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.

Objectives:
Communities are facing increasing stormwater flood risk driven by intensified precipitation, sea level rise, storm surge, urban development, and funding challenges. Many lack the tools and frameworks to develop holistic, effective, and actionable mitigation plans. This presentation will describe how to develop a stormwater flood resilience plan, providing communities with a roadmap to assess this risk and implement optimal, equitable, and actionable flood mitigation solutions.

Status:
The approach has been implemented in various municipalities across the US, customized to the specific needs and conditions in each community. Case studies in New York City, Virginia, and New Jersey will be presented.

Methodology:
The approach begins with the development of a stormwater flood risk map, leveraging hydrologic and hydraulic modeling. We will share guidance on adapting the model-building approach to the data and resources available and considerations on how to effectively share flood risk maps with stakeholders and the public. This is followed by an exposure and risk analysis that integrates the latest climate, modeling, and existing infrastructure data to assess and prioritize vulnerabilities. The presentation will cover how this step can be automated to facilitate efficient updates as new datasets become available. After the risk analysis we will present approaches to prioritize project locations and project types, leveraging additional datasets such as risk quantification, asset and infrastructure criticality, social vulnerability, community input, and economic indicators. We'll share dashboards typically created for this process to facilitate stakeholder engagement and support decision making. Using prioritized project locations, we'll describe the process for refining the model in these areas and developing solution concepts that can be used to develop project scoping and funding information, such as concept designs and cost estimates. Both cost estimates and risk quantification information can be used to develop a benefit-cost analysis (BCA). The BCA may be required for federal funding but also provides a policy and communication tool that helps communicate the need and justification for a given project and ensure strategic, cost-effective use of public funding. We will share additional automated tools that help conduct the BCA and are adaptable to each project based on the needs and data available. Finally, we will present public engagement strategies that have been used to ensure community-focused solutions. This methodology has been proven through multiple case studies, which will highlight key considerations and lessons learned for other municipalities interested in developing a stormwater flood resilience plan.

Findings:
Key findings demonstrate that integrating multi-dimensional data sets-such as H&H modeling results, climate projections, social vulnerability indices, and economic metrics-enables effective prioritization of projects and investments. Case studies from NYC, Virginia, and New Jersey illustrate how stakeholder engagement enhances the translation of data into actionable flood mitigation projects. These examples highlight scalable methods for combining technical methods with practical, equitable implementation strategies.

Significance:
This work provides critical guidance for municipalities and floodplain managers to adopt and implement Stormwater Flood Resilience Plans. By offering tools, methodologies, and real-world case studies, it equips communities to proactively address stormwater flood risks and adapt to evolving climate challenges. The insights shared foster collaboration and inform the development of resilient urban environments, ensuring sustainable and equitable solutions.

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.

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.

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.

Introduction:
With the current needs for balancing process intensification and operational cost, Membrane aerated biofilm reactors (MABR) stand out as an advanced intensification technology. Using gas-permeable membranes, MABR is bubbleless aeration technology where oxygen is effectively delivered to the biofilm grown on the biofilm surface (Houweling & Daigger 2019). Uniquely, MABR's gas-substrate counter diffusional pattern provides the opportunity to obtain 'Breathing Insights' by assessing the oxygen transferred to the biofilm which can be utilized to monitor, diagnose, and control biofilm and process performance. To this end, studies reported that the relationship between Oxygen purity in the exhaust gas and ammonia concentrations can be used to measure the response from the MABR to ammonia loads which indirectly indicates biofilm health or nitrification capacity (Houweling & Daigger 2019; Uri-Carreno et al. 2021). In accordance, a soft sensor named 'MABR fingerprint' was proposed based on the response of the MABR to the diurnal changes in the bulk liquid ammonia concentration (Yang et al., 2022; Cao et al., 2023). In such studies, the fingerprint concept was assessed based on the outcomes from steady state and dynamic simulations. However, validation of such concepts has not been performed in full-scale systems. In addition to the MABR fingerprint, based on exhaust oxygen purity, OTE and oxygen transfer rates (OTR) can be determined (Houweling & Daigger 2019). The obtained OTR can be translated into maximum nitrification rates (Max_NR) of the MABR. Hence, monitoring and comparing the actual daily nitrification rates (NR) with the Max_NR can, also, be used as a simple indication of biofilm nitrification activity. Therefore, in this study, we leverage the data from one of the largest ZeeLung™ MABR installations in North America, to evaluate the feasibility of using MABR fingerprint and NR/Max_NR ratio to monitor and diagnose MABR performance.

Operational information:
The data used in this study is from Hespeler WRRF, Cambridge, Ontario, Canada. The data covers a period of 5 months grouped into 5 phases as described in Table 1. Significantly, biofilm thickness was measured three times during the 5 months which had a clear gradient as biofilm thickness decreases over time. Detailed information on biofilm thickness are provided in (Lakshminarasimman and Parker, 2025).

MABR fingerprint plot:
The fingerprint plot is obtained by plotting the daily data of the Exhaust oxygen Purity (%) vs the bulk/effluent ammonia concentrations. In prior studies where data were obtained from model simulations, high correlation (above 0.9) was obtained between both variables (Cao et al., 2023). Accordingly, the fingerprint slope, referred hereafter as the daily slope, was obtained. Such fingerprints plots were not consistently observed with the actual daily, where correlations ranged between 0.5 and 0.9. Dirunal dynamics yielded two major shapes, presented in Figure 1. The Fingerprint was grouped into three major periods. The first is when the influent ammonia is increasing (the loading period), and two periods when bulk ammonia is decreasing (the recovery period). In addition to the daily slope, each period's slope was determined separately.

Monitoring MABR:
By examining the generated plots over different periods, the shape with exponential decay was observed mainly during the first two phases where relatively low ammonia loading rates were applied in comparison with phases III and IV. This can be referred to mass transfer limitations due to the very thick biofilm thickness (850-1000 micron), such effect was not mitigated when air flow rate increased to 6 Qair/m2/d from 4.5. Such a pattern started to disappear and an inclined line was observed when biofilm thickness started to be reduced in the following phase. This can be leveraged as a useful tool to control scouring and air flow rates to either reduce biofilm or overcome mass transfer limitation by higher air flow rates.

In Figure 2, the obtained slopes from different phases are presented. Clearly lower slopes were obtained at the phases closer to the time biofilm thickness decreased to 450 micron (Phase IV and V). It can be seen that such effect was captured clearly in the loading slope and to much lesser extent in the daily slope. A steeper slope indicates better response from the biofilm to ammonia load, especially when fingerprint plot are closer to those in Figure 1a.

In Figure 3, NR/Max_NR for different phases is plotted. It might not be as representative to biofilm thickness as the finger print plot, but it provides useful information on oxygen utilization by nitrifiers in the system. Phase I and V had low NR/Max_NR, but in the case of Phase I, this was due to the very thick biofilm thickness and low ammonia loads which probably led to higher growth of heterotrophs and other oxygen utilizing organisms. This is in agreement with microbial analysis performed, results not published. On the other hand, low NR/Max_NR at Phase V is mainly due to low ammonia loading rate which is confirmed from the fingerprint plot that shows relatively steep slopes.

Conclusion & significance:
This is the first study to examine, in full-scale with real-life data, off-gas based metrics to monitor MABR biofilm health and performance. This provides simple and easy to understand tools not only to monitor the performance but also to inform decisions.

Background
Biosolids management in the United States is shaped by evolving federal and state regulations, which influence wastewater solids processing technologies, marketing, distribution, and overall management costs. Recent regulatory revisions have been driven by environmental stressors such as climate change and Contaminants of Emerging Concern (CECs), particularly per- and polyfluoroalkyl substances (PFAS). PFAS compounds have become a primary focus local, state, and federal regulatory agencies, reshaping biosolids beneficial use and disposal practices nationwide.

A Risk Assessment for PFOA and PFOS in Biosolids has been conducted by the United States Environment Protection Agency (USEPA), with draft results having been released in January, 2025. The Risk Assessment process is a scientific, multi-stage process to evaluate the need for regulatory guidance on these compounds in biosolids. This analysis examines the recently released draft results, their implications, and their influence on new state regulations.

In anticipation of formal USEPA guidance, key states such as Michigan, California, Maine, and New York have adopted significant policy changes that have had far-reaching impacts. These state-level regulatory frameworks have influenced regional policies and created unique opportunities and challenges for utilities as they develop long-term strategies for managing wastewater solids. As regulations evolve, the landscape for biosolids beneficial use and disposal will continue to shift.

Objective
This analysis focuses on the USEPA Risk Assessment process and recent state regulatory changes, with the following objectives:

USEPA Risk Assessment
1. Review the standard Risk Assessment process used to develop Part 503 biosolids guidance.
2. Analyze the draft results for PFOA and PFOS, highlighting the risk ratios and their implications.
3. Outline next steps in the Risk Assessment process.

State Regulations
1. Identify states implementing PFAS reduction strategies, including sampling and limits for PFAS in biosolids.
2. Evaluate PFAS reduction efforts in Maine, Michigan, California, and New York.
3. Compare USEPA draft results to existing state standards and practices.

Methodology
Research for this analysis included:
1. A detailed review of the USEPA Risk Assessment process to provide historical context and its application for PFAS in biosolids.
2. An in-depth review of the draft Risk Assessment results released by the USEPA in January, 2025.
3. Analysis of state biosolid regulations, validated through surveys with state regulators to assess recent updates and their impacts.

Findings and Current Status
USEPA Risk Assessment
1. Traditional Risk Assessment processes include a Risk Management analysis to weigh cost-benefit impacts before releasing draft results. The process utilized by USEPA for the Biosolids Risk Assessment did not follow the standard process, releasing draft results ahead of completing the Risk Management process. This approach results in limited context provided for results and may lead to reactionary legislation at the state level.
2. The USEPA's assessment of PFOA and PFOS present in biosolids, the USEPA used a deterministic approach, producing a single worst-case risk value focused on farm family exposure. This approach does not reflect typical conditions and resulted higher risks for lower concentrations of PFOA and PFOS in biosolids.
3. Draft results will provide a starting point for determining regulatory limits for PFOA and PFOS in biosolids, with revisions to Part 503 unlikely in the next year. The Risk Assessment results will be reviewed internally by the USEPA and externally by third parties to verify accuracy and approach. This process may lead to further delays in regulatory changes due to USEPA's initial approach for conducting the Assessment.

State Regulations
1. California emphasizes source control, requiring PFAS monitoring to track reductions in biosolids. Results will be compared to USEPA draft numbers.
2. Michigan's 'Michigan Model' set a precedent for PFAS monitoring and limits, influencing neighboring states and earning USEPA recognition.
3. Maine and New York implemented unique strategies for biosolids management, showcasing varied regulatory approaches.

Comparative analysis reveals diverse strategies among states, driven by unique regulatory frameworks. These efforts provide a roadmap for adapting to USEPA guidance while addressing region-specific challenges.

Introduction
The Permian Basin is the largest oil and gas production basin in the United States. Management of the produced water generated from these activities has become a major issue facing oil & gas operators as regulators increase restrictions on the traditional disposal well method. This has led to the pursuit of beneficially reusing the produced water by treating to surface water discharge or industrial reuse quality. Treatment of Permian Basin produced water is exceptionally challenging due to its high salinity (≈15 percent). This paper will provide an overview of beneficial reuse drivers, regulations, treatment technologies and challenges.

Overview
During oil and gas extraction, produced water that is naturally present in the geological formations is brought to the surface along with the hydrocarbons. It is estimated that 20 million barrels per day1 (bpd) of produced water is generated in the Permian Basin from the 6.6 million bpd2 of oil production. The water contains a mixture of salts, residual oil, and naturally occurring radioactive materials. The exact composition varies by geological formation.

Beneficial Reuse Drivers
Disposal of produced water in deep wells (i.e., depths below the Wolfcamp shale formation) is understood to induce regional seismicity. In January 2024, the Texas Railroad Commission (RRC) suspended a total of 56 deep disposal wells in the Northern-Culberson Reeves Seismic Response Area (SRA) and Gardendale SRA (both located in the Permian Basin) due to a series of seismic events, shown in Figure 1. Produced water may also be disposed in shallow disposal wells (i.e., depths above the Wolfcamp shale formation) but have had their capacity curtailed because of limits on allowable formation pressures, shown in Figure 2. The RRC now requires pressure monitoring and recording for all new or amended disposal well permits3. These two regulatory actions coupled with increasing oil and gas production4 are driving the need for an alternative ways to manage produced water.

Regulatory Update
The term 'Beneficial Reuse' is in reference to Environmental Protection Agency's Oil and Gas Point Source Category, Subcategory E titled 'Agricultural and Wildlife Water Use'5. This subcategory grants the oil and gas extraction industry the ability to discharge treated produced water west of the 98th meridian for the propagation of agriculture or wildlife. Discharge under this subcategory is regulated by Texas Commission on Environmental Quality (TCEQ) through the Texas Pollutant Discharge Elimination System (TDPES). Currently there is only one finalized TPDES application to discharge in Texas, located in near the Eagle Ford Basin in south Texas. Three other applications (all located in the Permian Basin) are pending administrative review. Other regulated produced water management methods include recycling the produced water for use in hydraulic fracturing (requires no permit), treatment and land application (requires RRC permit), or treatment for industrial reuse (requires no permit, contingent on quality). Industrial reuse applications not only include cooling tower water makeup, but also novel concepts such as feed water for green hydrogen projects or use in data center cooling — both of which will be discussed further in the report. On January 8, 2024, the RRC issued a framework6 for produced water treatment pilot study authorizations for discharge via land application. The pilot framework is intended to minimize the regulatory hurdles of produced water pilot testing and provide produced water quality data to regulators. Further discussion of this framework and its potential implication will be discussed in the paper.

The New Mexico regulatory framework will also be discussed in the paper since the Permian Basin crosses State lines.

Treatment Technology and Challenges
Typical Permian Basin produced water quality is presented in Table 1. The key driver for treatment design is desalination with the two main technologies7 being membranes and thermal desalination. Both technologies produce a brine waste stream that must be managed through well disposal or crystallization; or recovered as an asset and used to harvest critical minerals or generate power8.

The desalinated water requires polishing treatment for ammonia removal and other trace compounds. There are three main options for ammonia polishing: biological, adsorption, and stripping. The paper will present techno-economic evaluation of ammonia polishing options conducted by the authors. A comparison of desalination and ammonia removal technologies are presented in Table 2.

The paper will present the latest the technology options, their development and implementation status, and publicly-available performance data.

Conclusions
Beneficial reuse of produced water offers oil and gas operators an alternative management option to the restrictions being placed on well disposal. As treatment technologies are piloted and commercialized, the full scale produced water treatment may become feasible based on relative economics. Regulatory permitting will also become more favorable as additional knowledge and understanding of produced water is gained.

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.

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.

Objective Computational
Fluid Dynamics (CFD) has proven to be a reliable and effective method for modeling secondary clarifiers in wastewater treatment plants. By simulating flow dynamics and solids distribution, CFD provides a detailed understanding of clarifier performance under various operational and structural configurations. This powerful tool enables plant operators and engineers to identify targeted solutions that enhance treatment efficiency and optimize plant operations.

Background
The Pomona Water Reclamation Plant (PWRP), operated by the Los Angeles County Sanitation District (LACSD), has encountered challenges related to its secondary clarifiers over the past decade. With the application of CFD the HDR team conducted a comprehensive optimization study to identify cost-effective modifications to improve flow and solids distribution in the mixed liquor (ML) channel and enhance clarifier performance, leading to higher treatment capacity.

Methodology
This study developed both two-dimensional (2D) and three-dimensional (3D) CFD models that reflect the physical characteristics and current performance of the clarifiers through calibration based on historical and field data. 2D CFD model, also known as HDR's high-accuracy clarifier model (HACM©), replicates the physical processes in the clarifiers using mathematical relationships to understand clarifiers performance impact from various modifications, such as flocculation baffle, mid-tank baffle, transversal launders, and channel baffle system. 3D CFD modeling was used in evaluation of hydraulic flow distributions among clarifiers, as well as solids concentration distributions.

2D Process Model Findings
A preliminary 2D HACM© CFD model has been developed using the plant's historical MLSS and flow data and refined through the effluent suspended solids (ESS) data collected in the field. The model provided insights of solids distribution in the clarifier (Figure 1), enabling the team to evaluate various modifications on clarifier performance (Table 1). In the base case with the existing configuration, the secondary clarifier has an ESS concentration of 39 mg/L. The preliminary modeling results indicate that replacing the existing 82ft-long launder with a combination of a 50ft longitudinal launder and five 18ft transversal launders could lead to a 33% reduction in ESS concentrations. Figure 1(b) shows that the shorter launder remediates the end wall effect, reducing turbulences caused by the wall and promotes a more effective settling zone. The proposed modifications, such as the combination of perforated flocculation baffle and mid-tank baffle, could further improve clarifier performance. As shown in Figure 1(c), the flocculation baffle and mid-tank baffle create a zone that promote solids settling and minimize resuspension of settled solids, resulting in a significant ESS concentration of 72% (Table 1).

Figure 1. Flow And Solids Concentration Distributions in Secondary Clarifiers Under Various Modifications

Table 1. Optimization Results with Various Secondary Clarifier Modifications

3D Model Findings
Results from the 3D CFD analysis indicated that solids distribution in the ML channel could be significantly improved with modifications such as a channel baffle. A critical component for satisfactory secondary clarifier performance is even solids distribution to the clarifiers. Under the base case scenario with existing configuration and without air additions in the secondary treatment system, the difference between the highest and lowest solids loadings across clarifiers is around 7%. In addition, as shown in Figure 2(a), the tracer response curve for clarifier 6 has a delayed time to peak and lower peak concentration, likely due to low velocity zones in the ML channel towards clarifier 6 (Figure 3(a)). The channel baffle provides an effective remediation by inducing additional mixing and enhanced local turbulence inside the channel (Figure 3(b)), which result in more uniform tracer responses (Figure 2(b)). The modeling results suggest that installing a baffle inside the ML channel can reduce the variation between the highest and lowest solids loadings from 7% to 2.5%.

Figure 2. Tracer Response Curves in (a) base case; (b) channel baffle case

Figure 3. Cross-sectional Views of the ML channel before Clarifier 6: Velocity Magnitude Distributions in (a) base case; (b) channel baffle case

Significance
The findings from this study highlight the potential for targeted modifications to significantly enhance secondary clarifier performance at the Pomona Water Reclamation Plant. By leveraging CFD modeling, the team identified and evaluated cost-effective solutions that address existing challenges, improve flow and solids distribution, and optimize clarifier efficiency. These proposed improvements not only enhance the plant's ability to manage higher hydraulic and solids loadings but also demonstrate the value of advanced modeling techniques in achieving operational excellence. This approach provides a replicable framework for similar facilities facing comparable challenges, supporting the long-term sustainability and reliability of wastewater treatment systems.lity and reliability of wastewater treatment systems.