Introduction:
Every water utility in the world goes through the process of creating capital improvement plans (CIPs). Some utilities are more proactive than others, and as CIPs are the formalization of prioritizing capital projects, all face the same challenge, trying to ensure the 'right' projects are prioritized for the available funding.

This paper will describe a new and reinvigorated approach to capital planning that looks to balance capital cost, with the risk reduction of completing a project and leveraging the benefits associated with each project to create balanced, equitable and flexible CIPs. A reinvigorated approach will be of interest to all water utilities wishing to streamline their CIPs. Whether under a financial burden or failing to deliver projects through lack of clear decision making and prioritization, this approach offers a clearer, objective and more defensible approach to capital planning.

Approach:
Applying a reinvigorated CIP approach involves comparing all projects using three common criteria, risk, benefit and cost. Risk when applied is termed risk reduction benefit (RRB). For CIP planning, the RRB is typically determined as the cost of asset failure if not replaced and project benefits. The benefit criteria are identified as a project's social, environmental and economic attributes; collectively called triple bottom line (TBL) and are the potential upside across these areas of building a project. The third common criteria to be considered is cost, the capital and operational cost of implementing a project. The CIP project and the associated common criteria are entered into a prioritization model designed to maximize TBL and RRB and minimize the cost exceedance of the entire CIP portfolio. Figure 1 shows the simple prioritization model. Although simple in concept, prioritizing using three criteria is complex and the approach uses Optimizer™ software by Optimistic to complete the calculations. The software that uses a heuristic learning algorithm, which is an approach designed to solve multi-criteria problems in a faster and more efficient manner that favors speed of process over absolute accuracy or completeness.

The TBL vs. RRB vs. Cost approach when applied to Atlanta made the CIP more comprehensible as each project had a business value and is removed the elements of doubt as to whether the 'right' project were being promoted.

Results:
Stantec applied an Optimatics model for Atlanta using a triple bottom line per dollar (TBL/$) and risk reduction per dollar (RRB/$) to evaluate project benefits and risks. This provided quantifiable and equitable justifiable decisions to governing bodies, regulatory agencies, funding entities, and customers.

The example shown in Figure 2 is taken from Atlanta's Enterprise-wide CIP shows how for the optimal CIP following re-prioritization, the application of annual budget was applied, and how funds for large capital projects were encumbered over more than one year, and projects of different types distributed to create a rolling comprehensible, equitable, and flexible CIP.

Conclusions:
All projects included in a CIP are important but prioritizing them based on triple bottom line per dollar (TBL/$) and risk reduction benefit per dollar (RRB/$) will mean that when scheduling is being determining in year 1, and revisited in subsequent years, will ensure that projects remain value and the changing risk through deteriorating assets are recalculated, moderate risk in year 1, may become a high risk by year 5; understanding the current risk and the potential for change in the future will ensure that, not only are 'right projects' being included, but they are also being designed and implemented at the 'right time'.

One fundamental need of this approach is that the optimization model is designed to run on a routine and periodic basis; for most water utilities this is likely to be on an annual basis. During subsequent updates, the CIP project parameters and cost assumptions can be reviewed and updated as needed. Concurrently, the TBL and RRB scores for those projects already included will be revisited and updated to reflect the passing of time. New scored projects will then be added to OptimizerTM, and a range of scenarios be recreated. Using the available revenues, and project schedules for the next 10-years, the CIP will be re-prioritized, and a new CIP created.

1. Introduction
Ultrafiltration (UF) is an important component of treatment schemes for water reuse due to its effective pretreatment for downstream processes like reverse osmosis. UF also plays a significant role in direct and indirect potable reuse because it can physically remove pathogens. However, UF fouling is a problem in many reuse process trains and is detrimental to long-term filtration performance. This research focuses on UF fouling mechanisms and its mitigation by coagulation pretreatments using iron salts. Earlier work largely considered conventional coagulation and electrocoagulation using aluminum salts, so this will be one of the first to implement electrocoagulation using iron salts. The motivation to evaluate electrocoagulation with iron salts is that it can induce Fenton reactions generating strong oxidants like ⋅OH that are capable of attenuating viruses thereby gaining virus removal credits and possibly improving other performance.
2. Materials and methods This research was conducted at Texas A&M University in cooperation with Orange County Water District to investigate the effects of coagulation on ultrafiltration.
1) Two secondary effluents. One was from the City of Bryan, TX wastewater treatment plant (WWTP), and the other was from the Texas A&M University WWTP. Both employ conventional activated sludge, and samples were collected after ultraviolet (UV) disinfection.
2) Filtration system setup and procedure. The hollow fiber UF membranes (Memcor©: S10N) were sealed in the home-made module. A constant filtration flux of 60 L/(m2⋅h) was employed for a 22-minute duration. Backwash cycles of 80 L/(m2⋅h) for 15 seconds were followed, as commonly practiced in municipal applications. Each experiment typically consists of 9 cycles of such filtration and backwash. Data were acquired using a written program in LabVIEW software to continuously monitor the pressure and automatically control the process.
3) Coagulation pretreatment. Coagulation and flocculation jar tests were performed with iron chloride added for conventional coagulation and with iron plate electrolysis for electrocoagulation.
4) Blocking law mathematical model. The exponent in constant flux blocking law formula is modelled to indicate sizes of colloids deposited in membrane pores or on the membrane wall.

3. Results Counter-intuitively, the secondary effluent with lower turbidity and TSS (shown in attached image 1) caused much higher fouling (shown in attached image 2). After comparing water quality parameters of two effluents, one hypothesis was proposed: UF fouling is driven by the feed water particle size distribution relative to the membrane pore size, especially when the new membrane is used. After measuring particle size distribution of two feedwaters (shown in attached image 3) and validating the size measurement by mathematical modelling, the hypothesis was proved, and the following membrane fouling mechanism was revealed: UF fouling is determined by nano-particle size distribution in the feed water and its comparison to the membrane pore size.
Nano-colloids were smaller than the nominal membrane pore size before pretreatment, allowing their deposition in the porous matrix of the membrane and making them difficult to be removed by backwashing. Coagulation pretreated flocs are much larger than membrane pores and deposited on the external membrane surface as a loose cake layer, thus easily removed by backwashing and alleviating both irreversible and reversible fouling. As a result, UF productivity was largely determined by colloid size. Electrocoagulation using iron performs the same as conventional coagulation with iron in terms of UF fouling mitigation, even though it can achieve virus inactivation. To exclude the synergistic effect of organics and harness ions and isolate the colloidal size effect, the permeate of Texas A&M WWTP effluent ultrafiltration was ultra-filtered as a feedwater because it contained above 90% of harness ions and total organic concentration in the effluent. It showed much less fouling than the effluent, so organic fouling effect mechanism was excluded in this study.

4. Significance to the industry Based on our findings, monitoring the UF feed water particle size distribution (especially in the nano-colloid range2 100 nm) is recommended during wastewater reclamation to optimize reuse process train performance and enhance water recovery. Conducting bench or pilot scale testing on sampled plant effluent will help inform the design of a more efficient UF system and further benefit the whole reuse process train.

The Filtration and Disinfection Facility (FADF) at DC Water's Blue Plains Advanced Wastewater Treatment Plant (AWTP) is the last process before discharging into the Potomac River. Averaging 384 million gallons per day (mgd) and peaking at 555 mgd, the FADF is one of the largest tertiary filtration facilities in the world. The FADF removes total suspended solids and total phosphorous to levels satisfying the AWTP's NPDES permit limits.
The FADF was built in the 1970s, expanded in 1990, and upgraded through a series of projects between 2002 and 2014. In 2013, DC Water witnessed their first filter underdrain failure. Since that time, DC Water has rebuilt some of the filter underdrains in-kind. In 2021, DC Water initiated the Filter Underdrain and Backwash System (FUBS) Upgrades Project. The project includes replacing the block type underdrains and dual-media system with nozzle type underdrains and mono-media. The upgrades will permit DC Water reduce their backwash and air scour rates, thereby reducing overall energy costs and potentially reducing maintenance needs. All while meeting the stringent NPDES parameters.
This presentation will cover DC Water's approach and lessons learned from the rehabilitation of the filters, including:
Selection of filter media and underdrain system
Modifications of the backwash system, modeled using computational fluid dynamics (CFD) and physical modeling
Rehabilitation of select filters for full scale media testing
Operation and performance of existing dual and select mono media filters
To evaluate filter media options, DC Water conducted a pilot study comparing mono-media against the existing dual-media (as control) in 6-in diameter PVC columns. Three media sizes were assessed with two media bed depths. This pilot study helped DC Water narrow down media sizing and depth preferences, the results of which were then carried into the FUBS project for further refinement. The FADF currently has forty filters, each containing two cells (eighty total filter cells). At the start of the FUBS project, over ten cells were out of service due to underdrain failure. Therefore, in advance of the main project, eight filter cells were designated for early upgrade through the DC Water High Priority Rehabilitation Program (HPRP). This early work restores capacity critical to facilitate the FUBS construction phase. Additionally, four of these cells will be utilized as full-scale demonstration filters for testing the short-listed filter media. Two filters will hold 5-ft bed depth of the smaller media (effective size 1.4 +/- 0.1mm), with the other two holding 5-ft bed depth of the larger media (effective size 1.7 +/- 0.1 mm). The filter performance is measured at the individual filter effluent using new online turbidimeters. The media performance will be evaluated against each other and an existing dual-media control filter. In addition to demonstrating filter effluent quality, filter runtimes and backwash process control will be compared amongst the three cells to assess volumetric efficiency. Ultimately, this full-scale demonstration testing will permit final media selection and filter control strategy optimization.
There are 8 washwater wells each containing a 40 mgd vertical turbine pump to supply backwash water and will be replaced with 12 mgd pumps. The wet well geometry does not meet current Hydraulic Institute (HI) design recommendations outlined in HI 9.8-2018. Poor approach conditions to pumps can lead to pump performance and/or maintenance problems. Although the current pumping system is functional, DC Water has witnessed vane tip cavitation at the pumps, reducing overall life of the equipment. A combination of both numerical methods and scale physical modeling was used to verify and optimize the intake approach conditions to ensure the new pumps would mitigate the existing challenges. The mono media also has lower air scour requirements which was met by reducing the existing blower speeds. The existing blower drives were modified to provide the specified air scour rates.
The initial pilot testing performed by DC Water demonstrates that the mono media can provide equal or better suspended solids and phosphorus removal as shown by Figure 1. However, to optimize the media selection the two media sizes that demonstrated the best performance are being further evaluated in full scale testing in four filter cells.
This presentation will illustrate how both computational fluid dynamics (CFD) and physical modeling tools led to robust and verified hydraulic design that will contribute to optimal pump and filter performance. The CFD model was run for the existing wet well conditions with and without a vaned flow conditioner at the pump inlet. Model results showed that adding a vaned flow conditioner to the inlet eliminated rotation and vortices entering the pump. Similarly, a physical hydraulic model constructed at a 1:4 scale also demonstrated that a flow conditioning basket was effective in dissipating all vortex activity and stabilizing flow entering the pump, as seen in Figure 3.
The filter upgrades provide:
Robust and reliable filter underdrain and backwash systems
Operational flexibility in future
Energy savings
The CFD modeling allowed for a broad exploration of approaches to optimize the pump intake system. The use of both CFD and physical modeling tools led to robust and verified hydraulic design for optimal pump performance.

Temperature Phased anaerobic digestion, thermophilic digestion (55°C, 131°F) followed by mesophilic anaerobic digestion (38°C, 98°F), was the process selected by the San Jose-Santa Clara RWF (SJ-SC) as the stabilization process for the overall facilities expansion and modernization projects, with the purpose of renewing facilities, increasing operating capacity and starting the transition of SJ-SC away from the use of sludge lagoons to manage biosolids. TPAD was identified as the preferred digestion alternative at SJ-SC as part of the 2010 Biosolids MTPAD was identified as the preferred digestion alternative at SJ-SC as part of the 2010 Biosolids Master Plan. The TPAD process was formed based on converting four existing anaerobic mesophilic digesters to serve as the thermophilic anaerobic digesters and connecting that system to the existing 12 mesophilic anaerobic digesters through a sludge cooling heat exchanger system.

One of the first questions the start-up team had to answer was how to seed the digesters. The regionally relevant operating thermophilic digesters within proximity to San Jose are at the EBMUD Facility in Oakland, CA and the Hyperion WWTP in Los Angeles, CA. Given the large volumes of sludge and haul distances and schedule impacts it was elected to start the digesters from a mesophilic seed sludge.
The implications of starting with a mesophilic seed sludge are important to understand as they impact the startup schedule and duration to process maturity. The primary challenge is that the biomass operating in the system are not representative of a thermophilic operation. Following seeding, the temperature was increased rapidly to the target operating temperature of 55°C (131°F), with no sludge feed to the system. With the temperature increase there was a significant increase in the volatile acids concentration in the thin seed sludge, increasing from 100 mg/L as acetate to approximately 417 mg/L as acetate, over the first 12 days of operation, after which the VFA levels were rapidly depleted, decreasing from 403 mg/L as acetate to 7.92 mg/L as acetate between days 14 and 17. This was indicative of the reestablishment of methanogenic activity in the digester, indicating that thermophilic tolerant methanogens are present in mesophilic sludge and feed sludge as well, suggesting using thermophilic seed sludge is unnecessary. Loading commenced around day 20 of operations, which coincided with a rapid increase in volatile acid levels within the digester, resulting a cessation of feeding on day 32. After a decrease on VFA levels loading recommenced, which lead to a further spike in VFA. However, rather than ceasing loading the loading rate was held relatively constant, until there was a sharp decrease in VFA levels around day 50. The rationale for this strategy was to provide sufficient substrate to generate the needed VFAs to maximize methanogenic growth rate, while not souring the digester. This strategy proved successful as, loading increase steadily to a maximum of 50,000 lb-VS/d for the single digester at start up, without further uncontrolled imbalance between VFA production and loading rate (Figure 1). Concurrent with onset of stable loading, biogas production stabilized, producing measurable levels within the digester (Figure 2). Based on these observations, it took approximately 40 days from first heating the digester until full thermophilic digestion was established and in balance (Figure 2).

Similar trends were observed in the subsequent 3 digesters started up. Additional evaluation of the data found that daily change in volatile acids was means understanding digester progress towards as stabilized system. Figure 3, plots the daily change in volatile acids the start-up for Digester 8, concurrent with the digester observed VFA concentration, as measured by titration. What is apparent is that during the population stabilization period days 1-40, daily VFA generation remained positive, with the exception of the initial drop prior to any loading. However, once loading commenced the VFA generation (change VFA mass per day) remained above zero. However, with the onset of methanogenesis (~ day 50) increasing negative generation days were observed along with zero days. With the maturation of the biomass both structurally and in concentration it is expected that the VFA generation rate will converge around zero. Utilizing the daily change in VFA maybe an effective indicator of process maturation, both from an onset of methanogenesis and longer-term stabilization of the process.

Since commissioning the digestion process has provided significant additional operational design related lessons learned. Overall, since conversion to TPAD the volatile solids destruction has increased from a typical value of 30-40% to 55-60%, resulting in less solids and more biogas (Figure 4). Another critical observation was in the cooling heat exchangers, where there was significant accumulation of struvite, that impacted the ability of the system to cool the sludge in the mesophilic phase (Figure 5). Interestingly, mesophilic digester performance was not negatively impacted, even while operating at ~115°F, suggesting for future TPAD systems cooling all the way down to conventional mesophilic temperatures may not be necessary.
This paper benefits operators and design engineers alike will gain valuable insight into the TPAD process operations and benefits.

Introduction:
Amid the accelerating impacts of climate change, the urgent need to mitigate greenhouse gas (GHG) emissions is more critical than ever, yielding commitments from developed countries aimed at achieving net-zero emissions by 2050. Wastewater treatment plants (WWTPs), a major source of direct emissions, contributes approximately 5% of global non-CO2 GHG emissions, largely in the form of methane (CH4) and nitrous oxide (N2O)[1]. Thus, there has been growing academic and industrial interest in the quantification of the direct, or Scope 1, emissions from WWTPs [2]. The standard method for estimating GHG emissions relies on the current IPCC guidelines, which use a simplified global emission factor (EF). However, this approach lacks the granularity required to capture the actual dynamics of GHG emissions from WWTPs [3]. To better quantify GHG emissions, prior studies have focused on investigating GHG emissions in relation to adopted technologies, received wastewater flows, and/or treatment level [4,5].

Therefore, the current study leverages a multi-level GHG quantification framework to demonstrate how operational patterns, compliance limits, and influent characteristics not only influence the total emissions but also their profile and distribution within the plant. This work is part of an ongoing NSERC project monitoring GHG emissions from Canadian WWTPs in which a multi-level approach is utilized combining various advanced measurement techniques, including gas/liquid sensors, optical gas imaging (OGI), drone-based sensing, aircraft imaging, and satellite imaging.

Methods:
The Canadian wastewater treatment plant featured in this study operates with a typical activated sludge treatment configuration. To monitor nitrous oxide, two Unisense® sensors were strategically installed to capture possible variation across the aeration tank. Methane (CH4) emissions were quantified using 16 ground-based sensors, complemented by a 3-day intensive measurement campaign employing drone-based and OGI techniques.

Results and discussion:
For over six months, liquid N2O concentrations were monitored at two locations in the aeration basin. The system typically is operated as a step-feed, with primary effluent entering the bioreactor through eight gates distributed along the aeration tank and regulated via gate openings. During the study, the reactor was tested under various modes; for example, Figure 1 shows the N2O emissions during typical operation with standard gate settings. Median daily N2O emissions were recorded at only 2.91 KgN-N2O/day, with occasional spikes exceeding 10 KgN-N2O/day. This corresponds to an N2O emission factor (EF) of 0.005 ± 0.0012 kg N2</Sub>O-N per kg TN, significantly lower than the IPCC EF of 0.016 kg N2O-N per kg TN [6]. This reduced EF can be attributed to the plant's compliance limits, which do not require nitrogen removal. Accordingly, the reactor operated near nitrifier washout conditions, with an average SRT of 3.4 days and median ammonia removal of less than 25% (Figure 1). It is worth noting that while non-BNR activated sludge systems typically exhibit higher emissions [5], the lower emissions observed in this plant can be attributed to operation at a washout SRT.

The average methane emissions from the plant were quantified at 1385 ± 871 kgCH4/day. This corresponds to 3.9—4.4 gCH4/m3 of treated wastewater and 3.2—3.5% of the influent COD load. These values are relatively high but fall within the typical range reported in the literature [4]. The distribution of methane emissions across the plant revealed unexpected insights. As shown in Figure 2, the aeration tanks and primary clarifiers were the largest contributors, accounting for approximately 60% of the total methane emissions. In contrast, digesters and gas burners combined contributed only 25%. The use of a handheld OGI camera proved instrumental in diagnosing emission sources and quantifying emissions from locations where drone-based measurements were unreliable due to adverse wind conditions. The handheld camera confirmed low emissions from the digesters, with no detectable leaks from covers or structural cracks. However, leaks detected in the dewatering building contributed approximately 6% of the plant's total methane emissions.

The resulting total daily GHG emissions of the plant are estimated to be equivalent to 47.727 metric tonnes of CO2. Interestingly, as shown in Figure 3, methane constituted more than 80% of the plant's emissions. This finding contrasts with typical literature reports, where N2O often accounts for more than 50% of plant GHG emissions [3,7]. This divergence can be attributed to (i) compliance limits that do not require ammonia removal, (ii) operational practices such as TWAS return and operation at a short sludge age, which promotes nitrifier washout, and (iii) the received influent, which contained elevated dissolved methane and high TSS concentrations.

Conclusion:
This study demonstrates how influent characteristics, operational patterns, and compliance limits shape GHG emissions in WWTPs. Methane contributed over 80% of total emissions, with aeration tanks and primary clarifiers identified as major sources-contrasting with typical findings where N2O predominates. These results highlight the importance of site-specific GHG monitoring and tailored mitigation strategies for effective emissions reduction in wastewater treatment.

INTRODUCTION
Per- and polyfluoroalkyl substances (PFAS) are persistent, bioaccumulative 'forever chemicals' that pose significant environmental and public health challenges due to their resistance to traditional wastewater treatment processes. Current PFAS treatment technologies applied in full-scale water and wastewater treatment processes primarily rely on phase transfer methods, such as ion exchange, adsorption, membrane filtration, and foam fractionation [1, 2], or high-temperature (350-1000°C) destruction processes like incineration, pyrolysis, and supercritical water oxidation [3-5]. However, these approaches are limited by inherent drawbacks, such as high energy consumption, high capital investment and operating cost, and operational complexity, making full-scale, in situ implementation by utilities challenging.

This study for the first time introduces a novel, bio-inspired, transition metal oxide-based catalyst for PFAS destruction at a mildly heated temperature of 80°C, offering a potential energy-efficient alternative. Attributed to the catalyst's low-temperature nature, the process can be integrated into existing heated solids treatment processes, such as thermophilic anaerobic digestion, thermal hydrolysis pretreatment (THP), or pre-pasteurization. The objective of this study is to assess the effectiveness of this catalyst on the destruction of PFAS compounds within the PFAS-accumulating matrices, including municipal wastewater, sludge, and sludge dewatering filtrate. The goal of the current experimental phase is to provide proof of concept and to understand the extent of PFAS destruction in such complex matrices.

Methods and Materials
Samples of treated wastewater effluent, pre-dewatered raw sludge (THP feed sludge), and dewatering filtrate were collected from WSSC Water's Piscataway Bioenergy Facility, a centralized biosolids processing facility that is designed to receive biosolids from six regional water resource recovery facilities (WRRFs), representing a potential full-scale application site for this technology for destroying concentrated PFAS compounds. The experimental design, including the setup of different sample matrices, spiked PFAS concentrations, catalyst doses, reaction temperatures, and reaction time, is shown in Table 1. Briefly, the experiments (Samples 1-36) involved dosing wastewater and sludge samples with synthesized catalyst and performing reactions at 80°C for 24 hours. Additional experiments (Samples 37-42) utilized a pressure vessel (Parr Instrument Company, IL, USA) to simulate full-scale THP conditions at 165°C for 30 minutes. Post-reaction liquid and solid phases were separated and analyzed for PFAS concentrations by following EPA Method 1633.

Results and Discussion Preliminary results of this study, Samples 1-18, are shown in Figures 1 and 2. As can be seen in Figure 1, approximately 57.3% to 69.4% of the total PFAS spiked before the reaction was destroyed. The destruction can be corroborated by the defluorination during the reaction shown Figure 2. It is interesting to observe that the amount of fluoride ion released from the reactions for both types of samples were approximately more than 10 times the stoichiometric release of fluoride (Figure 2). It should be noted that rather than the target concentration of 500 ppb PFOS as shown in Table 1, the actual PFAS concentration spiked into the shown groups before reaction turned out to be approximately 1,100 ppb PFOS with a significant amount of impurities accounting for about 10% of the added PFOS. The average concentration of PFOA+PFOS after the treatment was surprisingly reduced to only about 8.3 ppb, marking a PFOA+PFOS destruction efficiency of over 99% ± 0.03% on average. Furthermore, approximately 10.1% to 19.0% of the total PFAS spiked was adsorbed onto the catalyst. In the liquid phase, approximately 17.2% to 26.5% of the total PFAS were either transformed to other PFAS species identified by EPA 1633 or remained undegraded. It is noteworthy that the PFAS destruction across the sample types were insignificantly different (T-test, p > 0.05), indicating that defluorination in WRRF effluent samples was not affected by the more complex characteristics.

These preliminary findings demonstrate the potential of the studied catalyst for efficient PFAS destruction in wastewater matrices and further provide the confidence for testing samples with more complex constituents. Results from more complex samples, including sludge dewatering filtrate and THP feed sludge (Samples 19-42), will be made available in early 2025 and incorporated in the manuscript.

Abstract
Quaternary Ammonia Compounds (QACs) have long been recognized as niche contaminants in specialized industries outside of municipal wastewater treatment. They are known to affect biological processes, for example anaerobic digestion in agriculture settings. They are not regulated and are widely ignored as a factor for municipal wastewater treatment. Their use in everyday life skyrocketed following two pivotal moments: the ban on triclosan and triclocarban in soap products and the pandemic that resulted in widespread use of disinfection sprays across our society. Here, we report on two completely different wastewater treatment plants that had to deal with QACs causing upset to their biological processes (nitrification at one plant and anaerobic digestion at another plant). We employed contract labs to quantify QACs in influent wastewater along with toxicity testing. In one case, a new food preparation facility in Texas was utilizing cleaning products for daily routine cleaning and periodic deep-cleaning of specific equipment, unaware that the products contained QACs that could potentially cause an upset at the local wastewater treatment facility. One of their cleaning products they used was a detergent commonly used in households for dishwashing. Working closely with the local wastewater treatment, the facility significantly reduced their use of these products to enable them to safely discharge their effluent. At the other facility, QACs were attributed to upset startup with anaerobic digestion. We will present results on QACs and biological process function along with the models we employed to identify and remediate QAC issues.

Background
Quaternary ammonia compounds (QACs) are a class of compounds widely used for their disinfecting ability in the food industry for cleaning process lines as well as in the agricultural industry. QACs are the main active ingredient in disinfecting cleaner sprays (for example, Lysol) and liquid soap. QACs are widely used everyday, and they are widely detected in WRRFs (Mahoney et al., 2023).

QACs are used because they are intended to have negative consequences on microbial activity. Yet, WWRFs rely on microbial communities to carry out important processes, including nitrification and anaerobic digestion. While it is recognized that QACs can inhibit biological processes at WRRFs (Lu et al., 2024), they are rarely suspected to be the culprits for process upsets in everyday life. QACs are not regulated so they are not monitored. QACs are a broad class of compounds with several subgroups of chemicals. The variety of chemical types leads to a variety in inhibition.

This presentation will discuss completed results from two separate case studies on WRRFs that dealt with QAC problems. One was a small WRRF that knew where a primary source of QACs were originating from (Figure 1). We reveal how analytical chemistry work and modeling (Figures 1-3) allowed us to find another unsuspected source of QACs in the community. The second case study involved issues with QACs on the aeration basin that were caused by alterations in the sludge stabilization processes from supernatant recycle.

Methods and Results

Case Study 1
A small (<5 MGD) WRRF received discharge from a food processing facility, and was dealing with upsets to their mainstream biological treatment process. The facility worked closely with the WRRF to investigate their potential impact, substituting and reducing QAC-containing cleaning products and using a combination of toxicity testing of their discharged effluent with QAC analysis of wastewater to develop a management strategy. A dynamic model of the collection system upstream of the plant was developed to investigate ways of mitigating potential spikes in QAC concentrations that could cause problems for the WRRF. The model was developed using the GPS-X 8.1 simulator with an industrial pollutant library (Figure 2).

The investigation for the food preparation facility included two major tasks: (1) estimation of QAC concentrations and (2) toxicity testing. For the former, a process simulator was used to assess the dynamic impact of the discharge through a series of lift stations and altering their operation (depth used and flows) was modeled to show that they could lower the potential QAC spikes (Figure 3).

Toxicity testing revealed that the facility effluent did not decrease the measured SOUR, indicating it was not toxic to aerobic activity (including nitrification).

Case Study 2
A large (>50 MGD) WRRF employed a new process to improve anaerobic digestion. The process employed a pretreatment process that improved anaerobic digestion. However, the WRRF routinely monitored for QACs and noticed high concentrations in supernatant. The supernatant was recycled back to the head of the plant and coincided with decreased performance in the aeration basin. In this case, proactive monitoring of QACs allowed for easier assessment of the problem. QACs are not regulated so many WRRFs do not measure QACs. This case study will highlight lessons learned on how QACs can be released to the soluble phase and alter processes during startup.

A large utility monitored QAC in their aeration basins, raw influent and sludge processing units for 6 years. The data show a significant increase in QAC concentrations in the aeration basins. The increase correlates with the installation of a new anaerobic digester, likely caused by the recycle streams.

Introduction
Cloth media filters have been traditionally used for tertiary treatment at wastewater resource recovery facilities (WRRF), where effluent limits are less than 10 mg/L or 2 NTU (WEF MOP 8, 2017). When compared to more conventional granular filtration, this technology is attractive because of its lower head requirement (2.5-4 feet), lower backwash ratio (1-3%), and comparable hydraulic loading rates (3.5 gpm/ft2 to 7 gpm/ft2 respectively). Recently, the same cloth media filters have emerged as technologies suitable for primary treatment, offering far greater total suspended solids (TSS) and biochemical oxygen demand (BOD) removals than conventional primary clarification. To date, multiple pilot studies and a few installations have demonstrated TSS and BOD removals of approximately 80% and 50%, respectively (Caliskaner and al., 2020; Caliskaner and al., 2019; Caliskaner, 2022). This corresponds to an approximately 50% increase in removal, which is significant. This process can, therefore, be used to divert more carbon to the anerobic digestion process, leading to an increase biogas production in the order of 20 to 30 %, while, simultaneously, reducing the organic load to the secondary treatment, leading to a reduction in energy demand for aeration in the order of 20-25%. As the cost of electricity continues rising, it is anticipated that this process becomes more and more attractive.

Another significant advantage, when compared to conventional primary clarification, cloth disk primary filtration (CDPF) systems can remove approximately 50% more solids within approximately 20% of the footprint. This alone becomes a valuable tool for WRRFs that require additional secondary treatment capacity due to increased flows and loads, or more stringent discharge limits but have little to no room for expansion using conventional treatment methods and approaches. The later will be the case for San Francisco Bay Area's WRRFs, including Silicon Valley Clean Water's (SVCW) WRRF.

Methodology
SVCW is in Redwood City, CA. It is a Joint Powers Authority serving about 220,000 people living in the communities of Belmont, Redwood City, San Carlos, and the West Bay Sanitary District. The WRRF was designed to treat an average dry weather flow of 29 MGD, however, the current dry weather flow is 13 MGD. Considering the potential benefits of CDPF listed above, SVCW conducted a pilot project between November 2023 and April 2024 to evaluate the CDPF process at its WRRF (supplied by Aqua-Aerobic Systems, Inc.) (Figure 1).

Existing primary treatment consists of rectangular primary clarifiers (PC) that removes approximately 65% of the influent total suspended solids (TSS) concentrations and 35% of the biochemical oxygen demand (cBOD5) loading. Main goal of the project was to investigate the feasibility of replacing the primary clarifiers with CDPF as part of a major upgrade that is planned at the WRRF to meet the upcoming more stringent effluent quality requirements. Specific objectives of the CDPF pilot project were as follows:
1. Monitor the process performance for TSS, Chemical Oxygen Demand (COD) and 5-Day Biochemical Oxygen Demand (BOD5) removal at different hydraulic loading rates and compare this performance with the current plant primary clarification process side by side.
2. Determine the backwash ratio at different hydraulic and solids loading rates, and characterize the backwash water in term of TSS and verify mass balance.
3. Discuss the system operation and maintenance requirements.
4. Determine the number of required filtration units required.

Results and Discussion
Performance of the CDPF system is summarized in Table 1 and 2. The CDPF system achieved TSS removal rates above 80% despite a wide range of hydraulic and solids loading rates, while the TSS removal for the existing PC system ranged between 43 % to 68%. This shows that the CDPF not only significantly improves the primary treatment performance but also improves the consistency of the effluent quality. The pilot effluent TSS concentration ranged from 33.1 to 38.4 mg/L even if the HLR ranged from 1.5 to 5.3 gpm/ft2 and the SLR ranged from 4.6 to 12.4 lbs/ft2. This is a considerable advantage as more consistent effluent quality could lead to improvement in the secondary process. TSS and COD performance data collected during pilot testing are shown in Figure 2 through Figure 4.

Subsequent to the pilot testing, a technical evaluation study was conducted to determine the holistic impacts of implementing PF for SVCW. Based on the pilot performance results, the primary filtration process has been analyzed for its effectiveness, efficiency, and overall benefits to the existing and anticipated future processes. Key findings from this technical evaluation are listed below:
- Enhanced Treatment Efficiency: The primary filtration system improved TSS and BOD removal, reducing the loads on secondary treatment processes.
- Energy Optimization: Increased biogas production by 20-30% from enhanced solids capture in primary treatment.
- Footprint: The system requires smaller footprint compared to conventional methods, making it ideal for facilities facing land constraints.
- Wet weather Resilience: The system maintained over 80% TSS removal during extreme wet weather events, improving reliability.
- Regulatory Compliance: Project provided critical insights to meet future stringent Total Inorganic Nitrogen effluent limits.

Introduction.
The Merced Avenue Greenway Project is a transformative planning, design, and construction initiative focused on revitalizing a 1.1-mile urban corridor in the City of South El Monte, California. This stretch of Merced Avenue has long suffered from challenges including inadequate stormwater management, recurring flood risks, limited green spaces, and a lack of safe, accessible pedestrian and bike pathways. These issues have not only impacted water quality and urban sustainability but have also contributed to the area's vulnerability to climate change effects such as extreme heat and storm events.

The project was initiated as a response to these pressing environmental and community challenges, with a commitment to align with the goals of the Upper Los Angeles River Watershed Enhanced Watershed Management Program (ULAR EWMP). The ULAR EWMP prioritizes water quality improvement through the integration of climate-resilient stormwater infrastructure and green street designs. Recognizing the need for a holistic approach, the Merced Avenue Greenway Project incorporates strategies for stormwater capture and infiltration, vegetative habitat restoration, and enhanced mobility for pedestrians and cyclists.

The work includes the implementation of innovative stormwater Best Management Practices (BMPs) such as bioswales, permeable pavements, and rain gardens. Additionally, the project prioritizes urban greening efforts, with tree planting and native vegetation to reduce the urban heat island effect and support biodiversity. Community engagement has been a cornerstone of this project, with outreach programs designed to educate residents and foster their involvement in shaping the project outcomes.

This pilot effort aims to establish a replicable model for green street retrofits, addressing not only the immediate needs of Merced Avenue but also setting a precedent for sustainable urban design in similar communities. The outcomes of this initiative are expected to include improved stormwater management, enhanced water quality, increased community resilience to climate change, and a more livable urban environment.

Objectives.
To decrease flood risk, increase vegetative cover, restore habitat, improve active transportation, and reduce urban heat island effects.

Status.
The southern portion of the project is nearing construction completion. The northern portion of the project is currently in the planning and design phase, with a strong emphasis on community outreach and education.

Methodology.
The project leverages the Upper Los Angeles River Watershed Enhanced Watershed Management Program (ULAR EWMP) to implement climate-resilient stormwater BMPs and urban greening elements.

Findings.
The project will serve as a pilot for developing green street design standards and contribute to water quality improvement strategies in Los Angeles County.

Significance/Conclusion.
This initiative exemplifies an integrated approach to urban street retrofits, blending infrastructure improvements with community and environmental benefits.

One of the most challenging design problems for underground infrastructure, is to minimize disturbance/disruption, or 'pretend like we were never there'. In the case of the Bear Creek Relief and WF-G Interceptor improvements project, this challenge was further complicated with crossing the Trinity River, twice, with a 96-inch diameter gravity pipeline. To accomplish this, the owner and engineer collaborated with pipe manufacturers to design two inverted siphons with consideration to future system demands, eliminate the need for Portland cement concrete elements in the collection system, provide for cost-effective open cut installation, comply with USACE regulations, and navigate poor soil conditions - all the while maintaining uninterrupted service to customers and maintaining up to 84 MGD of average daily flow.

This presentation is intended to discuss the process and calculations taken to determine compliance of the siphon crossings underneath the Trinity River as well as showcase the manufacturing and construction of large diameter plastic pipe fittings.

Inverted Siphon Design:
The siphons were designed utilizing flow data provided by the Authority including 3-day hydrographs at selected locations from the Authority's model storm event. These hydrographs were provided for years 2040 and 2070, and the engineer designed for both worst-case scenarios, where the flow is the greatest and the lowest, at all locations. Low flow conditions are an equally important design consideration to ensure sedimentation in the siphon is kept to a minimum.

From this information, the engineer determined the Average Daily Minimum, Average Daily, Average Daily Maximum, and Peak Wet-Weather flows and used these values in the design of each siphon crossing based on their locations and characteristics within the system.

The initial designs for all siphon crossings were conducted through an intensive and iterative calculations process necessary to determine adequate siphon barrel diameters. InfoWorks ICM (Version 11.0) model was used to confirm the siphon design calculations. Following the preliminary design selection, the engineer modeled the siphon crossing designs to confirm the hydraulic capabilities of the siphon crossing designs with Peak, Daily Average, and Minimum Flows. (See Tables 1 & 2)

The models were later used to estimate the amount of expected sedimentation in each siphon during minimum flows over the course of 30-, 60-, 90-, and 365-days to confirm the design's reduction of sedimentation. These analyses were conducted independently of the preliminary design selection with the physical parameters of the siphon and the 3-day hydrograph (developed from flow information provided by the owner) used to corroborate the preliminary findings and design.

To model the sedimentation, the engineer modified the above mentioned 3-day hydrograph to remove the Peak Wet-Weather event and retain the dry weather flows to better approximate a worst-case scenario for sedimentation. The engineer determined the peak flow, occurring every third day, is unrealistic and that removing it would be a better approximation. The engineer repeated the dry weather flows from the hydrograph over 30-, 60-, 90-, and 365-days for sedimentation analysis. While sedimentation is shown in some cases in the results, the hydrograph analyzed does not include any Peak Wet-Weather events. Other assumptions were that the sediments are evenly distributed across the entire depth of flow, not near the bottom as it would realistically be expected, and that the sediment loading was approximately 24.4-mg/L (Metcalf & Eddy) with a specific weight of 2.65.

After confirming the siphon design met capacity requirements, the engineer designed an air jumper for each crossing in order to move odorous sewer gases across the length of the siphon crossing. Generally, the diameter of each air jumper duct was selected to best balance the available space in the cross-section of the siphon crossing and the air flow capacity of the duct.

Inverted Siphon Construction:
The engineer worked closely with the pipe manufacturer to ensure the constructability of the siphon fittings and lay schedule during the construction submittal process.

Multiple iterations of the lay drawings were reviewed to ensure the inlet and outlet inverts maintained their hydraulic requirements. (See Figure 1) During installation, care was taken to maintain flowline elevations to comply with the plans and submittal documents.

Motivation & Goals
The City of Orlando, Florida is a large, fastest growing, progressive, and sustainability minded community. Orlando's Water Reclamation Division of the Public Works Department provides wastewater collection and treatment services to the City's businesses and residents through the Iron Bridge Water Reclamation Facility, a 40 MGD plant, and the Conserv I Water Reclamation Facility, a 7.5 MGD plant. Currently, biosolids from each of the plants are dewatered, stabilized and hauled to land application sites or landfills for disposal. Regulations established by SB 712 restrict this practice during wet weather (when groundwater is within 2 feet of the surface), and landfills are often hesitant to accept biosolids during these periods. This has necessitated on-site dewatering and storage of sludge-a practice the City aims to minimize through the adoption of technologies that can reduce sludge volumes and eliminate reliance on land application.

As a proactive measure, the City is also seeking solutions to address contamination issues, specifically concerning per- and polyfluoroalkyl substances (PFAS), to safeguard water sources potentially impacted by biosolids disposal. After evaluating various management strategies, including composting, incineration, and drying, the City identified supercritical water oxidation (SCWO) as an innovative and cost-effective solution for both biosolids volume reduction and contaminant elimination.

The overarching project goal was to install, commission, and test a SCWO system at the City of Orlando's Iron Bridge Water Reclamation Facility. The measures of success for the project included (1) ensuring the timely preparation of the site and delivery/installation of the SCWO unit, (2) passing functional tests, and (3) continuously processing biosolids that meet volume and organics/PFAS reduction targets.

Methods
The SCWO system used converts organic-rich waste into clean vent gas and liquid effluent composed solely of water, inert inorganics and minerals. During the SCWO process, waste is heated and pressurized above the critical point of water (374°C, 221 bar), allowing it to enter a supercritical state. In this state, organics become highly soluble, facilitating the mineralization of persistent organic compounds like PFAS. The oxidation of organic matter generates energy in the form of heat, which is recycled within the process.

Samples were collected prior to influent wastewater screening, between the end of sludge handling and the SCWO system inlet, at the effluent of the SCWO unit, at the effluent of the plant's wastewater treatment process, and at the air emissions outlet of the SCWO system. At each sampling point, relevant parameters including flowrate, chemical oxygen demand, and PFAS were assessed and used to evaluate the performance. This sampling was conducted at baseline, during system startup, and at regular monthly intervals during system operation.

Results
The City received a grant from the Florida Department of Environmental Protection through the Clean Water State Revolving Fund in February 2024 for upwards of $800,000 (Table 1). After four months of site evaluation and planning, the SCWO provider mobilized the SCWO system to Orlando's Ironbridge facility and completed installation and start-up (including functional tests) within three months. At present, the SCWO system is in its third month of operation and has run multiple types of PFAS wastes including biosolids. Testing is expected to continue through February 2025 at which point an evaluation of whether to demobilize the unit or continue operation will be made (Figure 1). Results from initial PFAS testing reinforce previous research that showcase the ability of SCWO to non-selectively destroy >99% of PFAS analytes (Table 2) of different classes and chain length. Results are repeatable, as shown by data in Table 3 that was collected when treating the same PFAS waste through SCWO the following week.

Significance
This talk will explore the opportunities and challenges of conducting an on-site demonstration of emerging PFAS technologies, using the implementation of SCWO at Orlando's Ironbridge Facility as a case-study. The presentation will highlight key project enablers, including how funding was sourced, to inspire other facilities to support the adoption of emerging PFAS technologies.