Conference Papers

Since it was founded in 2013, Bioforcetech has been working to rethink biosolids treatment at every step of the process. Our work has culminated in a deeply sustainable system that harnesses the energy already available in biosolids to dry and carbonize it with little to no external energy. Our patented Bioforcetech BioDryer (designed in house) and P-Series Pyrolysis machines (licensed and engineered in partnership with Pyreg GmbH) work together to reduce material volume and weight by 90%, lock available carbon in place for centuries, and produce a valuable biochar material all with 99% less external energy requirement than a standard paddle dryer. The Bioforcetech system is modular, capable of handling 80% of all US plants by linking units together in series, so that a plant can begin processing now with room to build as their capacity grows. At present time, we are proudly the only commercially available functioning pyrolysis project in the USA, and are running our units under some of the most stringent permitting conditions in the world (We have received an SSI exemption from the EPA and have received full permitting from BAAQMD). At Bioforcetech, we know that change is possible through collaboration across sectors and industries, which is why we are also investing in finding new applications for biochar that will lighten the carbon footprint of other industries and help grow the market for the material across the world. Our wastewater treatment is of utmost importance to human health. The accumulation of PFAS, PFOA, and PFOS in wastewater effluents puts our industry in a unique position to aid in the removal of these substances from our population.At Bioforcetech we have taken the PFAS issue as a personal challenge to overcome, and we are now proud to share that testing conducted on our technology shows considerable promise for its ability to successfully eliminate these harmful substances from input materials completely. When continuously applied, these CEC's bioaccumulate into the soils we walk on, the groundwater we drink, and the plants that we eat. As described by the EPA, high accumulations of PFOA, PFAS and PFOS can cause serious health effects including increased cholesterol levels, issues with infant birth weights, adverse effects on the immune system, cancer (for PFOA) and thyroid hormone effects (for PFOS). While the production of these chemicals has been phased out in the United States, similar chemicals like GenX have taken their place and continue to be created. The presence of PFAS, PFOA and PFOS in biosolids makes even the most beneficial land application of the material a serious risk to human and environmental health. In September 2019, we at Bioforcetech initiated testing of our drying and pyrolysis process to determine our ability to eliminate CEC's from biosolids. To do this, Bioforcetech isolated a single large batch of biosolids and tested samples of this batch for PFAS, PFOA, and PFOS at each step of our drying and pyrolysis process. An initial sample was taken of anaerobically digested biosolids at 17% solids content, a second sample was taken of 91% solids content biosolids after the batch was dried in our patented Biodryer, and a third sample was taken after the batch was put through our P Five pyrolysis machine. The analysis of these three samples conducted by Vista Analytical Laboratory showed the reduction of 38 PFAS, PFOA, and PFOS compounds to below detectable levels after pyrolysis from a significant presence in both of the biosolids samples. In May of 2020, an EPA PFAS Task Force representative contacted Bioforcetech as part of a search for technology that could solve the PFAS issue. We were happy to work with the EPA to further test our technology, and found the results promising again. The tests conducted on our biochar samples by the EPA Task Force in August of 2020 confirmed undetectable levels of 41 PFAS, PFOA, and PFOS compounds that the task force tested. The results from the EPA's analysis including methods involved will be formally published in November of 2021. The results of multiple tests conducted and confirmed by different constituents shows great promise for the ability of Bioforcetech's system to remove PFAS, PFOA, and PFOS from biosolids completely. While more rigorous testing must be completed, we are motivated and inspired by the results thus far. PFAS, PFOA, and PFOS have permeated every part of our planet. Wastewater effluents provide a unique context where these chemicals can bottleneck together and appear at relatively high volume. It is therefore our responsibility as an industry to leverage this context and destroy PFAS, PFOA, and PFOS before it accumulates further in our soil, food and within our bodies. Solving this challenge is crucial to completing the Bioforcetech mission; to protect nature and human health by providing technologies that deliver a zero waste future, transforming organic waste into sustainable products. We are looking forward to continuing this work.

Public water agencies throughout the United States face many challenges with extending the reliable service life of their aging buried infrastructure. The San Jose/Santa Clara Regional Wastewater Facility (RWF) has the capacity to treat approximately 200mgd, with ongoing projects expanding this number. It is located in the City of San Jose (City) and has approximately 67,000 linear feet (LF) of buried wastewater process pipes, many of which were installed in the '50s and '60s and thus have exceeded their design life. Because of the potential terminal condition for some RWF piping, the City is using this Project to increase operational reliability and mitigate the likelihood of failure of their existing buried linear assets. If selected, the purpose of this presentation would be to share BV and the City of San Jose's approach to a large-scale piping condition assessment and rehabilitation effort. The presentation would include a description of the risk tool that BV developed exclusively for this project, condition assessment methods that were implemented, and rehabilitation methods that were selected. Fortunately for these agencies, many viable pipe rehabilitation methods have been invented to date, and there are often large pools of contractors vying for the job. Unfortunately for these agencies, there is rarely a platform available to share feedback or lessons learned from prior projects, even between neighboring cities. Furthermore, it is rare for an agency to embark on such a large, comprehensive project. Therefore, the largest benefit of this presentation would be the ability to share BV and the City's approach to delivering an on-time/under budget project, which started with developing a piping inspection prioritization tool and ended with rehabilitating pipes to provide an additional 50-year service life. In 2018, the City retained Black & Veatch (BV) for the Yard Piping Improvements Project (Project) to systematically assess all buried process pipes 8 inches to 144 inches at the RWF, which equates to approximately 60,000 LF of piping. Pipes at the RWF are comprised of many materials, but are primarily made of either reinforced concrete, ductile iron, or welded steel. The focus of the multi-year Project is to repair, rehabilitate, or replace (R/R/R) pipes, or portions of pipes, that are highest priority by virtue of their criticality and/or observed physical condition. In 2015, as part of a separate project, BV developed a condition assessment plan that provided a prioritized list of critical pipes for inspection, inspection protocol recommendations, and end of life estimates. The plan used weighted risk factors to determine the LOF (likelihood of failure) and COF (consequence of failure) for each assessed pipe. Depending upon identified pipe risk, inspection protocols and desired levels of inspection detail were determined for each pipeline. The final report produced in 2015 has served as the technical basis for the current Yard Piping Improvements Project, and the recommendations provided in that initial report have largely been followed. To date, approximately 36,000 LF of primary and secondary treatment piping has been inspected. Following each inspection, BV reviews the resultant condition data and makes R/R/R recommendations based on the findings. The Project follows an annual cyclical schedule whereby pipes are inspected during the regional dry-weather season, design work based upon these inspections occurs during the wet weather season, and R/R/R construction proceeds in the next dry-weather season. There is a separate service order for each year's pipe rehabilitation design, and a design-bid-build (DBB) project model is followed for each service order. Approximately 2,200 LF of the 36,000 LF inspected to date was identified to have severe deficiencies requiring R/R/R, and these pipe segments have since been rehabilitated. The scope for the first pipe rehabilitation service order contained primary effluent 96-inch reinforced concrete pipe (RCP) and an elliptical 87x136-inchpipeline. Beginning in the '50s, the RWF has slowly expanded to add more effective treatment processes and to increase the overall plant capacity. As a result of this expansion, there are many buried crossing utilities that preclude the feasibility of applying many traditional rehabilitation methods, resulting in a trenchless method focus. Ultimately, the 96' pipeline was rehabilitated with CIPP, and the 87'x136' was rehabilitated using a combination of concrete crown restoration with geopolymer material with an epoxy top coating. The second pipe rehabilitation service order, which is currently in the design phase, contains more primary effluent RCP including 78-inch, 96-inch, and 84-inch pipeline. CIPP was selected as a rehabilitation method for both the 78-inch and 96-inch pipelines, and concrete crown repair with a with an epoxy top coating selected for the 84-inch pipeline. The overall project is scheduled to be completed in 2026, with phases completed each year. The presentation of the Project, which has never been presented at a WEF Collections Conference to date, will focus on condition and risk assessment, selection of inspection methods and applications, the criteria against which rehabilitation alternatives are compared, planning and successfully executing pipeline rehabilitation.

Many New England communities are undergoing flow restoration efforts to improve the health of impaired waterbodies. One such waterbody is Englesby Brook, which drains an area of approximately 605 acres in Vermont's Burlington Bay watershed before flowing into Lake Champlain. Englesby Brook was designated as a stormwater-impaired watershed on the 2006 Vermont 303(d) list due to multiple impacts associated with excess stormwater runoff [1]. A Total Maximum Daily Load (TMDL) target was subsequently released, requiring an 11.2% increase in stream flows during low flow conditions and a 34.4% reduction in flows during the 1 year 24 hour storm event. To improve stream health in Englesby Brook, the City of Burlington Department of Public Works planned a number of stormwater projects. One such project was the retrofit of a stormwater basin called '08 Pond', a wet detention pond collecting runoff from 131.5 acres (21.7% of the Englesby Brook watershed). The proposed retrofit would have included expanding the existing pond footprint, excavating below the pond bottom, and creating additional storage above the existing permanent pool at an estimated 2015 cost of $400,000. This proposed project was estimated to reduce peak discharge from the pond by 63.4% for the 1 year storm [1]. However, recent advances in communications and control technology provided an alternative to this traditional expansion retrofit. To optimize flow through the 08 Pond, the City of Burlington decided to enhance the basin with continuous monitoring and adaptive control (CMAC) technology. CMAC systems leverage real-time site data, the weather forecast, cloud-based software, and flow controls (e.g., actuated valves) to predictively control the timing and rate of flow through stormwater facilities [2]. At 08 Pond, CMAC automatically draws down the pond below the normal pool in advance of storms, allows the pond to fill up targeting zero discharge during events, and performs a post-storm release. Model results show an up-to 80% reduction in peak discharge during the 1-year storm is possible through the use of CMAC at 08 Pond. Anticipated CMAC costs in early 2020 totaled $98,000. Following the retrofit completion in May, 2022 the City will have invested $105,000 to facilitate the installation of this innovative CMAC system. Data from a set of storms totaling 1.63 inches of rainfall in seven days at 08 Pond is shown in Figure 2. Englesby Brook 08 Pond is the second CMAC system in the City of Burlington. The first was the enhancement of an underground detention vault at the Greater Burlington YMCA in 2020. During an analysis period of 3/1/2020 through 11/1/2020, this project retained 70.2% of the stormwater volume during critical wet weather periods, compared to only 16.8% stormwater capture simulated for an identical passive detention system. This presentation will discuss how Burlington is working towards stormwater impaired waters flow restoration and parallel water quality requirements, the background for the Englesby Brook 08 Pond project and highlight aspects of the design, construction, and software configuration. Performance results will be shared for both the 08 Pond and YMCA CMAC projects.

There is an increasing emphasis on the impact of volatile gaseous emissions from area sources such as anaerobic treatment ponds, biosolids treatment processes, feedlot pads, compost windrows, and municipal wastewater sites, due to the concerns related to malodors, greenhouse gases, micropollutants, or bioaerosols. The estimation of emission rates are critical to support the assessment of environmental and social impacts such as nuisance and human health as well as climate change. Emission sampling is an essential stage in determining emission rates, where sampling methods seek to simulate the real emission scenarios. In a previous review (Liu et al. 2022), the benefits and disadvantages of a series of sampling methods (flux chamber, wind tunnel, static chamber, headspace methods) were compiled. The review showed there was lack of the understanding of the role of sampling methods, creating difficulties for industries or users in the analysis and interpretation of the emission data. Flux chambers are a commonly used method, due to the presence of standards, ease of operation and perception as a method that simulates real-world emissions. During method development, flux chambers were extensively tested to assess the impact of operational factors such as flushing rate and placement depth, however, experimental implications of different designs of flux chambers were limited. Based on the finding by Hudson and Ayoko (2008), 19 called flux chamber cylindrical devices were found out of 76 dynamic devices, while only 5 of 19 shared the same design in terms of dimension and operating system (Gholson et al. 1991, Sarwar et al. 2005). Such differences in design, limits the comparison of data and the establishment of an emission model for evaluating emission from area sources such as biosolids storage and application sites. In this research, four different flux chambers were used to measure the volatile emission rate from porous media using typical operating conditions (Table1). The comparison of flux chambers took into account inlet gas distribution system, chamber materials and variations in hood dimensions. The sweep gas flow rate in the chamber was varied from 1 L/min to 5 L/min. The results were interpreted using the relationship between gas velocity, turbulence intensity and the physical design of the device. Chamber II was set up based on the U.S. EPA flux chamber design (Kienbusch 1986) and tested as a benchmark. The emission rate measured using chamber III, which was duplicated from chamber II, showed 20%-60% variations, indicating the necessity of calibrations for each flux chamber before use. Compared to chamber II, variations of sweep air flow rate in chamber IV showed less effect on changes in the emission rate. However, the overall emission rate from chamber IV was higher, e.g. 103% higher at 1L/min flow rate. This difference was attributed to altered sweep gas jet direction which affects the circulation of sweep gas over the area surface and generated turbulence. To verify the hypothesis that sweep gas direction can affect the emission rate, axially vertical jets of sweep gas were used in chamber IV resulting in a higher emission rate compared to chamber II, while the increased number of jets further increased the measured emission rate (chamber I). The study findings emphasised the importance using a standardised flux chamber configuration, while linking the inlet gas distribution setups to recirculation motion in the chamber as well as the effects on emission rates from porous media. This is in agreement with prior studies conducted using CFD on liquid surfaces (Andreao et al. 2019). The outcome of this study will contribute to the more consistent use of flux chamber within which consistent, reproducible conditions could be established.

Introduction Per- and polyfluoroalkyl substances (PFAS) encompass a wide range of compounds, numbering in the thousands. These compounds, because of their properties, have been used in a variety of consumer and industrial products and, consequently, are widely distributed in the environment (Buck et al., 2011). Research focused on understanding the sources of PFAS in drinking water and have identified municipal wastewater reclamation facilities (WRF) as an important pathway (Clara, Scheffknecht, Scharf, Weiss, & Gans, 2008). Because PFAS are concentrated in wastewater solids (Rainey, 2019), WRFs introduce these compounds to the environment through land application of biosolids, potentially allowing PFAS to enter surface water and groundwater (Lindstrom et al., 2011). What has not been well studied is the potential for sewage sludge incinerators (SSI) to introduce PFAS to the environment or destroy it. The extent of PFAS thermal destruction (i.e., thermal degradation by-product formation or complete mineralization) is poorly understood. No published data currently exist on the fate of PFAS through an SSI, although limited information from other industries can be referenced. This paper documents the current understanding on the fate of PFAS through SSIs and the research currently underway to further our understanding. PFAS Thermal Behavior For a combustion process to achieve complete PFAS thermal destruction (mineralization), PFAS compounds would have to be driven to their thermodynamic endpoints of CO2, H2O, HF, or sulfur compounds, if present. Residence time, turbulence (mixing), and stoichiometry (the relative mixture of waste to fuel, oxygen, and other gas-phase constituents) within the flame zone impact the completeness of combustion (Lewis, 2008; Niessen, 2002). Published research and industry guidance indicate that complete destruction of PFAS requires high temperatures (Table 1) which exceeds typical temperatures in SSIs. Notably, this guidance is based on limited conceptual or laboratory-scale experiments and precedence on previous guidance established for hazardous waste incineration. The baseline research for these recommendations stems from USEPA and other international environmental agency activities. Taylor & Yamada (2003) published results of a simulated hazardous waste incineration experiment with limited air to account for non-ideal combustion conditions. Experiments showed less than 0.4% and 0.05% of the PFOS fed to the reactor were detected in the exhaust at tests conducted at 600°C and 900°C, respectively. Yamada, et al., (2005) published a similar laboratory-scale study that considered combustion of PFAS-impregnated textiles. Neither PFOA nor PICs were detected under non-ideal combustion performance. Taylor et al. (2014) found no PFOA emissions after combustion of gasified fluorotelomer-based polymers. Full-Scale Incineration Studies A few full-scale studies have been published on the fate of PFAS through incineration systems with only two considering an SSI. Loganathan et al. (2007) investigated eight PFAS through a wastewater treatment facility. PFAS were measured in dewatered solids fed to the incinerator and in the ash. No mention was made on the operating conditions or whether the bottom or fly ash was sampled. Findings indicated a significant transformation of the measured compounds (26 & 97 percent); however, some PFAS were still detected in the ash. A second study is currently underway at an SSI facility employing an fluidized bed (MacGregor, 2020). Samples were taken at all inputs and outputs of the SSI system and analyzed quantitatively for 28 PFAS. Preliminary results show that mass flows were reduced through the SSI processes for all quantitated PFAS, with the exception of 6:2 fluorotelomer sulfonate. The authors also noted that the inorganic fluoride content of the wet scrubber discharge water was over 10,000 times that of the influent flow plus the measured PFAS fed to the furnace, assuming mineralization. No other studies have been published on SSIs, but limited information can be found in literature investigating incineration in other industries. Lemieux et al. (2007) reported on the USEPA's study of feeding carpet treated with fluorotelomer products into a pilot-scale rotary kiln furnace. The emitted PFAS detected, primarily PFOA and PFHxA, did not change when feeding PFAS contaminated carpet or not. Aleksandrov et al. (2019) investigated emissions from a pilot-scale rotary kiln incinerator. No significant PFAS emissions were detected. Thermal By-Products Bench- and pilot-studies have examined decomposition of specific PFAS congeners and by-product identification; several studies documented thermal PFAS degradation by-products (Table 2). These studies show that PFAS will decompose at temperatures relevant to operating conditions of SSIs although by-product formation will be a concern. Funded Research The USEPA (2021) has recently sampled an SSI as part of a broader sampling program at a WRRF. Samples were taken from all major input and output streams of the multiple hearth for PFAS characterization. The samples are currently being analyzed for targeted, non-targeted, and total organic fluorine. Winchell et al. (2021b) provide a detailed discussion on these analytical techniques. A separate study led by Brown and Caldwell with support from the Water Research Foundation's Tailored Collaboration program will sample two SSIs, one multiple hearth and one fluidized bed. This study mirrors the USEPA from a sampling and analytical standpoint. The full-scale sample will take place during the winter and spring. Initial work has included site selection and workplan development. Including, estimating PFAS emissions at various destruction and removal efficiencies (DREs) based on targeted PFAS measured in initial dewatered cake samples. Figure 1 shows the PFAS emissions from one of the test sites remain above the reporting limits for the analytical method at relatively high DREs. This suggests specific PFAS will be detectable unless achieving high DRE, a question highly sought after by the industry. Conclusions Thermal treatment of PFAS through SSIs represents a potential wastewater solids process for destroying PFAS; although, significant questions remain regarding both the destruction efficiency and potential formation of undesirable by-products. Temperature is only one of the three key operational parameters that should be considered when assessing destruction capacity in combustion systems. The other two important factors include residence time and turbulence. A well-functioning SSI will submit PFAS to greater residence times and mixing (or turbulence) than the laboratory-scale research performed to date, further promoting PFAS destruction.

CSO 032 and Third Street Consolidation Sewer -- River Crossing Under the river, and through the levee, to the siphon headbox we go Statement of Purpose: Design evaluated trenchless techonologies, creative construction methods, but ultimately settled on open cut installation with innovative specification language to allow for contractor flexibility in order to construct the 107 MGD siphon under the St. Mary's River due to cost, risk, and schedule. Project Summary: As part of Fort Wayne's CSO Long-Term Control Plan, consolidations sewers are proposed to convey CSOs to the City's new CSO Conveyance Tunnel. Arcadis designed the consolidation sewer to convey flow from CSO 32 and the Third Street Lift Station. The CSO 32 and Third Street Pump Station Consolidation Sewer project entails 1200 LF of 66-inch pipe, 40 LF of 54-inch pipe, 140 LF of 84-inch pipe, a diversion structure that will intercept combined sewage flow from the Third Street Pump Station and convey it to Drop Shaft 09 (DS-09) located in Headwaters Park, modifications to CSO 032 to add a slide gate, and modifications to the Third Street Pump Station to add floatables control to the CSO outfall. Project was designed to convey 107 mgd of combined sewage into Fort Wayne's new CSO tunnel to reduce CSO overflows. Project challenges include open cut installation of the pipe through the St. Marys River and Army Corp of Engineering floodwall, deep installation, adjacent properties and utility conflicts, constructability concerns, and permitting. Status of Completion: Construction was complete in 1st half of 2022. Contractor Feedback Early in the design, Arcadis obtained feedback from contractors to discuss the Project and get their thoughts regarding trenchless and open cut installation methods based on their experience. Installation methods evaluated included open cut, jack and bore, horizontal directional drill, and microtunnel. River Crossing Coordination A challenging part of design was incorporating specification requirements for the river crossing to allow the contractor time and installation freedom for the crossing to ensure a low bid price. Work items were included for River Crossing, River Crossing Delay, River Crossing Event Cleaning, and Local River Measurement Gauge. The intent of the pay items were to share risk with the contractor during typical low river times and provide flexibility to the contractor during construction. Design Lessons Learned - Identification that a 100-foot working area across the St. Mary's River would be pursued to allow for flexibility in open cut construction. Contractor had the freedom to do an earthen cofferdam, portadam, sheet piling, or other method to install the three siphon pipes across the river. - Identification that the St. Marys River levels are different year to year and an extended construction period would allow for construction flexibility. - Need to plan for floatation and protection of pipes under the St. Mary's River. - Coordination with other projects in the area and the Hosey Dam downstream to adjust the river level to aid in construction, but limit impact to community. Construction Lessons Learned - Contractor will use all the allowable time in the Contract. - Contractor willing to work at risk to meet the project schedule. - Define material removed from the river. Material pulled form the river was uncompactable. Contractor brought in clay fill. - Multiple Stakeholders impacted by river lowering (directly after labor day) - Sheeting is not watertight. Up to 4 pumps operating (8 inch + 2/3 inch pumps) Conclusion: Due to thorough design evaluation, working directly with contractors, and creative design thinking, innovative specification language was added to the Contract to allow contractor freedom to factilitate the construction of the siphon under the St. Mary's River. The project was successfully completed on time and on budget. Other utilities will learn how trenchless options are evaluated and why ruling out open cut could be a mistake, the value of engaging contractors early in the design process, how specifications can be used to share risk with the contractor, and the value of understanding your assets.

INTRODUCTION The Saddle Creek Retention Treatment Basin (RTB) is a significant project as part of the City of Omaha's water quality program 'Clean Solutions for Omaha' to address compliance with their Long Term Control Plan to address combined sewer overflows. Prior to the construction of the facility, over 65 times per year, untreated combined sewage overflowed into the Little Papillion Creek (LPC) from the City's CSO 205 outfall structure. With the new facility in place, combined sewage will be diverted to the RTB to receive grit and screenings removal, disinfection, solids settling, and dechlorination before being discharged back to LPC. The Saddle Creek RTB project began planning and design activities in April of 2011. Construction commenced in Spring 2019 and is anticipated to start operations in the summer of 2023. This facility will provide storage and equivalent to primary treatment of combined sewage flows up to the permitted design flow rate of 160 million gallons per day (MGD) with the ability to screen, remove grit, and disinfect flows up to 320 MGD. Lower volume flows will be captured within the basin and will be pumped into the Little Papillion Creek Interceptor (LPCI) and conveyed to the Papillion Creek Water Resource Reclamation Facility (PCWRRF) for full secondary treatment. Larger volume flows will receive grit and screenings removal, disinfection, solids settling, and dechlorination before being discharged to the LPC. The facility will result in a significant reduction in the volume of untreated CSO, total suspended solids (TSS), and E coli bacteria entering the LPC. This presentation will describe how the Saddle Creek RTB will effectively and reliably capture and treat untreated combined sewage in compliance with regulatory requirements. FACILITY OVERVIEW The Saddle Creek RTB facility consists of a 3.3 million gallon (MG) underground concrete storage basin, with grit removal, mechanical screening, chemical disinfection, gravity effluent discharge, a dewatering pump station, as well as Headworks, Operations, and Chemical Buildings. The facility also includes a diversion structure, sewers, odor control, stormwater BMPs, driveways, and other appurtenances. Refer to Figure 1 for a Process Flow Diagram illustrating the various features of the RTB facility below ground. The facility operates during wet weather events. Prior to the completion of the Saddle Creek RTB project, an existing dry weather diversion weir directed dry weather and a portion of wet weather flow, up to 40 million gallons per day (MGD), was sent to the existing Dupont Grit Facility and ultimately to the LPCI. Prior to this project, any excess flow was discharged untreated to the CSO 205 Channel and eventually the LPC. The existing dry weather diversion pipes will be abandoned as part of this project and replaced with a new 60-inch sewer which will pass through a grit pit within the new facility's Headworks Building. The diversion weir will send flows using real time control and smart sewer technology to provide gate control of up to approximately 60 MGD to the LPCI before overflowing into the RTB influent sewer. This new diversion chamber will divert wet weather flow up to the peak treatment design flow of 160 MGD to the RTB. This diversion chamber configuration ensures that flow rates up to the design flow can pass through the RTB and does not increase the risk of upstream flooding during larger events. Captured volume in the tank will be pumped into the LPCI and conveyed to the Papillion Creek Water Resource Recovery Facility (PCWRRF) for full secondary treatment. Flows more than the facility capacity will be routed around the RTB and discharged into the LPC. Dry weather flow and some wet weather flows up to approximately 60 MGD will pass into a new grit pit, the diversion flow grit pit, constructed in the proposed Headworks Building. For flows passing through the RTB, large grit and other heavy materials will drop out via gravity into a second, larger grit pit, the RTB grit pit, prior to entering the screen channels. Downstream of the RTB grit pit, mechanically cleaned screens will provide for the removal of objectionable solids with the intent of protecting downstream equipment and controlling floatables. The facility includes three (3) continuous duty multi-rake screens with a clear opening size of ¾-inch. Disinfection must result in an effluent that meets E. coli and total residual chlorine (TRC) permit limits. Liquid sodium hypochlorite and sodium bisulfite will be used for disinfection and dechlorination. Above ground improvements include a building to house controls, grit and screening equipment, and chemicals. Refer to Figure 2 for a rendering of the finished facility. PROJECT COMPLETION STATUS In December 2018, the City received bids within the budget for the project and in February 2019, a contract valued at approximately $90 million was approved to build the Saddle Creek Retention Treatment Basin facility. Construction began in April 2019. Wade Trim performed design engineering on the project and is currently providing construction management services. The project is scheduled for Substantial Completion in Spring 2023. Refer to Figures 3 and 4 for construction progress photos. CONCLUSIONS The project's innovative use of a 'gravity in, gravity out' design for the RTB facility allowed for a reduction in pumping of significant flows. The use of real time controls and smart sewer technology will allow this facility to operate efficiently and effectively over a wide range of conditions, which have been evaluated through extensive hydraulic modeling and development of process control strategies. The use of instrumentation for flow and level measurement used in process control must incorporate redundancy and be flexible to allow for changes in available technology and must be compatible with other technologies being used at the facility and within the collection and treatment system.

In the past two decades, wastewater treatment plants (WWTP) have been undergoing a dramatic transformation from solely focusing on wastewater treatment to resource recovery of valuable byproducts from waste. Utilities are increasingly realizing the benefits of biofertilizer production, nutrient recovery, energy production, and water conservation and the value it brings to the overall bottom-line for the end user. Wastewater utilities are also uniquely positioned to bridge the demands of renewable energy production as well as reducing organic solid waste from ending up in landfill, both regulated in many states in the US. The US EPA has identified more than 1,300 facilities in the US that rely on anaerobic digestion to reduce organics from wastewater, however, per the American Biogas Council, an estimated 40% of all anaerobic digesters in the US are being underutilized. Digesters with excess capacity are energy sinks, requiring just as much heat and electricity when operated at under capacity as they do while fully optimized, but with very little return in the form of energy production (as biogas). This unused digester capacity can be utilized to anaerobically codigest landfill diverted organics to produce biogas, which in turn can be converted to biomethane or heat and electricity using a combined heat and power system. Increased biogas production is just one of the many benefits of introducing high strength biodegradable wastes from commercial and industrial establishments into municipal anaerobic digestion systems. Digestion systems can also be designed to produce Class A or exceptional value (EQ) biosolids that is returned to the market as biofertilizer or soil amendment. In anticipation of an upgrade from 5.0 to 7.7 MGD, Hermitage Municipal Authority in Pennsylvania undertook a major upgrade of their solids handling facility to increase treatment capacity. The facility only has secondary treatment, meaning there is no easy-to-digest, high calorific value primary sludge as a feed to the new anaerobic digesters. As part of the upgrade, one of the goals was to boost biogas generation and use it as the primary fuel in a combined heat and power (CHP) cogeneration system to offset process heat and generate renewable electricity. This lead to a solids management plan specifically design to address high strength codigestion of source separated organic (SSO) wastes imported to the facility, mostly focused on pre-consumer expired or contaminated food waste, all while still able to produce a US EPA approved Class A biofertilizer. A new two phased digestion system was built using two existing anaerobic concrete tanks on site and one new steel tank. This system includes a first stage thermophilic hydrolysis reactor to acidify high strength waste, followed by high rate mesophilic digesters. A new biogas collection and treatment system and a combined heat and power unit was installed. Subsequently, a second CHP system was installed to maximize biogas utilization with minimal downtime. A new depackaging system, capable of handling dairy/liquid waste was included as part of this initial upgrade. This limited use process justified the needs of the time since only one regional dairy had agreed to divert their pre-packaged, expired dairy waste to the wastewater plant for organics recovery. Subsequently, a second depackaging system was installed to widen the imported source separated organics profile, specifically to include the capabilities to extract organics from various packaged solid food waste. The design of the facility also include a staging area to receive imported packaged organic waste from grocers, large food manufacturers, dairy and other organic waste generators. More recently, a new innovative depackaging process was installed to improve organics removal efficiencies, reduce contaminant level in extracted organic slurry, and manage increased throughput of imported waste at the facility. The three depackaging units are now capable of handling both solids and liquid waste effectively. Since January of 2013, the facility has grown from having just one dedicated organics waste supplier to now receiving food waste from over a dozen major sources. The facility has since processed over 8,000 dry tons of solid waste and over 12 million gallons of high strength liquid waste. The facility utilizes a custom organics feed staging strategy in the advanced anaerobic digestion system, that allows an applied organics loading rate (OLR) in excess of 12 kg/m3 (0.75 lb/ft3) in the first stage thermophilic acid digester. The second stage mesophilic gas digester is fed at a rate of 3 kg/m3 (0.19 lb/ft3), which is typical of conventional digesters, but is capable of higher OLR input. The phased digester feed is a combination of secondary municipal sludge and depackaged organic high strength slurry, in some instances pre-heated prior to introducing it to the thermophilic digesters. The organics loading ratio on a mass basis for municipal sludge to imported waste ranges between 1 to 0.6 and 1 to 1, with 20 tons of municipal sludge for every 12 to 20 tons of organic slurry. The phased digestion system is a US EPA's Process to Further Reduce Pathogens (PFRP) equivalent process, designed to achieve Class A biofertilizers as the final product. The current bioenergy system is capable of treating over 125,000 cubic feet of biogas and generates up to 13,400 kilowatts hour of power. The goal is to convert the biogas into compressed natural gas (CNG) to capitalize on the renewable energy credits to improve the cities renewable energy portfolio. In addition to increasing the bioenergy and biofertilizer production, the authority collects tipping fees from food waste generators that offsets ratepayer contributions. Renewable bioenergy production using landfill diverted organics all occurs within this resource recovery facility. This synergistic approach will benefit the solid waste industry from having to find new ways to manage organic food waste, the energy industry from having to build new renewable energy facilities, and most critically the wastewater industry in maximizing existing infrastructure to produce biofertilizer, recovery nutrients, produce bioenergy, and conserve water all while generating revenue from tipping fees. The paper offers a concise methodology that illustrates this synergetic approach to a growing problem. The paper aims to cover the nuances of source separated organics pretreatment, anaerobic codigestion and related processes.

Introduction Per- and Polyfluoroalkyl Substances (PFAS) have been an increasing focus of the public, legislative bodies, and the regulatory community, and recent EPA activities highlight this focus with respect to biosolids(1). In October 2021 the EPA released its PFAS Strategic Roadmap, outlining EPA actions with respect to PFAS for 2021-2024: these activities include a risk assessment of PFAS in biosolids to be completed by 2024(1). EPA also announced its intent to pursue the classification of PFAS under the Resource Conservation and Recovery Act (RCRA). While it is no means certain that federal PFAS regulations for biosolids are forthcoming, some utilities have faced - or might face - increasing pressure to consider either i) reducing PFAS and microconstituent loads in biosolids, or ii) processes that provide an alternative product for land application. Conventional treatment processes such as anaerobic digestion or composting do not mitigate PFAS concentrations(2). Pyrolysis is an alternative solids process that is gaining interest as a possible approach to mitigate PFAS and microconstituents. Current literature is contradictory on the impact of pyrolysis on PFAS, with removal(3) and no removal(4) being reported. Thus, new experiments were conducted to determine the fate of PFAS during pyrolysis of biosolids, and results will be presented at the conference. In addition to knowing the impacts of pyrolysis on the fate of PFAS, practical considerations of pyrolysis such as generation of difficult-to-handle byproducts and side streams, dryer operations and costs, and product management need to be evaluated holistically. To approach this topic of PFAS removal via pyrolysis holistically, this presentation has three main objectives: 1. Define pyrolysis and the pyrolysis products generated from municipal biosolids 2. Determine the impact of pyrolysis on microconstituents, including PFAS, using novel, unpublished pyrolysis batch studies that investigate the fate of PFAS in biochar, pyrolysis-liquid, and pyrolysis-gas 3. Understand practical considerations for implementation of pyrolysis Objective 1: Define pyrolysis and pyrolysis products Pyrolysis is a thermal decomposition process that occurs at high temperatures (normally over 450ºC) under limited or no oxygen. Pyrolysis of biosolids generates solid, liquid, and gaseous products. The solid product, called biochar, is a carbon-rich product similar to charcoal that can be used as a soil amendment because it retains moisture(5). It can also adsorb nutrients from thickening filtrate and be used to improve grass growth(6). The non-condensable gases produced, called py-gas, contain energy rich constituents such as methane and hydrogen(7). The pyrolysis liquid can be composed of two phases: light non aqueous phase called bio-oil and an aqueous phase known as aqueous pyrolysis liquid (APL). The bio-oil, which can be used as a renewable fuel upon upgrading, is corrosive during combustion and difficult to handle, whereas the APL also contains organic compounds and sometimes high concentrations of ammonia that can be toxic to biological processes such as anaerobic digestion(8). Objective 2: Determine the impact of pyrolysis on PFAS and microconstituents Novel Research Approach Experiments will be conducted in a lab-scale batch pyrolysis system as described elsewhere(9). Dried municipal biosolids will be used as the influent feed, and effluent biochar, pyrolysis-liquid, and pyrolysis gas samples will be collected for PFAS analysis. In total, 37 PFAS compounds will be analyzed by PACE Analytical® in the solid, liquid, and gas phases to determine the impact of pyrolysis on the removal of PFAS from biosolids. These experiments will be completed by the end of 2021 and the analysis will be completed by March 2022. This experiment will be the first study to investigate the presence of PFAS in all three product phases (solid, liquid, gas) following pyrolysis. Results from Previous Lab-Scale Studies These results will be presented in light of Dr. McNamara's previously published data that found 3 possible fates of microconstituents during pyrolysis of biosolids: a. No removal: microconstituents reside with solids (e.g. metals) b. Volatilization: microconstituents leave solids and reside with pyrolysis liquid c. Transformation: microconstituents are chemically transformed Batch pyrolysis experiments revealed that pyrolysis removed triclocarban (Figure 1), triclosan, and nonylphenol from biosolids(10). Triclosan and nonylphenol volatilized away from the biochar and into the pyrolysis liquid; triclocarban was chemically transformed during pyrolysis. These results indicate that, while pyrolysis might likely remove PFAS from the solid biochar phase, PFAS might still likely reside with pyrolysis liquid requiring further downstream processing. The experiments and analysis to be completed by March, 2022 will confirm this hypothesis. Objective 3: Practical considerations for implementation of pyrolysis Pyrolysis has been extensively used for non-biosolids feedstocks but is not yet mainstream for biosolids applications, partly because of the overall operational complexity of these systems and cost considerations. Compared to biosolids land application, pyrolysis technologies represent a significantly higher capital investment for utilities since feed to pyrolysis must contain only 5 to 15% moisture, requiring thermal drying as a pre-requisite for pyrolysis. The capital and operational costs for drying could be very high depending on the moisture content of the influent biosolids(7). Including drying within the system boundary also makes the overall energy balance of a pyrolysis system less favorable. The energy available in pyrolysis gas and liquid products is approximately equal to the energy required for drying and pyrolysis of biosolids that are 20% solids. Based on anecdotal evidence from some of the demonstration facilities, phase-separation, i.e., separating the various pyrolysis products, downstream from the pyrolysis reactor can also be a challenge that could impact the quality of pyrolysis products for downstream applications. The bio-oil that is produced can be difficult to handle and potentially hazardous. To address the handling concerns with bio-oil, pyrolysis systems either need to run hot enough to not produce bio-oil or utilities need other plans for handling bio-oil post production. In short, while a potentially promising method for biosolids treatment, long-term operational viability of these systems for biosolids applications, sidestream characteristics, and emissions control requirements for these systems are yet to be proven. The potential benefits of pyrolysis include solids destruction resulting in less hauling costs, generation of pyrolysis-gas that could be co-combusted with digester gas or landfill gas, and generation of biochar which has potential as a value-added product and the potential to reduce PFAS. Biochar improves the soil characteristics by not breaking down readily, providing carbon sequestration and improving moisture-holding capacity of soils. Utilities considering pyrolysis have to weigh the potential benefits of the technology alongside costs and other operational considerations to determine the overall feasibility of the technology for full-scale implementation. Any government subsidies or credits to support PFAS removal, that might make pyrolysis more affordable to utilities, will also be reviewed and presented in this paper.

[Introduction The City of Kelowna Wastewater Treatment Facility (WWTF) is a biological nutrient removal (BNR) plant with capacity to treat approximately 70 MLD of raw wastewater. The facility produces both primary (fermented) solids and secondary (waste activated sludge) solids. The two (2) solid streams are thickened and blended to produce a mixed sludge, which feeds dewatering centrifuges. The undigested dewatered cake is hauled to the Regional Biosolids Composting Facility (RBCF) located near Vernon, BC for composting. The RBCF is jointly owned by the City of Kelowna and the City of Vernon and operated by the City of Kelowna. Undigested solids (including feedstock from Kelowna, Vernon, North Okanagan Regional District, Silver Hawk Utilities), and Lake Country Wastewater Treatment Plants (WWTP) are received at the RBCF and mixed with hog fuel or clean wood chips and composted to produce an organic soil amendment called OgoGrow that meets the BC Organic Matter Recycling Regulation (OMRR) Class A compost criteria. OgoGrow is used by the municipalities and marketed for sale to the public. The total annual processing capacity at the RBCF is capped at 27,000 wet tonnes per year and the City of Kelowna allocation is 18,000 wet tonnes. The current volume of undigested solids production at the WWTF exceeds the City's allocation at the RBCF and solids above 18,000 wet tonnes are sent to an alternative overage facility. As the City's population continues to increase an alternative biosolids management strategy is being considered. Diversion to off-site facilities would be part of a portfolio of biosolids management options. In addition, the City is actively pursuing infrastructure options that will reduce GHG emissions, and biosolids is one important avenue being considered. This paper discusses the feasibility of biosolids management options based on variations and enhancement of anaerobic digestion (AD), which might help address capacity concerns at the RBCF. Different options were analysed for biosolids volume reduction, energy generation and use, life-cycle cost, including sensitivity to select input parameters. A structured decision-making process, using a simplified triple bottom line (TBL) approach, is also included to provide a comparative evaluation of the options and inform the City on a number of important corporate considerations. Anaerobic digestion conceptual design The City defined the objectives of a new digestion facility in a previous study completed in 2020. A preferred AD alternative was identified and proposed to be located on a new site approximately two (2) kilometres away from the current WWTF. Fermented primary sludge (FPS) and thickened waste activate sludge (TWAS) would be pumped from the WWTF through a forcemain. The envisioned new AD Facility would be constructed in phases. In the first phase, the digesters would operate as mesophilic digesters and generate Class B biosolids. With approximately 50% removal of volatile solids through mesophilic digestion, capacity issues at RBCF could be alleviated. In the second phase, the digesters would operate as thermophilic digesters and flow-through vessels would be added for extended thermophilic anaerobic digestion (ETAD). Class A biosolids would be generated due to the thermophilic digestion process, allowing for an additional outlet for the beneficial use of biosolids. The digested biosolids would be dewatered, with cake being hauled to the RBCF for composting or directly to land application, depending on the project phase and operational needs. The initial phase costs were estimated at $78.1M at midpoint of year 2024 construction; the full buildout was estimated to cost $100.4M at midpoint of year 2024 construction. Advanced digestion options Concerns with the estimated high costs of the new Digestion Facility allowed for an additional review of options or variations of the preferred concept that could still generate either Class A or Class B biosolids, promote further reduction in volume (thus freeing up more space at the RBCF), and at the same time generate more biogas to help offset the operational costs of the new Facility. Five (5) options with different digestion configurations that could satisfy the City needs were developed with the 'delayed' ETAD option that was previously developed used as the 'control' option, as follows: -Option 1 - Mesophilic digestion that would generate a Class B biosolids product; -Option 2 - Thermal-hydrolysis process (THP) followed by mesophilic digestion (Full THP) that would generate a Class A biosolids product; -Option 3 - Thermophilic digestion that would also generate a Class A biosolids product; -Option 4 - Delayed ETAD that would initially generate a Class B biosolids product, and later a Class A product (control option); -Option 5 - Mesophilic digestion followed by THP that would generate a Class B biosolids product (but also eventually a Class A product after composting). The two (2) TH options (options 2 and 5) are based on CAMBI's TH technology and configurations. CAMBI has significant TH experience, with a high number of operating facilities in North America and around the world, hence their systems were selected as representative technologies for the purposes of this study. Table 1 provides detailed information on process parameters for each option. Technical comparison A high-level comparison of the five (5) different options will be presented at the full Conference paper, focusing on advantages and disadvantages of each. Financial comparison The five (5) options were compared financially in terms of capital, operation and maintenance (O&M) and life cycle costs. All options were evaluated with and without biogas upgrading to better understand its impact on O&M costs. It was assumed that all biogas produced would be sold to Fortis BC for the biogas upgrading option. Class D (-30% to +50%) cost estimates were prepared for the various options to provide a comparative basis for the evaluation and detailed charts will be included in the full Conference paper. Simplified triple bottom line approach A simplified Triple Bottom Line (TBL) 'plus' approach for structured decision making was used to make a comparative evaluation of the five options. The framework was based on the overarching perspective of 'sustainability' and uses a simplified multi-criteria analysis to integrate technical, environmental, social and economic factors such that a complete picture of the alternatives under evaluation can be provided. Weights were used for each criterium to reflect the City's values and provide a sensitivity analysis of the rankings. The following criteria and factors were selected based on discussions with City staff: -Technical: Biosolids volume reduction and dewaterability, complexity of operation -Environmental: GHG emissions, pathogen regrowth -Social: Odour emissions, Class A versus Class B biosolids -Economic: Life cycle costs GHG emissions and life cycle costs scoring were based on estimates assuming the City would consider two (2) different management strategies: -Generate Biosolids Growing Medium (BGM) from Class A biosolids and Class A Compost from Class B biosolids (emissions shown in Table 2); and -Generate Class A compost from either Class A or Class B biosolids (emissions not shown in this abstract but will be included in the full Conference paper). An initial scoring was conducted using the same weight for the technical, environmental social and economic criteria. Scoring was also conducted using different weights to look at the importance of both economic and non-economic factors and better reflect the City's concerns related to biosolids management. Table 3 shows the scoring and ranking with higher importance given to non-economic factors. Similar scoring tables will be presented in the full Conference paper for increased importance given to economic factors and also to social and environmental factors. Summary and conclusions Based on a simplified TBL 'plus' decision-making analysis, the rankings obtained, and sensitivity analysis conducted, both THP options were found to consistently be the highest scoring or ranking options for each of the management strategies evaluated. Addition of conventional AD as a subsequent step to reduce the volume of biosolids is an appropriate technology for the City to consider. There are a host of issues to consider when contemplating a thermal hydrolysis facility associated with AD. Some municipalities are considering this process as an entirely new facility that would include TH/digestion and related infrastructure. Others are examining options to modify their existing anaerobic digestion process to accommodate TH pre-treatment and to expand or alter the energy producing elements of a facility. Post-digestion THP ranked consistently in first when composting was considered for all Class A and Class B biosolids.

Introduction: The San Antonio Water System (SAWS) is investing over $1.2 billion dollars in its wastewater collection system, targeting over 5,200 miles of sewer main repairs, in response to city-wide sanitary sewer overflows (SSOs) and infiltration and inflow (I&I) issues. This work is under mandate from an Environmental Protection Agency (EPA) Consent Decree and is on target to be completed by 2025. One result of this Consent Decree has been an increase in package rehabilitation projects aimed at improving the worst performing sewer main segments in 'scattershot' groupings. SAWS has identified over 200 of these package rehabilitation projects to maintain the schedule of the Consent Decree. Plummer Associates Inc. (Plummer) was selected to perform the design of five small diameter package projects, together totaling over 43,000 LF of gravity sewer mains. These projects included the rehabilitation of more than 130 small diameter (8'-21') sewer main segments by various rehabilitation methods including cured-in-place pipe (CIPP), pipe bursting, open cut replacement, abandonment, and open cut rerouting. Purpose: This presentation will focus on successful project management and lessons learned for five multi-method package rehabilitation projects from preliminary design through construction. Package rehabilitation projects present a high level of risk to design and construction schedules due to the number of unique project sites, each possessing its own set of requirements for successful design and timely rehabilitation. Early design stages included data collection, condition assessment, planning for field investigations, determining agency coordination required for each site, identifying real estate conflicts, and classifying items with the highest risk to the project schedule. Methods used for organizing, classifying, and clearly presenting the overwhelming amount of data collected during these early stages was widely successful and will be discussed in detail. Subsequent design phases emphasized the prioritization of critical path activities. Critical path sequencing for these package rehabilitation projects can often be complicated due to the number of unique project sites and it may change several times during design as additional information is gathered. Successful management of these critical path activities, as well as lessons learned and unforeseen complications, will be discussed. Finally, bidding and construction administration of these projects highlighted other lessons learned and our experiences with material delays, rapidly changing material prices, real estate complications, third-party utility coordination, and contingency quantities will be discussed. Benefits of Presentation: Attendees will learn about key items to consider in the design of package rehabilitation projects, important points for successful construction administration of such projects, and how to implement big approaches to the management of small diameter sewer repairs. Owners, design engineers, and contractors will gain insights to successfully manage future package rehabilitation projects though design and construction. Status of Completion: The five package rehabilitation projects discussed in this presentation are in various stages of completion as stated below. - SAWS BPC Central Small Diameter Package 4A: Construction completed March 2022 - SAWS BPC Central Small Diameter Package 4B: Construction is substantially complete with final completion scheduled for January 2023 - SAWS BPC Central Small Diameter Package 4C: Project is currently under construction with final completion scheduled for January 2023 - SAWS Multiple Sewershed Package 17A: Construction is substantially complete with final completion scheduled for December 2022 - SAWS Multiple Sewershed Package 17B: Project is currently under construction with final completion scheduled for November 2023 Conclusion: This presentation will highlight the project approach, challenges, and lessons learned in the management of design and construction for five small diameter (8'-21') sanitary sewer package rehabilitation projects from preliminary design through construction.

High hydrogen sulfide (H2S) concentrations are commonly seen in biogas produced from anaerobic digestion process in municipal water resource recovery facilities (WRRFs). These H2S concentrations cause the corrosion of concrete and steel, increases biogas conditioning costs, compromises the functions of cogeneration units, and leads to sulfur dioxide emissions. In addition, elevated dissolved sulfide levels in the sludge can inhibit the overall digestion process. Traditional methods of removing the sulfide have relied on chemical dosing into the digesters or biogas scrubbing, both increasing the costs of biogas utilization, often maintenance intensive and can present relatively high environmental impacts. This may lead to other issues including unnecessary adverse odours and less efficient operation of power generating assets. Biotechnologies (i.e. aerobic or anoxic biotrickling filtration) have recently emerged as cost-effective and more environmentally friendly alternatives (Munoz et al. 2015). Nevertheless, these biotechnologies are still limited by their high investment costs and their generated byproducts such as sulfuric acid and/or elemental sulfur slurry that need further processing or disposal (Kraakman et al. 2019). This paper explores the full-scale implementation of a relatively new process called 'micro-aeration' (MA). MA is a process integrated technology that employs a very small amount of air introduced into the anaerobic digester to raise the redox potential to partly oxidize the sulfides to elemental sulfur and remove it from the digester together with the digested sludge. Traditionally, exposure of the anaerobic digestion process to oxygen has been avoided due to its perceived negative effects on growth and activity of obligate anaerobes, especially methanogens. However, in recent years numerous studies have reported the potential beneficial effects on anaerobic digestion in terms of digestion process stability and digested sludge dewaterability when a small volume of air or oxygen is injected into the sludge (Jenicek et al., 2014). The MA process has been shown to reduce H2S in the biogas and sulfides in the waste stream by more than 90% (Ngheim et al., 2014, Jenicek et al., 2017). For this reason, MA has the potential to revolutionise sulfide removal in anaerobic digestion. However, the basic mechanisms involved in micro-aerobic sulfide oxidation are not fully understood and control strategies for MA are still being optimised. Complex biological and chemical interactions occur between sulfur, oxygen, iron, and phosphorus throughout the anaerobic digestion processes, which are well characterized in literature (Batstone, 2006). Despite recent developments in whole plant process simulators (Hauduc et al., 2017), and modifications to the anaerobic digestion model (ADM) (Flores-Alsina et al., 2016), the implications of these interactions, including within the MA context, have not been fully explored. This paper presents an increased understanding of the MA process by specifically reviewing the performance of a full-scale MA application by Sydney Water and by proposing a process model capable of representing the performance observed at full-scale MA and considers biological and chemical interactions. A review of other full-scale MA applications is also presented. METHODOLOGY This investigation comprised the following steps: Literature review of the existing MA process configurations and performance. Including recently reported full-scale pilot testing (Kraakman et al, 2019). Critical review of over three years of process data for a Sydney Water installation including MA conditions, solids and biogas balances and analysis of the sulfur balance around the digestion treatment process. Development of a process model for an existing installation using the SUMO platform with integrated sulfur chemistry. This involved developing an anaerobic digester process unit with capabilities to set up aeration conditions and calculate oxygen transfer for uptake by digester biomass and use in oxidative processes such as sulfide oxidation by Sulfur Oxidizing Organisms (SOOs). Figure 1 shows the Sumo process schematic of the modelled installation. RESULTS Analysis of the process data on the MA trials showed that normal H2S concentrations in the biogas of approx. 1,000 ppmv can be reduced by up to 92%. However, there is a clear trend when studying air flow rates and H2S removals where a normal removal of around 50% was achieved at air flows of 177 NL/m3 reactor volume-day or higher, with a maximum observed oxygen consumption of 6.65%/m. Moreover, increasing the oxygen to sulfide ratio did not necessarily increase H2S removal. Results for biogas H2S removal and impacts on methane content due to the dilution mostly by the nitrogen in the MA air injected are summarized in Table 1. These sulfide removals translate in an increased biogas quality for energy recovery in WRRFs with potential to lower costs of biogas conditioning. In terms of digestion performance, no statistical differences were observed in total solids reduction, biogas production and cake solids achieved when the MA was performed compared. General process model calibration was performed following the International Water Association's Good Modeling Practices Unified Protocol and the SUMO Process Simulator (Dynamita, Lyon, France). Calibration of the sulfur chemistry in the raw sludge and the digesters without MA was first achieved by estimating the particulate fraction in the influent sulfur speciation, and by considering the collection system operation in terms of iron addition, discharge of biological sludge from a neighboring treatment plant, and internal sulfur recirculation from a chemical scrubber targeting H2S. To calibrate the process model, model parameters needed to be adjusted to match the observations from the MA trials. Most critical seems the affinity constants and its related rate of sulfide oxidation in the model compared to default microbial and chemical kinetic parameters when applied to full scale digestor systems. Two sulfide oxidation pathways are identified for oxidation of H2S, one mediated by SOOs and another chemically mediated in the presence of a metal. From literature in the subject, it is still unclear which pathway would dominate, and simulations using the developed model in this project showed that both mechanisms have the potential to yield the oxidation rates needed to match results obtained. Given the research conducted by Van der Zee et. al. (2007), Jensen et. al (2009), and Ruan et. al. (2017), the MA model currently considers the biological oxidation as the most significant mechanisms for sulfide reduction during air injection. A better understanding of the residual iron-ion levels in the digester feed sludge and actual mass of the different sulfur species will be useful to refine the model. CONCLUSION This investigation presented a process model for a better understanding of the sulfur chemistry during the digestion process, with biological oxidation likely to be the most significant mechanisms for sulfide removal during the MA process. MA is a promising technology for sulfide control in anaerobic digesters; this investigation showed that up to 92% H2S removal can be achieved, although the performance to date has been variable for various reasons. Lower H2S level in the biogas decreases biogas treatment cost for energy recovery thus contributing to the economical and sustainable performance of the energy recovery process of waste sludge digestion at wastewater treatment facilities.