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Gulf Coast Authority (GCA) owns and operates five regional industrial and municipal wastewater treatment facilities in the state of Texas. Like many municipalities in the United States, GCA experienced a sharp increase in solids disposal costs at three GCA facilities in the Houston area: the Bayport Industrial Wastewater Treatment Facility (Bayport), Washburn Tunnel Industrial Wastewater Treatment Facility (Washburn Tunnel) and Blackhawk Regional Wastewater Treatment Facility (Blackhawk). All three facilities use belt filter presses for solids processing, with the dewatered solids hauled to landfills for disposal. In November 2020, GCA engaged AECOM to evaluate alternative solids processing technologies and determine an economical, long-term strategy for each facility. A key component in this evaluation was to not only look at cost impact, but to also consider additional risk factors, such as the risk of new technologies and emerging contaminants, such as poly- and perfluorinated compounds (PFAS). The project evaluated over 35 solids handling technologies, organized into treatment trains by thickening, stabilization, dewatering, and post-dewatering. Initially, a long list of technically feasible solids handling technologies was created to evaluate all options. Fatal flaw screening was used to eliminate individual technologies from the list based on the criteria developed by GCA and AECOM, which included safety, regulatory risk, capital cost, operational complexity, etc. GCA and AECOM collaboratively used a paired-analysis criteria to develop a short-list of alternatives. The paired analysis process allowing a ranking of priorities for each facility. For example, one would compare reliability to operational cost and determine which is a higher priority. This process produced a ranking matrix that was used to further reduce the potential set of options for evaluation to be between five and seven alternative treatment trains for each facility. Alternatives were selected specifically to include options covering the full range of potential dried solids content. Capital costs and operating cost details were developed for each of these options, allowing a quantitative evaluation of each short-listed alternative. Life cycle costs were evaluated for each option with timeframes provided by GCA. The project team completed a thorough analysis to summarize the advantages, disadvantages, and capital and operating costs for the selected alternatives. Combined with the identified risks, this allowed for a further refinement of alternatives. For example, the unknowns of future PFAS regulations were viewed as a strong disadvantage of land application alternatives. Typical solids technology evaluations assume static conditions, i.e. a capital cost of $X and a solids disposal cost of $Y. The GCA and AECOM team wanted to develop a more helpful tool and created a sensitivity analysis based on tipping fee impacts, capital cost impacts and technology performance assumptions. An example of this analysis is provided in Figure 1. This sensitivity analysis provided GCA with an incredibly useful tool to assess not only the current most economical options, but also be able to identify when other options should be considered. For example, a thermal drying system may not be economically feasible now, but if the tipping and disposal costs exceed a certain amount shown in the sensitivity analysis, thermal drying should be considered. The presentation will provide an overview of the project evaluation that was conducted including impacts on risk, future regulations, and the sensitivity of the different options to the assumptions. The presentation will also include a summary of the steps taken since the completion of the memo including further optimization of the existing dewatering facilities. Beyond just the technical aspect of this project, it was a great example of how teams can effectively resolve conflict. Many projects start out well, but once out of the 'honeymoon phase,' tensions can rise, miscommunications can occur, or there can be an incident which results in the dissatification between parties. The opposite occurred on this project. A few weeks after kick-off, there was a misunderstanding on project scope. This resulted in the team diverging on actions and expectations. This was quickly identified, a 'stop work' was issued, and key members from all parties had a call to discuss. Within 24 hours of the issue being identified, it was completely resolved and the rest of the project was a textbook example of true partnership between parties who had never worked together.

Renewable Water (ReWa) operates a number of treatment facilities in the upstate region of South Carolina. The Lower Reedy WRF facility consists of primary and secondary treatment and has used anaerobic digestion for residuals stabilization for approximately two decades. The existing anaerobic digestion facility consisted of a single digester tank of approximately 1.5 million gallons volume and did not have any a process redundancy. ReWa recently undertook a capital project to construct a new second anaerobic digester tank at the facility to provide process redundancy and provide additional capacity to handle increased residuals production from the treatment facility. The new anaerobic digestion tankage has an operating volume of approximately 1.5 million gallons volume and consists of a post-tensioned concrete tan with a fixed concrete dome cover and linear motion style mixing. The new digestion complex also includes a new digester control house, hot water boiler and digester heating system, membrane digester gas storage facilities and a new enclosed waste digester gas flare. Future work, Phase II with design currently underway, includes rehabilitation of the existing digester complex to extend operating life and improve digester heating and mixing systems. However, late in the construction phase as start-up and commissioning activities for the new facility were nearing completion the existing digester experienced a process failure and had to be removed from digestion service. This process failure resulted in the inability to seed the new digester from the existing on-site digester using an indigenous sludge seed. As a result, the start-up and commissioning team, consisting of representatives from ReWa, the construction contractor, and the design engineer had to make a 'last-minute detour' from the initial start-up plan and import anaerobically digested seed sludge from another ReWa facility. The team was able to rapidly pivot to an imported seed sludge approach and develop a new start-up plan, including revised process control monitoring and measurement tools, to successfully start the anaerobic digestion facilities and restore on-site stabilization activities. The new digester seeding plan utilized approximately 525,000 gallons of imported seed sludge from the ReWA Mauldin Road WRF and represented a total imported seed mass of approximately 250,000 pounds total solids. Seeding was accomplished over a period twelve (12) days from 04/05/2021 to 04/16/2021. During seeding activities, the digester was also fed some indigenous primary and secondary seed sludge from the Lower Reedy WRF. After sixteen (16) days on 04/20/2021 the digester reached its full operating volume and began to overflow and was able to receive 100% of the indigenous Lower Reedy volume and mass and off-site management of these materials was able to cease. Included as figures are the following: Figure 1 & Digester Total and Volatile Suspended Solids Figure 2 & Digester In-Tank VSS/TSS Fraction Figure 3 & Digester In-Tank pH Figure 4 & Digester In-Tank sVFA/sALK Ratio Figure 5 & Digester Daily Feed Volume

l to both the solids retention time (SRT) and hydraulic retention time (HRT). Anaergia's two-part Omnivore AD platform triples capacity of existing digesters to maximize existing WRRF infrastructure and provide redundancy. Anaergia's sludge screw thickener (SST) (Fig. 1) recuperatively thickens digestate to decouple SRT from HRT, allowing digesters to operate at significantly higher solids content. By separating water from digestate, excess water is removed and returned to plant headworks for additional treatment and/or nutrient recovery, while thickened solids (typically 12% TS) are returned to the digester (Fig. 2). Digestate is therefore thickened up to three-fold (6-8% TS) thus tripling F:M ratio and enabling organic loading rates up to 0.33 lb-VS/ft3/day. By decoupling SRT from HRT, Omnivore ensures SRT well over 15 days required for regulatory compliance and stable digester operation. Mixing is an essential and often overlooked component of the AD process and has historically been limited to technologies that operate effectively at lower solids content. To ensure proper mixing in higher solids conditions, Omnivore employs Anaergia's robust low-speed and high-torque permanent synchronous magnet (PSM) mixers (Fig. 3). These high-efficiency propeller mixers are designed to effectively mix high viscosities that result from thickening digestate and resist ragging. Omnivore mixing achieves a high standard of mixing performance, over 90% of the digester volume continuously mixed above critical velocity (0.3 ft/s) ensuring maximum volatile solids destruction, biogas production, avoiding settling of grit, and homogeneity de-risking upset events such as rapid rise. The cost-effective retrofit has the ability to unlock additional digester capacity and increase redundancy while simultaneously improving digester performance. With the additional AD capacity created, WRRFs can rapidly accommodate increased internal sludge loads, high strength waste (HSW) for codigestion, and improve plant resiliency. Application: South San Francisco-San Bruno Water Quality Control Plant (WQCP) capital improvement planning identified a need for additional AD capacity and initially prescribed construction of a new AD facility. Design by Carollo Engineers incorporated Omnivore retrofits to the existing AD system to cost-effectively provide necessary capacity and avoid the need to build an additional digester. The retrofit also provides flexibility for future codigestion of HSW and increased biogas production. In late 2020, construction was completed to retrofit Digester 1 (0.83 MG) with the Anaergia Omnivore high-solids digestion (HSD) system. The technology package included one skid-mounted sludge screw thickener (SST) for recuperative thickening, three high-solids submersible PSM digester mixers, three mixer service boxes, and all ancillary equipment for a complete Omnivore system. Existing mixers were removed from Dig. 1 and replaced with new PSM mixers. Mixers were selected for low energy demand, low operation and maintenance cost, and efficient performance. Platforms installed provide access to Anaergia service boxes (Fig. 3), which enable in-situ mixer access without interrupting AD operations. Each mixer is mounted to a vertical post inside the digester allowing for height and attack angle adjustments to achieve optimal mixing, resuspend settled grit, and break scum accumulation in upper layers. The SST and accessory equipment were installed adjacent to Dig. 1, reducing pump energy, footprint, and impact on WQCP operations. Validating Omnivore HSD: Dig. 1 was brought online on January 5, 2021. Recuperative thickening was initiated in February and achieved steady performance in April (Fig. 4). Third-party performance testing was conducted in conjunction with Anaergia from April to July 2021. The below performance criteria were evaluated and achieved (Table 1): - Min. volatile solids reduction (VSR) above 57% for 80% of the time over 90-day test period, over a 30-day moving average (Fig. 5) - Demonstrate stable digester operation with volatile fatty acid (VFA)/alkalinity ratio <0.2 (Fig. 6) Testing further confirmed successful HSD in Dig. 1 as demonstrated by increased digester feed volumes, TS loading, and VSR, as well as steady OLR and VFA/alkalinity ratio. Note that design was developed to meet performance requirements and operational objectives requested by WQCP representatives and does not maximize use of Dig. 1 volume. Operation at higher solids would further increase digester capacity for future growth needs or codigestion. Mixer Performance Test: A third-party Lithium-ion Tracer test was conducted to confirm achievement of mixer performance requirements. The independent study (1) validated achievement of Anaergia's high-performance mixing standard (>90% of digester volume >0.3 ft/s) and (2) aligned with computational fluid dynamics (CFD) modeling of mixer performance, which indicated superior performance compared to alternate mixing technologies. Adequate mixing efficiencies were observed from the Tracer test washout curve (Fig. 7), which demonstrates low data scatter (high R2 value). Temperature profile indicated uniform temperature distribution within Dig. 1, with a 1-degree C maximum variance between maximum and minimum temperatures (Fig. 8). Total solids concentration was +/-10% of the mean value, indicating homogenous digester operation (Fig. 9). Tracer test findings are compatible with CFD analysis by Anaergia for the WQCP. The analysis modeled Dig. 1 and various mixer technologies present at the WQCP (Anaergia PSM, linear motion, and pump mix). The model was calibrated with published submittal sheet parameters for each mixer type and actual dimensions of Dig. 1. The model compared energy usage and mixing performance (as measured by percent of tank volume above critical velocity) for each technology at 2%TS and 6%TS. The model demonstrated that PSM mixers are more effective and efficient in delivering mixing performance (Tables 2-5), with equivalent or reduced energy usage compared to linear motion mixing (up to 54% reduction in energy consumption). Moreover, analysis demonstrated a greater portion of tank volume at or above critical velocity when using PSM mixers vs. the alternatives. Results of the CFD analysis demonstrate further advantages (i.e., greater delta in volume above critical velocity) in high solids conditions, such as those resulting from Omnivore thickening or codigestion with high-solids food waste and evaluated as part of the lithium tracer testing. Recuperative Thickening Performance Test: An SST-focused 5-day performance test demonstrated acceptable operation of the recuperative thickening system (Table 6). In addition, an extended 30-day test completed at the request of the WQCP demonstrated continuous and overnight operation. Summary: The Omnivore system effectively addressed the biosolids and residuals management needs of the WQCP leveraging existing infrastructure and provided third-party validated performance improvements. As a result of the project's success, the below benefits were delivered to the WQCP: - Avoided major capital expenditure of an additional digester - Addressed capital improvement needs - Redundant digester capacity - Reliable production of stabilized biosolids - Improved digester performance - Improved mixing performance - High-efficiency mixers with lowest overall lifecycle cost - Future-proofing for load growth and changes in feedstock composition - Enable codigestion of organic waste - Support for increased biogas production and energy neutrality A similar solution may be replicated at other WRRFs to cost-effectively improve biosolids management while significantly enhancing the ability of municipalities to leverage existing infrastructure for meaningful resource recovery. This session will discuss the considerations, advantages, and applications of implementing HSD at WRRF such as the WQCP. It will further detail third-party acceptance testing data demonstrating the successful operation of the Omnivore system and HSD processes, and achievement of a new standard in high-performance mixing. Discussion will include agreement between the in-field performance testing and modeled mixer perform

Abstract Overview: As industrial digesters and wastewater treatment plants become more efficient, the biogas industry has seen an increased interest in the production of renewable natural gas (RNG) for pipeline injection from biogas. We will specifically look at the installation at the City of Lincoln Nebraska's Theresa Street Water Resource Recovery Facility. This dual stage membrane technology provides increased methane recovery with a shorter payback period over cogeneration equipment. Abstract: The city of Lincoln has two Resource Recovery plants, the Northeast, and Theresa Street, which processes all the sludge for the city. They are rated for 5MGD & 27MGD respectively. The Theresa Street plant has three (3) egg shaped digester with a capacity of 1.1million gallons each, with a combination of municipal and industrial waste. The biogas was used in existing Waukesha engines (900kW) for the past 25 years, producing 40% of the electrical needs for the plant. They ran on untreated biogas and had reached the end of their useful life. In 2017 a study looked at four options: 1.) Replace with new engines, 2.) Send raw or treated biogas to a University of Nebraska Lincoln facility for boiler fuel, 3.) Produce RNG as vehicle fuel for the city bus fleet, 4.) Produce RNG for injection into the Black Hill utility pipeline. The final decision was for Option 4, RNG into the local Black Hills pipeline. The equipment & installation was publicly bid in March of 2018. Construction groundbreaking was in May of 2019 and Commissioning was completed November 9th, 2020. The upgrading equipment was purchased from a single system supplier, which consisted of Hydrogen Sulfide Removal, Gas Compression/Moisture Removal, Siloxane/VOC Removal, & a Two-Stage Membrane System for Carbon Dioxide Removal. The Hydrogen Sulfide consists of a single media vessel with pelletized iron hydroxide. This media is a full iron product and works through chemi-adsorption, pulling the sulfur into the pores of the media & reacting with the iron hydroxide. This static bed H2S Removal was chosen for its minimal impact of operations of the plant, as it does not need daily monitoring. The compression system is a LeRoi flooded screw compressor, which pressurized the gas to +200psig before sending it to the moisture removal system. In the moisture removal system, the gas is cooled to 40°F driving as much water out of the gas before reheating to 80°F. The reheating allows a 40°F separation from dew point, creating a relative humidity of approximately 25 percent, which is necessary for the Siloxane/VOC Removal System. Specific types of activated carbon were selected to remove the Siloxane and VOCs present at the time of start-up. It is imperative that gas is free of measurable siloxanes and VOCs prior CO2 Removal System, as to not foul the gas separation membranes. The CO2 is designed as a two-stage system where the first stage removes over half of the CO2, before passing the retentate onto the second stage. The second stage removes the remainder of the CO2, and the permeate is recycled back to the inlet of the compressor. The final gas quality meets the Black Hills specification Higher Heating Value of 950 Btu/cf min, CO2 < 2%, Oxygen <0.2%. The two-stage membrane system provides methane recovery of over 95%. The project cost was $8.6 million, with an additional $1 million provided to Black Hills as a 'transportation fee', paid monthly at $15,000. The forecast is to sell 100,000 dekatherms annually. The RNG is earning D5 RINS and Low Carbon Fuel Standard Credits in the California vehicle fuel market. Yearly revenue is estimated at $2.6 million. The city is currently working on getting a dual pathway approved for D3/D5 RINS to increase the overall revenue. With the sale of the RNG, the plant is exporting more BTUs than they are consuming (Electrical & Natural Gas) and consider themselves NET Zero! With great success comes some challenges. The project faced an early season snowstorm, and subsequent flooding stopping the construction. Then COVID restrictions caused project delays for material deliveries and work arounds for the contractors & subcontractors due the number of people on site, etc. There were also lessons learned regarding the upgrading equipment. Originally an air-cooled oil cooler was installed indoors, but the building heat load was calculated incorrectly and the HVAC could ventilate the room properly, the unit was relocated outdoors. Additionally, clearance above the indoor siloxane removal vessels was tighter than expected and heat tracing on an outdoor drain line was inadvertently turned off, which lead some freezing issues. In conclusion the plant is very happy with the choice to produce RNG, as it has similar O&M for gas cleaning when compared with cogeneration, with increased revenue. The system was designed for 2033 biogas production, and space is available for doubling the capacity of the site.

As utilities nationwide plan to increase their sustainable practices into the future, they are evaluating various methods to maximize beneficial use of their resources, especially biogas. Such biogas utilization programs primarily consist of boilers or cogeneration but can also be coupled with wind or solar programs. In Fairfield, CA, the Fairfield-Suisun Sewer District (District) plant is already an industry leader by employing biogas cogeneration, solar photovoltaics (PV), and wind turbine sources to generate renewable energy and produce the majority of its electricity use onsite. When looking to replace systems and further advance their energy program, the traditional simple business case evaluation was not sufficient and new analysis tools and methods were required. The District treats an average of 14 million gallons per day of wastewater collected from its sewer shed. Plant influent is a combination of both domestic and industrial sources. The District has two mesophilic anaerobic digesters that process the primary sludge and waste activated sludge. Furthermore, the plant loads approximately 8,200 gallons per day of a mix of candy waste and dairy sludge to its digesters as part of the high-strength waste (HSW) program to enhance the digesters' energy yield that generates revenues at the plant. the District currently operates an aging 900 kilowatts (kW) cogeneration engine. Recently Brown and Caldwell (BC) completed a Digester Gas Utilization Master Plan for the District. This analysis faced many complicating factors: - Multiple electrical generating system, including existing net-metered solar PV - Pacific Gas & Electric (PG&E) time-of-use rate schedule - Other potential electric tariffs, such as bioenergy market adjusting tariff (BioMAT), net energy metering (NEM2), and net energy metering multiple tariff (NEM-MT) - Standby charges for new installed capacity - Grant funding opportunities - Variable facility electric load The core of any financial energy evaluation is the value of produced electricity. A behind the meter energy production system offsets imported utility power and derives value by reducing the electric bill. With electric rate schedules growing more complicated and relying on time-of-use rates and larger demand charges, calculating a more accurate estimate of the value of produced electricity requires a much more in depth and comprehensive analysis & the average cost of electricity using 12 months of utility bills is often misleading. The method BC developed to size and evaluate the benefits from a new cogeneration system included: - Minute by minute data for digester gas production - Solar and wind generation profiles - Facility load electricity usage profiles - Variable quantities of HSW and resulting digester gas production - Natural gas supplemental fuel to the engine system - Medium- and low-pressure digester gas storage - Internal combustion engine output based on part load efficiency - Hourly electricity generation, use and import/export calculations - Costs and value derived from the energy system This manuscript will present the methodology used to complete this novel approach to engine evaluation as well as the benefits and drawbacks to this approach relative to the industry standard method for engine evaluation. Finally, this manuscript will discuss the economic impacts and biogas utilization, which minimized flaring while optimizing time of use with energy production, based on this analysis. The basis of design for sizing equipment is based on historical digester gas (DG) production data with additional capacity for future increases in DG produced by increased HSW receiving. Historical and anticipated DG production is presented in Table 1. This table summarizes the anticipated annual average and 90th percentile DG production. It also provides the maximum fuel requirement for the gas conditioning system design basis. Figures 1 and 2 provide a frequency analysis of the historical and anticipated ranges of DG production without and with HSW addition, respectively. As noted in Figure 2, the addition of HSW causes bimodal distribution in the frequency analysis. To perform the engine sizing analysis, the minute fluctuations observed in DG production were simulated to reflect the dynamic operating conditions of the engine(s). DG generated from HSW codigestion was simulated on a minute-by-minute basis and layered on top of the current DG production for small (70,000 gallons per week) and large (140,000 gallons per week) HSW scenarios to simulate engine power output. It was assumed that HSW deliveries only occurred during weekdays, which influence the amount of HSW available for the weekends, shown in Figure 3. Ideally HSW is fed continuously over a 24-hour period, the analysis assumed a less than perfect distribution after morning deliveries as shown in Figure 4, which is similar to the District's current HSW feed strategy. Figures 3 and 4 show simulated above average DG production from HSW during weekdays and midday. These normalized data distributions were implemented for both HSW programs and adjusted based on the incoming HSW volume. These simulated DG data were used to assess four engine size scenarios with and without natural gas blending. Additionally, these scenarios were evaluated under two different DG storage options (high and medium pressure). Based on the DG storage and utilization analysis along with the economic analysis, the District elected to move forward with the one 1,100 kW engine design. Based on the assumptions used in the analysis and the best information available at the time of the analysis, this engine design provides the greatest net present value over the range of HSW programs. This allows the District to ramp up the HSW program at a preferred rate. Additionally, the District decided that the design will not include gas storage and will rely on natural gas blending to smooth out peaks in gas production, take advantage of spark spread, and reduce flaring due to insufficient DG fuel to operate the engine at its minimum capacity.

Background Citizens Energy Group (Citizens) owns and operates two advanced wastewater treatment plants (AWTPs) that serve the City of Indianapolis, IN : Southport AWTP and Belmont AWTP. In total, the AWTPs treat a combined average annual daily flow of 210 million gallons per day (mgd). Solids management includes dewatering and incineration, with a small fraction of cake transported for landfill disposal. Approximately 220,000 wet tons (wt) of cake are processed each year. While incineration has been a reliable solids management option for the utility for many years, the existing incinerator capacity is projected to be insufficient for future loadings. Recognizing existing solids handling constraints, Citizens elected to embark on a WWTP Sludge Management Update to explore and understand the feasibility of other potential solids management practices and to identify opportunities to improve the existing program, reduce program costs, and provide flexibility to management options as the incinerators near capacity. Objective The WWTP Sludge Management Update was initiated to identify cost-effective and energy efficient solids processing technologies to supplement Citizens' existing technology, multiple hearth incineration. As part of the Project, Material Matters completed a biosolids market assessment and regulatory evaluation for the Southport AWTP to provide support to Citizens to better understand the biosolids end use market, and the demand for various biosolids products in and surrounding Indianapolis. The market assessment is of critical important for a utility of this size & with cake production of over 15 truckloads per day. The market findings will be utilized by Citizens in combination with the preliminary Arcadis Process Selection Memo, to achieve the following objectives: 1. Assess market demand for each product in agricultural and non-agricultural markets; and 2. Estimate costs associated with product management for each product considered. The Biosolids Market Assessment included six products (including unstabilized cake) from technologies which can be implemented for long-term planning, as summarized in Table 1. Methodology The in-depth market analysis established product quality characteristics, quantified production (Figure 1) and specifications for each Class A/EQ and Class B product and quantified outside-the-gate costs for product management. Additionally, Material Matters engaged with local utilities and state regulators current biosolids management practices and potential future regulatory requirements for beneficial use of both Class B and EQ biosolids products in Indiana. The analysis also included interviews with Indiana water pollution control facilities (WPCFs) with design flows greater than two million gallons per day (mgd), third-party contractors (TPCs), regulators, agricultural extension agents, and potential outlets identified within approximately a 50-mile radius of Indianapolis. Findings and Current Status Our effort revealed Indiana's unique local marketplace and state regulations strongly favor beneficial use of Class B biosolids, with robust Class B land application across the state (Figure 2), so there is no major end-use driver for Citizens to invest in costly Class A/EQ technologies for the successful development of a beneficial use program. Results from the project identified opportunities for Citizens to enhance pretreatment oversight and identified multiple low-cost outlet options, including Class B directly into the local agriculture market for various processing alternatives (Figure 3). Findings from the biosolids market assessment and regulatory review was a key economic input to Arcadis' Energy Flow Model tool, which is the interactive deliverable that compares the economic and energy balance of each technology considered. This presentation will discuss the project approach and unique market findings & where upgrading to Class A/EQ is not always the most cost effective option.

Background and Objectives The San Antonio Water Systems' (SAWS) Steven M. Clouse Water Recycling Center (SMCWRC) operates as a centralized sewage sludge treatment facility for the sludge produced at Leon Creek Water Recycling Center (LCWRC), Medio Creek Water Recycling Center (MCWRC) and by its own liquid water treatment process. All plants combined have a permitted treatment capacity of 187 MGD and disposes of approximately 450 wet tons of biosolids per month. The sewage sludge treatment consists of mechanical thickening (gravity belt thickeners and centrifuges), anaerobic digestions and dewatering (belt filter presses and sand drying beds). The filtrate from both thickening and dewatering is sent back to the head of the SMCWRC liquid treatment process. Historically, SMCWRC has alternated periods of high and low polymer usage with an average around 19 lbs/dry-ton from 2018 to 2020 (see Figure 1). The year 2021 has been the exception for SAWS. The polymer use has averaged 23 lbs/dry-ton from January to September 2021. Initially it was believed the high polymer demand was due to recovery needed from challenges during the cold weather during the week-long snowstorm of February 2021. However, as the weather stabilized, the polymer usage did not decrease. The SMCWRC operation staff was approached by their chemical vendor and recommended to utilize hydrogen peroxide to improve dewatering. The hydrogen peroxide is intended to oxidize ferrous iron present in the solids to ferric iron which combines with the soluble orthophosphate. High concentrations of soluble phosphorus have been shown to reduce dewatering performance. According to previous iron measurements, SAWS operations would not need to add supplemental iron since enough ferrous sulfate (residual from odor control at the collection system) is available in the wasted solids. A full-scale hydrogen peroxide dosing unit was installed in July 2021 to pilot the recommended treatment. The objective of the pilot is to demonstrate that hydrogen peroxide treatment can increase solids concentration in the BFP cake, decrease dewatering polymer usage, decrease soluble phosphorus concentrations and is economically viable as compared to other commercially available processes. The economic viability of this method will be evaluated depending on several items that include: 1 Polymer usage reduction 2) Iron available for regeneration 3) Need for supplemental iron 4) Reduced solids disposal costs 5) Reduced solids transportation costs 6)Reduced maintenance costs due to struvite reduction post digestion The proposed presentation described in this abstract will summarize the results obtained after months of operation. Methods Before the installation of the pilot, a bench scale jar test was performed to determine the recommended peroxide dose. Post-digestion sludge samples were collected and dosed with increasing hydrogen peroxide concentrations while measuring dissolved orthophosphate concentrations. The optimum dose was determined to be around 400 mg/L hydrogen peroxide reducing the orthophosphate concentration from 230 mg/L as P to 50 mg/L as P. A full-scale hydrogen peroxide dosing unit was installed at SMCWRC and doses approximately 300 gallons per day of Hydrogen Peroxide into the belt filter press feed pumps header. Digested sludge (pre-H2O2 dosing) and belt filter press filtrate samples are collected twice a week. The dissolved orthophosphate concentration is measured on both samples. Other data regularly collected by plant staff include sludge flow, polymer use, digested solids concentrations and cake dryness. Preliminary Results As shown in Figure 2, there is an immediate measurable reduction in soluble orthophosphate concentration in the belt filter press filtrate after hydrogen peroxide dosing starts. The concentrations of soluble orthophosphate have continued to decrease slightly but so has the digested sludge soluble orthophosphate concentration. These results seem to indicate that hydrogen peroxide is successful at oxidizing iron and thus removing some phosphorus from solution and into the cake solids. The removed phosphorus is not recycled to the headworks and contributes to an overall phosphorus decrease in the system. The polymer use data and cake dryness was also reviewed to determine the effectiveness of the peroxide treatment. Figure 3 shows the belt filter press cake concentration in % total dry solids. The data shows a lower than typical cake dryness between January and April of 2021 and a quick improvement and sustained dryness between 17.5 and 18% TS afterwards. The installation of the peroxide feed did not seem to significantly increase or decrease the performance of the of the belt filter presses. Moreover, the cake dryness seems to be related more closely to the volatile solids fed into the BFPs. The higher the input volatile solids concentration, the higher the volatile solids loading rate and thus a decreased performance. Biosolids with high volatile solids concentrations are known to be more difficult to dewater and thus produce wetter cakes. Subsequently, the polymer use was analyzed to determine if the sustained performance of the BFPs was achieved while allowing operators to reduce their use of dewatering polymer. Figure 4 shows the 30-day running average of the polymer use during 2021. There was no perceived reduction on polymer use after the implementation of the peroxide pilot. The polymer use is at their highest this year after the dosing of peroxide. Sensitivity test will be conducted in the upcoming weeks by deliberately lowering polymer concentration and measuring cake TS concentration. It is possible that time is required for operators to develop a sensitivity to the new system and feel comfortable lowering polymer doses. On September 30th, the bench scale jar test was performed again to confirm the recommended peroxide dose. Figure 5 shows the ortho-P reduction at different hydrogen peroxide dosages. The current set-point is still valid for the full-scale pilot. Periodic jar test will be performed in the upcoming months to adjust hydrogen peroxide dosing as the soluble orthophosphate concentrations reduce in the system. Current Status and Future Work As of October 2021, phosphorus, solids and peroxide dosing data is continued to be collected. Polymer jar testing is being scheduled to determine if a change in coagulation polymer formula is required. Peroxide dosing will be reevaluated if polymer is replaced with a different formula. Trend analysis will be applied to study the changes over time in measured variables including dissolved orthophosphate concentration, soluble iron, polymer use, digested solids concentrations and cake dryness. Kendall's tau test will be used in this work to identify any trends in the variables of interest by testing for significance at a P value of 0.05, and Sen Slope estimator will be used to determine the magnitude of change over time. In addition, the dataset for each measured variable will be plotted versus time on a quarterly time period. If any pattern was identified, Seasonal Kendall test will be used in trend analysis. The Seasonal Kendall test is used to explore seasonal variations by comparing data from different years within the same season. In a Seasonal Kendall test, the dataset for each measured parameter will be plotted separately using a quarterly schedule, such as comparing May data only with May for different years. The data limitation in trend analysis will be 5 years (about 20 data points). Based on the data obtained thus far, a life cycle analysis will be performed to determine if hydrogen peroxide dosing is beneficial from the standpoint of reduced maintenance costs due to lower phosphorus concentrations. These results will be compared to other commercially available phosphorus recovery technologies that advertise improve dewatering performance. These results will be available for presentation at the Residuals and Biosolids Conference 2022.

herent value contained within Wastewater, Biosolids and Other Organic Wastes (OOW) is being realized to varying degrees across the world. Atkins are currently engaged in the development of several Biosolids Strategies globally and recognize the opportunity to drive circularity, implement zero waste and zero carbon strategies from leveraging the potential to develop 'Bioresources Products' from wastewater and Biosolids. Markets for Bioresources Products, environments and technology readiness vary, thus understanding the specific drivers, opportunities, challenges, and constraints attributed to a specific client or region is key when devising the ideal combination of Bioresources Products. Atkins have recently completed a market assessment for Thames Water Utilities Limited (TWUL), the UK's largest water and wastewater services company and NEOM a city of the future in the North West of the Kingdom of Saudi Arabia. Thames Water, commissioned Atkins to carry out a Bioresources Review and Market Study to support them in defining their future Bioresources business model. NEOM commissioned Atkins to develop a regional biosolids strategy, with a focus on resource recovery. The potential options for resource recovery from Biosolids and OOW are ever increasing as innovations in technology are enabling recovery and utilization (as outlined in Figure 1) and economic demands are developing. There is not a 'one size fits all' solution for how water utilities should exploit bioresources from wastewater and biosolids. The optimum approach is dependent on various local factors such as market maturity, the regulatory framework, and the environment in which the company resides, as well as internal strategic drivers and, to varying degrees the incentive mechanisms available. Atkins evaluated eighteen potential bioresources, ranging from well-known end products such as Ammonia and Biomethane to products from more emerging and embryonic processes such as Enzymes and Bio-ethanol. For each bioresource, key areas of interest were assessed: - Technical requirements were evaluated to understand the potential processes and associated complexity in comparison with current standard water industry operations. A review of technical readiness levels was also carried out for each bioresource & with particular focus on suitability for deployment in the water industry. - Compatibility of the bioresource recovery process required with standard wastewater treatment infrastructure and with recovery of a range of bioresources, as recovery of some bioresources will compliment and some will compete. - To identify bioresources with high value potential, an understanding of the potential scale of production and revenue potential was developed. - A UK focused market assessment for each bioresource was developed. A comprehensive report was produced to discuss each bioresource in depth, along with a summary slide pack that summarized the entire research findings, providing a broader perspective and delivering the essential messages to TWUL. Figure 2 shows an example of the summarized assessment carried out for enzyme recovery from biosolids. Figure 3 provides an extract of the final summary table which details the key findings and recommendations to TWUL based on the assessment. An example of some of the bioresources investigated are shown in Figure 3. In addition, to aid strategic decision-making, a bioresource compatibility assessment was carried out to understand relationships between the recovery of multiple products. There are many possible products that can be extracted/synthesized from wastewater and sewage sludge. However, due to the locations of the recovery technology within the standard Wastewater Treatment Works (WwTW) process and upstream/downstream implications, recovery of one product may have an adverse or incompatible relationship with the recovery of another product. Conversely, some products may be compatible in terms of resource recovery or even positively influence each other's recovery/synthesis. An assessment of product compatibility was undertaken and a summary of the bioresource compatibility assessment is shown in Figure 4. The results of the study highlighted several key bioresources that have an immediate benefit case. For example carbon dioxide recovery from flue gas and biogas upgrading is of particular interest due to the recent carbon dioxide shortages and UK government intervention. The next steps may include developing whole life cost models to demonstrate feasibility, pilot plant trials or full-scale implementation. Recognizing the potential change to regulations in the UK regarding biosolids end product use, the study included various biosolids treatment and disposal options. The UK Water Industry Bioresources Strategies have shifted to almost 100% recovery to agriculture and a predominance of treatment via anaerobic digestion/ advanced digestion. Due to the UK regulators currently reviewing the regime for biosolids treatment, storage and use, associated requirements restricting the application of nutrients and stakeholder concerns about emerging hazards, further investigation into bioresources from thermal treatment is recommended as it may provide the right balance between outlet risk mitigation and a sustainable management solution for biosolids. A study into pyrolysis / gasification products was recommended which may involve developing outlets for bio-oil, biochar and syngas and further R&D into bio-oil upgrading and biochar utilization. A key lesson learnt that should be considered for future studies is that collaboration between clients and consultants is imperative. The steer from the client on the direction of their strategy will influence the technologies, products and markets that need to be evaluated. Otherwise, there is a risk that lots of time and effort will go into looking at products that are not viable. Atkins and TWUL used a two-phased approach where we initially carried out a high-level overview of all potential resources (as presented in this abstract) with planned future targeted research into the more viable options. Future studies should include a high-level Porter's five-force analysis for each product. This will highlight competition in the industry, potential new entrants to the industry, power of suppliers, power of customers and threat of substitute products. This analysis would allow us to further understand opportunity and barriers of entry to market for various products. Another key lesson is that nationally there is not a good level of data available on what products the market really needs. There needs to be more joined up thinking around resource recovery at a national level, where the key challenge will be unlocking collaboration across multiple sectors. The study provides a snapshot of each bioresources' maturity in terms of technological advancements and market potential at this point in time. It is hoped that this work will help to inform the development of UK biosolids strategies, bioresource recovery R&D plans and help the UK water industry realize and capture the value in their 'waste'. Furthermore, these insights and tactics could be adopted on a global scale to maximize the value of waste.

NEW Water (Green Bay Metropolitan Sewerage District) located in Green Bay, WI is a wholesale provider of wastewater treatment services to 15 municipal and two direct industrial customers in Northeast Wisconsin. NEW Water treats on average of 41 million gallons per day (mgd) at its two wastewater treatment facilities in Green Bay and De Pere. NEW Water has processed biosolids using incineration (multiple hearths) since the 1974. NEW Water needed to replace the biosolids handling facility at its Green Bay Facility to meet more stringent environmental regulations, increased capacity needs, and to replace an aging infrastructure. The solids upgrade project to address these concerns is called the Resource Recovery and Electrical Energy project (R2E2). The R2E2 project is the most capital expensive project in the history of the utility. Facility improvements included in the project are: - Mesophilic anaerobic digestion - Centrifuge dewatering - Scalping drying - Fluid bed incineration - Advanced air pollution control equipment - Biogas cleaning - Biogas storage - Biogas internal combustion engine generators - Heat recovery - Thermal oil system - Nutrient recovery - Odor control - New primary substation. The most unique aspect of the R2E2 project was the pairing of anaerobic digestion with incineration as these technologies are traditionally used separately from each other. The project signified a change in organizational philosophy at NEW Water: treating waste as a resource to recover, rather than something to dispose in the most cost-effective manner. While NEW Water needed to address regulatory, capacity, and infrastructure concerns, the organization took advantage of an opportunity to become a Utility of the Future through this unique approach. The R2E2 project has addressed operational concerns while saving ratepayers money by generating electricity from digestion and recovering heat from processes. The R2E2 project is a resource recovery project that was initiated because of stricter environmental regulations, the need to increase capacity, and need to replace aging solids processing infrastructure. There were also aspects of the project that included energy efficiency improvements and renewable energy components. The project has provided the organization with an opportunity to recover biogas from high strength waste through anaerobic digestion. The recovered biogas is treated and supplies two biogas electrical generators capable of producing a total of 4 MW of electricity. The flue gas from the fluid bed incinerator, along with the jacket water and exhaust gas from the biogas engines, is used throughout the processes for building heat, sludge drying, and digester heating. The new fluid bed incinerator has the capability to operate autogenously without the use of auxiliary fuels (diesel or natural gas). This technology replaced two multiple hearth furnaces that required significant amounts of supplemental fuel (natural gas) in order to operate. There has been a 32% reduction in the purchase of utility electricity since the R2E2 project has been in full operation since May 2018. In 2021, the R2E2 facilities are generating close to 45% of the Green Bay Facility's electrical needs. In 2020, the R2E2 facility recovered 120,163 MMBtu's of heat from the fluid bed incinerator and biogas engines. The recovered heat is used for building heat, sludge drying, and digester heating. The project includes the ability to receive high strength waste. In 2020, the facility received over 24 million gallons of high strength waste that was used to produce biogas. The R2E2 project saves customers approximately $2,000,000 per year in avoided energy costs. Year to date annual recovered costs are provided below. 2021 Recovered Costs (through September) - HSW Revenue - $248,610 - Heat Recovery - $308,472 - Electrical Offset - $1,270,290 - Total - $1,827,372 Project process alternatives (seven alternatives evaluated) were reviewed and scored by staff utilizing a multi-attribute utility analysis that included the following criteria: Operations, Social/Community Impacts, Environmental, and Financial. The cost of each alternative was estimated, including the costs of construction, operation and maintenance, engineering, and NEW Water administrative and legal costs. The costs were used to estimate the 20-year and 40-year present worth of each alternative. Sensitivity analyses focusing on areas of uncertainty (cost of energy, capital costs) were performed to further refine the cost-effectiveness for each alternative. The R2E2 alternative was selected because it had the lowest life cycle cost and had helped mitigate exposure to escalating energy prices. All of the R2E2 project improvements are currently operational, with the exception of the nutrient harvesting system. This presentation will discuss project need, systems start-up and optimization. It will also present the most current operational data, including energy recovery. Operational challenges will be presented.

Biogas fueled combined heat and power (CHP) has been a cornerstone of resource recovery and renewable energy generation at wastewater plants for over 50 years. However, In the past decade, however, making the case for new CHP projects within the US has become increasingly difficult due to historically low energy prices and a scarcity of O&M labor. CHP remains in the interest of many utilities as an excellent way to achieve sustainability goals, but thoughtful and creative designs are needed to make projects work economically. By focusing on heat recovery aspects of CHP, a project to utilize biogas can also serve as an opportunity for a fundamental heating system upgrade at a WRRF while also providing positive economics. This paper provides insight into CHP design strategies that can be used to drive projects forward in a financially viable way, with a focus on the heat recovery portion instead of the more typical focus on electric power generation. Waste heat recovery is often an afterthought in most cogeneration discussions, but in reality it can be the tipping point for positive economics. It also is one of the most site specific and engineering intensive aspects of CHP design. Understanding the types, quality, and amount of waste heat to be generated and matching these sources to existing plant heat demands, hot water loops, boiler feeds, condensate return systems, and controls is a crucial part of the design process. The supporting case study for this paper is a recent CHP design by the Columbus Division of Sewerage and Drainage (DOSD) in Columbus, Ohio. DOSD is currently installing two 1.4 MW reciprocating CHP engines at its Jackson Pike WWTP which treats an average influent flow of 68 MGD. The plant's existing heating systems use steam for heating the water loops that ultimately heat their digesters as well as for space heating for buildings (Figure 1). There are three sets of boilers installed in different locations at the plant, all installed under different contracts and in different eras. This resulted in various steam and condensate systems that are not highly integrated and require the plant staff to operate multiple heating systems at once. The desire to implement CHP was driven largely by city wide sustainability goals, but DOSD staff also recognized the opportunity that a CHP project presented to unify and optimize their core heating systems. Arcadis was engaged to design the CHP system while focusing on developing heat recovery solutions that integrated into the existing plant systems, optimized energy recovery, and offset future capital projects by upgrading heating infrastructure. The design included the following elements: - Jacket water heat exchangers to deliver medium-grade heat to existing digester heating water loops. - Reduction of flow and temperatures of existing digester heating loops to maximize heat transfer from CHP. - Heat Recovery Steam Generators (HRSGs) to recover high-grade exhaust heat and produce steam for space heating. - Repurposing oversized digester heating boilers to service the entire plant steam system as a backup to CHP. - New cross-connection between two existing steam headers to unify systems. -Reconfiguration of condensate returns and centralization of deaeration equipment. - Retirement of aging building heating boilers while eliminating a capital project to replace them. The amount of CHP engine heat rejected into the jacket water loop was sufficient to heat the digesters even in the most demanding winter scenario (Table 1). However, in order to maintain the similar hot water supply temperatures into the sludge heat exchangers, a flow reduction in the primary hot water supply circuit was required. The plant staff experimented during the colder months of 2019/2020, changing pumps speeds and hot water circulation rates in their supply loop while monitoring digester temperatures. It was found that the primary hot water supply flow could be reduced by 25% while maintaining hot water supply temperatures at each sludge heat exchanger. The new reduced flow operation allowed a greater temperature rise across CHP heat exchangers and ultimately more effective heat recovery while also reducing pumping energy. Existing steam to hot water converters in the digester heating loop will also be maintained for backup when the CHP system is offline. HRSGs installed on the engine exhaust will be used to provide additional heat recovery and inject steam into existing building heating systems. These HRSGs needed to fit into an abandoned venturi scrubber building (Figure 2) which was being repurposed to house the new CHP system and eliminate the need for constructing new buildings or containers. An additional layer of complexity for this site is that Jackson Pike WWTP is a site with historically significant and preserved building architecture, so any building modifications needed to minimal and/or in line with historical standards. The HRSGs were designed in a vertical configuration to make better use of the tall but narrow building orientation. Existing building mezzanine grating, preserved to the largest extent possible, provide access to the exhaust system components reaching upwards towards the building roof. Figures 3 and 4 illustrate the final exhaust piping design work that delivered an intricate layout solution in the existing space while adhering to all back-pressure, acoustical, and accessibility constraints. Analysis of existing digester boiler capacity and actual digester heating loads revealed that the digester boiler system was oversized by approximately 5X. In contrast, the existing building space heating boilers were being operated a maximum capacity every winter with no redundancy at all. These boilers were also of 1970s vintage and in need of replacement with a capital project. A new steam cross connection was designed between the digester heating boilers with excess capacity and the aging and overtaxed building heating boilers. This will allow the building heating boilers to be retired without replacement, eliminating the need for a boiler replacement capital project which was counted as a capital credit to the cogeneration project economics. The existing digester heating boilers will now serve as a single backup system to heat the entire plant when the CHP engines are offline. A key finding during design was that unifying heating systems did not require large amount of capital spending, but it did require a large amount of engineering effort and brainpower. This is perhaps best exemplified in the condensate collection and return systems that needed to be reconfigured and reconceived. Currently, three different condensate return systems are dispersed throughout the plant and only return water to their dedicated boilers. Under the CHP project, all condensate returns will be rerouted to a centralized deaerator which will be equipped with sophisticated boiler feedwater pumping controls that deliver the feedwater to the various boiler systems as needed including the HRSGs installed with CHP (Figure 5). Table 2 shows the economic analysis of the CHP project with the above mentioned advanced heat recovery design approaches incorporated. The economic benefits from maximizing the amount of useable heat were significant. The CHP system could heat the entire digester systems while also providing 61% of the building heating in winter (on top of generating ~3MW in green power). This led to a minimized about of natural gas consumption needed to heat the balance of the plant and significantly brought down O&M spending. Also, by avoiding a capital project to replace existing building boilers, a capital credit was applied to the CHP project which played a considerable role in the financial success of the project. These heat recovery benefits served as the tipping point for the CHP project become financially viable while also providing a pathway for the plant to upgrade its core heating infrastructure. The bidding was executed in December 2020 with construction award expected in early 2021. By using heat recovery to help make CHP viable, DOSD and the City of Columbus now have a financially and operationally sensible project to make significant achievements towards city wide GHG reduction goals.