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Absorption of ultraviolet (UV)-visible (Vis) light by the liquid phase of wastewater sludge during biological digestion was studied. Sludge samples were obtained from batch anaerobic and aerobic digestion experiments conducted at mesophilic and thermophilic temperatures, as well as influent and effluent of a full-scale anaerobic digester. In tandem with acquiring the UV-Vis spectra, the concentration of soluble parameters was measured. Integrated areas under the spectra in the UV and Vis regions were calculated as AUV and AVis, respectively. For the batch experiments, the computed areas increased with digestion time. In addition, a power-law function was able to describe the correlation between soluble chemical oxygen demand (SCOD) concentration and AUV for anaerobic digestion at 35 °C and 45 °C, and aerobic digestion at 55 °C. Coefficients of determination (R2) for the mentioned cases were between 0.812 and 0.933. Furthermore, power-law functions also described a correlation between SCOD and soluble ortho-phosphate concentrations during batch anaerobic digestion at 35 °C (R2= 0.921) and 45 °C (R2= 0.812). Moreover, analysis of the data obtained from the aerobic digestion experiment suggests that the mass of UV-absorbing matter linearly decreased over time during aerobic digestion at 45 °C (R2= 0.925) and 55 °C (R2= 0.996). The outcomes of the current study indicate that the integrated area under the UV spectrum of sludge filtrates reflects the progression of biological digestion of wastewater sludge under thermophilic and mesophilic conditions, which can be used for process monitoring and optimization.

INTRODUCTION Sustainability is increasingly more important for the operation of wastewater treatment plants. To meet sustainability goals and better energy recovery, the current business as usual approach to anerobic digester operation is not ideal. Improving digester operation is crucial for effective energy recovery. Having a reactive approach to digester foaming prevents optimal digester performance and causes other problems like digester failure, poor biogas recovery, uncontrolled release of contaminated waste to the environment and odour. Figure 1 shows some of these impacts. The best way to mitigate digester foaming is through robust design, but if this is not possible there are several operating conditions that can be improved to control foaming. Sydney Water Corporation (SWC) recognised the importance of preventing anaerobic digester foaming. Digester foaming at SWC plants has been caused by multiple different issues and foam management can therefore be largely reactive. There are operational methods and digester design features in place at some plants that aim to reduce the occurrence of the impacts of foam events, however this is not widespread or consistent. Investigation into 5 plants was undertaken to determine the likely causes of digester foaming and gas entrainment and the most effective ways to manage this and where possible through design changes as upgrades occur. For plants where design changes are not possible in the near future, key operating conditions were reviewed, early warning signs for digester foaming events determined and management practices recommended to mitigate digester foaming. METHODOLOGY Digester foaming was investigated at 5 SWC Water Resource Recovery Plants (WRRP), including Cronulla, Malabar, Warriewood, West Hornsby and Hornsby Heights. Digester operation data was analysed to determine the likely causes of digester foaming issues and recommendations on proactive and reactive measures for foam management including how to prevent or mitigate foaming at these plants and across broader SWC plants were established and operator training provided. Digester operation parameters and recommended monitoring were also outlined. Best practice digester design to minimise foaming and maximise energy production was investigated, drawing on international experience. These design components were presented to SWC designers, along with recommended implementation methodologies. RESULTS The main issues causing digester foaming at the SWC plants investigated were seasonal foaming related to activated sludge processes, lack of effective redundancy or contingency measures associated with the digester process, and illegal industrial discharges to the incoming sewer. There are other fundamental operating issues that cause digester foaming, such as running with one digester offline for extended periods (for example, at 2 plants digesters were offline due to issues with digester lids, which resulted in excessive volatile solids load in remaining digester/s particularly when food waste was accepted), turning off mixing, high volatile solids loading rates in digesters, poor temperature control, unstable feed to the digesters, and large step changes in temperature and feed. Figure 2 shows the volatile solids (VS) loading rate and specific volatile solids loading rate (SVSLR) in the primary digester at one of the plants where primary and secondary digesters are currently operated in series. At this plant, there is inadequate solids retention time (SRT) in the digesters, as well as a high VS loading to the primary digester. The average VS load to the primary digester was 3.74 kgVS/m3.d and a peak loading rate of 4.5 kgVS/m3.d, where the recommended range is 1.6-3.2 kgVS/m3.d . Therefore, the anaerobic digesters are operated beyond the typical recommended VS loading rates. The high VS loading rate is also exacerbated by the unloading/loading sequence of flow, which results in intermittent VS loading, rather than constant loading across the day. The high VS load impacts the stability of the sludge and increases risk of foaming in the digesters. The SVSLR is a variation of VS loading rate that considers the VS in the digester as a function of active biomass. However, SVSLT may not account for the feedstock other than the wastewater sludge such as high strength organic matter. The maximum recommended SVSLR for mesophilic digestion without any pre-treatment is 0.16 kg VS/kg VS in digester day. As shown in Figure 1, along with the VS loading rate, the SVSLR for the primary digester is consistently above the recommended limit, making it vulnerable to the digester foaming and failure with fluctuation in digester loading rate. Best practice digester design to avoid foaming issues and maximise energy recovery include the use of standpipes for surface overflow (see Figure 2) and emergency withdrawal via p-traps (see Figure 3), minimisation of the top water surface area, installation of fixed covers and external gas storage, the use of pumped mixing to reduce short-circuiting and having adequate redundancy to ensure that there is no single point of failure. Digesters should have a conical shape to facilitate grit removal and more efficient mixing. Wasting foam from the surface in secondary activated sludge processes will also minimise the amount of trapped foam, improving conditions in the downstream digesters. Rolling out design changes in a systematic way as digesters are taken offline for planned maintenance is an effective way to facilitate continuous removal of foaming issues from upgraded digesters. In addition to benefits of maximising energy generation, achieving maximum hydraulic capacity within existing digesters by having external gas holders and running digesters full may allow capital upgrades of digesters to be delayed for a number of years if not decades, further improving sustainability of WRRPs. Where design changes cannot be implemented, there are operational improvements that can be made to manage digester foaming and increase energy production. Generally, if there are filamentous bacteria in the activated sludge bioreactor at a plant, there is a high likelihood of foaming in the digester. These foaming incidents are manageable through adjusting the operating parameters in the activated sludge plant. Digesters should be brought online slowly with small step increases in feed and temperature over time. A common misconception is that digester mixing should be turned off to control a foam event, however mixing should be turned down. Digesters should be operated with a top water level high into the lid, with sprays used to suppress foam and move foam to wasting points. Digested sludge should be withdrawn from the top and bottom of the digester, and consideration given to alkalinity correction when the pH in the digester starts to drop. Running the digesters without any safety factor and running some process equipment at loading rates higher than designed for will increase the risk of process upsets that could also contribute to foaming. Allowing a safety factor in terms of solids retention time and volatile solids loading provides plants with the ability to cope with under upset conditions and avoids the need to detune the digesters and the plant to minimise the risk of foaming. CONCLUSION By successfully managing digester foaming and operating digesters in a manner than maximises power generation, WRRPs can achieve more effective energy recovery and meeting energy sustainability and neutrality goals. Some fundamental issues that generally arose to cause digester foaming were: -Running with one digester offline for long periods resulting in much higher loadings and shorter SRT than originally designed -High VS loading rates in the digesters -Reduced effective SRT due to mixing being turned off and accumulation of grit and screening -Mixing generally not designed for current solids loading due to intensification -Poor temperature control for the digesters -Unstable feed to the digesters -Large step changes in temperature or feed due to heater failure or storm conditions Foaming subsequently resulted in lower biogas production, high costs for digester reinstatement, and poor run times on biogas engines due to poor biogas quality. Robust digester design which minimises digester foaming and gas entrainment is the most preferable management mechanism, and changes to digester components can be implemented over time as maintenance is undertaken. Where design changes are not possible, operational improvements can be made to greatly reduce digester foaming. This paper outlines some best practice measures that can save millions of dollars by avoiding catastrophic foaming events and will help maximise biogas production and energy generation.

Rising chemical and sludge disposal costs, an uncertain future for biosolids disposal, and operator shortages; are some issues shared by many wastewater utilities today. The Kalamazoo Water Reclamation Plant (KWRP) dewatering upgrade case study presents a road map for other utilities on how to address the pressing issues many utilities face today by incorporating pilot testing, and utilizing operations and maintenance staff input in the equipment selection and design process, selecting the equipment to produce the driest cake, configuring equipment in a way to minimize odor and maximize the potential for future expansions, and by visualizing data to fast track the operator training process. This presentation presents a history of the plant, its past and present concerns related to biosolids, and an overview of its dewatering facility commissioned in 2022. KWRP, located in western Michigan, serves approximately 190,000 people. KWRP previously used sludge incineration, but the incinerator was abandoned in 1999 due to the implementation Title V EPA, a stringent air quality regulation for flue gas from incinerators. Until the most recent upgrade discussed here, the gravity-thickened primary sludge and waste-activated sludge from the biological nutrient removal (BNR) process were combined and dewatered together using four belt filter presses. Because a sizable pharmaceutical production plant is in the service area, activated carbon is added to the BNR process to absorb micropollutants. In 2001, because of the closure of the incinerator, KWRP started to produce Class A biosolids using the RDP lime addition and pasteurization process. This class A sludge production process did not last long. The plant experienced too many difficulties with operating and controlling the installed RDP process for the required sludge production throughput. Michigan's rising costs for land application fees were another factor for discontinuing that process. In 2008, the utility moved to 100% landfilling sludge, taking advantage of relatively low disposal cost: $17.5/wet ton. From 2008 to the present, the plant has faced a steady rise in disposal costs, on average 13.0% /year; cake dryness requirements (%TS) have also tightened. Maximizing the dryness of the dewatered cake and reduction of disposal volume became a priority for the Dewatering Facility Upgrade. Additional objectives for the upgrade included minimizing the odor source and improving the operational environment in the sludge dewatering facility, designing a flexible set up to adapt future changes in post-dewatering solids-handling, and to ensure the selected equipment is intuitive for operators to dial-in and maintain. KWRP believes pilot testing provides the most accurate data for decision-making and solidifying the facility design. The city opened an invitation for paid pilot testing to all interested manufacturers in 2014. Eleven manufacturers and six technology alternatives participated. After testing was completed, centrifuges were selected as the equipment of choice, for being the lowest annualized cost option in present-worth with the possibility for simple future expansion. (Figure 1). Figure 1: Annualized Total Cost for Kalamazoo Sludge Dewatering Options After receiving proposals from vendors, the city organized operators' visits to other water reclamation facilities and equipment manufacturing and equipment service facilities to gather KWRP staff input during the selection process. Among the equipment evaluated, Centrisys was selected for several reasons: The central location for repairs was fundamental for the centrifuge manufacturer choice, along with access to their top technical and optimization leaders in the company. Simple operation and maintenance of the hydraulic scroll drive, in comparison to a gearbox drive, was also a critical factor for the equipment selection. The hydraulic scroll drive was also preferred for its ability to generates higher torque than gear box to maximize the cake dryness. Three Centrisys CS26-4 units were installed in 2021 and successfully started up in 2022 (Figure 2). The project design includes the necessary infrastructure to support the current installation along with the possibility of an additional fourth Centrisys CS26-4 if needed. The upgrade resulted in the immediate improvement in sludge dewaterability: before the upgrade a 2-meter Andritz belt filter press was generating 16-17% cake; after the upgrade, the centrifuges now generate cake in the range of 21-24%, which translates to a disposal sludge volume reduction of 20-30%. The timing was just right: When pilot testing began, disposal costs were $30.90 per ton. In 2022, it was raised by 44% over the previous year to $92.71/wet ton, making it one of the highest in the region. Figure 2: Centrisys CS26-4 Installation at Kalamazoo Water Reclamation Plant Working through the volatility of disposal costs and uncertainties in the regulatory climate, KWRP has selected ancillary equipment to accommodate future changes better. Instead of open-top conveyors, cake piston cake pumps are now used to move the dewatered biosolids. The piston pumps can generate operating pressures up to 1,500 psi. In the case of either future regulations of emerging contaminants like PFAS, or increasing disposal costs, where further processing of the dewatered cake by means of sludge drying are required, facility additions can be accommodated by a simple reconfiguring of the pipes. The selection of the cake pumps over open conveyors minimizes the source of odor. The small amount of odorous gas generated from the decanter centrifuges and the cake pumps is now treated through activated carbon filters to improve the operator environment. Another design consideration for ease of operation is the addition of Valmet total solid meters to the centrifuge feed lines (Figure 3). The centrifuges have forward control of the polymer dosing systems: taking the measurements from the TS meter and the flow meter and pacing the polymer rate by specifying the polymer dose in lb/dry ton, rather than just a pump speed, in the control panel. This setup makes training new operators easier by giving real-time trends for the operators to learn about the plant and specifically dewatering operations. Additionally, having the polymer dose input (lb./ton) at the centrifuge which resembles what the operators learned for the operator training exam aids staff in being able to visualize the data. This in turns helps KWRP to shorten the initial training period for dewatering operations and more quickly move operators to the next level of training: tuning the centrifuges and to take on tasks such as selecting better polymers to get more out of their new equipment. Figure 3: Installed Valmet Meter KWRP addressed these challenges via a data-driven, and operator-centric approach for their biosolids dewatering facility upgrade. The primary pieces of the KWRP story are: the support from the community in funding the pilot testing piece of the dewatering equipment evaluation, the operator site visits to learn about the equipment, and the inclusion of innovative technologies such as real time solids measurement and visualization. In close collaboration with the equipment suppliers, KWRP found the winning ticket for navigating uncertain regulatory market conditions and preparing the plant for the future.

An Odor Attribution Study was undertaken for an Air Quality Management Agency that included gathering extensive data from specific sources and ambient locations to better understand odor impacts within the local communities. The study was 'one-of-a-kind' in that it combined multiple innovative techniques for identifying fingerprint odorants attributed to specific odor generating facilities. Odor has historically been an issue in this area for decades. Over the years, various odor mitigation approaches have been undertaken with varying degrees of success. While the number of odor complaints from residents has decreased in recent years from a peak of 3,500 in 2015, the high number of complaints (1,500) reported in 2018 indicates a persistent and ongoing odor issue. The odors in the area originate primarily from three closely located facilities including: -Facility A: An Anaerobic Organic Material Digestion Facility -Facility B: A Solid Waste Resource Recovery Park (a recycling facility, a composting facility, and a landfill) -Facility C: A Water Resource Recovery Facility (WRRF) Other natural sources were also considered (e.g.; bay, estuary). The goals of the project were to determine the contribution and variability of odor causing compounds from these facilities and develop a strategy for measuring how often and at what concentration these potential odor causing compounds may be passing into the local community. The study approach went beyond using the traditional, common practice of using odor threshold or odor intensity as the measure of odor nuisance. Instead, Weber-Fechner (persistency) curves were used as part of the Odor Profile Method (OPM) developed by Dr. Mel Suffet of the University of California-Los Angeles. The usefulness of the OPM lies in the fact that the human nose is, for the most important odorants, many degrees more sensitive than the standard chemical compound identification analytical methodologies. Examples of the OPM results are shown in Figure 1 and illustrate the odor intensity reduction with dilution (persistency curves) as well as the character of the dominate type of odors at each dilution (e.g.; musty, rancid, sweet). This illustrates how odor intensity and odor character changes as it travels from the different odor sources into the community, demonstrating the 'peeling the onion' phenomenon. The OPM approach was combined with comprehensive chemical compound identification analyses, lab olfactometric analyses, field olfactometry sampling, as well as a proton-transfer reaction time-of-flight mass spectrometer (PTR-TOF-MS) to provide targeted measurements of specific VOCs to identify chemical fingerprints associated with the different sources. Comprehensive chemical compound analyses resulted in the following key findings in terms of fingerprint odorant types attributed to each facility: -Facility A - Anaerobic Organic Material Digestion Facility: Sweet, Rancid, Musty -Facility B - Solid Waste Resource Recovery Park: Rancid, Sweet, Sulfur -Facility C - WRRF: Sulfur, Decaying Vegetables The field surveys using field olfactometers were undertaken on a regular basis over a period of 18 months. Figure 2 shows a BLOB map of the likely odor impacts in the community and the contributions to the odor intensity from each facility based on the odor character descriptions during the in-field odor olfactometric assessments. The PTR-TOF-MS provided real-time (1/sec) 'chemical fingerprints' of over 550 tracked compounds and showed that the plumes from each facility were unique for the key odor sources at the facilities and that the contribution of each facility could be quantified. Plumes and/or odors in the communities were also collected. The plume data (concentration and ratio between individual species) were then fed into Sartorius Multivariate Analysis (MVA) software to determine correlations between facility plumes and community plumes. The data correlations were determined using Principle Component Analysis (PCA) which identified where plumes within the communities originated, including the facility releasing them. It also confirmed the results that were obtained using the in-field olfactometric analyses, the OPM analyses, and the lab chemical analyses as well as the lab olfactometric analyses that the odor signature is unique for each facility. The findings provided a solid basis for developing a method to employ ongoing monitoring along each facility's fence line, or at other locations in the community. The preferred monitoring system would include multiple sensors, weather station, data processing and visualization platform, and auto bag sampler (at community locations). The autosampler would fill a bag sample for remote analysis by proton-transfer reaction (PTR). This successful study provided an improved understanding of the relative contribution of odor causing compounds from the three adjacent facilities by assigning specific fingerprint odorants to each and provided insight as to how the unique odorants impact the local community. These findings are considered essential to better: 1.Inform future actions to reduce odors (best practices, enforcement, rules) 2.Establish methods to measure progress on facilities' future odor reduction actions 3.Educate the community in terms of what's causing the odors, how complex they are, and teach them how to characterize odorants to better inform ongoing improvement efforts.

Odor detection threshold determination following international standards, ASTM E679 and EN13725, is the primary odor parameter of choice used in odor assessments worldwide. While this is a tool that, when coupled with air dispersion modeling, provides an understanding of the first layer of odor impact in the community and is commonly used for odor regulation around the world, the assessment of odor threshold is only one parameter of odor. Odor intensity and characterization (odor profiling) provide more important information related to true receptor impact from the perspective of when these odors will be a nuisance. Odor profiling, through descriptive analysis, is a sensory science term used to describe methodologies utilizing a panel of trained assessors to identify and describe specific sensory attributes about a test sample (qualitative) and scaling the intensity of these attributes (quantitative). The food, beverage, and consumer product industries have formally use descriptive analysis to obtain critical information about the appearance, aroma, flavor, and texture of products for over 70 years. These methods can be used to document odor profiles of samples collected from facility odor sources. As described by other researchers, further considering odor descriptors with dilution methods will help to understand how the odor profile may change from the point of emission from the stack to point of impact at the stakeholder as it dilutes in the air. The odor profiles of odorous sources are the perceived response of a complex mixture of chemicals in the air. While hydrogen sulfide is targeted (as the Celebrity) in work at water resource recovery facilities, there are many other compounds present from multiple chemical families, e.g., organic sulfur compounds, organic acids, amines, VOCs. Many of these compounds (the entourage of the Celebrity) have extremely low odor thresholds below the low ppb levels of hydrogen sulfide. State-of-the-art molecular odor analysis by SIFT-MS provides quantification at these sub-ppb concentration levels utilizing the same samples submitted for odor perception evaluation. This combined analysis including odor threshold, odor intensity, odor descriptors, and molecular analysis on the same sample provide access to direct relationships not available before for a broad range of wastewater issues and studies. This paper will present examples comparing the full odor profiles from multiple emissions sources. Inlet and outlet sample comparisons show one case where odor descriptor profiles are similar even with reduction in odor threshold and molecular concentration values and in another case, odor descriptors shift significantly with lower reduction in odor threshold values. A review of odor characters and molecular concentrations of other samples show how data relationships provide a deeper understanding of the odor sources and thus provide direction for improving in odor impacts in the community.

PFAS in biosolids have undoubtedly become a major topic and concern for the public and the industry. Some state regulations are outpacing federal regulations, forcing utilities to consider alternative biosolids management strategies. Therefore, interest in thermal technologies has grown substantially. New incinerators are difficult to install, rendering torrefaction, pyrolysis, and gasification as possible treatment process options. However, information is scarce on the mass balance of PFAS, and specifically fluoride, through these processes and their end products. This project will i) develop methods to quantify PFAS, total organic fluorine, and inorganic fluorine in end products, ii) generate lab-scale data on the fate of PFAS and fluorine through torrefaction, pyrolysis, and gasification, and iii) generate an LCA tool that is user friendly to incorporate critical aspects (e.g. energy, carbon footprint, as well as PFAS fate) for assessing thermal technologies.

This presentation provides an update on the progress of two PFAS fate studies through high-temperature biosolids processing systems. PFAS testing at two full-scale sewage sludge incinerators was recently completed under Water Research Foundation Project #5111 and results are expected for publication at the end of 2023. Preliminary PFAS sampling was conducted at the Silicon Valley Clean Water biosolids pyrolysis system and a lab-scale unit commissioned to mimic its operating parameters under a Water Environment Federation collaborative research project. Formal PFAS sampling is expected to occur this summer for the lab-scale unit and early 2024 for the full-scale pyrolysis system. This presentation presents several insights into test plan development and the status of analytical tools available to characterize the fate of PFAS through these systems. Key considerations include identification of relevant operating parameters and emission control devices for process technologies, limitations in reporting limits for gross organoflourine assessments, and recommended best practices for reporting PFAS detection and destruction and removal efficiency data.

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.

APPLICABILITY Solids thickening is an indispensable unit process for process intensification of biosolids treatment. The fluctuations of feed sludge characteristics often impact the stability of the thickening process, reduce process capability, and increase operation and maintenance costs. Often, the optimization of sludge thickening is focused on meeting performance requirements as detailed in specifications. This study expands the assessment of sludge thickening by including both thickening equipment and its up- and downstream infrastructure from a process capability perspective. The presentation will benefit engineers and utility operators in better design and troubleshooting of sludge thickening processes with designed thickened sludge solids total equal to or higher than 6%. INTRODUCTION The practice of wastewater treatment is evolving to transform wastewater treatment plants into WRRFs with the adoption of advanced wastewater treatment and solids handling equipment, processes, and systems. Enhanced sludge thickening plays an important role in achieving footprint reduction, chemical and energy efficiency, and process control of solids handling [1]. Several studies have suggested that enhancing sludge thickening plays an important role in achieving energy self-sufficiency [2]. Studies showed that improvements in primary sludge (PS) and waste activated sludge (WAS) thickening significantly increased biogas production [3]. Thickened sludge with higher than 4% total solids could be sufficient for achieving a positive energy balance in two-step AD processes. Sludge thickening is taking an increasingly important role in process intensification in biosolids treatment, either through pass-through thickening prior to sludge digestion or recuperative thickening integrated with digestion processes. Centrifugal thickening is one approach to achieving high-rate sludge thickening. The control of the thickened sludge total solids (TS) usually involves the control of Relative Centrifugal Force (G-force), solids retention time, differential rotation speed between centrifuge bowel and screw, and polymer dosage. The application of an in-line density meter or pressure-indicating transmitter could provide control signals for optimizing the performance of centrifugal thickening through mechanical adjustment of the size of thickened sludge outlet [4] or adjustment of the specific gravity of thickened sludge through air injection [5]. Feed sludge characteristics have a significant impact on the performance of thickening centrifuges. The variables of the sludge characteristics include hydraulic loadings, solids loadings, and the mixing ratio between PS and WAS. The fluctuation of feed sludge characteristics could negatively affect the performance of thickening centrifuges and interrupt subsequent operations of biosolids processes. At the same time, fluctuations in feed sludge characteristics are expected and should be accommodated in the design of sludge thickening. The objective of this study is to investigate two cases of centrifugal thickening installations, respectively equipped with GEA and Centrisys thickening centrifuges. This study will provide practical recommendations for mitigating potential bottlenecks in achieving 6% TS of thickened sludge. This study will introduce the use of process capability assessment as a tool for O&M. METHODS Collection and organizing of site information. One challenge for thickening improvement is to systemically document and organize the site information associated with sludge thickening. This study investigates the design and operation of thickening centrifuges and the immediate upstream and downstream unit processes of the thickening centrifuges at two water resource recovery facilities (WRRFs). The design conditions of the two thickening centrifuges systems are summarized in Table 1. The process capability of sludge thickening is affected by both performance of the thickening centrifuges and the performance of up and downstream infrastructure, including wet wells, sludge transfer pumps, the design of process piping, and flow measurement devices. In this study, we developed a check list for a detailed documentation of the thickening unit process as well the immediate upstream and downstream processes, as shown in Table 2. Process capability assessment. Process capability assessment is a manufacturing tool to gain process performance knowledge by analyzing a measurable property of a process to the specification [6]. In this study, an easy-to-use process capability assessment tool is developed for operators to document the thickening performance as a record for understanding process performance and preventative & predictive maintenance of the thickening equipment on a monthly basis. RESULTS A scoring matrix is developed based on the assessment checklist (Table 2) for the evaluation of the positive and negative factors impacting efficient thickening for the two WRRFs. The scoring matrix is used as a survey and communication method to collect opinions from operating crew, maintenance crew, and engineers. Figure 1 shows an example of the scoring matrix. The scoring matrix will be further developed to document the progressive process improvement of sludge thickening. As it is not practical to adjust feed sludge TS in a controlled approach at WRRFs, the impact of solids loading on the performance of sludge thickening is evaluated through time series analysis and histogram analysis of feed and thickened sludges. Figure 2 shows the time series analysis of the feed sludge and thickened sludge TS. As illustrated in Figure 3, histogram analysis of the same set of data reveals the process operation in respective to specified performance (Table 1). Hydraulic loading of thickening centrifuges could be readily adjusted by throttling feed pump. The impact of hydraulic loading is evaluated in terms of solids recovery ratio under different thickened solids TS. As shown in Figure 4, a trade-off exists between hydraulic loading and the solids recovery under the same thickened sludge TS. The results of Figure 4 is based the WRRF 2. A similar curve will be developed for WRRF 1 for this study. Figure 5 shows the change of apparent viscosity as sludge is thickened to TS of 2.5%, 4.5%, 6.0%, and 8.5% respectively. The significant increase in thickened sludge viscosity leads to a higher transfer pump discharge pressure. Depending on different process piping design, the thickened sludge transfer pump's discharge pressure varies 90-110 PSI for WRRF 1 and 70-100 PSI for WRRF 2. It is necessary to size the thickened sludge transfer pump appropriately to minimize process interruption due to insufficient pumping capacity. Figure 6 provides an example of the developed process capability assessment method for monthly evaluation of the performance of thickening centrifuges. The assessment serves as a standard approach to understand the process stability and capacity in related to specified performance requirements. CONCLUSIONS This study documented the impact of sludge characteristics on the performance of thickening and subsequence sludge transfer. The significant increase of sludge viscosity when thickened from 4% to 6% TS requires a design of higher discharge pressure of thickened sludge transfer well. The findings of this study suggested that special attention is needed in the design of the process piping, pumping, and process controls to realize the capability of thickening equipment. The process capability assessment tool applied in this study provides plant operators with means to document and understand the performance of thickening centrifuges. The method developed in this study could be applied to the process capability assessment of other types of thickening technologies beyond thickening centrifuges in WRRFs. This method can serve as a communication tool between the operation and maintenance crews/departments, as the results addressed both process performance and equipment conditions. With the adoption of more advanced and sophisticated solids handling equipment, developing comprehensive process capability assessment tools for respective unit processes may lead to improved performance and reduced life cycle costs of solids handling at WRRFs. This study adopts process capability assessment in evaluating the performance of sludge thickening based on two types of centrifugal thickening machines with different control mechanisms. Attendance at this presentation will benefit design engineers interested in designing centrifugal thickening as part of the process intensification of solids handling in WRRF. The presentation will provide practical suggestions for understanding the process capability of installed thickening equipment for performance improvement.

[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.

Municipal wastewater treatment plants (WWTPs) generate and emit greenhouse gases (GHG) throughout the plant via a number of activities and operations such as pumping, aeration, mixing, and sludge dewatering and digestion. As part of the collective efforts to achieve a 2050 'net-zero' emission goal, public utilities such as New York City, City of San Francisco (CA), City of Edmonton (Alberta), City of Calgary (Alberta) and Salt Lake City (UT) have started including quantitative sustainability indices as important factors to be evaluated when major capital improvements and O&M modifications are being planned for their water infrastructures. GHG emissions is one important sustainability index. In Canada, GHG emissions from major WWTPs are required to be reported to Environment and Climate Change Canada. A typical WWTP produces three major types of GHG: carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O), both directly and indirectly. Direct GHG emissions occur at the site due to fuel consumption and the physical, chemical, and biological treatment processes. Those emissions are fugitive, heterogenous, and time-varying. Currently, three approaches are available for estimating GHG emissions from WWTPs. The first approach uses 'emission factors', such as the IPCC database, to estimate the rate at which a pollutant is released into the atmosphere (or captured) as a result of specific process activities. The second approach involves 'engineering principles and judgement' to estimate emissions based on engineering principles and judgment, using knowledge of the chemical and physical processes involved. Neither the first nor the second approach involves direct measurements. Rather, empirical coefficients are assumed which, often times, are not representative of the actual emissions at specific treatment facilities. The third approach may utilize emission monitoring systems such as the flux chamber method or the tracer method, which unfortunately are all based on point sampling, unable to capture the spatial and temporal heterogeneity of the GHG emissions at WWTPs. Due to the lack of monitoring method, so far, water utilities still rely on using the first two approaches for estimating their GHG emissions. Therefore, a robust field measurement approach is needed that is capable of capturing the dynamic, fugitive emissions at WWTPs. To achieve this, we have developed a hybrid method integrating the long range open-path Optical Remote Sensing (ORS) technology and inverse Dispersion Modeling (iDM) to continuously quantify GHG emissions from the wastewater treatment facilities on a real-time basis. The ORS instrument used in the field campaign consisted of an open-path tunable diode laser spectroscopy (OP-TDL) for CH4, a CO2 sensor, a portable meteorological station and 3-D sonic anemometer to record temperature, air pressure, relative humidity, and wind vector, and an open-path fourier transform infrared (OP-FTIR) for N2O. Both the OP-TDL and OP-FTIR scanned along multipaths to capture the 'big picture' of GHG plumes for dispersion model input for emission estimation. Backward Lagrange Stochastic model (bLS) was used to estimate the methane emission rate in real time. The system was first applied in the Bonnybrook WWTP, with an average daily flow of 324 million litre per day, located in Calgary Canada. Field measurements were conducted in autumn 2021, and spring of 2022. Signals were continuously captured and inverted to calculate the path-integrated concentrations of GHGs, with which the iDM model calculates the emission rates. The measured emission rate for methane ranged from 64-97 kg/hr, with the corresponding emission factor of 0.04-0.06 kgCH4/kgBOD5. For carbon dioxide, the measured emission was averaged at 0.29 ton/yr. Seasonal variations have been noticed. The team is currently working on calibrating a BioWin process model for simulating/predicting GHG emissions using the field measured emission data. Additional field measurements are also planned at a WWTP located in southeast US. This presentation will describe the newly developed ORS-iDS methodology and present the detailed results of continuous measurement from the field campaigns conducted during different seasons. The site-specific emission factors (EFs) developed based on the measurements have been compared with the literature and the IPCC values, which will also be presented to show the inaccuracy of using empirical, non-site specific emission factors. The diurnal and daily variation of emissions will also be characterized and presented.

Introduction Greenhouse gases (GHGs) such as methane and carbon dioxide are common byproducts of chemical reactions within collection systems but are less commonly considered by municipalities during sustainability analyses. Understanding the scope of the impact of these GHGs requires an understanding of their relative effects on global warming. The Intergovernmental Panel on Climate Change (IPCC) created the Global Warming Potential (GWP) metric to compare different GHGs via an equivalency to carbon dioxide (CO2e), the reference gas. Methane has a GWP of 28, meaning that it has 28 times the impact on global warming as compared to carbon dioxide. After outlining and studying the theoretical reactions of sulfide generation in wastewater collection systems and calcium nitrate dosing for sulfide prevention, we hypothesize that dosing calcium nitrate for odor and corrosion control significantly reduces the overall impact of GHGs emitted by wastewater within collection systems. Objective In the proposed paper, we will set the groundwork to understand the theoretical mitigation of methane generation resulting from calcium nitrate dosing in US wastewater collection systems, as well as test the theoretical mitigation with a use case in Manatee County, FL. Theoretical Methodology In an untreated collection system, an anaerobic BOD reduction occurs in the wastewater as follows (all reactions assume methanol as carbon source for simplicity and consistency in comparison): SO4= + 4CH3OH → S= + 4H2O + 2CH4 + 2CO2 In a collection system being dosed with calcium nitrate for sulfide prevention, the intent is to drive an anoxic BOD reduction in the wastewater instead of anaerobic, which occurs as follows: 6NO3- + 5CH3OH → 5CO2 + 3N2 + 7H2O + 6OH- While more CO2 is generated in this reaction versus the anaerobic reaction, no methane is produced. Based on the comparison of these reactions and the GWP of methane, for every 1 lb of sulfide prevented, 25.25 lbs of net CO2e is prevented. Assuming that all GHGs are fully released from the wastewater into the atmosphere, we calculate that a maximum of 11.83 lbs CO2e can be prevented per gallon of 3.5 lb NO3-O/gal solution dosed into collection systems as part of an odor prevention program. In fiscal year 2021, theoretically a maximum of 71,887 metric tons of CO2e could be prevented as a result of all the chemical shipped to customers in the US by Evoqua for use in odor prevention. While it is recognized that a municipality choosing an odor prevention program will be incurring additional GHG emissions via transportation, manufacturing, provision of service, etc, the analysis of the use case study will focus explicitly on changes in GHG emissions specifically related to the theoretical reactions described above in relation to calcium nitrate dosing into the collection system. Application Manatee County Utilities (MCU) operates an expansive collection system involving over 800 lift stations (LS) with many long retention time force mains. The collection system conveys over 22 million gallons per day (MGD) of flow across three service areas to a corresponding wastewater reclamation facility for each service area. To significantly reduce corrosive conditions, MCU set a target atmospheric hydrogen sulfide (H2S) control objective of 20 ppm average and 50 ppm peak. MCU utilizes multiple solutions within their program, including calcium nitrate and pH shift technologies, to achieve these goals. For additional knowledge and to establish a baseline, we decided to also test the methane mitigation from dosing other chemicals by testing sites treated with magnesium hydroxide and calcium hydroxide. Four portions of the collection system were selected for sample testing. Two portions, N4B force main to N1B LS and Greenbrook 2 force main to Lakewood Ranch Riverwalk LS, are treated with calcium nitrate. Another section, Pope Road Master LS, receives flow treated with magnesium hydroxide. The final section, Tara 20 LS, receives flow treated with calcium hydroxide. A portable H2S gas monitor was deployed at each injection point and each control point to log continuous sulfide measurements. Grab samples were taken for dissolved sulfides, pH, temperature using gas detector tubes and a calibrated Hach portable pH probe. Gas samples were collected from the headspace of the wet wells using tedlar bags and CO2/CH4 concentrations analyzed via GC/MS by a certified third-party lab. Samples were collected at periodic intervals based on route efficiency and record keeping. Results and Discussion From six sample sets taken from the N4B force main to N1B LS, five showed a decrease in methane concentration from the injection point to the calcium nitrate-treated control point, with an average decrease in methane concentration of 38%. Half the samples showed an increase in CO2 emissions at the control point. Similarly, five of the six sample sets collected at the Greenbrook 2 force main to Lakewood Ranch Riverwalk LS saw a decrease in methane concentration with an average decrease of 13%. CO2 results from Greenbrook 2 mostly decreased in concentration, but only by small fractions. More data is needed to draw conclusions regarding CO2 results. Overall, methane was broadly reduced with nitrate treatment, with an average of 24% reduction in methane emissions during nitrate dosing. The CH4 concentrations at Pope Road Master LS treated with magnesium hydroxide were similar to that of the control points treated with calcium nitrate but showed lower CO2 values. The CH4 and CO2 concentrations at Tara 20 LS treated with calcium hydroxide were similar to the results obtained from the control points of N4B force main to N1B LS and Greenbrook 2 force main to Lakewood Ranch Riverwalk LS. This paper will go further into the analysis of the results, discussing outliers, testing challenges, and comparing test results to theoretical assumptions. We will also discuss the immediate and future steps to support the project, such as utilizing a continuous method of data collection for more robust data to decrease standard deviation. Another municipality has expressed interest in continuing the research within their collection system, which will provide more information on methane mitigation regarding different collection system designs, climates, and wastewater characteristics. We will also discuss the long-term sustainability target of evaluating GHG emission impacts from the full life cycle of calcium nitrate dosing for odor control, including manufacturing and transportation impacts. Benefits The theoretical mitigation calculation method would allow any municipality to calculate the methane mitigation they are achieving as a result of their odor control program utilizing calcium nitrate, making it easier to quantify the sustainability benefit of the program and communicate it with their community. As sustainability metrics become more important, including GHG metrics, these calculations can play a critical role in quantifying the overall GHG impact of the wastewater treatment and collection system and providing an additional method of GHG reduction. In the case of Manatee County (the County), the benefits are less theoretical. The County conducted a GHG Audit that was completed in June 2020, and while it took into consideration the wastewater treatment plants and overall utility operations, it did not examine GHG emissions from the collection system. This audit recommended a reduction of nearly 3,000 metric tons of CO2e a year to reach net zero by 2040. Understanding GHG emissions and particularly methane mitigation of the odor prevention program could allow MCU to demonstrate a more robust view of the wastewater contributors towards GHGs for the County as well as provide potential solutions towards the recommended reduction goal through a method that neither party may have considered beforehand. Whether or not wastewater authorities or utilities have their own GHG goals, they can provide benefit to their municipalities that are more likely to have them, as well as build public support through communicating the sustainability impacts of their operations.