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Introduction Clean Water Services (CWS) is a wastewater, stormwater, and watershed management utility serving the populous of Washington County, Oregon through implementation of a watershed based NPDES permit. CWS operates 4 water resource recovery facilities (WRRF), of which two are advanced treatment facilities producing Class B biosolids through mesophilic anaerobic digestion and centrifuge dewatering. Struvite fertilizer is manufactured from thickening and dewatering liquors. The NPDES permit requires phosphorus removal to 0.10 mg/L from May to October, accomplished with a combination of enhanced biological phosphorus removal (EBPR) and chemical phosphorus removal by alum addition in primary and tertiary processes. The ramification in solids processing is that there exists significantly different sludge dewaterability characteristics between the summer and winter months. In the winter of 2014, faced with outlandish polymer doses (~80 lbs. active/dry ton) CWS completed a consultant assisted (The Centrifuge Guy) optimization of the dewatering process that led to a new sensibility in centrifuge operation focused on achieving the lowest total cost for biosolids production. The subsequence of this original optimization has been the development of an intelligent biosolids system that appropriates technology, software, and human resources to achieve total cost efficiency in the biosolids management program, in both materials and labor. Centrifuge Operation Dewatering operators are burdened by triumvirate goals; high cake solids, low centrate or filtrate solids, and polymer dose control. Relationships between the three are not simple and site specific. Maximizing one parameter often leads to sacrificing the others. When the goals are aggregated and presented as the component costs of haul, polymer, and recycled solids and as the total cost, the job becomes clear. Beginning with simple spreadsheet tools, CWS has advanced cost driven centrifuge operation to real-time SCADA displays and trending. A centrifuge replacement project offered the opportunity to add instrumentation to the process to advance real-time analysis to real-time control. Process analyzers (Valmet) were installed on the feed sludge line and cake chute for total solids (TS) and on the centrate drain line for total suspended solids (TSS). Previous iterations of cost calculations relied on daily laboratory data and operator analysis of cake solids by moisture analyzer Technology employed in the new system enabled true real-time information. It has also enabled new control automation modes. In TSS control, the polymer dose is adjusted by the PLC to maintain a centrate TSS setpoint for quality control in the feed to fertilizer manufacturing. Data and Report Automation An immense amount of data must be generated, transformed, analyzed and maintained to meet the requirements in the 40 CFR Part 503 regulations as well as to comply with biosolids management plans required by state agencies. An immensity of human resources can be expended to manage this flow of data. Manual transmission of data between databases is not only time consuming but also increases the odds of erroneous data. CWS has implemented smart technologies and digital solutions to automate much of this data management. A prime example of this is the installation of smart scales used to weigh biosolids trucks. Previously weigh tickets would be collected at the end of the month and hand entered into a spreadsheet on an individual hard drive. Utilizing the smart scale, all the ticket data is automatically imported into a SharePoint site that tracks each load as it happens, including weight, vehicle number, and application site destination. Field reports are provided by the applier as they happen and field completion status is continuously updated. The biosolids annual report required by Oregon DEQ contains 21 sections of information to be filled in and an additional 40 pages of supporting documentation. With all the information now located in Hach WIMS and SharePoint databases, the report is largely auto-populated, requires little manual entry, and a final review. Communication and Visualization Power BI has been deployed extensively for communication to managers and stakeholders, but also for visualization of operational efficiency by process control analysts. These dashboards display information ranging from average monthly cake solids to fuel price history and transactions to financial information like budget to actual expenditures. The value of these dashboards is that they aggregate data from different data generators and make it easily accessible to anyone inside or outside CWS. Ongoing Development Efficiencies are continuing to be found by CWS staff. Integration of GIS software is underway to facilitate field application planning that will minimize the distance and number of times that application equipment must be moved to a new site. GIS systems can also be used as visual interfaces providing an array of data on application sites as well as for customizing application rates down to the detailed level of specific sections of an individual field. CWS is also undertaking the agronomy aspect of land applying biosolids as an in-house function. Although it is a small part of the total cost of biosolids utilization, there is the potential for cutting a high amount of waste from the process. Empowering the biosolids management staff with agronomy education and skills can make it possible for a single individual to make a single site visit and accomplish a suite of tasks; field inspection, soil sampling, meeting with hauling and application operators, and developing the personal relationships with landowners that are vital to the success and future of beneficial reuse of biosolids.

Overview: Pyrolysis is the thermal decomposition of organic matter at elevated temperatures (250-750 °C) in an inert atmosphere (i.e., in the absence of oxygen). During pyrolysis, volatiles including contaminants of emerging concern (CECs) such as PFAS are driven off into a high heating value gas phase that can be harnessed for biosolids drying or other onsite energy use. The remaining solids are a carbon-rich biochar with high nutrient content suitable for direct land application or blending into high value fertilizer product. Pyrolysis represents a critical tool to sustainably manage biosolids and support effective resource recovery for nutrients and energy. Pyrolysis will become increasingly valuable as biosolids management options are expected to be further constrained by state and national policies including landfilling bans, land application restrictions, competition for compost capacity, and federal PFAS regulations. Located in Rialto, CA, Rialto Bioenergy Facility (RBF) provides an important case study as the largest biosolids pyrolysis facility constructed in North America. It is designed and permitted to process 300 tons per day (TPD) (equivalent to 75 dry tons per day, DTPD) of dewatered biosolids from municipal WWTPs. The facility is owned by Anaergia, who is responsible for design, construction, financing, operations, and maintenance of the facility, as well as feedstock management and marketing and distribution of the biochar end-products. Low temperature belt dryers and a subsequent Anaergia-developed and -patented high-temperature pyrolysis process converts Class B Biosolids into a biochar product (Class A) for use as a fertilizer. The facility's drying operations currently operate continuously, twenty-four (24) hours per day and seven (7) days per week. The proprietary pyrolysis system will begin commissioning in Q1 2023 with commissioning data and lessons learned to date available for conference date of May 2023. The goals of this plant include: -Maximizing biochar value by eliminating PFAS and other contaminants of emerging concern (CECs) while maximizing carbon and nutrient yield -Maximizing heat recovery for autothermal drying -Meeting South Coast Air Quality Management District (SCAQMD) permitting limits -Demonstrating successful full-scale operation of biosolids pyrolysis Process Description: Feed Handling: RBF receives up to 300 tons per day of dewatered biosolids from municipal WWTP's in Southern California, which are transported to the facility via end-dump truck. The offloading area at RBF includes one (1) below-grade reception bin dedicated for biosolids receiving. The bins are vented to an odor control system and piston pumps are used to transfer the biosolids to a storage silo, prior to pumping to the belt dryers for processing. Drying: The dewatered biosolids are dried to 90% total solids (TS) in two (2) 5-tph evaporation capacity belt dryers. While the pyrolysis system is in construction, dryers currently recover heat from CHP engines on site; the dryers will ultimately recover heat from the pyrolyzer via thermal oil. Dryer foul air passes through an ammonia scrubber, regenerative thermal oxidizer (RTO), and SOx scrubber to meet SCAQMD requirements before being released to atmosphere. Dried product recycle is used in the dryers to produce a granular Class A dried biosolids product. From the dryers, the dried biosolids are pneumatically conveyed to a nitrogen blanketed biosolids storage silo with truck loading, or conveyed to the pyrolysis system for carbonization. Pyrolysis: Biosolids from the dryer are forwarded to a 3.5 tph indirectly heated pyrolysis unit where the biosolids are converted in the absence of oxygen to pyrogas and biochar. Biosolids are processed at temperatures up to 1600 degrees F with adjustable residence time to maximize fixed carbon yield while eliminating PFAS and other CECs (see Table 1). Out of the pyrolyzer, the biochar is cooled to below 40 degrees C before being forwarded to bagging or storage. Pyrogas generated via this process is sent through heat traced pipe directly to the thermal oxidizer. Thermal Oxidizer, Heat Recovery, & Flue Gas Cleaning: The pyrogas from the pyrolyzer is processed directly in a multi-stage low-NOx thermal oxidizer (TO) with >2 seconds residence time. The TO is used to eliminate volatile organic compounds (VOCs) and contaminants of concern in the pyrogas, release their available heat while keeping NOx limts below 200 ppmvd@3%O2. Downstream of the TO, flue gas passes through a thermal oil heat exchanger from which recovered heat is directed to the dryers to achieve energy neutral operation. Flue gas is subsequently treated via Selective Catalytic Reduction (SCR), SOx scrubbing, and mist/particle elimination. This system provides best available control technology (BACT) and is permitted in SCAQMD among the nation's most stringent with NOx <30 ppmvd@3%O2 and SOx <1ppmvd@3%O2. Downstream of the flue gas cleaning equipment, induced draft fans are used to motivate the pyrogas and flue gas through the system while maintaining a slight vacuum through the entire system to eliminate any fugitive emissions. Biochar End Use: Carbon- and nutrient-rich biochar produced at RBF will be transported approximately 15 miles to a local Anaergia-owned fertilizer blending facility. The product is a nutrient-balanced fertilizer with high levels of nitrogen, phosphorus, and potassium, with significantly lower carbon intensity than traditional fertilizers. As a carbon-negative product, carbon removal credits from biochar production will be sold on the voluntary market. This approach maximizes the value that can be realized from the biochar product, allows direct to consumer sales to commercial agricultural operations, and facilitates direct replacement of conventional commercial fertilizers, reducing barrier to entry for end-users. As the remaining mass is approximately one-eighth to one-tenth that the inbound biosolids, the biochar may be much more readily managed. Research conducted by Anaergia indicates that crops perform equally as well when fertilized with blended biochar product as with conventional commercial fertilizers. Numerous studies indicate additional environmental benefits from use of biochar for agriculture, which may be referenced in the presentation. Benefits for Biosolids Generators: In addition to environmental benefits associated with pyrolysis and biochar use, RBF pyrolysis provides operational benefits to biosolids generators. RBF is contracted to receive biosolids from municipal generators throughout Southern California. RBF provides municipalities with a Class A biosolids management outlet and can offer guaranteed and/or fail-safe capacity. As a regional biosolids disposal option, RBF allows municipalities to achieve reduced vehicle mileage associated with hauling of biosolids to farther-flung alternative outlets, as well as improved service reliability and hauler availability resulting from reduced trip time. Pyrolysis at RBF offers destruction of PFAS and other CECs, providing 'future-proof' compliance to WRRFs for anticipated regulations pertaining to biosolids management and land application. Lessons Learned: Lessons learned from the design, permitting, construction, and commissioning phases of North America's largest biosolids pyrolysis facility will be shared. Data presented will focus on air emissions, mass and energy balances, and analysis confirming PFAS and CEC destruction through the operating pyrolysis system. Discussion may include favorable applications and various delivery approaches.

Food waste disposers (garbage disposals) are present in nearly 60% of US homes and are used primarily for hygiene and convenience. However, given the current trends of reducing food waste and loss, diversion of organics from landfills, and resource recovery at wastewater treatment plants, disposers are uniquely positioned to become important tools of sustainability. They assist with food waste reduction by responsibly managing the unavoidable portion of our household kitchen waste and limit the amount sent to landfills. Nine US states have recently adopted regulations to prevent food waste from entering landfills, but cities are looking for more solutions. Sending food waste instead to our wastewater treatment plants through disposers allows for recovering clean water, energy, and nutrients. Although using disposers to address environmental challenges may seem counterintuitive, much information is available to dispel common myths and misconceptions, supporting the rationale for encouraging the use of these common household appliances. According to the USEPA, 15% of all residential food waste is managed via sewers, mainly by using food waste disposers (garbage disposals). However, food waste remains the largest fraction of our municipal solid waste. As communities look for alternative solutions to manage food waste and divert organics from landfills to meet state and local mandates, governmental officials should consider existing research and literature supporting the expanded use of disposers. They provide the least expensive option for managing food waste, result in lower global warming potential than landfilling, and can help reduce overall costs for wastewater treatment plants. An evaluation in five different US cities determined that typical homes with disposers reduce food waste in garbage by 30%, and there is an opportunity to divert more with proper education and outreach. This presentation will provide much background information on existing research and available case studies. Parallel to the growing trend to divert organics from landfills, several wastewater treatment plants across North America are focusing on resource recovery the conversion of waste to clean water, energy, and fertilizer. Plants with anaerobic digesters are particularly equipped for resource recovery, with some plants even utilizing commercial and industrial food waste for codigestion feedstock to augment biogas production in their anaerobic digesters. There is also an opportunity to rely on residential food waste disposers to supply feedstock to augment biogas production. Widely accepted and present in approximately 60% of all the U.S. homes, disposers have traditionally been used for convenience and hygiene because they facilitate immediate elimination of food scraps from the kitchen. Since food waste is largely removed during primary clarification and is transferred to digesters, and produces more biogas than sewage sludge, disposer use increases biogas production. Food waste is also high in carbon relative to the nutrients phosphorus and nitrogen, and because many wastewater treatment plants are carbon deficient, it can also improve nutrient removal efficiency. Unfortunately, disposers are often overlooked and misunderstood as viable tools to promote organics diversion and resource recovery. In 2013, to quantify the energy balance and nutrient removal impacts of residential food waste disposers, Harold Leverenz and George Tchobanoglous utilized BioWin wastewater modeling for a community of 130,000 assuming 10%, 50% and 100% adoption of disposers. Three different wastewater treatment plants were modeled, including a conventional activated sludge plant with nitrification, a Modified Ludzack-Ettinger (MLE) plant, and a Bardenpho plant, all with anaerobic digestion with combined heat and power for using biogas. On a net basis, energy produced is higher than demand for sending food waste to all three treatment plants. In addition, there is a negligible increase in nutrients entering each of the plants from food waste disposers, even at 100% usage, and more importantly, there is moderate improvement in the removal of nutrients. More extensive BioWin modeling of the impacts of food waste on wastewater treatment plant was conducted under the direction of George Nakhla of Western University and later published in 2019. This research confirmed food wastes (FW) are an excellent resource for energy recovery through generation of biogas from anaerobic digestion, and as carbon for nutrient removal. This modeling also investigated the impact of food wastes on operational costs, effluent quality, and energy benefit for CAS, MLE, A2O, Bardenpho, as well as sidestream processes. Simulations were conducted at FW addition of 0, 50, and 100% penetration of food waste disposers for a 10 MGD plant. All scenarios employed chemical P removal using ferric chloride to achieve an effluent total P of 0.5 mg/L. The four processes were simulated for four different operational conditions using MWW and FW characteristics from literature. Total operational costs were calculated for aeration, biosolids disposal, and the chemicals required for dewatering, P removal, and P precipitation in anaerobic digesters (BNR processes only). Net operational costs were calculated by deducting methane energy from total operational costs for CAS and by subtracting methane energy and glycerol cost from the total operational costs for the three BNRs. Glycerol cost was estimated based on the quantity of glycerol COD needed to achieve the same effluent TN for the plants without FW as the plants with FW. Results indicate insignificant impact of food waste on effluent BOD quality. Effluent nitrogen concentrations for CAS with/without FW addition were similar, indicating no impact of FW on nitrogen removal. In contrast, with FW addition TN levels for MLE decreased by up to 8 mg/L for all four cases. A2O and Bardenpho also showed that TN decreased with FW addition by 1-2 mg/L. FW addition enhanced nitrogen removal for BNR processes. FW addition increased biosolids production for the four systems by up to 11%. Biogas generation also increased by 38% with FW 100% addition in all four cases. FW addition increased aeration demand by up to 12%-22%. Iron dosage for chemical P removal slightly increased by 3% for CAS and MLE, contrary to significant drop for A2O and Bardenpho, indicating that FW addition enhanced biological P removal with decreasing chemical dosage. Similarly, FW addition increased chemical uses for dewatering by <11% for all processes. FW addition also decreased external carbon addition for nitrogen removal. The estimated saving for external carbon based on glycerol were up to 3504 - 3822 lb/day for MLE, 355-732 lb/day (A2O), and 527-1170 lb/day (Bardenpho). FW addition increased total operational cost by up to 8-11% (CAS and MLE) and by 3%-4% (A2O) but decreased it by 3%-4% (A2O) and by 5-9% (Bardenpho). With FW supplementation, net operational costs decreased by 4%-8% (CAS), 63%-78% (MLE), 40%-46% (A2O), and 54%-62% (Bardenpho), indicating a substantial net cost saving for BNR processes. The net cost savings were because FW enhanced biogas production and nutrient removal which decreased chemical addition for P removal and external carbon for nitrogen removal. FW addition increased net total energy by 6484-6947 kWh/d (CAS), 6759-6942 kWh/d (MLE), 7153-7258 kWh/d (A2O), and 7159-7246 kWh/d (Bardenpho). FW addition decreased effluent nitrogen for BNR processes and increased biosolids and biogas production. Aeration cost increased with FW addition while chemical cost for P removal decreased for A2O and Bardenpho processes. FW addition decreased net operational costs and net total total energy. The impact of FW positively increased with higher solids removal in primary clarification. Based on this modeling, and the trends to divert organics from landfills and improve resource recovery, municipal officials should consider the potential role of residential food waste disposers.

PROBLEM STATEMENT/PURPOSE: Prince William County Service Authority (PWCSA) owns and operates the H.L. Mooney Advanced Water Reclamation Facility (AWRF) in Northern VA. The AWRF is nestled in a residential community with parks and a walking path along the property line. The AWRF first implemented odor control in 2001, and subsequently upgraded the system in 2011 to provide odor control for preliminary treatment and solids thickening processes. To further reduce odors at the AWRF's property line and beyond, PWCSA is completing a design-build project that includes the assessment of odors at the AWRF through sampling and dispersion modeling, evaluation of odor control technologies, and the design and construction of the chosen system. The purpose of this abstract is to present the odor sampling, monitoring, and extensive dispersion modeling that led to the current design (2022) and future construction (2023) of a 95,000 CFM centralized odor control facility at the AWRF.

BACKGROUND:
The AWRF is located in Woodbridge, VA, approximately 30 miles outside Washington, DC and is in close proximity to several livable communities, nature parks, and walking paths. The AWRF is designed to treat 24 million gallons per day (mgd) average daily flow with current flows in the 14 to 16 mgd range. The AWRF has an existing packed tower chemical scrubber odor control system that treats odors from preaeration, screening, grit removal, and gravity thickening processes at the AWRF. Odorous air from solids dewatering and incineration are routed out of a high stack for improved dispersion. However, odor control improvements are needed to reduce odors within the AWRF site and reduce odor excursions into neighboring residential communities and walking paths outside the AWRF property line.

METHODOLOGY:
In the summer of 2021 odor sampling was conducted at various source locations throughout the AWRF to characterize the odors onsite coming from untreated sources and assess the treatment of the existing odor control facility. Odor sampling was completed during summer months to obtain samples under worst-case conditions (warm weather, higher anticipated odors). The sampled untreated process sources included the equalization basins, primary clarifiers, aeration basins, solids processing building odor exhaust (untreated odors routed to the high stack), and the incinerator exhaust stack. In addition to the untreated odor sources, sampling was also completed on the chemical scrubber inlet and outlet to assess the system performance. The odor sampling completed included: -US EPA Surface Emission Isolation Flux Chamber -Grab samples collected for olfactory odor analysis by ASTM E679 -Odor speciation using ASTM D194 -Reduced sulfur compounds using USEPA Method TO-15 (GC/FPD detector) -Field measurement of H2S using Acrulogs and Jerome 631X H2S meters -Ammonia, Amines, and Dissolved Sulfide with Colorimetric Detection Tubes -Temperature and pH Sampling data was evaluated and used to characterize the types and concentrations of odor species present at the AWRF, and to determine the odor emission rates from each odor source for use in the dispersion model.

RESULTS:
The results of the sampling showed the solids processing building exhaust to have the highest dilution to threshold (D/T) value, followed by turbulent zones of the primary clarifiers, anoxic stages of the aerobic basins, and quiescent zones of the primary clarifiers. The chemical scrubber exhaust results showed the system to be effectively reducing odors from the treated sources. The speciation sampling resulted in the detection of four odor compounds including hydrogen sulfide, methyl mercaptan, dimethyl sulfide, and dimethyl disulfide. Ammonia was also detected in samples from the solids processing building. D/T results were used to develop the odor emission rates (OERs) for each odor source. OERs were developed by translating sampled values into odor units per second (OU/sec) based on airflow and odor magnitude. The OERS were used as inputs for the baseline emissions model, also known as the AERMOD dispersion model. Meteorological data for the AERMOD dispersion model was sourced directly from the National Oceanic and Atmospheric Administration archives for representative observation sites. The most recent three years of available data (2018–2020) were used in this analysis and surface data was obtained from the Quantico Marine Corps Airfield, which is 8 miles south of the AWRF. The resultant impacts calculated by AERMOD are expressed in odor units per cubic meter of air (OU/m3) and can be compared directly to the sampled D/T values. Several scenarios of modeling were completed to evaluate existing conditions, identify the most impactful sources of odor dispersion, and assess potential treatment solution results for the sources. The baseline dispersion model, or existing conditions scenario, showed the predicted impacts from the sampled odor sources on site and their impact outside the AWRF fence line. Figure 1 provides the baseline scenario potential impacts. The worst-case D/T concentrations predicted to reach a given area are shown with the color/label. Based on the baseline scenario, the odor source impacts of the AWRF would be noticeable, and potentially a nuisance, for all areas above 7 D/T (shown in yellow in Figure 1). This includes the communities to the north and east of the AWRF, which have maximum odorous impacts of 7 to 10 D/T. The wide impact of the 3 D/T contour extends beyond the frame of this view, which suggests that the AWRF could potentially contribute to ambient odors greater than 1 mile from the fence line. Individual sources were modeled and showed the solids processing building exhaust and the aerobic basin anoxic zones to have the greatest D/T dispersion impact. Before additional treatment options were evaluated, an odor impact criterion, or D/T fence line goal, was developed with PWCSA during several workshops. Virginia odor criteria are plant-specific, and a survey of Virginia plants showed criteria generally range from 5 to 10 D/T with different averaging time requirements. It was determined that the impact goal should be one that minimizes the risk of negatively impacting neighbors but is balanced with controlling increased cost that will be incurred if goals are excessively tight. For PWCSA, the recommended goal of 100 percent compliance with 7 D/T (1-hour impact goal) at the fence line was used for the evaluation of the model. Once the odor impact criterion was determined, six (6) additional modeling scenarios were developed to evaluate the impacts from treating/reducing odors from the untreated sources. The scenarios were as follow: 1.Treatment of solids processing building exhaust (assumed 90% D/T reduction from solids processing) 2.Coverage and treatment of the primary clarifier odors (assumed 95% D/T reduction from solids processing) 3.Combination of 1 and 2 (treatment of solids processing and primary clarifier odors) 4.Combination of 2 and treating EQ basin odors (assumed 50% D/T reduction from EQ basins) 5.Combination of 2 and covering and treating odors from the aerobic basin anoxic zones (90% reduction of odors from anoxic zones) 6. All control alternatives combined The different modeled scenarios showed the greatest odor reduction results for control scenario 6 (all sources treated), followed by control scenario 3 (primary clarifiers and solids processing building treated). Although control scenario 6 reduced the 7 D/T line impact slightly more than control scenario 3, both scenario results show benefit and bring the 7 D/T line close to the fence line. The model predicted dispersion results from scenario 3 are shown in Figure 2. All six of the scenario results will be shown in the presentation.

DISCUSSION/CONCLUSIONS:
The sampling and modeling results were used to identify the primary clarifiers and solids processing building as additional sources for odor control treatment at the AWRF. Once the sources were determined, a capacity assessment was completed on the existing system which showed it did not have sufficient capacity to treat the additional sources. A complete treatment technology evaluation was completed for the AWRF based on the airflows, odor species present, and required treatment for dispersion. Ultimately, the team decided to move forward with a new centralized chemical scrubber facility re-using the existing vessels and a new vessel to meet the design capacity of 95,000 CFM. Chemical scrubbers were chosen based on the sampling results, odorous airflow capacity requirements, and site space constraints. The presentation will provide insight and potential project path solutions for other utilities looking to evaluate the odor impacts from their treatment facilities on neighboring communities, experiencing odor complaints, or wishing to evaluate dispersion modeling uses.

INTRODUCTION Wasatch Resource Recovery (WRR) is an existing anaerobic digestion facility located in North Salt Lake, Utah, next to the South Davis Sewer District's South (SDSD) Wastewater Treatment Plant. WRR has anaerobic digesters that became operational in March 2019. Figure 1 is a picture of WRR. WRR receives organic waste streams, such as fats, oils, and grease; food scraps; liquid waste; pre-consumer food waste; and bottled waste. The digesters are operated at mesophilic conditions (approximately ~95 degrees Fahrenheit) and are equipped with gas mixing. The biogas produced from the anaerobic digesters is treated to renewable natural gas (RNG) standards while the digestate is dewatered to achieve 14 to 16 percent cake solids and then hauled off for land application. The centrate from the dewatering process is sent to a sidestream ammonia recovery process before it is conveyed to SDSD WWTP for further treatment. Wasatch Integrated Waste Management District (WIW) owns the Davis Material Recovery and Transfer Facility (Figure 2), which is a mixed waste receiving and processing facility located in Layton, Utah. The facility processes residential waste generated in Davis and Morgan Counties. WIW is interested in diverting the organic fraction of the mixed waste from the landfill to WRR for anaerobic digestion and biogas production. This paper evaluates the feasibility of anaerobically digesting the organic fraction of municipal solid waste (OFMSW) from WIW's Recovery and Transfer Facility using the existing digester capacity at WRR. The Study Objectives were to: -Determine the required pre-digestion processing of the OFMSW for digestion at WRR -Conduct digester capacity analysis to determine the available digester capacity at WRR to accept OFMSW from WIW -Determine biogas and biosolids production and side-stream impacts from WIW's OFMSW -Determine if the business case is economically feasible for both WRR and WIW METHODOLOGY The MSW from WIW will need major pre-processing and additional polishing steps before it will be suitable as feed to anaerobic digesters. WIW recovers metals, plastics, cardboard, etc. from MSW and operates a trommel screen that results in 2-inch minus product. The organics would be recovered from the 2-inch product using an organics extrusion press (OREX) system to produce the OFMSW wet cake for trucking to WRR. Further processing would be required at WRR where an Organics Polishing System (OPS) would be added to further polish the wet cake to remove glass and grit prior to digestion. Figure 3 shows the proposed process flow diagram for the business case evaluation. The digester capacity was evaluated based on organic loading rate and hydraulic retention time (HRT). Specific chemical oxygen demand (COD) load limit of 0.5 (.i.e mass of COD loading per day per mass of volatile solids in digester) and minimum HRT of 15 days were used as the evaluation criteria for the digester capacity analysis. RESULTS AND DISCUSSION Analysis of the digestion capacity at WRR found that there was available digester capacity for acceptance of OFMSW. All of the OFMSW from WIW could be accepted because of its higher solids content. The higher solids content was compatible with the lower solids content of the FOG and food waste currently being fed to the digesters. Adding the OFMSW increased the biomass in the digesters and improved the food to microorganism ratio for stable digestion operation. The key costs and parameters for the base case of the business case evaluation is shown in Table 1. The key parameters that had significant impact on the business case were residual distribution cost, OFMSW material quality, RNG value, and the chemical cost used in sidestream treatment at WRR. The business case assumed the residual and rejects distribution cost for all scenarios would include WIW backhauling the rejects and residual from WRR. Since the cost of trucking the cake material from WIW to WRR included the round-trip mileage and costs for going from the Davis Facility to WRR to the landfill/compost facility to the Davis Facility, it was assumed that there were not any additional costs to backhaul. A sensitivity analysis was conducted to evaluate how the business case shifts with varying key parameters. The sensitivity analysis focused on the following parameters: -HSW (assumes the quality of the OFMSW could be improved) -Sidestream chemical costs are offset by revenue from recovered ammonia as ammonium sulfate -Increased RNG value CONCLUSION As shown in Table 2, the best scenario was the one with sidestream chemical costs being offset by ammonia revenue. This suggests that a reasonable cost for digestion of OFMSW is possible, with the right conditions. Distribution costs of residuals and rejects are a major cost and back hauling of materials is a crucial element of a successful project. Additionally, a higher value for RNG, as well as revenue from ammonia recovery, to offset the sidestream chemical cost are necessary. A tipping fee is necessary for profitable WRR operation, unless WIW takes the residuals and rejects as planned.

The presence of PFAS in biosolids has resulted in significant challenges for the municipal wastewater industry, especially for those utilities who land apply biosolids for beneficial use. In addition, the State of California and serval municipalities across the country have regulations in practice that have developed programs to reduce Short Lived Climate Pollutants (SLCP), which include the diversion of organic waste from landfills and reduce methane emissions. With climate change and a greater focus on a circular economy, these practices are very likely to become more common throughout the country. With these challenges comes opportunities making it an exciting time for solids treatment in our industry. The Windsor Water District (District) in California owns and operates a 2.25 MGD Water Reclamation Facility (WRF) that currently uses sludge ponds for storage and stabilization of the waste activated sludge (WAS) and sludge generated by the advanced wastewater treatment (AWT) clarifiers. The District currently contracts with an outside service provider that specializes in sludge dredging, dewatering, and disposal for beneficial use. Figure 1 shows the existing solids treatment process flow diagram. The District established specific goals for their future solids management, including 1) eliminate current reliance on outside contractors for biosolids disposal, 2) increase beneficial use of biosolids, 3) reduce truck traffic and the associated carbon footprint by increasing the solids content of biosolids hauled offsite, and 4) provide management option in the future for surrounding municipalities. To achieve these goals, the District selected Hazen to evaluate technologies and advanced treatment options for producing Class A biosolids without considering anaerobic digestion due to size and only producing WAS and AWT sludge. All options require mechanical thickening and mechanical dewatering prior to implementation. The following technologies were considered and evaluated 1) thermo-chemical hydrolysis (TCH), 2) lime stabilization, 3) composting 4) drying (thermal drying, solar drying, and biodrying), and 5) biodrying followed by pyrolysis. Thermal drying and biodrying options were selected for further evaluation on a life cycle cost basis, which showed that the options were similar. The District selected the biodrying followed by pyrolysis. This option meets the District's needs for the future and eliminates the reliance on land application should land becomes scarce or future regulations for PFAS are in place. In addition, biodrying requires approximately 30% the energy needed for thermal drying. Figure 2 shows the new solids treatment process flow diagram. The new process thickens combined WAS and AWT sludge prior to dewatering, biodrying and pyrolysis to produce a biochar for beneficial use. Rotary drum thickening (RDT) was selected for continuous operation, while the selected centrifuge dewatering operation will be limited to one shift per day Monday through Thursday. Therefore, storage of thickened sludge (THS) prior to dewatering is required. In addition, the biodrying is a batch process and pyrolysis operation is continuous. To integrate these unit processes to operate as one continuous system, it was important to size the unit processes for the sequence of operation and to optimize performance. Since mechanical thickening and dewatering equipment is unavailable at the existing WRF, bench tests on the WRF's WAS sludge samples were conducted to understand the performance of the selected thickening and the dewatering technologies along with their required polymer dosage. The bench test results showed 3 to 6% total solids (TS) with greater than 92 % solids capture rate for the RDT and 16% TS with greater than 95% solids capture for the dewatering centrifuge. The biodrying batch time is inversely proportional to the dewatered cake concentration. After working closely with the BioDryer manufacturer, BioForceTech (BFT), it was determined that 8 units would be needed for a feed concentration of 16% TS. A dewatered cake feeding and sequencing schedule to the BioDryers was developed to optimize biodrying performance. The BioDryers are sized to dry 16% TS cake to 75 to 80% TS feed into the pyrolysis under future average annual conditions with one unit out of service. Under normal operation, all 8 units will be fed at a reduced load. The system is designed with a supplement fuel source beyond the energy provided by the pyrolysis for biodrying under future maximum month conditions. Under this condition 35% of the thermal energy need is provided by the supplement fuel, which is natural gas for our system. When the pyrolysis is not operational the BioDryers will produce Class A biosolids with TS greater than 90%. With the system sized for 16% TS dewatered cake, it was important to optimize the dewatering centrifuge performance to ensure a minimum of 16% TS was achieved. This required that the centrifuge feed be well blended, have a concentration range between 2 and 3%TS, and that phosphorus release not acquire within the sludge storage tank (SST) during storage. This was achieved by utilizing a jet aeration and mixing system within the SST and diluting the thickened sludge within the SST with unthickened combined WAS and AWT sludge. In addition, the chopper pumps were used for the mixed pumps to limit the effect of the thickening polymer conditioning on the upstream dewatering performance. The SSTs were sized to provide sludge blending and storage when dewatering is not in operation and one of the SSTs is out of service under future annual average conditions. The pyrolysis unit was sized to process the dried cake under future average annual conditions without redundancy. The pyrolysis energy balance and biochar production were based upon the results of sludge sampling for proximate, ultimate and heat value analysis. The new solids treatment system will have odor emissions control systems for new processing including the pyrolysis. This paper discusses a performance optimization and energy saving case study utilizing an integrated design involving the modification of solids treatment at a water resource recovery facility (WRRF). All stakeholders realized a novel outcome they all achieved their objectives. This paper will benefit utility managers, operation and maintenance (O&M) practitioners, and engineers by providing: -a highlight of the novel biodrying and pyrolysis system sizing, -optimization of solids handling prior to biodrying, and -the lessons learned during the detailed design process

Anaerobic digestion of particulate substrates like municipal sludge is a multi-step biological process that begins with hydrolysis: the breaking down of larger macromolecules into small molecules amenable to fermentation. As seen in Figure 1, hydrolysis is the rate-limiting step for sludge digestion and this recognition has resulted in the creation of many different technologies over the last 20 years to try to speed up the hydrolysis process. Development of these technologies has generally been pursued to maximize the efficiency of existing anaerobic digestion assets including increasing volatile solids (VS) destruction and biogas generation. Of these technologies, thermal hydrolysis has had staying power and become the 'de facto' sludge pretreatment alternative most commonly proposed for digestion process intensification. As its name implies, the thermal hydrolysis process (THP) enhances hydrolysis by treating wastewater solids with high temperature. An established THP technology applied in North America, thermo-pressure, utilizes a combination of high temperature and high pressure to facilitate the breakdown of sludge solids. The typical advantages of this THP include intensification of digester capacity typically two-fold, i.e., doubling the allowed VS loading rate, reduced sludge viscosity facilitating digestion at much higher total solids (TS) concentrations, higher VS destruction and biogas yield, improved dewatering resulting in higher cake dry solids content and less wet biosolids cake product transportation, as well as a high-quality end-product for beneficial reuse. The principal disadvantages of this THP typically cited include operational complexity, specialized staff technical knowledge and skills to operate and maintain the high temperature and pressure systems as well as the increased ammonia recycle loads associated with higher VS destruction. The discussion above assumes that THP is used as pretreatment for anaerobic digestion, but as shown in Figure 2, there are at least four different process configurations for using THP. It may be used for hydrolysis of both primary and waste activated sludge (WAS) labeled Pre-Digestion All in the figure. To maximize the benefit per dollar spent on capital as well as operating and maintenance cost, THP may be used only to improve hydrolysis of the more difficult to digest WAS, labeled as Pre-Digestion WAS-only. THP may also be used to treat digestate the benefits of doing so include achieving high cake solids concentrations in subsequent dewatering and producing a sterile product. The filtrate or centrate, containing the bulk of the solubilized organics, may be recycled to the digester to increase biogas production and reduce the organic load recycled to the liquid treatment plant. This is labeled Post-Digestion. One may also consider intermediate THP, that is feed digestate to THP prior to further digestion, as another strategy to reduce the cost of implementing THP. Finally, one may feed dewatered sludge to the THP so that THP is used to improve solids quality prior to disposal, regardless of the level of treatment prior to THP, labeled Post-Dewatering. The application of THP to date has been limited to larger plant sizes as shown in Figure 3. Most of the THP facilities in North America are at large facilities such as Blue Plains (Washington, DC), TRA CRWS (Dallas, TX), Bonnybrook (Calgary) and others. In the last several years smaller package THP units have been introduced to the North American market for medium size plants, of which there are two installations at plants rated 60 ML/d or 15 mgd (Franklin, TN) and 113 ML/d or 30 mgd (Pontiac, MI), which are still relatively large the majority of plants throughout North America are much smaller. An alternative to thermo-pressure is thermo-alkaline hydrolysis which uses elevated temperature and pH for hydrolysis and is a technology that can be readily applied at small and medium size plants. This type of THP addresses the complexity and high temperature/pressure issues by using lower processing temperatures and ambient pressure with the tradeoff of adding an alkali chemical. It can be used in either a Pre-Digestion or a Post-Dewatering configuration. In other words, thermo-alkaline is also an option for facilities that do not have any form of sludge stabilization. There are 13 full-scale facilities of this technology operating in North America since 2006. Most of those facilities use the Post-Dewatering configuration to create Class A quality high-solids liquid fertilizers. Operation of thermal-alkaline hydrolysis in one of the Pre-Digestion configurations is a more recent direction for this technology in North America. Pre-Digestion has been more commonly utilized in Europe. Lystek is operating at several small plants rated 5 to 15 ML/d (1.3 4.0 mgd) and several medium size plants rated 27 to 50 ML/d (7 14 mgd); some of these recycle a portion of the thermally hydrolyzed product back to anaerobic digestion for additional solids destruction and biogas generation. The technology is also used at the regional 400 ton/day Organics Material Recovery Facility at the Fairfield-Suisan Sewer District plant in Fairfield, CA. Lystek is currently developing the Pre-Digestion configuration. Pondus has one installation in North America at a plant rated 106 ML/d (28 mgd) in a Pre-Digestion configuration, with more than ten similar systems installed in Europe at facilities as small as 38 ML/d or 10 mgd. THP for small and medium size plants is arguably an even better value proposition than at large plants because smaller facilities often dispose of biosolids in liquid form and may have inefficient, or even no, digestion and/or dewatering processes. THP can improve product quality and reduce viscosity to improve disposal of liquid biosolids, allowing direct subsurface application on arable land, so that there is no need for the farmer to store the product prior to land application. Table 1 compares the thermal-alkaline hydrolysis (from both Lystek and Pondus suppliers) with more widely known thermo-pressure hydrolysis processes (from Cambi, and other suppliers). The difference in complexity and operating conditions are included. Note than Pondus is the only technology that treats solids at typical thickened solids concentrations as commonly used for anaerobic digester feed. The Lystek system uses potassium hydroxide to improve the fertilizer value of the product. The thermo-alkaline processes can be used to provide substrate for biological nutrient removal systems. Thermo-pressure and the Pondus system are typically used to improve anaerobic digestion performance, in other words to increase VS destruction so that biogas production is increased and the mass of residual biosolids is reduced. The Lystek technology, by comparison, has historically been used to convert residual biosolids into a marketable fertilizer product and only more recently starting to be applied as pretreatment to improve anaerobic digestion. The goals of THP may be different at different size plants. At large, urban plants the focus may be to maximize energy recovery and minimize the mass of residuals needing disposal, while reducing the use of chemicals where possible. Thermo-pressure THP is well suited to this application. Large plants are also better equipped to meet the complexity and specialized staffing requirements of thermo-pressure THP. The increased recycle ammonia load may be addressed by implementing another specialized sidestream treatment technology also feasible at a large plant. At smaller and especially rural plants, the ability of some thermo-alkaline THP to convert partially or unstabilized sludge into a marketable fertilizer product would be prized. Improving hydrolysis is of limited value to a plant that does not implement anaerobic digestion or where the biogas from anaerobic digestion is flared because the flow is too low to make cogen or other energy recovery options viable. However, with higher prices of natural gas, sale price premiums for renewable natural gas, and small cogen units like microturbines, implementing anaerobic digestion with thermo-alkaline hydrolysis at small plants is becoming increasingly feasible. Implementation of THP at smaller facilities also opens the opportunity for public-private-partnerships to reduce risks and securing private equity, or public-public-partnerships to gain economy of scale and overcome challenges due to skilled labor and part-time dewatering operations. Thermo-alkaline THP is less complex and operates at lower temperature and pressure conditions than thermo-pressure THP systems. In addition, Post-Dewatering configurations allow unstabilized solids to be treated by THP, so that the technology can be applied at plants without anaerobic, or any, digestion. That has allowed thermo-alkaline THP technology and its benefits to be implemented at plants as small as 5 ML/d or 1.3 mgd.

Background Water reclamation facilities (WRFs) have increasingly been investigating and implementing co-digestion of organic materials as a method to generate revenue through tipping fees and to increase biogas (and energy) production. Co-digestion provides an excellent opportunity to divert organic wastes from landfills thereby reducing greenhouse gas (GHG) emissions. Further, co-digestion helps beneficially reuse this organic matter through renewable energy production and facilitates recycling nutrients and organic matter to soils, creating a sustainable reuse cycle. However, successful implementation of co-digestion program requires a clear understanding of organic waste characteristics and pre-processing requirements, digester stability during co-digestion, upstream and downstream process impacts, operational challenges, biogas quantity and quality, permitting requirements and economics. This presentation will share the author's experience from multiple bench scale, pilot and full-scale studies on potential benefits, unintended consequences and lessons learned for implementation of co-digestion program. Methods/Approach The study will present results from studies performed for multiple clients as well as research studies using variety of organic wastes (e.g. food waste, FOG, poultry, creamery, whey wastes). The client projects range from full-scale demonstration of food-waste extraction to bench scale studies using industrial organic wastes. The research projects include those funded by Water Research Foundation to evaluate un-intended consequences of co-digestion as well as evaluation of biogas quality during co-digestion. The presentation will address extraction of organic materials from Municipal Solids Wastes (MSW), comparison of source separated organics (SSO) and MSW extraction approaches for co-digestion, polishing requirements for the MSW extracted organics, digester stability/performance at pre-determined volatile solids loading rates (e.g. pH, volatile solids reduction, COD, alkalinity, foaming potential), biogas quantity and quality at various loading conditions using different organic wastes, dewatering performance of co-digester sludge (e.g polymer demand, percent solids), centrate quality, and dewatered cake characteristics. Further, the presentation will include key lessons learned (operations, regulatory, etc.) from a three-year full-scale food waste extraction and co-digestion demonstration project. Most of the co-digestion studies were performed in mesophilic anaerobic digesters. While the scope of evaluation varied among the studies, in general, a holistic evaluation was performed in these studies to better understand the impact of co-digestion. Digesters without organic wastes (sludge-only) and with pre-determined amounts of organic wastes were operated to selectively identify the impact of organic waste addition. Results Select Results from these studies are present below. Pre-processing of Organic Wastes An organic extrusion process (OREX, Anaergia Corporation) that uses differences in viscosities of organic and inorganic materials was used in the extraction of organic materials from MSW during a full-scale demonstration study at Silicon Valley Clean Water (SVCW) facility, Redwood City, CA. The OREX extracted organics had a solids content of approximately ~35%. The volatile solids content and COD were approximately 83% and 325,000 mg/L, respectively. The soluble COD was approximately 7,000 mg/L. The extracted organics was then polished using a paddle finisher to remove residual impurities (plastic gloves, bags, spoons, etc.) and dilute the pulp to a percent solids content of ~6% to facilitate transfer to the digester. The percent volatile solids and total COD of the polished waste were approximately 88% and 60,000 mg/L, respectively. A preliminary economic evaluation to compare SSO program and MSW extraction of organics indicated that, MSW extraction is more economical for this facility. However, the results can vary at other facilities based on site-specific conditions. Figure 1. (a) Municipal Solid Waste, (b) OREX extracted organic waste and (c) polished organic waste. Organic Waste Loading and Biogas Yield The volatile solids loadings varied from ~0.04 to 0.2 lb VS/cu.ft./day in the studies performed using a variety of organic wastes. The ratio of organic waste to sludge VS loading varied from ~10 to 100%. Results from these studies indicated that, in most cases addition of organic wastes to the digesters not only increased the total biogas production, but it also increased unit biogas production. In most cases, the digesters did not experience any process upsets. The pH did not vary by more than 0.2 to 0.5 units in most cases. The volatile solids to alkalinity ratios were well below 0.1 (a general criteria for digester stability), except in one case using poultry blood waste. However, the high ratio due to the addition of poultry blood waste did not upset the digester performance. Figure 2 shows the biogas yield in two bench scale studies using pre-processed food waste and raw organic waste. Figure 2. Specific methane yield during co-digestion of (a) pre-processed organic waste and (b) crushed raw organic wastes in sludge from two WRRFs. X-axis shows ratio of organic waste VS to sludge VS. Biogas Quality As part of a Water Research Foundation study, biogas quality during co-digestion of variety of organic wastes were evaluated for six different treatment plants Figure 3. Summary of select VOC levels in biogas from sludge and selectively from organic wastes from participating WRRFs In general, co-digestion increased the concentration of VOCs in biogas using some of the organic wastes, lowered the siloxane levels, and increased or decreased ammonia and H2S levels depending on the organic waste. The extent of these changes varied from plant and the type of organic wastes. Dewatering, Cake Odor and Centrate Quality In general, at an organic waste VS to sludge VS ratio of up to 25 to 30 %, a decrease in the net mass of dewatered cake was observed. When the amount of organic waste added increased more than 30%, the mass of dewatered cake increased compared to sludge-only digestion. The polymer demand generally increased during dewatering of co-digested sludge. Headspace total volatile organic sulfur compounds (TVOSCs) levels were measured to identify cake odor production. In general, addition of organic wastes at up to 25% of sludge VS appeared to increase cake odor. At higher organic waste loading the cake odor production significantly decreased compared to sludge-only digestion. In many cases, addition of organic wastes increased the levels of mono-valent salts and ammonia. The bivalent cation levels decreased due to organic waste addition. Lessons Learned Key lessons learned include: -A discussion with local permitting agencies prior to initiation of co-digestion will help tailor the scope and expedite the program -A clear communication with generators of organic wastes is critical to ensure the quantity and quality of organic waste supply -A Technology Impact Analysis to document and implement various process and infrastructure improvements needed prior to implementation of full-scale co-digestion program is required -A hot water system is required to effective pumping of FOG waste and prevent its deposition in grease pits.

The City of Cumberland, Maryland is a city resting in the Appalachian Mountains on the western side of the state. The City operates the Cumberland Wastewater Treatment Plant (WWTP), an advanced wastewater treatment facility with an annual average design capacity of 15 MGD to meet the needs of its ~20,000 residents. In 2008, the City started the solicitation process for a Heat Drying Facility (HDF) that would process all of the biosolids generated at the WWTP into a Class A EQ product for beneficial reuse. The treatment process at the time included Biological Nutrient Removal (BNR) that was being upgraded to an Enhanced Nutrient Removal (ENR) process, along with an Anaerobic Digester and Lime Stabilization process to treat their biosolids. NEFCO began operations of the HDF in late 2010 and operations went smoothly. In 2013, the City informed NEFCO that there would be an extended shutdown of the Anaerobic Digester for maintenance work. During most of 2013 and 2014, NEFCO processed undigested sludge from the WWTP through the HDF. It is no secret in the biosolids industry that the treatment of undigested biosolids comes with a long list of associated issues. Undigested sludge leads to highly variable feedstock quality that will impact both processing capabilities and product marketing options. The Primary Sludge will be more odorous, will contain a large amount of grit and trash, and has a fibrous nature that will significantly impact the quality of the dried biosolids. Facilities processing undigested will experience finished product with less size uniformity, low product densities caused by high fiber content, stronger odors from both dewatered sludge cake and finished dried product, and higher generation of dust. The undigested sludge will also increase wear on major pieces of equipment and limit throughput of the facility during periods of low density. These issues also coincided with an increased demand on the HDF, as there was no longer any solids destruction from the Digester. This led to a very challenging time for operations with a longer processing schedule, increased staffing, and frequent unplanned shutdowns. The NEFCO team developed approaches to handle these challenges, made it through these issues, and got back to regular operations once the Digester came back online in 2014. In 2020, the City again announced plans to shut down the Digester. However, this time it appeared that it may be a permanent shutdown as the City was struggling with the financial case to repair the Digester for reliable operation. Being a smaller facility, the savings from utilizing the biogas produced by the Digester was not enough to make for an attractive return on investment. Realizing that the approaches used in 2013/14 would not be sustainable for long term operations, NEFCO developed a plan to optimize the drying process to mitigate the issues brought on by an undigested feedstock. The team started by reviewing the data available from the 2013/2014 Digester shutdown and summarizing the processing issues from that period and what was done to address them. The team also consulted with staff in NEFCO's Detroit facility, which also processes undigested sludge, to prepare some lessons learned from their operations that could help with the adjustments in Cumberland. A plan was then developed which focused on a combination of operations and process equipment adjustments, evaluating the major solids handling systems that are part of the drying process and looking for ways to adjust their operation to address the bottlenecks. This included the centrifuge dewatering system, pugmill mixer, product screener, and crusher mill. For each piece of equipment, the team consulted vendors and reviewed O&M manuals from manufacturers to come up with a list of action items to be taken. This list of action items was then assigned to team members and ranked in priority to produce an overall action register to guide the efforts. By far the most important process-related task was to address the issues with the sludge feed to the centrifuge. The shutdown of the Digester had led to excessive amounts of trash being present in the sludge, which was frequently plugging the feed line to the centrifuge. NEFCO worked with their Corporate Leadership to expedite the procurement and installation of a grinder system to deal with this trash problem, which led to a significant improvement in plant operations. One of the greatest benefits of a biosolids drying facility is the final pelletized product, which has significant fertilizer and alternative fuel beneficial uses. There were still several product-related issues, dealing mostly with the poor size distribution and low density of the product. The team continued to work its way through the action register, making incremental changes that eventually began to show improvements. Some of the changes were counter intuitive to what might be expected, such as adjustments to the crusher mill. The crusher is meant to take the oversized portion of the product from the screener and bring them back down in size so that they can be recycled to the front of the process as part of the pugmill mix. The issue that came up in Cumberland was that after the Digester was shut off, the product became more pliable and would get flattened by the crusher instead of breaking apart. These flattened pieces would not mix well or be broken up in the pugmill, leading to an accumulation of them in the recycle bin that would then cause issues for the operators trying to control the level in the bin. The answer here came from the advice from the Detroit facility, which had experienced this in the past. They had increased the gap between the rolls in the crusher to reduce the number of pellets being flattened. It was initially thought that this would cause more issues, allowing larger pellets to make it to the recycle bin untouched. However, this change did have a positive impact on the product being sent to the recycle bin and helped the operators maintain their bin levels. This is just one example of a meticulous process to improve the plant's operations and quality of the final biosolids product. Similar efforts were put into reviewing the operation of the pugmill mixer and screener to try and stop pellets from getting too big in the first place. Figures 1 & 2 below show the significance of these changes, measured by performing a sieve analysis on the product stream before being screened. Throughout the process of working on these tasks, the operators of the plants diligently ran sieve tests on a regular basis, on top of their normal lab work, to understand how the changes they were making were impacting the product quality. The reduction in the amount of material on the #4 and #5 Tyler mesh screens was a major goal of the project that was able to be reached by the hard work of the team. A final achievement of the team was the increased throughput of the facility. Much of the equipment works more efficiently and effectively when operated at its design throughput, so through all the work put in to address the issues from the change to an undigested feedstock the processing capacity of the plant was pushed to a higher level than it ever had been. This has led to much more efficient utilities usage rates and other consumables on a per ton processed basis. The plant also now operates on a similar schedule to when it was processing digested sludge, a welcome relief to the dedicated operating staff at the HDF. The effort to address the change in the sludge in Cumberland has turned into a Continuous Improvement activity for the plant, and the team still regularly meets to work on improving operations at the facility. €ƒ Figure 1: Pellet Size Distribution from before Improvements, shown in % by weight retained on sieve screens measured in Tyler Mesh # Figure 2: Pellet Size Distribution (based on Tyler Mesh #) from after Improvements, shown in % by weight retained on sieve screens measured in Tyler Mesh #

Abstract Municipal sludge anaerobic digestion is an engineered biological treatment process wherein a mixture of diverse microorganisms mediates the biochemical transformation of wastewater sludge organics to methane. To anaerobically digest organics more efficiently to methane, the process-enabling microbial communities need to be further investigated and related to process function. The current industry standard for anaerobic digestion process modeling relies on anaerobic digestion model 1 (ADM1). However, ADM1 typically uses default kinetic coefficients to model bioconversion rates considering only an average microbial community. But the average microbial community in municipal anaerobic digesters may be a poor representation of the complex and diverse microbial communities known to dwell among various anaerobic reactors. Consequently, current models can be inaccurate, and this can negatively impact implementation and process efficiency. In this study, we build upon our previous work to relate process function and microbial community information in anaerobic digestion. The central goal of this work is to better model methane production from municipal sludge by leveraging quantitative microbial community data to select the most appropriate Monod kinetic parameters based on the identity and abilities of the specific microbes present in a given digester. Anticipated outcomes will be broadly applicable and of particular interest to the municipal anaerobic digestion and waste management industry, and the methods developed can be potentially applicable to other biological treatment, such as nitrification or anammox processes. To achieve this goal, 20 full-scale operating mesophilic anaerobic digesters were sampled. Source digesters were selected to represent regionally significant sectors and a diversity of microbial community profiles, a vital factor when seeking to relate process function and microbial information. Community activity was measured via specific methanogenic activity (SMA) assays. Prior to SMA setup all bulk digester biomass was normalized to 7 g/L VSS, macro and micronutrients were supplemented, alkalinity was standardized to 6 g/L sodium bicarbonate, titanium citrate reducing agent added and allowed to completely degas at 35 °C with continuous impeller mixing. To determine SMA and kinetic parameters, each bulk digester sample was partitioned into 24 different reactors, each 250 mL working volume and fed 8 model substrates in triplicate representing critical intermediates in the biochemical transformation pathway from complex organics to methane; a custom, automated respirometer system recorded high resolution methane production data via biogas scrubbing for liquid and solid substrates and headspace pressure measurement was used for hydrogen gas substrate (Figure 1). Hydrogen SMAs were evaluated differently due to concerns regarding gas permeability and substrate to microbe ratio, so 160 mL working volume serum bottle reactors were used with 26.5 mL biomass volume. DNA was extracted from digester set samples including 3 samples from endogenous decay control reactors and 3 reference samples from initial digester inocula, and repeated for all 20 digesters surveyed, yielding 600 microbial community samples for analysis. Absolute quantitative microbial community data were generated via a microbial spike-in method, wherein a known quantity of two commercially available microbes (ZymoBIOMICSTM Spike-in Control I D6320) were added to digester samples prior to DNA extraction, and subsequent 16S rRNA gene amplicons were sequenced. Artificial neural network (ANN) modeling will be used to correlate significant microbial consortia from microbial communities fed model substrates to kinetic parameters and evaluated by a leave-one-out cross validation. The resulting model will predict kinetic parameters relevant for ADM1 based upon the microbes present in a digester sample. This study is currently in progress with SMA values, Monod kinetic parameters, and microbial community analysis partially completed. All laboratory evaluations to generate SMA datasets and DNA extraction and sequencing are completed. Preliminary results from SMA evaluations for 6 digester sets showed satisfactory variation among substrates, with median values as low as 1.2 and up to 12.3 mL CH4/g VSS-h for cellulose (CEL) and glucose (GLU) & hydrogen (H2), respectively (Figure 2). Within substrate groups, less variability is observed among SMA values from different digester sources with the exception of hydrogen, varying between 11 and 34 mL CH4/g VSS-h in the first and third quartiles (Figure 2). Among the 6 digester sources presented, two were municipal with both receiving primary solids and WAS and one also co-digesting dairy processing waste from cream cheese. Notably, the municipal digester treating only biosolids had among the lowest SMAs for all substrates, whereas the municipal co-digester was more similar to industrial digesters and was significantly higher for butyrate SMA among all 6 digesters. Additionally, municipal digester SMAs for cellulose were significantly higher than industrial (p-value 0.00002), 3.3 ± 0.7 and 1.9 ± 0.03 mL CH4/g VSS-h, respectively. These comprehensive SMA profiles using 8 model substrates can serve as a holistic method to evaluate and compare activity between digesters. Figure not included due to space constraints. Variability in terms of SMAs within substrates groups or in other terms, between digester sets is vital for being able to detect microbial consortia involved with specific substrate conversion to methane and ultimately to quantitatively correlate function (Monod kinetic coefficients) to microbial community. Initial results of microbial community analysis revealed little change in microbial communities following substrate additions, but interesting clustering has emerged to reveal clear patterns. The detection of microbes found in a control group containing a gut microbiome standard (ZymoBIOMICSTM) allowed for sensitivity analysis. Findings from a subset of data show that our microbial community DNA sequencing and bioinformatics method can detect down to 0.097 ± 0.017 % relative abundance, based on 0.066 % of Methanobrevibacter 16S rRNA sequences present in gut microbiome standard. Additionally, 99.99 % of DNA sequences from the gut microbiome standard were detected, representing 12 of 15 microbial genera with 0.01 % found in the remaining 3 microbes undetected. Comparing the same 6 digester sets represented in Figure 2, a 2-dimensional principal coordinate analysis showing 47 % of total variability based on dissimilarity, shows 6 distinct clusters (Figure 3). Each point in the figure represents a single microbial community from a reactor receiving a model substrate. The relative distance between points indicates the degree of dissimilarity, so points closer together show less dissimilarity and point further apart more dissimilar. Colors denote digester source and native feedstock shown in the legend. All clusters uniquely represent a digester source apart from two municipal digesters in yellow and purple, while the shapes denote substrate fed during SMAs. These municipal digesters were significantly different in terms of their SMA activity profile, the more active of the two co-digests dairy processing waste; however, their tight clustering in PCoA analysis still shows that relative to four industrial digesters their microbial communities as a whole, despite different substrates and activity were nearly identical. Differences between industrial and municipal digester microbial communities will help to inform Work will continue to further investigate these microbial communities and will ultimately help to unravel their functional connections. Holistic SMA profiles using 8 model substrates and quantitative absolute abundance methodologies using commercially available internal standard spike-in controls are effective tools applicable to all anaerobic digestion studies, but may be especially relevant for municipal biosolids digestion and co-digestion where differences in SMA and microbial communities can be more challenging to differentiate. We anticipate that predicted Monod kinetic parameters are grounded in digester microbial community data and can be an input to ADM1 for improved process modeling.

INTRODUCTION The Town of Cary, NC Utilities Department serves a population of roughly 175,000. Cary is a regional leader in sustainability and climate change mitigation with an ambitious goal of reducing town wide GHG emissions by 25 percent by 2025 and by 100 percent by 2040. A high-level study conducted in 2011 showed water and wastewater services account for approximately 60 percent of Cary's municipal GHG emissions. More recently, in conjunction with GHG emission accounting research led by the Stantec Institute for Water Technology and Policy, Cary developed a comprehensive emissions inventory for their three water reclamation facilities (WRF), one water treatment facility (WTF), and one major pump station to both measure progress related to emission reduction activities and to incorporate GHG impact analyses in alternative selection processes. One of the WRFs included in the inventory is the 18 million gallon per day (MGD) Western Wake Regional Water Reclamation Facility (WWRWRF), commissioned in 2014 and discharging to the Cape Fear River. The WWRWRF solids handling facility includes belt filter press thickening of waste activated sludge (WAS) and thermal drying via two BioCon dryers with a combined capacity of 1,489 wet pounds per hour. The dried biosolids are processed through a pelletizer and distributed as a Class A product for land application. The facility's original design included an energy recovery system (ERS) that would combust dried biosolids to generate heat for the drying process, thereby offsetting natural gas consumption. The ERS was removed from the design with the intent to revisit installation in the future. In October 2022, Cary commissioned Stantec to assess the GHG emissions impact of installing an ERS using the newly developed GHG inventory tool. The purpose of this paper is to provide an overview of Cary's GHG emission inventory tool, understand is applicability for utilities of all sizes and treatment technologies, present the results of the GHG emission impact analysis and provide considerations for incorporating GHG evaluations in facility planning and alternative selection processes. METHODOLOGY Cary's GHG was developed for a baseline year of 2021 and is an Excel-based calculator specifically focused on water and wastewater facility emissions. The calculator sources reference data and equations from the Local Government Operations Protocol, IPCC Guidelines, EPA GHG Emission Factors Hub, EPA Waste Reduction Model, and the Biosolids Emissions Assessment Model (BEAM). The tool was developed with a user-friendly interface and can be quickly updated annually to monitor emissions over time or applied as a decision-making tool by comparing capital improvement or operational optimization alternatives. Energy recovery systems accept and combust dried biosolids from a dryer and recover the waste heat from the combustion process for dryer operation. The end product is ash, which can either be disposed via a landfill or beneficially reused as a construction material amendment. The heat produced by the ERS offsets the natural gas required to heat the dryer. WWRWRF's 2021 GHG inventory was used to assess the theoretical GHG impact of installing an ERS. Installation of an ERS is anticipated to impact GHG emissions in five areas: 1.Reduced natural gas combustion by the dryer 2.Reduced GHG offset from biosolid land application 3.Reduced end-product hauling 4.Increased electricity consumption from ERS equipment motors 5.Increased direct emissions from combustion processes There are several energy recovery technologies available to WRFs. However, this evaluation assumed the Veolia ERS system would be installed as it is designed to integrate with the BioCon dryers already in operation at the WWRWRF. The design criteria assumed a throughput of 1,489 lb/hr, consistent with the existing dryer system nameplate capacity and energy consumption estimates were provided for the full system capacity and are summarized in Table 1. The GHG impact from the ERS was assessed for 2021 only and during that year the WWRWRF dryer throughput averaged 636 lb/hr. Electricity consumed by the ERS system was estimated by multiplying the expected energy draw at design capacity by the ratio of the actual and design loads. The ash production rate is approximately 40 percent of 2021 dried biosolids production rate and the average hauled distance for ash disposal was assumed to be 30 percent of that of biosolids land application. Based on Veolia-reported values, the ERS is assumed to provide 68 percent of the dryer's heat demand and the remaining is provided by natural gas combustion. While the ERS does require some consumables for flue gas treatment such as urea, emissions associated with its transport were not included as consumption is estimated at less than one tote per year. In addition, no changes in facility or administrative costs were assumed. There is not current guidance on GHG emission estimates from an ERS. Therefore, solids combustion emissions were calculated using the 'Combustion' tab in BEAM, which is specifically intended for solids incinerators. BEAM calculates Scope 1 emissions from solids combustion as well as the biogenic CO ‚‚ emissions that arise from the conversion of the organic matter in the solids to CO ‚‚. Per LGOP and IPCC guidance, biogenic emissions can be estimated and monitored but do not need to be included in a facility's inventory. RESULTS Results of the analysis are presented in Table 2 and Figure 1 and show the existing and theoretical (with ERS) emissions in 2021. The results of this analysis show that installation and operation of the ERS system would have increased 2021 solids handling related GHG emissions by 36 percent. Nearly all of the ERS combustion emissions are as nitrous oxide, which is particularly difficult to estimate, with significant variability in emission factors. As such, actual emissions may vary based on how well the energy recovery system is maintained and operated. The difference in GHG emissions is also heavily influenced by the elimination of land application practices, which currently provide Cary with a significant emission offset. This is demonstrated in Figure 1, which shows there would not be any 'negative' emissions without land application practices. As previously mentioned, Cary may beneficially reuse the ash product for construction materials, but this practice is not expected to provide the same magnitude of offset since it does not directly increase carbon sequestered biomass. While a more complete evaluation of all financial, environmental, and social impacts of the technology alternative is recommended, this work demonstrated Cary's ability to quickly and effectively quantify the GHG emission impact of a technology alternative. In addition, this evaluation revealed the tradeoffs within the circular economy as an alternative intended to reduce reliance on fossil fuels may result in reduced production of value beneficially reused biosolids.

INTRODUCTION The City of Fort Worth's (City) Village Creek Water Reclamation Facility (VCWRF) implemented a major change to its biosolids processes using design-build-operate (DBO) delivery. During the summer of 2022, the facility started its new centrifuge dewatering and thermal dryer system and now produces a high-quality dried Class A product, resulting in significant cost savings, reduced odors, more regulatory certainty, flexibility, and greater public acceptance. PROJECT OVERVIEW AND BACKGROUND The VCWRF is a 166 million gallons per day (mgd) activated sludge treatment plant. Prior to the project, it had dewatered its anaerobically digested solids with belt filter presses (BFPs) and added lime to produce Class AB biosolids (Figure 1). Each year the facility land applied approximately 29,000 dry tons of material to approximately 40,000 acres of ranch and farmland in the North Texas area. After a comprehensive master planning process, the City made the decision to convert its biosolids operation to a thermal drying process. This was motivated by multiple factors, including: 1.Odor concerns from dewatered solids. 2.Regulatory uncertainties associated with the lime-stabilized Class AB biosolids previously produced by the VCWRF. 3.Public concerns over biosolids land application that are mostly odor related. 4.Increasing hauling distances to land application sites. 5.Increasing costs of biosolids management. The City chose to implement the project using a DBO approach, and contracted with the selected DBO contractor, Synagro, in December of 2019 after receiving multiple proposals. By the summer of 2022, the facility was successfully operating and producing Class A dried biosolids pellets. FACILITY AND ITS OPERATION The VCWRF biosolids facility is located on a separate property located a mile north of the main plant (Figure 2). Anaerobically digested biosolids are pumped to the biosolids site where they are stored in three storage tanks, the largest of which has a capacity of 5 MG. Biosolids are then dewatered by centrifuge, dried in one of the largest rotary drum dryers ever constructed for a biosolids facility with an evaporation capacity of 14,000 kg/h, and stored in silos for truck loading (Figure 3). Process wastewater is pumped back to the VCWRF for further treatment. Odorous air is treated by two bioscrubber systems for hydrogen sulfide and ammonia, and exhaust gas from the rotary drum dryer is treated by a regenerative thermal oxidizer. The existing dewatering belt filter press and lime facility is still available and maintained as a backup system. PROJECT DELIVERY AND LESSONS LEARNED The City decided to implement the project using a DBO delivery approach, funded in part by a Texas Water Development Board (TWDB) Clean Water State Revolving Fund loan. With the selected DBO approach, risk is shared between the facility owner and the DBO contractor (Figure 4), but the owner loses some control over the details of the work. This provides the DBO contractor with greater flexibility and control over cost and schedule, which for this project allowed the contractor to control cost and schedule to minimize change orders during an unprecedented economic climate: COVID pandemic, the 2021 Texas Freeze, and growing inflation. A dryer facility is more akin to an industrial process than a traditional wastewater facility. In addition, as a DBO the City was not provided with as much detail on the new dewatering and dryer systems during design as would traditionally be provided. Jacobs supported the City's review of the designs, provided construction observation, and reviewed acceptance test procedures and results to support the City's management of the contract and verify that the work was consistent with the DBO contract requirements. Together the project team worked with Synagro to address challenges as they arose, including those related to the material recycle loop, foaming, and other issues. The facility is designed to manage biosolids to 2040 (Table 1). Class A biosolids production was achieved in July of 2022, marking a major milestone for Fort Worth and the DBO team. At that time the facility began formal 'acceptance testing' which consisted of a contractually mandated evaluation to verify that the newly installed infrastructure was working as designed. The City and team continue to address various punch list items to shift fully into the operations phase of the project, but this marks a major milestone for the City and for the residents of Fort Worth. The DBO Contractor is responsible for all operation and maintenance activities at the biosolids facility, including those for existing dewatering infrastructure (belt-filter presses) as well as the new dryer facility. THE PAPER This paper will describe the thermal drying project and lessons learned including: 1.A brief overview of the dryer project's history and motivations, 2.Description of the new facility and its operation, highlighting some of the key features of the drying facility, including systems for heat recovery, efficient water usage, pellet recycling, and use of digester gas as a supplemental heat source. With the new biosolids product, benefits to the City include reduced product odor, significantly less trucking, wider diversity of product use options, better use of digester gas, and operating cost savings 3.Lessons learned through the project's unique delivery approach. For example, collaborating with the TWDB brought significant cost savings for the City but presented other unique challenges. The TWDB did not have pre-existing procedures for design build projects, so TWDB staff worked closely with City staff to satisfy the requirements of both entities. Lessons learned from this collaboration that can benefit other utilities on future TWDB-funded projects will be presented. For example, because of the significant schedule constraints on the project, the project team executed an early package for construction of the building foundations that allowed construction to begin sooner while the rest of the design was completed and reviewed. 4.Operation and maintenance overview of biosolids processing operations, including the operating term and undertakings that the DBO contractor will satisfy during the term of the contract. BENEFIT OF THE WORK The work presented in this paper will benefit WRRF Utilities who seek alternative methods of implementing biosolids management solutions, as well as consulting engineers and the contracting community.