Conference Papers

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

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

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

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

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

Prevalent biosolids management practices treat wastewater treatment facilities as cost sinks, leaving them to pay ever increasing disposal costs for biosolids. Utilizing hydrothermal carbonization (HTC) to convert wastewater solids and organic wastes into valuable products turns wastewater treatment plants into sustainable, revenue producing assets. Hydrothermal Carbonization, or HTC for short, is the cornerstone technology in SoMax BioEnergy's suite of solutions for organic wastes. SoMax BioEnergy's HTC process is a continuous thermochemical process that utilizes moderate temperatures and pressures of ~350F & 430F (180C & 220C) and less than 580 psi (40 bar). The HTC reaction has variable retention times based on the feedstock from as short as thirty (30) minutes and up to four (4) hours. When considering biosolids processing, HTC's greatest advantage is that the reaction takes place in an aqueous environment, eliminating the expensive process of drying biosolids prior to processing. The HTC process + drying of the BioCoal product, uses less energy than drying the equivalent biosolids alone. In fact, HTC uses the water present in the biosolids as the primary reactant to perform chemical reactions. The key reactions that occur during the HTC process are dehydration, hydrolysis, decarboxylation, and condensation, all of which result in a product with higher C:O ratio than original feedstock. Hydrothermal carbonization of biomass generates a biochar-like solid product, known as hydrochar, and a nutrient rich process water. Comparing hydrochar to the original feedstock, it is more easily dewatered, has greater fuel characteristics, sorption capacity, and has added benefits when used as a soil amendment, such as increased fixed carbon and carbon sequestration potential. Research institutes across the globe are creating value added bioproducts from hydrochar ranging from concrete additives, to battery electrodes and activated carbon. Considering alternative methods of biosolids processing (land application, compost, and anaerobic digestion), HTC is the most carbon efficient, creates the lowest greenhouse gas emissions, and utilizes a much smaller footprint. The hydrothermal carbonization thermochemical process is also more robust as it is not subject to the same sensitivity issues biological processes encounter. The Borough of Phoenixville Wastewater Treatment Plant, in Pennsylvania, has partnered with SoMax BioEnergy to build the first commercial scale hydrothermal carbonization facility in North America. While European and Asian countries already utilize HTC to treat organic wastes including woody biomass, sewage sludge, digestate, food waste, and even municipal solid waste, North America has yet to implement this technology. This changes with the Borough of Phoenixville project, which at the time of writing this abstract, has over $1,000,000 in project funding has come from county and state grants and is under construction with commissioning set for Q1 of 2022. At capacity the Phoenixville HTC project will process ~15,000 tons of prepared 15-20% solids feedstock, generating over 1,500 tons (d.b.) of BioCoal (hydrochar). SoMax BioEnergy and the Borough of Phoenixville are implementing a two-stage approach to maximize the benefits of the HTC facility to align with the Borough's sustainability goals. The first stage of the project is utilizing HTC for treatment of sewage sludge within the plant and surrounding wastewater treatment plants to process biosolids. The second stage will expand the HTC feedstock to include food waste from the Borough and surrounding businesses. Stage two includes introducing gasification technology that utilizes the hydrochar as a solid fuel to power the wastewater treatment plant and put electricity back on the grid. The Borough Council and Management team sees electricity generation from waste they would have paid to dispose of as a win-win situation and steps in the right direction to accomplishing their 2035 goal of 100% clean and renewable energy. The Borough of Phoenixville HTC project, when fully realized will generate over 150% of the electrical demand of the WWTP, covering all electrical and thermal demands of the HTC process, while utilizing the excess electricity for other borough owned properties. Over the 20-year project lifespan, it is expected to generate over $35,000,000 in savings with a capital equipment payback period of around 7 years. In Spring of 2020, SoMax BioEnergy's hydrothermal carbonization solution received recognition from the U.S. Department of Energy as a Phase One winner in the Water Resource Recovery Prize and this fall was 1 of 6 Phase Two submissions. Unfortunately, the Phase two winners are to be announced the second week of November, just missing the deadline of the abstract submittal. In this presentation, SoMax BioEnergy will: 1) Introduce the Hydrothermal Carbonization (HTC) technology 2) Compare HTC to the status quo WWTP technologies 3) Share research developments and HTC product applications 4) Use plant data to discuss the impacts of HTC on effluents and overall mass and energy balances of the plant 5) Talk about DEP permitting and pathways forward for beneficial use 6)Discuss the experience that is commissioning a new technology

Introduction
The Morrisville Biosolids Gasification Pilot Project (the Project) demonstrated that Ecoremedy's Fluid Lift Gasification technology can reliably dry and gasify industrial volumes of dewatered biosolids without bulking agents or fossil fuel. The Project garnered international interest and was lauded by industry experts during tours.

This case study explores how a public-private partnership enabled piloting of this innovative technology. After briefly reviewing design, construction, permitting, and commissioning, this presentation will summarize key accomplishments, including a summary of "lessons learned" during this historic project.

Design and Construction
The Morrisville Municipal Authority (MMA) is developing a new wastewater treatment facility (WWTF) at a nearby industrial park to replace the existing WWTF. The goal of the Project was to demonstrate Ecoremedy's FLG technology at the existing WWTF for potential inclusion at the new WWTF.

The MMA provided a greenfield site and waste supply to the Project through a pilot agreement signed in July 2018. Within one year, Ecoremedy completed design, construction, and Phase I permitting. The Project was self-financed by Ecoremedy under a Build-Own-Operate-Maintain model and operated on a tip-fee basis. Startup extended from July 2019 through February 2020, after delays from COVID-19. After commissioning, the Project operated until August 2021.

Ecoremedy completed engineering design in only three months. This was possible by leveraging decades of past success with high-ash, high-moisture manure-based feedstocks, including a week-long demonstration with composted biosolids. The Project was a 7x scale-up from past commercial projects.

A single process train was designed to operate for both Phase I loading (up to 4,536 wet metric tons/yr of undigested cake at 18-22% solids from the MMA's filter belt press) and Phase II loading (18,144 wet metric tons/yr of regional merchant capacity, with 22,680 wet metric tons/yr of total system capacity). It was designed to convert cake to three end-products without shutting down or retooling: concentrated minerals (ash fraction), carbon-rich biochar, and dried Class A product (permitted as an EPA recognized "Alternative Fuel").

The Project was housed in a single-story post and beam, metal-clad building (30 m long x 15 m wide with an eave height of 8 m) adjacent to the MMA's dewatering building. Pumping was not possible, so a receiving building was added to accept roll-off containers from MMA and cake hauled in from off-site. The building was selected for easy deconstruction due to the temporary nature of the pilot location.

Permitting
For Phase I, Ecoremedy submitted a Request for Determination of eligibility for a Permit By Rule (PBR) as a captive waste processer with de minimis air emissions. The PA Department of Environmental Protection (PA DEP) granted the PBR permit, with additional flexibility for R&D activities. Without previous biosolids gasification air data, air emissions were modeled using stack data from Ecoremedy poultry litter gasification projects. The elemental analysis of biosolids is similar to poultry litter for energy comparison.

Phase II air permitting required stack testing to validate emissions modeling as a minor source status, or potential de minimis source.

PA DEP granted a general waste permit for Phases I and II, as well as a Phase III expansion to multiple process trains (99,790 wet metric tons/yr). Following precedent from past FLG projects and similar technologies, the Project was deemed a non-incineration technology in PA, and later by the United States Environmental Protection Agency.

Operations
The Project was designed for continuous round-the-clock operation. Due to site-specific conditions and circumstances caused by COVID-19, Ecoremedy operated the facility with daily startup and shutdown on a five-day work week for two years. Automated operations were overseen by two operators per shift.

Project Results and Lessons Learned

Major successes of the Project include:
• Autothermal gasification of biosolids with temperatures across the gasifier and oxidizer ranging from 815 C - 1093 C and natural gas used only during start-up
• Fully automated biosolids drying with temperature drop across of 400 C across the dryer
• Sustained throughput of over 1.4 wet metric tons per hour with two-shift operations and daily shutdown
• Incoming PFAS levels ranged from 1 - 400 ppb per compound in pressed biosolids. 36 PFAS compounds were each reduced to non-detect (<2 ppb) in concentrated minerals after gasification.
• Non-detect odors from Ecoremedy process discharge during steady-state operations
• Consistent production of granular Class A biosolids > 90% TS with low-dust, suitable for land application and use as an EPA-recognized Alternative Fuel
• Consistent production of concentrated minerals suitable for land application or landfill
• Technology-wide determination from US EPA that FLG is not subject to the Sewage Sludge Incineration (SSI) Rule

Lessons learned include:
• Upgrades were needed for the mixer, material handling, bucket elevator, and odor control systems
• When possible, excess thermal energy recovered from the biosolids should be used to preheat the stack for plume abatement due to negative public perception of steam
• To prevent overnight freezing of a carbon filter, 24-hour operations and a condensing venturi scrubber are preferred with a targeted RH of 60%
• Direct pumping of dewatered biosolids to the mixer is preferred to avoid overworking the cake during material handling

Project Completion
On August 23, 2021, when the plant was offline for the weekend, a fire started in the receiving building. No one was injured. The fire marshal's official report ruled the cause of the fire as accidental. There was insufficient time left in the pilot agreement to rebuild and resume operations. Ecoremedy and the MMA agreed to conclude the pilot.

Next Steps and Conclusion
As a result of the Project's successes, the MMA remains interested in the potential of Ecoremedy's gasification technology to halt the rising costs and environmental hazards associated with biosolids disposal. The industrial park where the new MMA WWTF is being constructed has changed ownership and now requires the new WWTF to be completed (estimated 2026) before Ecoremedy can begin construction. At the time of this writing, Ecoremedy is evaluating project sites near Philadelphia for a regional merchant facility, with a general waste permit already granted for 99,790 wet metric tons/yr.

Knowledge gained from the Project, including the Lessons Learned above, were applied to the design of the Edmonds Project near Seattle, WA. The Edmonds Project has a design capacity of 12,927 wet metric tons/yr of dewatered biosolids, with co-gasification of all grit and screenings, and will be installed in 2022.

This paper will present the challenges overcome and advancements made by this historic project, including the operations data in the figures and tables following this abstract.

The purpose of this presentation will be to discuss how the design used an Electrical Resistivity Imaging survey to find a highly feasible bore path under a river for Horizontal Directional Drilling. A recently completed project will be use a case study as well as another project with very similar conditions, but different outcomes due to the different approaches to geotechnical exploration. To reduce annual overflow volume for the Sanitation District No. 1 of Northern Kentucky, a new 18-in gravity siphon sewer was needed to convey flow across (under) the Licking River in Wilder Kentucky. The Licking River is tributary to the Ohio River and located just south of Cincinnati. The width of the river where the new siphon sewer crossing is located is between 300 and 400 feet, depending on the river level. Horizontal Directional Drilling (HDD) was the selected method of construction selected for the new siphon sewer. Since the proposed Licking River Siphon is a gravity system and connects into upstream and downstream sewers, the bore elevations had to be within a rather tight tolerance. From prior experience and challenges with HDD not maintaining line and grade, specifically along a riverbank where cobbles and boulders can often be found, Hazen and Sawyer utilized Electrical Resistivity Imaging (ERI) to find an optimal bore path. Standard split-barrel soil borings and rock cores were also used to calibrate the ERI survey, but they were not solely relied upon to determine the best bore path. Cobble and boulder fields are very hard to identify with only standard soil bores. Another prior HDD project on a very similar river crossing will be discussed where the cobbles and boulders led to construction delays and overruns, until ERI surveying was implemented. This presentation will also discuss other lessons learned related to trenchless and open-cut construction, such as inadvertent returns (frac outs), high river water, HDD tracking systems, production rates in hard rock, bidding document interpretations, USACE permitting, and various other issues. Part of this sewer project was located in a railroad's property which added its own design and construction challenges. The project was successfully completed in 2022 with the HDD being very close to the specified line and grade.

WSSC WATER is nearing completion of the Bio-Energy project to thermally hydrolyze and anaerobically digest all biosolids from their five Water Resource Recovery Facilities (WRRFs) at a centralized facility to produce a Class A biosolids. As part of this project, thermal hydrolysis pretreatment (THP) and mesophilic anaerobic digesters are being constructed at the Piscataway WRRF to provide the necessary stabilization to meet regulatory requirements as well as produce valuable digester gas, which will be converted to renewable natural gas (RNG) suitable for pipeline injection. See Figure 1 for an overall process schematic. The Bio-Energy project will fundamentally change how WSSC WATER manages biosolids, allowing a focus on long-term sustainable end products with a Class A dewatered cake biosolids, and RNG suitable for pipeline injection and use as vehicle fuel. The project will reduce the greenhouse gas emissions and result in significant operational cost savings. But with these benefits comes one of the biggest challenges of the Bio-Energy Project to treat the additional nutrient recycle loads that will be generated from sludge imported from the other WRFs and increased even more by THP and anaerobic digestion. Total nitrogen recycle loads from the Bio-Energy Project must be limited to ensure the Piscataway WRRF can maintain compliance with effluent discharge limits. A two reactor ANITATM Mox sidestream treatment process will startup concurrent with the digestion process to treat high ammonia filtrate from the Bio-Energy dewatering process. Managing filtrate generation in coordination with startup of both the Digester and Sidestream processes is essential to maintaining process compliance at Piscataway WRRF. Figures 2 and 3 present digester and sidestream treatment startup graphs. This presentation discusses the integrated startup plan for anaerobic digestion and sidestream deammonification at the Piscataway WRRF to meet multiple goals: - Stable startup of both biological systems, minimizing potential for digester souring, biological washout, etc. - Limiting nitrogen recycle to Piscataway WRRF - Expediting the commissioning schedule as much as practical to allow WSSC WATER to reap the benefits from this facility as soon as possible. Phase 1 Preparation and Seeding Phase 1 involves preparation and biological seeding of both digestion and sidestream deammonification, initially with one digester and one reactor. - Digester 1 will be partially filled with disinfected utility water to a minimum level to initiate pump mixing. The headspace will be purged with nitrogen to prevent an explosive atmosphere as methane concentrations increase. Steam will be used to bring the water to the mesophilic temperature range. Then liquid seed sludge will be imported from the DC Water Blue Plains Advanced Wastewater Treatment Plant (WWTP), which is thermally hydrolyzed and Class A. The digester is now ready to receive hydrolyzed sludge from the Bio-Energy THP process. - Sidestream deammonification has a similar preparation process. The first treatment reactor will be mostly filled with virgin media. Process flow from the WRRF will be introduced to the reactor to condition the media and promote biological attachment. Media conditioning will continue into Phase 2 - Digester Ramp Up to Piscataway Load. Once conditioning is complete, media with annamox biology from an operating ANITATM Mox process will be introduced to the reactor. The sidestream deammonification process is now ready to begin receiving filtrate. Phase 2 Digester Ramp Up to Piscataway Load Indigenous sludge from the Piscataway WRRF will be thickened, screened and dewatered prior to THP. THP throughput will be increased from approximately 4 dry tons/day (dtpd) up to the full Piscataway load, approximately 16 dtpd over approximately 30 days. During this ramp up, the ratio of volatile solids feed to volatile solids under digestion will be kept below 10%. At the end of Phase 2, Digester 1 will reach its normal operating level. Digester 2 will be prepared with water, nitrogen purge and heating before Digester 1 contents are split to Digester 2. Digestate will not be withdrawn during Phase 2 and no filtrate will be sent to the sidestream deammonification process. Phase 3 Sidestream Reactor 1 Startup and Initial Acclimation During Phase 3, digester feed will be held constant at the Piscataway WRRF load (16 dtpd). This period will be used to build the volume under digestion, establish robust mesophilic anerobic digestion microbial communities, and fine-tune operations prior to introduction of imported sludges. Digester withdrawal also begins during Phase 3 to generate filtrate to be used in the Sidestream Deammonification Reactors biological startup. Filtrate sent to the sidestream deammonification process will increase in both concentration and mass loading of ammonia (nitrogen), allowing the annamox bacteria to grow and acclimate to THP filtrate, increasing treatment capacity. During Phase 3, ammonia concentrations in the digesters and filtrate will also be increasing, and will be accounted for when calculating digester withdrawal and filtrate generation and dilution rates into the sidestream reactor. The sidestream process will start in moving bed biofilm reactor (MBBR) mode, with any sludge collected in the clarifier wasted to drain. Phase 4 Sidestream Reactor 1 Acclimation and Reactor 2 Preparation Digester 1 and 2 continue building the volume under digestion, establishing robust mesophilic digestion microbial communities, and fine-tuning operations during the 16 dtpd hold period. The influent ammonia concentration and load will be gradually increased to sidestream reactor 1. Dilution water will be adjusted to meet target feed concentrations and the mass loading will be gradually increased. RAS recycle will be initiated, and the sidestream process will convert from MBBR to integrated fixed-film activated sludge (IFAS) mode. Sidestream Reactor 2 will be prepared for startup, including conditioning of virgin media, introduction of seeded media and phased influent loading. Earlier startup of sidestream Reactor 2 represents an optimization from the initial startup plan, which deferred sidestream reactor 2 startup until reactor 1 was fully acclimated and performance tested. Phase 5 Increased Digester Loadings, Sidestream Reactor 1 Fast Acclimation and Reactor 2 Initial Acclimation After the digester 16 dtpd hold period, sludge will be imported from the four remote WSSC Water WRRFs to increase sludge to the Bio-Energy process. Both digesters will reach normal operating level, and digester withdrawal will be carefully managed to ensure filtrate does not overwhelm the sidestream reactor treatment capacity or exceed total allowable Bio-Energy recycle limits. While there is additional in-tank volume reserved for rapid volume expansion, once the digesters are full feed volume will generally match withdrawal volume, so sidestream treatment capacity must be sufficient to maintain total recycle load below plant limits. Sidestream Reactor 2 seeding and phased influent loading will commence at the conclusion of the Sidestream Reactor 1 slow acclimation period, and follows the same approach as reactor 1. Phase 6 Steady State Digestion and Sidestream Deammonification Phase 6 begins as the Bio-Energy process reaches full sludge load, with all indigenous and remote sludge being treated through THP and digestion. Both digesters will be in steady state operation. As Sidestream Reactors 1 and 2 complete ramp up to full treatment load capacity; startup will be complete, sidestream will be in steady state, and final operation and performance testing will commence. Conclusion Sidestream deammonification is critical to the successful implementation of WSSC Water's Bio-Energy Project, mitigating the impacts of increased nutrient recycle from THP and digestion with imported sludge from WSSC Water's remote WRRFs. The concurrent biological startups of sidestream treatment and digestion must provide stable startup of both biological systems while staying below nutrient recycle targets, all while maintaining an advantageous startup and commissioning schedule. The detailed planning undertaken for this facility allows for all parties to be fully informed and prepared moving into this integrated startup process.

A Public-Private Success Story for Biosolids Management in Northern California James Dunbar, PE, General Manager, Lystek International Limited Jordan Damerel, PE, Director of Engineering, Fairfield-Suisun Sewer District The Fairfield-Suisun Sewer District (FSSD) and Lystek International Limited (Lystek) have built a progressive public-private partnership (P3) to provide solutions to the biosolids management challenges faced by Northern California wastewater agencies. FSSD is a special district (located 45 miles northeast of San Francisco) and has a history of looking for progressive approaches to wastewater treatment technologies. Lystek is a Canadian-based private company with a patented biosolids treatment technology, a thermal-chemical hydrolysis process employing high-speed shearing, alkali pH, and low-pressure steam injection (Lystek THP). The Lystek THP process hydrolyzes biosolids and residuals to produce a concentrated liquid that has multiple applications in resource recovery, including as a Class A biosolids fertilizer (LysteGro), and a digester enhancement (LysteMize). This paper will present the background of biosolids issues in Northern California and the steps taken by FSSD and Lystek to be leaders in overall biosolids solutions, resource recovery, and high-value beneficial uses. The San Francisco Bay Area relies on a diverse portfolio of biosolids outlets. More than 1,500,000 wet tons of biosolids are generated each year from almost 40 wastewater treatment plants. The solids treatment processes employed by the various plants include digestion, lime-stabilization, mechanical drying and solar/wind drying. The management outlets include incineration, landfills (both for disposal and alternate cover material), composting, and agricultural land application. For many years, there were economical outlets for the seasonal volume fluctuations and land application requirements of regional governments. About 15 years ago, it became clear that alternative solutions needed to be explored due to increasing volumes and a desire to capture the value inherent in biosolids. Individual agencies and sub-regional groups started to investigate potential solutions and spent considerable time, effort, and money in this area, however, a lack of financial commitments by both the private sector and public entities prevented any real progress in finding a proven solution. In 2016, Lystek and FSSD entered into a +20-year partnership to develop an onsite solution for biosolids management and resource recovery. The partnership agreement allowed the development of the Fairfield Organic Material Recovery Center (OMRC) as a regional biosolids and organics management facility, owned and operated by Lystek, leveraging under-utilized infrastructure and assets at the FSSD plant. The Fairfield OMRC location is ideally situated to provide a regional solution, straddling the edge of urban density which provides biosolids quantities, and an established agricultural community seeking soil amendments. The partnership between FSSD and Lystek has successfully created a complete solution for utilities in the Bay Area through Lystek's efficient process, on-site storage solution, and development of a strong market for the Class A biosolids fertilizer. The OMRC accepts residuals year round, is able to store the fertilizer during inclement weather periods, and land applies fertilizer throughout the year as field conditions allow. The material is classified as a Class A biosolids by USEPA (Part 503 standards), and has received a bulk fertilizer registration by the California Department of Food and Agriculture (CDFA). This dual-designation material has allowed LysteGro to be widely used and accepted by area farmers and ranchers as a fertilizer (Figure 1) to avoid the use of chemical and synthetic fertilizers. The use of Class A LysteGro is now accepted in multiple counties which have historically been restrictive to traditional Class B biosolids and its land application practices. The other major component of the FSSD-Lystek partnership involves enhanced digestion and biogas generation. FSSD operates anaerobic digesters to treat wastewater solids and utilize the biogas for onsite co-generation (electricity plus heat for the digesters). This reduces the overall plant energy dependence on fossil-fuels sources. Through the LysteMize process, a portion of the Lystek THP treated biosolids can be re-fed to anaerobic digesters to increase volatile solids destruction and boost biogas yields. The LysteMize process was initiated at FSSD in 2018, refeeding 10% - 30% of processed biosolids from FSSD and third party generators to the digesters. Due to new California legislation related to organics diversion from landfills, generators of undigested biosolids who send their material to the OMRC are able to obtain diversion and recycling credits for the volumes processed with this enhanced digestion. The LysteMize process has measurably increased biogas quantities generated compared to historically generated volumes. At the greater than 30% refeed rate, gas levels have increased by approximately 17% compared to pre-feeding quantities. There is also a noticeable increase in biogas yield (the cubic feet of methane per lb of influent VS) as a result of the increased digestibility of the hydrolyzed material. Since Lystek became operational, there have been additional regulatory and market changes in options for biosolids management. Private companies, primarily landfills, have banned or limited the amount of biosolids they are willing to accept, stressing winter outlets for biosolids. In addition, regulatory requirements have been established, mandating organic material diversion and increased recycling goals, further limiting landfills' ability to offer beneficial uses on a year-round basis. These changes have resulted in a growing customer list of utilities utilizing the Fairfield OMRC as a secure, sustainable biosolids management option (Figure 2). This successful P3 partnership between FSSD and Lystek has offered regional agencies a reliable, sustainable and cost-controlled biosolids management solution. Generators now have a local management facility which produces and manages a Class A biosolids fertilizer, and reduces GHG emissions through additional biogas recovery in the FSSD digesters. The successful LysteGro management program has sold and applied more than 250,000 tons of CDFA registered fertilizer (Figure 3), and substantially grown the market and demand for the product. Increasing fertilizer value has provided the opportunity for revenue sharing opportunities with generators who send their biosolids to the FSSD OMRC. This paper will present a case study of this regional processing facility and discuss the successes and challenges experienced over this time.

With many municipalities having excess anaerobic digester capacity, anaerobic co-digestion (AcoD) provides an opportunity to improve biogas recovery while potentially reducing landfilling of organic municipal waste streams. In the United States, 12% of municipal solid wastes are yard trimmings (YT), which are often sent to landfills or composting for disposal (US EPA 2021a). However, YT landfilling and composting releases 475-1100 and 20-130 kg CO2 eq. per dry ton of fugitive methane (CH4) and nitrous oxide emissions per year, respectively (Brown and Chang 2014; Zhu-Baker et al. 2017). Utilizing yard trimmings as a co-digestion stream improves energy recovery, meets higher renewable energy credits (REU) credit standards than food waste and fats/oils/grease, and reduces climate impact due to fugitive emissions of CH4 and N2O. In this work, we developed nature-inspired bacterial enrichments for cellulose degradation and use them to pretreat common yard wastes to the Southwest and a stock chemical cellulose mixture. We evaluate the impacts of pretreatment using our inoculum and its improvement of CH4 production and landfilling offsets through sludge reduction as part of AcoD with thickened sludge. We cultivated lignocellulose-degrading batch inoculum over 10 generations based on feces obtained from Oryctolagus cuniculus domesticus, who primarily eat hays, grasses, and leafy matter with a digestive retention time of about 4 days. The inoculum were exposed to a variety of typical Phoenix yard waste & lantana and grass & or purchased cellulose. Each generation of inoculum was inoculated for 10-14 d, and then 1/10 of the total volume was added as seed for the next inoculum generation. An inoculum was used as the seed for fermenting reactors with 5-14 d hydraulic retention times (HRTs). Rehydrated plant matter was fed into the fermenters at 40 to 80 g DW/L each of lantana, grass, and cellulose. Fermented material was also fed to anaerobic co-digesters. Thickened sludge and seed anaerobic digester inoculum were provided by the City of Mesa, Arizona's Northwest Water Reclamation Plant (MNWWRP). To test pretreatment coupled with anaerobic digestion, AcoD reactors were fed the same amount of thickened sludge as the control plus an additional amount of material from the fermenters to maintain a 19.2-d HRT. We had two controls in the system: (1) only thickened sludge fed to control reactor was operated at a 25-d HRT to mimic MNWWRP; and (2) the same amount of thickened sludge was fed as a control plus 80 g DW/L undigested plant matter at a 19.2-d HRT. The reactors were allowed to operate at least 3 HRTs to achieve steady state prior to taking the data reported here. To ensure reactors would not sour, the pH in all reactors was kept at 7.5 ± 0.2 using NaOH for pH adjustment and CaCO3 to improve buffering capacity. We monitored pH, total and soluble COD (TCOD; SCOD), total and volatile solids (TS; VS), CH4, hydrogen gas, the volatile fatty acids (VFAs) of formate, acetate, propionate, butyrate, valerate, and caproate, and lignocellulose content based on an Ankom 2000 fiber analyzer. YT prefermentation provided increased solubilization of plant matter to VFAs and with negligible biogas production. For example, VS decreased an average 29% at a 14-d HRT with 80g DW/L loading of YT. At the same time, SCOD increased 20% leaving the reactor, with 6.3% being converted to VFAs. While the analysis is still in process, it appears that proteins in the leaf matter and some hemicellulose were hydrolyzed to soluble forms. Our initial results show that AcoD fed prefermented YT has higher CH4 production and better volatile solids reduction than the control or AcoD with untreated YT. As an example using the prefermented YT discussed above, Figure 1 shows that AcoD fed prefermented YT and thickened sludge averaged the highest CH4 production, 330 mg CH4/d, versus 270 mg CH4/d for the control and 160 mg CH4/d for AcoD with untreated YT. The AcoD with prefermented YT also achieved the highest sludge reduction, 52%, versus 40% with the control and 43% AcoD with untreated YT. At the same time, the AcoD with prefermented YT had a lower yield of CH4 per g VS reduced (610 mL CH4/g VS) versus the control (914 mL CH4/g VS). This lower yield is likely due to lignocellulose being highly recalcitrant. The encouraging results with AcoD fed prefermented YT could have far reaching impacts on the wastewater and AcoD community. Based on these results for 4000 m3 (~879,000 gallon) capacity anaerobic digester, AcoD fed prefermented YT produces 184,000 m3/yr more CH4 than the control and 805,000 kg/yr of YT diverted from landfilling. In addition, the gas produced from YT qualifies for D3 cellulosic RIN credits as part of the EPA's Renewable Fuel Standards program versus other co-digestion streams like food waste and fats/oils/grease (FOG), which qualify for D5 RIN credits. Based on September 20, 2021, data, D3 RINs were worth $1.13 more than D5 RINs (US EPA 2021b).

ABSTRACT Utilities are more and more frequently resorting to real-time control systems that intentionally block flows in interceptors to take advantage of available in-line storage during storm surges to combat overflows from sewers. Many utilities are also more and more frequently extending their pump station's wet wells into the sewers feeding the wet well to raise NSPSH and to effectively enlarge their wet wells, improving pump performance. Both practices have significant operational end environmental value. Overlooked in these efforts are the impact of often quite significant internal pressures on pipes with joints not capable of containing these pressures. Surcharged sewers with leaking joints, when pressurized even a few feet, pass massive volumes of water outside the sewer into the surrounding pipe bedding and pipe trench backfill. When hydraulic grade lines subside to normal (open channel) operating levels, the sewage pushed outside the pipes pours back into the pipe, bringing bedding fines that eventually result in pipe bedding envelope failure and pipe collapse. This paper identifies the causes, mechanisms of failure, evidence of likely failure if surcharges, inspection techniques to identify pipes at risk if surcharged, and rehabilitation methods once a pipe is thus compromised. This paper is relevant to any utility considering or using in-line storage. Relevance, Usefulness, and Takeaways Surcharging interceptors can result in catastrophic and hugely expensive repairs if the pipes are not prepared to contain the pressures. Determining if a pipe can handle the pressures sometimes requires more than CCTV inspection. This paper provides suggested assessment measures utilities can use protect themselves from these failures as well as identify the rather involved corrective measures needed if the wrong pipes are surcharged. Demonstrated Results The project used to demonstrate these condition assessment techniques and remedial measures is largely complete. This presentation will contain meaningful photograph and video clips to convey the lessons learned.

CASE STUDY: FORT LAUDERDALE, FL STORMWATER USER FEES A successful collaboration between Stantec and the City of Fort Lauderdale resulted in adoption of a new stormwater fee structure that represents an innovation in the apportionment of stormwater cost to parcels in relation to the benefit of services received. Passing all required legal tests in 2022, it will provide resources for the City to enhance the resiliency of its stormwater systems in light of a changing climate. The project included a detailed revenue sufficiency analysis to evaluate stormwater rate revenue needs over a multi-year projection period, cost allocation effort and fee design, as well as robust stakeholder engagement. STORMWATER USER FEES: A PROGRAMMATIC APPROACH For coastal cities ' especially those on the gulf and south Atlantic ' hurricanes, tropical storms, and heavy rains are part of a resident's everyday weather vocabulary. Many areas are experiencing weather extremes ' record high and low temperatures, more frequent flooding and droughts, and larger storms. No matter the location, events like these place constraints on municipal flood control systems, cause erosion, and disrupt fragile ecosystems essential to healthy waterfront living. Add in aging infrastructure, urban sprawl, and changing stormwater regulations and you've got water-related pain points for any city management team. Without a dedicated funding source, it becomes difficult to manage stormwater and even more difficult to do so proactively. Many communities have begun looking for ways to fund new systems and improvements to existing ones. Historically, funding for stormwater programs has come from property taxes, but it's not a perfect system. This has led some municipalities to establish a stormwater utility that incorporates charging a separate stormwater fee. These communities recognize that an organized approach to stormwater allows for proactive management of the system, provides an increased level of service, and addresses aging infrastructure. A dedicated funding source makes future planning possible. Doing so equitably from a fee perspective, however, doesn't have to be challenging. STORMWATER USER FEE DEVELOPMENT Fort Lauderdale is known as the 'Venice of the Americas' for its coastal proximity and extensive canal systems. In the face of rising sea levels, this presents a key challenge as the community looks to adapt and become more resilient to changes in the environment. Doing so requires generational investments in stormwater infrastructure. The first group of which was set to occur in Fiscal Year 2021 and cost $200M. These investments would provide stormwater pump stations and new passive systems in the most vulnerable neighborhoods. The City has had a stormwater utility and fee since the early 1990s. Over time, periodic adjustments to the fee have been made to generate more revenue ' although the fundamental structure has remained the same. To build consensus in the community for a new approach, the City undertook a multi- year effort to raise awareness, define the critical issues, and ultimately enact a stormwater fee structure to provide the resources needed to meet the community issues head on. The first component of this study was to perform a revenue sufficiency model in which all projected cost requirements of the utility are calculated year-by-year, then a plan for the rate adjustments necessary to support the expenditures was devised. In the case of Fort Lauderdale, the City needed 54% more revenue in the next fiscal year to satisfy their near-term capital and debt service needs. This presented a significant challenge and precipitated the next step in the analysis, which looked at the metrics used to assign cost to parcels that benefit from the stormwater program. Impervious area or gross area of the parcels served are commonly used as a basis for stormwater fees. The Fort Lauderdale stormwater utility used impervious area. However, as each city is different, it is often prudent to consider the options and alternatives that best match the underlying developmental characteristics of the community to make this decision. INNOVATIVE, AFFORDABLE, AND MOST IMPORTANT, EQUITABLE Fort Lauderdale's stormwater issues were being acutely felt in the roadways, with much of the utility's efforts going into keeping roads unblocked and passible. As part of a tiered hybrid rate structure, Stantec determined that a trip generation rate would reflect the estimate of a given parcels' roadway utilization. Exploring the link between motor vehicles and water quality degradation would better (and more equitably) connect the cost of service and the underlying cost of managing stormwater with the unique benefit that each parcel receives. Using the Institute of Transportation Engineers (ITE) survey data, the trip rate component is based on ITE traffic calculations reflecting the average usage for a given parcel type. For instance, a single- family home has 9.44 trips per day on average. This number was then multiplied by a cost per trip to determine a component of the new stormwater fee for each parcel. Trip generation rates were used to recover 20% of the overall revenue requirement. Given the substantial amount of cost and acute organizational focus on keeping roads clear and passible, this had the desired effect of distributing the utility's cost more in proportion to the benefit conveyed to parcels. The remainder of the cost (80%) was recovered in conventional impervious area-based fees. Applying trip generation rates to stacked vertical development such as condos enhances equity as it requires those customers to pay for their beneficial use of the roadway system. A key component of the study was ensuring that the fee could meet all legal requirements. This was especially important given that the City was transitioning from stormwater being billed on a monthly utility bill to an annual non ad valoerm special assessment. Additionally, the innovative form of the fee structure was one the City didn't want to take chances. To validate the fee, the City went through the bond validation process by which the City sued itself and the judicial system made a ruling as to the validity of new fee and the City's ability to impose it. This effectively set a judicial precedent and ensured that the City could use the revenue source to bond against. Given the magnitude of the investments contemplated in the study ' $200M in 2020 and an additional $200M five years later ' the ability to access credit markets was of paramount importance. Ensuring that the stormwater fees placed into service would meet the applicable legal tests was factored into each step of the analysis. LESSONS LEARNED FROM CUSTOMER ENGAGEMENT The new stormwater fee structure needed to not only be easy for the community to administer, but more importantly, easy for the community to understand. Once the new fee was developed, extensive public outreach was performed to inform the public about the new trip component, share ways property owners could review their assessment, and address concerns regarding the new methodology before the new fees became effective. Multiple mechanisms were used to advertise six public meetings, including the City's social media pages, City website, neighborhood meetings, and the neighborhood app Nextdoor. A very thorough web portal was designed to allow citizens to easily review their billed units and review frequently asked questions. In the end, this successful collaboration between Stantec and the City resulted in adoption of a new fee structure with credit policies. The newly modernized stormwater fee structure enhances equity by recognizing the full benefit of service that parcels receive. While stormwater management can be costly, it is a necessary investment. Stormwater utilities are becoming increasingly vital for communities to have a dedicated funding source for proactive management and the financial responsibility can be distributed fairly.

Abstract Anaerobic co-digestion (AcoD) offers an opportunity to treat food waste (FW) using extra capacity of municipal digesters but is susceptible to reactor souring. We develop a novel model to explore the conditions where FW AcoD reactors sour based on varying organic loading, hydraulic retention time (HRT), and feeding mode (continuous vs. semi-batch). The model includes typical biomass present in AcoD, common FW components (carbohydrates, proteins, lipids) and their hydrolysis products, pH and chemical speciation, alkalinity and pH, and select fatty acid inhibitions. With a long enough HRT and especially with continuous feeding, increasing food waste loading improved pH stability, biogas yield, and methanogen accumulation. AcoD operated with semi-continuous feeding was more sensitive to lower HRT than AcoD with continuous feeding. For example, feeding food waste having 200 g/L TCOD required a minimum HRT of 10 days for continuous feeding, but 20 days for 2-days in the semi-continuous mode. The best indicators of the onset of souring were bicarbonate total alkalinity below 1500 mg CaCO3/L and VFA greater than 500 mg/L as acetate. The model and its results will help designers and operators determine and monitor crucial parameters for industrial application of AcoD. Introduction: The Food and Agriculture Organization (FAO) reports 130 million tons of food waste (FW) are produced annually, accounting for one-third of the global food production (Gustavsson, Cederberg, Sonesson, Otterdijk, & Mcybeck, 2011). In anaerobic co-digestion (AcoD), FW is digested with municipal sludge, increasing energy production as methane (CH4) and reducing materials sent to landfills. However, the steady operation is a big challenge for FW co-digestion plants, restricted by the OLR and hydraulic retention time (HRT). In this work, we utilize mathematical modeling to explore causes of AcoD reactor souring (i.e., pH < 6.0, washout of methanogens, and no CH4 production) taking into consideration FW loadings, HRT, and feeding mode. Material and Methods: Our food waste co-digestion model (FWDM) was based on models by Young et al. (2013) and Batstone et al. (2002), as illustrated in Figure 1. Reactor simulations first involved feeding thickened wastewater sludge (ThS) alone to establish steady state conditions. Then FW was co-fed at the same volumetric flow rate as ThS. ThS and FW composition were based on Young et al. (2013) and Kupferer (2020). The ThS feed has 50 g TCOD/L, 43 g/L total solids, and a pH of 6.55. The FW has 50-200 g TCOD/L, 10-32 g/L total solids with 41% carbohydrates, 32% proteins, and 27% lipids, and a pH of 5.2. Chemical speciation and pH were calculated using the proton condition (PC). The model also included inhibition functions for pH, VFAs, and H2. Operational parameters including flow rates, HRT, and volumes of the digester and gas phase were based on conditions for AD reactors we used to evaluate AcoD in the lab. The model was implemented in MATLAB using an ordinary differential equation solver, ODE15s. Mass balances on each element in the system achieved < 0.00001% error. Results and Discussion: We explored the impact of FW organic input concentrations from 50-200 g TCOD/L, HRTs ranging from 8 to 30 days, and system operation mode (continuous or semi-continuous). For system operation, the reactors were simulated as continuously fed, fed once per day instantaneously, fed once every two days instantaneously, and fed for 8 hours per day. Similar trends for souring were observed for a wide range of operating conditions. In brief, souring was directly caused by depletion of bicarbonate alkalinity with the addition of FW. As an example, we present simulations with reactors being fed semi-continuously every 2 days with ThS and 200 g/L-TCOD FW at HRTs ranging from 15 to 30 d. With addition of FW, the organic loading increased to 19 and 21 g TCOD/L-d in the 18-d and 20-d (HRT) reactors, respectively. Figure 2a shows that the 18-d HRT reactor soured (< 6.0) at about 47 d after FW feeding began, but the 20-d reactor remained maintained a pH of 6.5-7.0 for the duration of the simulation. The added food waste and rapid hydrolysis of carbohydrates and proteins in it caused a rapid increase in fermenter and methanogenic concentration in both reactors (Figure 2b); consequently, the fermenting bacteria produce higher concentrations of VFAs, mostly acetate (Figure 2c). VFAs averaged 1300 mg COD/L in the 18-d reactor between feedings, versus 400 mg/L in the 20-d HRT. At the same time, bacteria consumed NH4+ and HCO3- for metabolic purposes, reducing HCO3- concentration in the 18-d reactor from an average of 3000 mg CaCO3/L to 830 mg CaCO3/L between feedings; for comparison, the 20-d HRT reactor showed HCO3- from 3200 to 2200 mg CaCO3/L between feedings. The combination of significant reduction in NH4+ and HCO3- buffering capacity and the formation of significant amounts of VFAs depleted system alkalinity in the 18-d HRT reactor, causing the pH to decrease to < 6.0 on day 47 after FW feeding began. Our results also showed (not in a figure) that continuous feeding avoided souring at HRTs as low as 10-d HRT, because spreading out the feeding process prevented fermenters from rapidly fermenting carbohydrates and proteins to VFAs that destroyed HCO3- alkalinity. Conclusions: Our modeling predicts that souring occurs when HCO3- alkalinity decreases to <1500 mgCaCO3/L with a commensurate increase in VFAs to >500 mg CaCO3/L. These parameters must be monitored as predictive indicators for FW AcoD souring. Our results also show that continuous feeding avoided souring making, it an operational advantage over feeding semi-continuously for several hours every one or two days.

The City of Chelsea, MA is strategically located as a gateway between downtown Boston and North Shore communities and is home to a vibrant, diverse population and industry that contribute significantly to the overall wealth of the region. Chelsea is served by the Massachusetts Water Resources Authority (MWRA) for water supply and wastewater collection. Many MWRA interceptors and a major regional headworks and pumping station are located in Chelsea. Like many other coastal communities in New England, Chelsea is serviced by a mix of combined and separated sewer systems that were built more than a century ago and are at the end of their service life. This outdated infrastructure hinders new development and growth, especially in the context of increased precipitation and coastal-induced inundation risk due to climate change. As a response to this concern, Chelsea has embarked on a city-wide master plan for sewer separation and infrastructure upgrades to systematically work towards attainment of the following three main goals: 1. Allow for future growth by progressively upgrading drainage infrastructure able to accommodate future population and increased stresses from climate change; 2. Eliminate CSOs by separating existing combined sewer areas and; 3. Reduce inflows to sanitary pipes from public and private properties that currently decrease available system capacity and increase operating costs to the City. In order to create this ambitious program, a significant modeling effort was carried out following a multi-step process. The first step consisted of building and calibrating a city-wide drainage model to help understand points with weak level of service and estimate peak flow and volumes reaching the MWRA interceptors and combined sewer overflows during dry and wet weather events. The City-wide model was built in Infoworks ICM using pipe network data from multiple sources such as record drawings, GIS, field inspections, and recently collected ground-level LiDAR information captured city-wide. The second step of the process consisted of developing conceptual level pipe layouts with the goal to achieve sewer separation city-wide and improve level of service. The conceptual level plans were developed using a 'best case scenario' approach (i.e. assuming an ideal drainage network can be built without necessarily accounting for other factors such as utility conflicts or permitting issues for new outfalls). The reasoning behind this approach was the desire to delineate a network able to attain optimum hydraulic performance based on natural topography and street layout and then work backwards, if needed, when conflicts identified during later phases of the process require this layout to be modified. The conceptual storm and sanitary systems were then incorporated into an Infoworks ICM model, which was used to fine tune the conceptual network (e.g. pipe slopes, pipe sizes necessary to provide the desired level of service or flow velocities for a given event). The third step was a planning level engineering effort where a street-by-street evaluation at each sewershed was performed. The feasibility and actions needed to go from the current condition to the proposed condition in the conceptual model were evaluated and alternative actions proposed when identified conflicts could not be resolved. The fourth and final step consisted of packaging and phasing the execution of the sewer separation and inflow reduction projects based on feasibility, City's priorities and constraints, as well as interim system conditions. This product is the City's new Master Plan for Sewer Separation and Drainage Infrastructure Upgrades, which will provide a systematic approach to drainage infrastructure improvements over the next few decades.

Executive Summary: South San Francisco-San Bruno Water Quality Control Plant (WQCP) incorporated high-solids digestion to cost-effectively provide necessary capacity and avoid the need to build additional digester tanks. Following third-party validation of healthy digester operations in high-solids conditions, the WQCP advanced a food waste co-digestion pilot in partnership with a nearby waste management authority. The pilot demonstrated significant increase in biogas production, without negative impact to digester health. The initiative not only sets the stage for the WQCP to advance energy-neutrality but also supports achievement of state-level organic waste diversion mandates in California to support greenhouse gas reductions. Background: The WQCP identified a need to rebuild the plant's three existing digesters due to seismic concerns and built additional AD to meet future load growth. While capital planning initially called for new construction of five (5) digesters total, Carollo Engineers conducted an alternatives analysis considering high-solids digestion to more cost-effectively achieve the required digester capacity. Carollo evaluated a scenario pairing two (2) conventional AD with one (1) high solids digester employing Anaergia's Omnivore high-solids digestion platform. 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. To ensure proper mixing in higher solids conditions, Omnivore employs Anaergia's high-torque submersible propeller mixers (Fig. 3). These high-efficiency mixers are designed to effectively mix high viscosities that result from thickening digestate and resist ragging. By applying mixing energy directly to digestate, 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 Carollo evaluation indicated that the proposed configuration leveraging high-solids digestion would deliver equivalent digester capacity to the originally planned five (5) tanks. Further, lifecycle cost analysis confirmed that the high-solids alternative would not only achieve CAPEX savings but OPEX savings, resulting in approximately 10% overall savings over the project life. OPEX savings to the WQCP primarily result from improved mixer energy efficiency and reduced polymer consumption associated with dewatering. Application: 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 Anaergia propeller mixers. Mixer selection was validated and informed by computational fluid dynamic (CFD) modelling, the results of which are summarized in Tables 1-4. The model demonstrated low energy demand, improved tank mixing, and energy-efficient mixing performance, particularly in high-solids conditions (6% TS), as compared to linear motion and pump mix alternatives. 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. 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 5): -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. 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 CFD modeling of mixer performance, which indicated superior performance compared to alternate mixing technologies. Co-Digestion Pilot: In July 2022, following successful completion of performance testing, the WQCP began a pilot program to receive 1-2 deliveries per day of slurried food waste. The organic slurry is produced at the South Bayside Waste Management Authority's Shoreway Environmental Center. The materials recovery facility (MRF) employs an Anaergia Organics Extrusion (OREX) press and Organics Polishing System (OPS) to remove contamination from commercial source separated organics and create a clean, homogenized, pumpable organic slurry. The slurry is pumped into 5,000-gallon liquid tanker trucks and hauled approximately 15 miles from the MRF to the WQCP. The slurry is fed to Dig. 1 for co-digestion with indigenous biosolids. The high-solids digestion upgrades have facilitated the pilot by provided excess capacity for external feedstock, as well as high-solids mixing capability within the digester to maintain digester health and mixing performance. WQCP monitoring indicates significant increases in biogas production since the initiation of high-solids digestion and co-digestion, respectively. Ongoing data collection during the pilot will inform planning and design of food waste receiving and biogas utilization upgrades to facilitate long-term co-digestion and advance energy-neutrality at the WQCP. Note that the high-solids digestion 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 expanded co-digestion. Conclusion: The Omnivore system effectively addressed the biosolids and residuals management needs of the WQCP leveraging existing infrastructure; provided third-party validated performance improvements; and facilitated a successful food waste co-digestion pilot. 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 co-digestion of organic waste -Increased biogas production and energy neutrality 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 co-digestion, and improve plant resiliency. A similar solution may be replicated at WRRF throughout North America to cost-effectively improve biosolids management while significantly enhancing the ability of municipalities to leverage existing infrastructure for meaningful resource recovery and energy neutrality.