiency. The maximum OP-P removal achieved was 97% with aeration on a DO setpoint and Mg(OH)2 addition at a ratio Ca2++Mg2+:P of 1.3:1 (Figure 2). NH3-N removal averaged around 10-20%, with more efficient removal measured in the tests aerated at a DO setpoint. Ammonia-N removal was assumed to be due mostly to precipitation as struvite, with moderate ammonia stripping available at the pH values measured in these tests. No nitrification was observed in PAD most likely due to free ammonia (FA) inhibition. Alkalinity removal in each test surpassed what was calculated as the alkalinity consumption due to the predicted struvite formation, indicating that further coprecipitation reactions with struvite could be occurring. Finally, implementing aeration and mixing on TH-AD solids consistently achieved about 20% total COD removal across the pilot. However, when the influence of mixing was eliminated, total COD removal decreased by nearly half, suggesting that physical shear from the mixing pumps played a significant role in breaking down colloidal COD into soluble forms, which were more readily biodegradable. Persistent pilot research can lead to striking the balance between chemical and aeration costs, phosphorus removal benefits, struvite control to protect downstream equipment and treatment efficiency, as well as additional VSR achieved from PAD. This research will influence the DSST design modifications and operation in a future plant upgrade at ATP as well as provide key takeaways for plants with similar issues with scaling precipitates altogether.

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

In the realm of local governance, navigating biosolids management projects requires adept engagement with local government elected officials. This presentation delves into the intricate challenges surrounding the comprehension of biosolids technologies and regulations among policymakers, emphasizing the paramount importance of a transparent policy development process. From selecting alternatives to assessing options and developing criteria, this multi-step approach empowers elected officials to weigh choices effectively. By elucidating these complexities and advocating for a robust decision-making framework, stakeholders can expedite the journey of biosolids management projects across the finish line, ensuring informed and impactful outcomes. The development of a biosolids strategy is unique for every utility and region. There is no 'one-size-fits-all' approach as biosolids management strategies weigh heavily on quantity, quality, and available regional markets combined with state and federal regulations. Thus, navigating the selection of a particular strategy can prove to be challenging and often depends on multiple factors. One important factor is the desire of the agency to embrace sustainability and reuse. This is a key consideration as processes that implement a more sustainable approach to recycling and reusing biosolids are also more cost intensive. In far too many cases, we hear about utility policies or projects that were almost enacted but never received approval by the elected board and in some cases, it was squashed before even getting on a board agenda. We can call this 'getting across the finish line'. In some cases, much effort was expended in completing various studies and analysis for a particular project or program, yet for one reason or another, it just never got put into action because someone within the hierarchal structure decided that it was not politically feasible. It is my belief based on experience that 95% of the overall effort is in getting the project through the last 5% of approvals (with the final approval being the elected body). That said, it means that much more effort should be placed on political strategy to ensure successful approvals are obtained, enabling the program to move forward with implementation. Specifically, the strategy should involve a concerted effort towards a formal policy adoption process. Without that, projects will continue to stagnate, and progress towards a more vibrant utility will stall. Utilizing the Kraft policy process model, utilities can more effectively implement solutions through gaining approval and acceptance by elected officials. The policy process model is comprised of six steps that form the lifecycle of a policy -- or policy cycle. The six steps of the policy cycle are: - Agenda setting -- this represents the recognition of a problem combined with a definition of what the problem is. - Policy formulation -- this involves the development of a policy which seeks to remedy the identified problem. - Policy legitimation -- this involves the determination of authority for government to enact the policy. This step can involve all three executive branches through their checks and balances of laws enacted, enforced or challenged as well as public perception of the policy. - Policy implementation -- this involves the enforcement and execution of the policy after the law is enacted. - Policy and program evaluation -- this involves the study of the efficacy of the policy in solving the original problem. - Policy change -- this is a change or modification to the existing policy after new information is obtained and evaluated. A pivotal step in the policy formulation step is the assessment of alternatives. Kraft's policy approach to assessing alternatives and using criteria involves thoroughly evaluating potential options based on predetermined criteria. This includes analyzing factors such as cost, effectiveness, sustainability, and political feasibility for each policy alternative. By doing this, utilities can employ a systematic process to weigh the pros and cons of each alternative before making a final selection thereby guiding their elected board transparently and strategically through the policy evaluation process. By providing policy alternatives to the elected board or council, combined with analysis of criteria of each alternative, the elected body will be able to weigh each alternative and make an informed decision. This also enables the board to retain appropriate power and authority over the decision, while limiting options so that they are not overwhelmed with too many complexities that create confusion and indecisiveness. In this presentation, we will evaluate a case study involving a private sewer lateral policy in Pinellas County, Florida, that used an alternatives analysis approach to policy adoption and by doing so, successfully adopted a comprehensive policy with unanimous approval. This case study will include specific materials that were included in the board packets that provided summarized information for each option and therefore encouraged a more transparent process for decision-making. Then, we will take this approach and show how it could be applied to evaluating alternative options for a biosolids management strategy. In conclusion, I will summarize all of the key takeaways and provide reference materials that can be used to help guide the process. I will also provide an update on the ongoing activities of the Southeast Biosolids Association (SEBA) and the progress that has been made in standing up the organization as well as the significant advocacy efforts that are underway. Additionally, I will review the call to action for membership and staying vigilant in advocacy efforts that support the sustainable and beneficial use of biosolids.

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.

Energy consumption and greenhouse gas (GHG) emissions are the two important factors to consider when water utilities plan for sustainable capital upgrade and operational modifications of wastewater treatment plants (WWTPs). Researchers have reported the use of several methods, such as flux chambers, drone flux methods, optical gas imagers, etc. for monitoring the fugitive GHG emissions, mainly methane (CH4) and nitrous oxide (N2O), from WWTPs. However, limited by the short duration of most monitoring technologies, only 'snapshot' data can be obtained, necessitating extrapolation of the limited data for estimating the annual emissions. Extrapolation introduces substantial errors as it fails to account for the temporal variations of fugitive GHG emissions. This multi-year project, starting in June 2021, has performed a screening and evaluation of a variety of technologies, consisting of sampling- and non-sampling-based, point and long spatial-range, mobile and stationary methods. The technologies that are suitable for monitoring GHG from WWTPs have been selected to develop a tiered, cross-validating approach to cost-effectively characterize the temporal dynamics of both plant-wide and process-specific GHG emissions. This presentation will start with a brief introduction of how the team has combined satellite imagery, ground based open-path and closed-path optical sensing, optical gas imaging, flux chamber, dispersion modeling, and low-cost sensor network, for measuring fugitive GHG emissions from WWTPs, followed by a detailed case study of how a satellite imagery-based algorithm was developed for capturing the complex, temporally and spatially heterogeneous CH4 emissions associated with the biosolids treatment process at wastewater treatment plants. Satellite remote sensing has been widely used in finding and quantifying natural gas leaks in oil & gas facilities and methane emissions from landfills. However, to date, the use of satellite imagery for analyzing methane emissions from wastewater treatment has been extremely rare, if not none, for which the likely reason is that the low pixel resolution of earlier satellite images is not able to capture the relatively smaller plumes from wastewater treatment plants. Recent advances in satellite technology have made significant progress in methane monitoring that high-resolution tracking capability has become available. This allows for the development of image processing algorithms to capture the methane plumes from facilities of smaller footprints such as the WWTPs. This study has developed an algorithm for characterizing the long-term CH4 emissions from the biosolids handling process using the high spatial resolution Sentinel-2 data. Sentinel-2 satellite imaging, despite of its fewer spectral bands than hyperspectral satellites, is of a superior spatial resolution of 20 m x 20 m and a more frequent revisit intervals of 3 days in the study areas. This feature is especially beneficial for tracking time-varying fugitive emissions for sources with relatively lower intensity plumes such as the biosolids treatment process at WWTPs. Three representative WWTPs, with the following three different biosolids handling processes, have been evaluated in this study: Plant #1, conventional anaerobic digestion; Plant #2, intensified anaerobic digestion with thermal hydrolysis process; Plant #3, biosolids dewatering only with no anaerobic digestion. The short-wavelength infrared (SWIR) bands 11 (1560--1660 nm) and 12 (2090--2290 nm) of Sentinel-2 were used to retrieve methane column concentrations by analyzing reflectance differences between the spectral bands and across multiple satellite passes. Satellite images taken between 2019 and 2023 were processed to retrieve the CH4 column concentration distributions. Digital image processing techniques were developed and used for extracting the time- and space- varying features of CH4 emissions, revealing the daily, monthly, seasonal, and annual emission variations. Figure 1 summarizes the data processing procedure. Emission hotspots were identified and corroborated with ground-based measurement using an infrared optical gas imager. The findings reveal the 'ever-changing' dynamic nature of fugitive CH4 emissions from the biosolids handling units, as shown in Figure 2 and Figure 3, indicating the importance of performing continuous measurements for estimating the annual CH4 emissions. Emissions from the three biosolids processing facilities are also quantitatively evaluated for a comparison. This study demonstrates the feasibility of using satellite imagery to capture methane plumes from the biosolids processing area inside a WWTP, demonstrating the value of using satellite images for cost-effectively localizing emission sources and estimating plumes based on the column concentrations. On the other hand, the data also suggests that satellite imagery by itself is not a self-sufficient method. Hence, while satellite imagery serves to cost-effectively provide a 'big picture' view of the long-term emission dynamics as well as to localize emission hotspots, a full quantification of fugitive CH4 emissions requires incorporation of additional data such as meteorological information and ground-based measurements.

EXECUTIVE SUMMARY (100 words maximum) Thermal Hydrolysis process (THP) is a well stablished technology with more than 25 years of experience. Different configurations of the biosolids line have been trialled to maximise the efficiency of the mass and energy balance. One successful configuration is the Intermediate THP (ITHP) arrangement, with THP in between two anaerobic digestion phases. A full ITHP biosolids line was built and is now in operation giving the expected preliminary results as those found at lab scale (Rus et al., 2017): an average 510Nm3/tDS biogas yield, 60-65%VSR, and an increase in dewatering of 7 percentual points so far (from 18%DS to 25%DS). INTRODUCTION Thermal hydrolysis process (THP) has proven to be an efficient pre-treatment for sludge before anaerobic digestion (AD), by thermally enhancing hydrolysis, the rate limiting step in AD (Shana et al., 2013). Early research (Shana et al., 2012, Mills et al., 2014) showed that a new configuration of THP and AD technology can further enhance the efficiency of THP in the biosolids line. The positive results found at lab scale led to the construction of the ITHP pilot plant at Basingstoke STW, UK, to evaluate its viability at a more realistic scale in Rus et al., (2017). The success at the large pilot plant took this process one step further, with several full-scale options being considered by the water industry. In 2020, one of the municipal wastewater treatment plant decided ITHP was the best option for their site and the concept has now been implemented there. This paper covers the initial phases of commissioning and preliminary results obtained YEAR CASE STUDY WAS IMPLEMENTED 2021 to 2024 CASE STUDY DETAIL Specific Issue: A municipality in Europe needed to develop a new biosolids strategy for their wastewater treatment plant. The sludge design throughput was to be 11,729 tonnes of dry solids per year (tDS/y), with an average of 23tDS/d going into the site at the time (2021). The plant has two 8,000 m3 digesters and one existing 7,500 m3 digester. The municipality was interested in maximizing biogas generation for electrical energy production and heat and improving dewaterability of the final digestate to minimise final cake haulage costs to incineration. Approach: In 2021, the municipality started their process of construction of an ITHP facility which included design, execution, completion, pre-commissioning, remedying defects, and staff training (Figure 1). They already were running the first two digesters in parallel and the 3rd one in series therefore they did not need to rearrange the biosolids flow line (figure 2). The required additional parts were a dewatering stage between 1st stage digestion and the THP to bring digestate from digesters 1 and 2 from 3% to 16%DS. The THP unit (1 stream of CambiTHP B2), and a boiler for steam generation. Methods or summary of activities: The company had historical data from 2021 where site performance was collected prior to the installation of the Cambi THP system in the spring of 2023. This data gathered information on flows and loads into the site and 1st stage AD (2 digesters) and 2nd stage AD, final dewatering dry solids, biogas generation and CHP electrical output was collected. Biogas yields and volatile solids reduction (VSR) was calculated. In June 2023, the THP plant was commissioned, and a guarantee period started later in 2024. The same data was collected for this period. Summary of outcomes and measurable impacts: Figures 3 and 4 show the overall VSR percentage and gas yields in terms of m3 biogas per Volatile solids in the feed (m3/tVS). The green line shows the point in time where the THP started to operate. Steady state was reached in March 2024. The hard blue lines are the average for the periods delimitated by the green line (introduction of the THP). The light blue shadow is the standard deviation (SD) for that same period. During the ramp up of the ITHP plant, the 2nd stage digester reacted very well, with a steady increase in performance both in terms of VSR and associated biogas yields. The transition from a conventional AD to an enhanced AD (i.e. preceded by THP) was smooth. Once steady state was reached, the guarantee period started. We can observe the average VSR during this period was 60% and gas yields stabilised around 550m3/tVS fed. This was what Cambi expected to obtain given the initial conditions of 40%VSR and 400m3/tVS fed. The average throughput during guarantee period was 22.8tDS/d equivalent to 8322 tDS/year, successfully maintaining a similar throughput to the previous 2 years (figure 5). On final dewatering, Figure 6 shows preliminary results, with most recent data showing 25%DS from 17.7%DS average prior to ITHP. Since the plant requires several retention times for the process to stabilise, we expect dewatering to reach steady state in the coming months. Important lessons learnt and critical success factors The key factors in delivering this project were to ensure the THP is embedded correctly into the Biosolids line, with a good control on pre-THP dewatering. Ensure there is good knowledge on the expected increase in the rate of biogas release in the 2nd stage AD (after the THP). Including in the design a robust mixing system which allows for a quick extraction of biogas from the digestate column. During installation and commissioning of the THP, good communication with the plant operations team was essential, with support during ramp up when needed and weekly data output observation. Reaching steady state was achieved successfully as planned thanks to a detailed, non-aggressive plan for ramp up was in place. Training and engagement of operations from the earliest stages of project proposal through to delivery is essential to ensure they feel ownership of the new technology at their plant. The extent to which the outcomes are sustainable Overall, the preliminary results obtained from commissioning of the ITHP have been very encouraging. Table 1 summarises preliminary outcomes. Savings of haulage and incineration together with the increase in biogas generation make the CapEx investment cost efficient. Nevertheless, these are initial results. Data will continue to be gathered and presented to give an update of steady state ITHP performances at the plant.