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.

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:
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.

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.