This paper tends to showcase how the path of a biosolids management planning (BMP) project transitioned from a single, linear solution toward a multifaceted 'Road Map' with multiple options and key decision points based on probable future scenarios. A 35-year BMP was developed which provided flexibility to accommodate future changes in environmental, regulatory, cost, public perception and technology development aspects of biosolids treatment and beneficial use. Keywords: Biosolids Management Planning; Triple Bottom Line Plus; Greenhouse Gases. This decade has seen an unprecedented increase in global awareness of environmental and human health concerns, climate change, 'forever' pollutants like plastics and per- and polyfluoroalkyl substances (PFAS), and viral infections. National and regional governments and private entities have implemented significant responses, from net zero commitments, biosolids land application bans due to PFAS, elimination of single use plastics, and monitoring human infection rates through wastewater. This paper presents the findings of a biosolids management planning (BMP) project, showcasing how the project path transitioned from a single, linear solution toward a multifaceted 'Road Map' with multiple options and key decision points based on the probable future scenarios considering the upcoming regulatory changes. EPCOR owns and operates the wastewater management facilities in the City of Edmonton, Alberta, Canada, including Gold Bar Water Resource Recovery Facility (GBWRRF) and Clover Bar Biosolids Recycling Facility (CBBRF). The CBBRF also receives the sludge generated at Alberta Capital Region Wastewater Treatment Plant (ACRWWTP), which is owned and operated by ACR Wastewater Commission, a partnership of 13 municipalities surrounding Edmonton. In both plants, the blend of fermented and thickened primary sludge and thickened secondary sludge are fed to anaerobic digesters, and then is sent to the CBBRF. The CBBRF uses lagoon treatment and produces thickened biosolids for land application and dewatered biosolids for agricultural land application, silviculture (biomass trees), and mine land reclamation sites. The GBWRRF currently treats the wastewater from approximately 1.0M population equivalent (PE) whereas the ACRWWTP treats the wastewater from approximately 0.36M PE. Both plants are planned to expand substantially as the population in the Edmonton region grows. The total projected serviced population of these two plants in 2060 (2.9M) is more than double the current population (1.4M). A BMP project was conducted to address the expected increase in biosolids production, in which the trending topics including treatment technology advances, environmental and social impacts, and resource recovery were recognized and incorporated. A regulatory review was first conducted to understand the provincial, federal, and global regulatory contexts for biosolids management and their influences on provincial legislation. Then, a total of 38 product/market combinations and 28 technologies were evaluated within a triple bottom line + technical framework, by assigning importance weight factors of 25%, 25%, 30%, and 20% to environmental, social, economic, and technical categories, respectively. Several criteria under each category were defined and the options were scored from 1 to 5 per criterion, with the lowest scores and the lowest costs being the most favourable. A total weighted score was achieved per option, based on which the options were ranked and compared. Six product categories, nine market categories, seven technology functional groups were evaluated (Table 1). Thereafter, the market and technology options were aggregated into eight potential 'Strategies' that included technology sequences to create biosolids treatment trains and the range of markets available for the products created by those treatment trains. Evaluation of the eight Strategies (Figure 1) highlighted that there are critical decisions that will need to be made to determine the path forward to ensure the best use of capital infrastructure budget allocations. Therefore, rather than selecting one or two linear Strategies for more detailed evaluation, a Road Map approach (Figure 2) was developed that identified key decision points and capital projects required along the BMP planning horizon. Strategies 1, 3, and 6 scored the lowest (Figure 1) and were selected for the Road Map development (Figure 2). The Road Map identified two key future decision points - the first decision point is based on digester capacity expansion and the second is whether to continue with seasonal biosolids markets or transform to non-seasonal markets. At each decision point, the Road Map provides a path forward, developing three pathways for the BMP. The 'Diversified Pathway' continues with digestion but diversifies the biosolids markets with non-seasonal products. The 'Traditional Pathway' is most like the current approach, continuing with digestion and biosolids products for seasonal agronomic markets. The 'Transformational Pathway' is based on discontinuing digestion and generating biosolids products suitable for non-seasonal markets. A rough (i.e., one) order of magnitude cost analysis indicated that the three pathways had essentially the same net total cost (capital, O&M, and market costs) through the BMP horizon (2024 through 2059), with the cost of the Transformational Pathway being slightly higher (15%) than the others (Figure 3a). The GHG emissions showed a much wider difference between the three pathways, identifying the Traditional Pathway facilities was about 40-50% higher than the others (Figure 3b). The Traditional Pathway was the only pathway with lagoons still in use in 2059, and 60% of the 2059 GHG emissions for this pathway would be derived from the lagoons. The Transformational Pathway showed the highest potential for carbon sequestration through the product/market options considered for this Pathway (Figure 3b). The findings of this project can inform the scientists and practitioners through a real-time example, that traditional linear budgeting and planning approaches no longer provide the agility required to meet the uncertainties and rapid changes facing utilities. This multidimensional BMP analysis indicates that other factors than cost will also be likely to be significant considerations in the BMP decision points, such as GHG emissions, regulations such as potential limits on emerging contaminants, further development of the emerging thermal technologies, public perception, risks, and demands on the footprint and facilities.

Introduction The capillary suction time (CST) test is an established method of evaluating the dewaterability of stabilized wastewater solids and has been used primarily to evaluate different flocculants, flocculant demand, or to determine the differences in dewaterability between solids generated under differing conditions. Many variables exist in modern dewatering processes which offer opportunities for optimization. Flocculant make down systems are now tunable with regard to mixing energies, make down concentrations can be easily changed, and the system may or may not include an aging or feed tank. Often times there are options to dose flocculant at multiple points in the solids feed ahead of dewatering equipment. Feed solids concentration and rheology can also have an effect and pre-dilution of the feed offers another control point to gain efficiency. Clean Water Services (CWS) (Washington County, Oregon, USA) is undergoing the development of CST testing procedures to evaluate, predict, and recommend full-scale dewatering process optimization strategies. Procedure The CST apparatus itself is a simple device that measures electrical continuity between two sets of contacts. The contacts rest on a piece of filter paper, a conditions solids sample is applied to the center of the filter, and water is drawn out across the paper. A timer is initiated when the water reaches the first set of contacts at radius 1, and stopped when it reaches the second set of contacts at radius 2. The lower the time the more easily water is withdrawn from the solids, and the more dewaterable the sample is considered to be. CWS utilizes an OFITE (Houston, Texas, USA) CST apparatus (Part No. 294-50). Although simple in concept, the CST test requires a well thought out procedure and careful technique to improve the accuracy and repeatability of the results. The manufacturers instruction manual contains procedure recommendations including using a syringe or pipette to transfer the conditioned sample to the sample holder, thoroughly cleaning and drying the sample blocks and electrodes between tests, and repeating a minimum of three times and averaging results. Additional notes state that temperature and solids concentration have significant effect on results, and that 5 repetitions per test are recommended. The consequence of these procedural nuances is that it will take a significant amount of time to evaluate a single solids sample at a single flocculant dose through 3-5 repetitions. Over the course of the time required, two major effects can be seen to skew results. First, when evaluating anaerobically digested solids the initial sample will be at a temperature of approximately 37 C for a mesophilic system. Depending on sample size and ambient lab temperature the sample may cool as much as 10 C over the run of 5 repetitions. Second, the made down flocculant solution, whether prepared in the lab or taken from the full-scale system will be aged up to one hour over the trial run. The goal with any bench test is to duplicate as exactly as possible the full-scale system. The procedure under development at CWS attempts to achieve this in multiple ways. The test is considered to be a field test, meaning that it is performed as close to the dewatering process as possible. The flocculant solution is sampled as close to the dosing point as possible to account for activity changes in the piping run from the make down system to the dosing point. The solution is used in the test as quickly as possible, ideally under 1 minute, and a fresh sample is taken for each test. A 4 L dewatering feed sample minimizes temperature changes. In the test itself a 60 mL syringe is capped and inverted, plunger removed, and a 5 mL sample of solids and corresponding polymer dose are concurrently pipetted into the syringe. The plunger is inserted enough to make a seal, the syringe is placed tip up, the cap loosened and the plunger depressed to a volume of 30-40 mL. The cap is tightened and syringe is shaken 30 times in a back and forth motion to effect flocculation. The cap is removed and the conditioned solids are pressed to the end of the syringe, then displaced into the sample holder. Results Initial results of procedure development and investigation of effect of flocculant solution aging illustrate the inherent variability in the test and increases in CST time from flocculant that has been aged on the lab bench. In Figure 1, a dose curve of CST time is shown for the same solids sample conditioned with the same fresh flocculant and run on side by side CST instruments. Although the curves have the same shape, there is chance variability in the CST at a dose of 14 lb. active/DT. The effect of solution aging can be pronounced as shown in Figure 2. Here, two separate runs are shown where the dose remains at 20 lb. active/DT but the solution has aged on the bench up to 30 minutes. Summary The CST test may prove to be a useful tool to support operational decision making and to evaluate the effect in dewaterability of solids treatment processes. The method is however, sensitive to technique and procedure and the nuances of the analysis as a representative bench test must be considered if the resulting data are to be useful. The future of this work, to be completed by time of manuscript include a full procedure, evaluation of effect of flocculant aging, solids sample temperature, flocculant solution concentration, and dosing point. These data will be accompanied with a correlation to full scale operational performance.

Biosolids Master Planning in Tulsa, Oklahoma to Develop a Sustainable Biosolids Management Program The Regional Metropolitan Utility Authority (RMUA) is responsible for the plant infrastructure as well as the operation and maintenance of the 16 million gallon per day (MGD) capacity Haikey Creek Wastewater Treatment Plant (HCWWTP) in Tulsa, Oklahoma. To evaluate the future needs for treating and handling biosolids generated at the HCWWTP, the RMUA authorized engineering development of a biosolids improvements facility plan and concept level design of needed facility upgrades. For the past 19 years, unstabilized biological sludge from the aeration process has been thickened and then hauled to the Tulsa Southside WWTP for treatment via anaerobic digestion and land application. However, this practice requires hauling of 9-10 tanker trucks a day to the City of Tulsa's Southside WWTP and requires significant coordination between the two plants. The goals of this study were to identify existing conditions, estimate future loadings (up to 24 MGD) , and evaluate cost-effective alternatives to upgrade the HCWWTP to a stand-alone facility, produce biosolids product that could be beneficially used, and define a solution that is not only within the RMUA budget constraints, but defensible (with no regrets) to RMUA and its two partner agencies, the Tulsa Municipal Utility Authority (TMUA) and Broken Arrow Municipal Authority (BAMA). The study provided an opportunity to not only investigate technologies for producing Class B or Class A biosolids for beneficial use, but also to consider adaptability to changing regulations and potential energy savings and reductions in carbon emissions. The following outlines the steps which were used to develop an updated solids management plan and concept level design for RMUA. 1.Existing and Future Conditions - This task included an evaluation of existing solids handling processes at the HCWWTP and the ability of the existing facilities to meet future projected loadings. Estimates of future quantities of solids production were made to determine appropriate sizing of solids management equipment in the near term (next 5 years) and into the future (20 years). This analysis was used to develop appropriate sizing criteria for all solids handling system components such that any deficits in capacity needs and the timing of equipment upgrades to eliminate those deficits were identified for future planning tasks. 2.Evaluation Criteria Development and Identification of Appropriate Technology Solutions -Through a workshop discussion with RMUA staff, the universe of technology alternatives was discussed with the goal of identifying potential biosolids management solutions and appropriate evaluation criteria consistent with RMUA goals and objectives were established. These criteria and potential technology options were defined in a workshop with RMUA stakeholders as well as engineering subject matter experts and the relative importance of these criteria determined. Fifteen biosolids management options as compared to the status quo were then identified in a collaborative process for consideration by the stakeholder team. The evaluation criteria previously developed was then applied against the potential technology solutions aimed at meeting RMUA goals. Figure 1 shows the result of the weighted scoring of these alternatives. At the conclusion of this criteria development and technology options identification, six potentially viable alternatives were selected by RMUA for further evaluation compared to status quo including: - Chemical-Thermal Hydrolysis - Mesophilic Anaerobic Digestion - Composting - Thermal Drying - Mesophilic Anaerobic Digestion plus Thermal Drying - Mesophilic Anaerobic Digestion, Thermal Drying plus Pyrolysis 3.Plant Simulation Evaluations - Existing whole plant simulation models for the HCWWTP were modified to analyze and evaluate the 7 alternatives identified to determine overall impacts on process performance, energy recovery and use of existing assets (tankages and equipment). Outputs of the simulations included overall energy balances, green-house gas emissions, and process performance compared to status quo. The outputs of this modeling exercise were then presented in a workshop with RMUA staff and used to further define the short-listed alternatives for further investigation and refinement. 4.Cost Evaluations - The simulation models formed the basis for conducting capital, O&M and life-cycle cost analysis of the 8 short-listed alternatives identified. Comparative cost evaluations were developed including vendor quotes for large equipment and cost estimating data from previous engineering project experience. Cost estimating tools were then used to compare capital, O&M and life-cycle costs for each alternative. These costs were then considered alongside the non-monetary evaluation criteria identified to develop a cost-benefit analysis. Figures 2&3 show the results of these cost and cost-benefit analyses. An interactive workshop was then held with RMUA stakeholders to fully vet the alternatives and determine three potential technology options for implementation. 5.Site Visits - The RMUA stakeholders then toured three representative technologies in Oklahoma including anaerobic digestion, thermal drying and composting. At the conclusion of the site visits, RMUA stakeholders agreed that while all three technologies could work for them, composting was the best choice due to simplicity of the process and production of a marketable product. 6.Implementation Planning - Implementation of the composting alternative was defined in terms of phasing, scheduling and budget planning to ensure the design and building of composting dewatering and composting facilities with the right capacity will be developed at the right time to meet the City's near-term and long-term needs. Through their engineering partner, City of Tulsa was able to apply for and secure grant funding from the USDA for 20 percent or$ 9.8 million of the total project cost (estimated at $48 million). Project Status One of the most interesting aspects of the project was that based on the previous biosolids management study done in 2014, preconceived solutions of anaerobic digestion and improved dewatering to then land apply biosolids cake was thought to be the solution that would be recommended. However, by revisiting potential solution options and redefining what criteria were most important, several different solutions were reconsidered. Ultimately, site visits conducted by RMUA Staff proved to be extremely helpful in the selection of the composting process that is proven, simple to operate and produces a biosolids product with multiple uses. This selection really paid off when grant funding became available that the compost production process proved to be qualified for, saving the RMUA nearly $10M in costs. This part of the story will be detailed in the paper and presentation. The Haikey Creek Wastewater Treatment Plant Biosolids Improvements Project has been approved and is in the design phase of a 10.2 dry ton per day capacity aerated static pile composting facility expandable to 15.3 dry tons per day in 2060. Major facility components include gravity thickener improvements, sludge storage, new centrifuge dewatering as well as a new covered aerated static pile facility. This case study will present details and results of the entire planning process which will provide planners, engineers, administrators, and owners with insight into the planning process used to select the right solution using specific owner driven criteria as well as costs to choose the right solution for their biosolids management needs.

In 2023, the North Shore Water Reclamation District (NSWRD) developed a comprehensive Biosolids Master Plan (BMP) to leverage opportunities for the regionalization of solids handling facilities that were in need of renewal and modernization. The BMP addressed operational and maintenance challenges, optimized resource recovery, and made plans for current and future regulations, within the framework of stakeholder goals and values. The NSWRD BMP planning process is complete, and a discussion of the planning approach, considerations, and the selected alternative will be presented. This approach to biosolids master planning could be implemented by any water resource reclamation facility seeking to take a holistic approach to their biosolids management program, solids handling technology, and the operational requirements of their solids processing. The NSWRD serves around 300,000 residents north of Chicago and processes a total average of 63 million gallons and 7,785 dry tons of Class A Exceptional Quality (EQ) biosolids per day. The NSWRD is composed of three water reclamation facilities (WRFs), Gurnee WRF, Waukegan WRF, and Clavey Road WRF, and a regional biosolids drying facility (Figure 1). The drivers for completing this BMP included the following: Capacity constraints , aging assets, operational challenges associated with the drying and marketing of unstabilized solids, and other regulatory considerations. At the onset of the planning effort, a collaborative effort was undertaken by the NSWRD and the Brown and Caldwell team to develop a set of guiding principles to keep the plan aligned with the long-term goals of the NSWRD's. Those program goals and objectives are listed below: - Modernize NSWRD's aging solids handling assets in a cost-effective manner that balances program goals with stakeholders' financial interests. - Create solids handling solutions that can incorporate innovation and are operation and maintenance (O&M) friendly/easy to own. - Improve regulatory and market resiliency by creating solutions that lend themselves to program flexibility and redundancy. - Set a course that supports environmental stewardship, including reduction or recovery of energy, and the creation of marketable biosolids products. - Create an adaptable plan that can be implemented to leverage current assets and address near-term challenges, while prioritizing those projects that address the NSWRD's goals for the future. The preferred alternative was selected through a two-phase planning process, with numerous collaborative and iterative rounds of analysis and screening. In Phase I of the planning process, the planning team established the operational, economic, and environmental baseline for the existing biosolids management program at NSWRD and performed a regulatory and market assessment of the current biosolids land application landscape. In Phase II, the team performed a biosolids stabilization and biogas management technology pre-screening and an intensive three-round alternatives analysis, Each round of the analysis provided some clear trends. An outline of the number of alternatives, the objective of each round, and a summary of those takeaways are presented in Figures 2-5. The selection of the preferred alternative was made through a multi-criteria decision-making process in which the alternatives from round 3 were compared on cost and relative benefit. This process facilitates the selection of the program that provides the best value to the District by considering a variety of specific factors that the District's staff weigh in order of importance. A dashboard of these results is shown in Figure 6. The preferred alternative implements an advanced regionalized digestion and drying program that generates renewable energy and a high-quality Class A EQ product. It also consolidates solids management at the Gurnee WRF over the next 20 years. The regionalized thermophilic anaerobic digestion (TAD) and belt drying program will be located at the Gurnee WRF, with pipeline injection of the upgraded biogas or renewable natural gas (RNG). At full implementation, solids from Waukegan WRF and Clavey Road WRF would be conveyed via tanker or forcemain to Gurnee WRF for fully regionalized digestion, dewatering, and drying, with the option to convert to a Class A temperature-phased anaerobic digestion system in the future. A process flow diagram of the preferred alternative is shown in Figure 7. The preferred alternative maximizes operational resiliency and resource recovery while reducing costs through consolidating solids processing and utilizing existing assets. After the selection of the preferred alternative, an implementation plan was developed for the biosolids program by dividing the BMP into sub-projects to distribute construction costs across the twenty-year planning time frame. During the BMP process, the NSWRD staff identified several concerns that could arise from regulatory changes, community impacts, and market conditions. The team prepared conditional projects in response to those concerns. They are not part of the core BMP, but were identified, discussed, modeled, and cost estimates were prepared. The intent was to give NSWRD some insight into what changes may need to occur to mitigate the risks of those future challenges. The preferred alternative and conditional projects for the BMP are summarized in Table 1. The NSWRD selected a new biosolids management program that addresses the drivers and issues as well as meets the stated goals by reducing solids, providing resiliency, adding redundancy, and creating renewable energy. Results and takeaways from throughout the planning process will be presented.

PROBLEM STATEMENT/PURPOSE: In the Spring of 2020, the Little Patuxent WRF digesters had been running for a little over year when an anomaly occurred; the digesters began dropping in temperature. The purpose of this case study is to walk through the complex troubleshooting process that led to discovering an unexpected root cause. The troubleshooting and eventual solution to the temperature issue shed light on the fact that it was just a symptom of a much more systemic ailment. The clue that led to the discovery of the systemic issue was a mysterious sudden significant change in sludge density that appeared in historian data on Christmas Day 2019. The case study will then detail the investigation into the chronic issue and the eventual testing and recommendation of mitigation strategies. The forensic team included the Little Patuxent operations group, HDR experts, and industry experts notably the late Dr. David 'FlocDoc' Jenkins. The case study will wrap up with key take aways from both a process mechanical design and an operations perspective. This case study will focus on the trouble shooting methodology. BACKGROUND: Between 2017 and 2021 the Little Patuxent WRF in Savage, MD underwent a 2-phase biosolids upgrade with the first phase incorporating gravity and belt thickening, anaerobic digestion, phosphorous removal, sludge holding, and centrate deammonification. The 2nd phase added a dryer facility that included sludge conveyance, Cake storage, belt dryers, dried biosolid conveyance and storage. The case study that is the topic of this abstract occurs during a period when phase 1 was fully constructed and online and phase 2 was still under construction. METHODOLOGY: The initial temperature drop trouble shooting involved heat and mass balance evaluations centered around the digester heating recirculation and heat exchange system (heating loop). These evaluations showed that flow through the heating loop was slowing causing a compounding issue of heat exchanger fouling due to inadequate scouring velocity and a laminar flow condition both of which degrade heat exchange capacity. These issues occurred suddenly after the digesters had already been in service for over a year. The cause was found to be gas entrainment in the pump suction piping as well as gas binding at the recirculation pump impeller. Piping and pump modifications were made to address the acute issue of gas release in the heating loop. The case study will detail the modifications made, but in general they involve: - Modify piping to convey versus trap gas release - Trial and eventual purchase of a different type of recirculation pump. Parallel to the modifications made to heating loop the investigation continued into finding the root cause of the out of the ordinary gas release in the sludge. Online sludge density data revealed that the sludge density rapidly decreased from an SG of 1 to an SG below 0.95 at the end of 2019. Figure 1 - Historian data showing a divergence in digester pressure level vs. radar level beginning on Dec. 25 2019 Grab samples taken at various digester depths confirmed the accuracy of the online density monitoring. 3 potential causes around the date of the density change were identified an investigated. Those potential causes were: - A polymer spill - An annual dairy shutdown - A filament bloom in the bioreactors The case study will detail how the cause was narrowed down to the filamentous bacteria Microthrix that thrives during the cold season. Microthrix mitigation strategies were developed, tested, and implemented. These included but are not limited to: - PAC dosing trial - Chlorination at various locations - Selection control o Swing zones o Internal recycle location o Scum removal improvements Figure 2 - This chart summarizes the key parameters during the initial troubleshooting period. The digester radar-pressure level is the sludge density indicator, and it shows that by late August 2020 Microthrix impact on the digesters had subsided. The most recent data will be included in the case study. RESULTS: With the mitigation strategies implemented on the liquid treatment side of the process, Microthrix continues to cause difficulties during the cold season. Microthrix thrives on grease and the grease flow to the plant has only increased since 2020. A change that improved primary scum removal ended up being the most effective mitigation. The County is also working on rehabilitating a grease digester that has been offline for 20 years to further limit the impact grease has on the process. The pump and piping modifications originally implemented on one primary digester have continued to perform well and are now being implemented on the 2nd primary digester. DISCSSION/CONCLUSIONS: Filamentous bacteria such as Microthrix and Nocardia can be a perennial ailment on the liquid treatment side at wastewater plants that can also have downstream effects on the solids treatment side of the process. This case study will conclude with the author's lessons learned from a process mechanical perspective, and the co-authors lessons learned from an operational perspective. Generally these include but are not limited to: - Microthrix: o Results from PAC trial o Results from chlorination trial o Results from selection changes - most effective o Generally Microthrix is hard to combat in greasy environments - Digester heating loops should be designed to covey gas to the maximum extent possible - Digester recirculation and mixing systems should react to changing sludge density.

Charlotte Water (CLT Water) is the largest public water and wastewater utility in the Carolinas, serving more than a million customers in the City of Charlotte and greater Mecklenburg County. CLT Water owns and operates five major wastewater treatment plants (WWTPs) with an average treated flow of 78.1 million gallons per day (mgd). Additionally, CLT Water oversees one of the largest class B biosolids programs in the southeastern United States, operating with 17,000 acres of permitted agricultural land in both North and South Carolina and producing over 100,000 wet tons (WT) of biosolids annually. CLT Water's largest WWTP is McAlpine Creek Wastewater Management Facility (McAlpine Creek), with an average treated flow of 41.3 mgd and 60,000 WT of biosolids produced annually. There are three major regulatory categories that are required in order to meet the Class B land application biosolids standards: (1) metals concentrations, (2) vector attraction reduction, and (3) pathogen reduction. This paper will focus on volatile solids reduction (VSR) - the vector attraction reduction alternative CLT Water uses to meet land application standards, the financial impact of a sudden failure to meet the VSR requirements, and the troubleshooting and optimization steps taken to address the issue experienced and to improve the overall solids treatment process. McAlpine Creek is a regional solids processing facility, which in addition to treating the solids produced at the plant, it also receives primary sludge (PS) and waste activated sludge (WAS) from the Sugar Creek WWTP (Sugar Creek) for treatment. McAlpine Creek is designed to receive primary solids from Sugar Creek through a dedicated force main, which connects to McAlpine Creek's primary solids gravity thickeners (GTs), while WAS from Sugar Creek, also designed to be pumped through a dedicated force main, connects to a combined WAS well at McAlpine Creek. Even though the infrastructure exists for Sugar Creek PS and WAS to enter directly into McAlpine's solids treatment train, due to a history of hydraulic overloading of the GTs, Sugar Creek's PS and WAS were being sent through gravity sewer lines and entering McAlpine Creek through the influent flow. McAlpine Creek solids treatment train currently consists of primary clarification, primary sludge gravity thickening, WAS centrifuge thickening, anaerobic digestion of thickened primary sludge (TPS) and thickened waste activated sludge (TWAS), and finally centrifuge dewatering of digested sludge. CLT Water meets the vector attraction reduction requirement by achieving a minimum of 38% VSR through the anaerobic digestion calculated on a monthly basis. Typically, McAlpine Creek achieves the minimum VSR requirement with a comfortable buffer, achieving around 45% VSR, without any major issues. In July 2022, operational staff became alarmed when they noticed a trending decline in VSR results prompting the need for immediate operational changes to be made. The efforts however were not enough to avoid a VSR failure of 36% in July 2022, which prevented CLT Water from land applying the biosolids. Instead, CLT Water had to landfill the entire July biosolids production, totaling over 4,000 WT which cost the City approximately $500,000. Operational efforts to troubleshoot the problem continued for several months past July 2022 with improved success later in the fall and through the same summer period of 2023. The main strategies implemented were: (1) digester feed optimization by improving performance of gravity thickeners, (2) VSR calculation method evaluation, and (3) data tracking and proactive sampling. Improving GT performance included adjusting pumping flow rates, throttling existing valves, and replacing malfunctioning valves from primary clarifiers to GTs to improve PS % solids from <0.5% to 1.0-1.5%. Another significant change was reverting the Sugar Creek PS and WAS transport and tie in points to their original design (PS connected to GTs and WAS connected to a combined WAS well), Sugar Creek's solids were no longer going to McAlpine Creek's influent. Additional optimization trials included actions related to polymer use, configuration of duty/standby GTs, and installation of TSS probes and VFDs on Sugar Creek's PS pumps to McAlpine Creek. While a few of the optimization trials did not cause any improvements, several of the strategies yielded positive results and improvements of PS thickening, digestion, and consequently, volatile solids reduction. CLT Water staff went beyond operational changes and started evaluating the VSR calculation method used by the CLT Water biosolids program for many years. There are two main allowable VSR calculation methods including, approximate mass balance and Van Kleeck. CLT Water uses the latter method. After initial research, staff learned the Van Kleeck calculation underestimates the VSR whenever there is grit accumulation inside digesters. Several digester cleanout projects at various WWTPs were performed over the last ten years including at McAlpine Creek confirming that significant grit accumulation does occur inside CLT Water's digesters. With this information, CLT Water started calculating VSR using both methods and tracking the results side by side. The evaluation showed that the approximate mass balance method yields a slightly higher VSR result and proved to be more representative of CLT Water's process due to the proven grit accumulation. Finally, based on the VSR calculation method evaluation, CLT Water decided to more closely monitor percent solids going into the digesters to predict any potential issues sooner, giving staff adequate time to make operational changes to avoid future failures. Additionally, CLT Water found it to be beneficial to run an EPA-approved alternative test (40-day anaerobic digestion bench test) during months that the percent solids based on historical trends were expected to decline. The 40-day digestion bench test was performed in August 2022, as an immediate response to the July 2022 VSR failure, and proactively conducted in the Summer of 2023. By continuing to perform the alternative test early in the months known to suffer from percent solids falling-off, if by the end of the month the calculated VSR results do fail, staff can use the results from the 40-day digestion bench test to meet the EPA requirements and potentially not interrupt any land application operations and incur unexpected landfill costs. This paper will detail out the multi-approach strategy taken by CLT Water staff to troubleshoot and optimize processes around thickening, anaerobic digestion, and VSR calculation which resulted in many lessons learned, benefits around the overall solids treatment processes, and significant cost savings in the biosolids beneficial reuse program.

Wastewater utilities are increasingly engaged in projects that beneficially utilize biogas in renewable energy applications. Although the degree to which the biogas must be cleaned or upgraded will depend on its end use, the removal of hydrogen sulfide (H2S) to varying degrees will always be required. Historically, hydrogen sulfide has been treated using chemical scrubbers or adsorptive processes, but these tend to be costly and maintenance intensive. The addition of small amounts of oxygen, whether by air or high purity oxygen systems, to anaerobic digesters has been reported to be an effective and economical mitigation measure for hydrogen sulfide. The Pierce County Department of Public Works and Utilities (County) uses digester gas at their Chambers Creek Wastewater Regional Wastewater Treatment Plant to power boilers which were installed in 2016. Although the boilers are relatively new, the County has had to replace fouled boiler tubes approximately every six months of operation due to the levels of hydrogen sulfide in the biogas (2200 ppm, on average). (Figure 1) Consequently, the County requested that Brown and Caldwell (BC) evaluate different technologies to reduce hydrogen sulfide concentrations to levels closer to boiler manufacturer recommendations (10 parts per million by volume [ppmv]), which would in turn reduce maintenance and costly tube replacement. Although the use of sacrificial media is a feasible alternative and one that the County may implement in coming years, the level of treatment required for the current biogas hydrogen sulfide concentrations would require frequent and costly media replacement. BC recommended that the County pilot microaeration, which would not reduce H2S concentrations to the levels required but rather extend the life of any adsorptive/sacrificial media and reduce associated operating costs. The pilot design was informed by a literature review conducted prior to implementation in order to ascertain appropriate design and control parameters and to review the particular importance of biogas residence time in gaseous hydrogen sulfide removal efficiency and air requirements for effective sulfide reduction. Residence times of approximately five hours showed a relatively consistent removal of 90%; the results of the literature review on air quantity required was mixed. Various sources indicated that, in pilot systems, approximately two to three times the theoretical air requirement was needed to affect the anticipated hydrogen sulfide reduction, while in full scale systems, about four times the theoretical air requirements are needed, potentially due to mixing and oxygen transfer as well as different surface area-to-volume ratios. A linear relationship between mass of air supplied and mass of H2S removed was reported to be approximately 2.05 kg O2/kg H2S removed, which is again four times the theoretical value based on oxidation to sulfur. Finally, oxygen concentrations in the digesters subjected to microaeration were found to be on the order of 1-2% The Chambers Creek microaeration pilot was designed in two phases. Data on two digesters receiving the same feed loads (total and volatile solids) were collected as part of phase one, prior to the beginning of aeration, in order to baseline existing conditions and variations in digester operation (see Table 1). Data were collected for approximately five months between August and December of 2021. Phase two began in January of 2022; one digester was chose as the treatment digester, and one as the control. 90 scfh of plant air was introduced into the sludge feed line upstream of the treated digester through an air injection assembly, with data continuing to be collected on both digesters for comparison. The initial aeration dose was chosen based on the County's desire to maintain the minimum reported oxygen level of 0.2% in the digester so as to minimize disruption to the digestion process. At biogas sulfide loads of approximately 16kg/day, the air flow rate of 90scfh corresponds to a ratio of 1.03 kg O2/kg H2S and a molar ratio of 1.09 mol O2/mol H2S. At these ratios, approximately 12% removal in hydrogen sulfide (mass basis) in the aerated digester was realized after three weeks of operation. Both the mass and molar ratios are generally lower than those identified in the literature review, data that, when coupled with the significantly lower biogas residence time, indicate that lower aeration rates may still positively impact sulfide removal. The full-scale demonstration of micro-aeration at Pierce County, resulted in an approximate 15% reduction in the biogas hydrogen sulfide levels; a reduction less that that reported possible in the literature. An evaluation of the data, digester microbial population data and digester gas system inspection provided valuable lessons learned surrounding the implementation of microaeration at scale. These include: - The addition of small quantities of oxygen do not negatively impact the anaerobic community. - Surface area is critical for microaeration to successfully remove H2S - Digester gas management systems in systems with microaeration should be designed such that biofilm and sulfur management are possible (Figure 2) - Microbial community analysis indicates that primary H2S metabolism is likely to be in the biofilm and not the bulk digestion phase. - Online monitoring is critical to process success and control, with feedback control (Figure 3) - Digestion processes that have relatively small headspaces (ex. egg-shaped digesters, submerged fixed covers) may want to consider ex-situ treatment of H2S. This paper will discuss the results of this pilot as well as the lessons learned and how they may be applied to future installations to mitigate the challenges of this emerging process.

Introduction Clean Water Services (CWS) is a public utility providing wastewater, stormwater, and watershed management to the residents of Washington County, Oregon, USA. Among the utility's facilities is the Rock Creek Advanced Water Resource Reclamation Facility (WRRF), a 45 MGD (dry weather) campus that manages the solids stream through mesophilic anaerobic digestion, centrifuge dewatering, and land application of Class B biosolids. CWS has recently completed the design, construction, and commissioning of a modern dewatering system at the Rock Creek AWRRF. Project Overview The existing dewatering equipment consisted of a single Humbolt Bird centrifuge dating to 1990. The size of the machine dictated 24/7 operation to keep up with solids production. Redundancy was provided by keeping a spare rotating assembly (bowl and scroll) on site, and maintenance staff were able to effect a complete change out in the course of an 8-hour workday. The original emulsion polymer make down system was comprised of a Dynablend unit, aging tank with mixer, transfer pumps, a 5,000 gallon feed tank, and 3 dosing pumps. After failure of the Dynablend a single static mixer was used for polymer make down. Over time two additional polymer dosing locations were added upstream of the original location at the centrifuge. Before installation of the Humbolt Bird centrifuge, solids dewatering was done with 4 belt filter presses which were still on site. The project began with removal of the four belt filter presses to make space for the installation of two GEA Watermaster CF 8000 centrifuges. The solids processing building was retrofitted for seismic resiliency as part of a 50-year earthquake preparedness plan. The polymer system was entirely rebuilt, requiring a temporary system using polymer totes. The existing flat bottom bulk polymer tanks were replaced with conical bottom tanks with transfer/recirculation pumps. Three Velodyne VeloBlend VM-P polymer make down units were installed to serve both thickening and dewatering applications and the mixed aging tanks were removed. The ability to use the 5,000 gallon feed tank was retained as an option for both maintenance of the polymer system and providing solution aging. Three polymer dosing points were designed with automatic control and flow measurement where the intermediate dosing point included a static mixer on the solids feed line immediately downstream of the dosing point. The system also included instrumentation to measure the feed solids density (%TS) and the centrate TSS (Valmet, Finland). This instrumentation enables real time cost control calculations and automated polymer dosing to maintain centrate quality. The system is shown in Figure 1. Commissioning The mechanical start-up of the system was impressively trouble free. CWS enjoys the benefit of in-house controls, electrical, instrumentation, maintenance and engineering staff and requires two rounds of operational readiness testing (ORT) that provides early identification and remediation of functional issues. The problem encountered is not at all uncommon and was that the system did not immediately meet performance specification. The performance specification called for the system to achieve 95% capture, and 24% TS cake at a maximum polymer dose of 27 lbs active per ton of dry solids. While the capture could be achieved at the limit of the polymer dose, the cake solids could not be met. While this is not unusual for start-up of a new system, the reduction in cake solids from the old to new system was alarming. The old system was consistently achieving cake solids between 22 and 23%, the new system was fluctuating between 20 and 22% (Figure 2). As with any new system, time is needed for optimization. The operations staff was familiar with dewatering optimization procedures having been trained to tune the process to lowest total cost and began learning the new system. The primary question to answer was in the polymer system. To ensure that the system was utilizing fully activated polymer in the most efficient way possible, a matrix was developed to systematically adjust one polymer variable at a time and analyze performance. Additionally, a static mixer was installed downstream of one VeloBlend to see if there was a difference in more polymer activation energy. The primary variable is the polymer solution concentration and the secondary variables are polymer make up with or without static mixer, injection point, and aging tank. Each condition is run for one day and three sample sets of cake and centrate are analyzed. The matrix becomes complex and time consuming. There are 8 solution concentrations at three dosing points for 24 combinations. Those are tested with and without the static mixer, then with and without aging for a total of 96 conditions. This type of evaluation will not only optimize the process, but find the limit of cake solids at the optimal condition. To date staff have found an optimal solution concentration of 0.24% active over all conditions and insignificant effect of other conditions, except for best results dosing at point 1 which is at the machine. The next test is to rerun the matrix using the aging tank, and adjusting aging times. Summary This abstract, presentation, and manuscript describe a dewatering modernization project incorporating features from the culmination of 10 years of dewatering optimization at CWS. It underscores the pitfalls of performance specifications and guarantees, the time needed for full optimization and elimination of causes of non-performance. By the time of conference the evaluation will be complete and a discussion of resolution of contract, to the degree possible, will be available for inclusion.