INTENDED OBJECTIVE: Biosolids from water resource recovery facilities (WRRFs ) are increasingly used for agricultural and recreational land purposes due to their sustainable means to replenish macronutrients. However, the relatively high phosphorous content of biosolids limits certain applications. This study aims to identify optimal locations for recovering vivianite and subsequently phosphorus, to allow class A biosolids reach ideal phosphorus levels. INTRODUCTION: Global consumption rates of synthetic fertilizers per unit of cropland have increased 3 to 8 times over the past half century (Lu et al. 2017). Class A biosolids are increasingly explored as an alternative to commercial fertilizers due to their effective means to replenish carbon and macronutrients (Gilmour et al. 2013). However, the N:P ratio of biosolids is typically lower than commercial fertilizers which can cause an accumulation of phosphorus when applied to soil, increasing risk for eutrophication (Penn et al. 2002). Therefore, it is critical to implement efficient phosphorus-removal technologies/techniques within the biosolids treatment train to improve the N:P ratio and limit the amount of phosphorus that result in the cake. Therefore, this study aims to analyze the P mass balance of the Blue Plains advanced wastewater treatment plant in Washington, DC as well as its vivianite characterization in full-scale. The process sampling, modelling and analysis led to identification of potential locations for vivianite recovery, and initial estimations on how much the P content in our class A biosolids might be reduced by recovering vivianite upfront. MATERIALS AND METHODS: Sampling campaign: Samples were collected in DC Water Blue Plains over a 3-month period (Mid-February to Mid-May 2022). Quantitative analysis: Phosphorus is measured by the EPA 365.1 method. Scanning Electron Microscopy with Energy Dispersive and Mossbauer Spectroscopy: Prepared by method in Prot et al. 2021. Modelling method: Visual Minteq version 3.3 with DOC SHM model RESULTS & DISCUSSION P mass balance at Blue Plains and P content in biosolids product Blue Plains advanced WWRF achieved a 98% incoming TP removal over its primary (enhanced-chemical phosphorus removal) and secondary systems through iron dosing. The removed P is diverted to the solids fraction and results in a Class A biosolids product (BLOOM) with 2.88% P (dry weight basis) and 28-32%TS (Fig.1A). The P:N ratio of our product is 1:1 and thus higher in P content than the target of 1:2 P:N for typical fertilizers. Decreasing P content in BLOOM by 50% or thus recovery 60% of vivianite would increase the value and applicability of BLOOM. Vivianite formation and formation potential along the Solids Treatment Train A total Fe/P molar ratio of 1.5 or greater allows for optimal vivianite precipitation (Cong et al. 2017) which is reflected in DC Water treatment flow diagram (Figu 1). Vivianite was detected in primary thickened sludge, blend of thickened primary (PS) and waste activated sludge (WAS), and digested sludge b ased on sequential extraction method in Wang et al. 2021. This was also further supported by the clear co-location of Fe and P in SEM images (Figure 2A and 2B). These locations are consistent with the vivianite scaling seen in primary sludge gravity thickening lines and centrifuge lines in the facility. Through quantitative analysis, the vivianite mass flow in thickened primary sludge, blended PS/WAS and digested solids accounted for 8%, 52%, and 49% of the incoming P to the plant (Fig. 1). These vivianite ranges are like those reported by iron-dosing plants in Prot et al. 2021 and Wilfert et al. 2016. Estimation of P recovery potential needed to impact Class A biosolids P content Based on the current vivianite-P levels in the three identified locations (Fig. 1), sludge after anaerobic digestion contained the highest level of vivianite-P. This is likely due to higher orthophosphorus levels after thermal hydrolysis treatment which allows for additional vivianite formation with Fe(II). This notion is supported by the low levels of Fe(II) concentrations after anaerobic digestion indicating that most of it is bound (Fig. 1). We estimated how much vivianite recovery efficiency we might need to decrease the P content in the BLOOM with an ideal target of ~0.014 kg P/kg TS and acceptable target of 0.022 kg P/kg TS. Given the highest vivianite levels in digested sludge, a recovery efficiency of at least 40% with ideally 70% is sufficient to meet our targets (Fig. 3). Utilizing vivianite recovery technologies such as magnetic separation (80% of vivianite recovery in digestates according to Wijdeveld et al. 2022), and other alternative options could provide the potential recovery target needed to improve BLOOM. CONCLUSIONS Based on current vivianite-removal technology efficiencies, removing vivianite will significantly impact the phosphorus levels in BLOOM. Results suggest that after anaerobic digestion is a preferred and feasible option to implement recovery technology due to its high vivianite content as well as the opportunity to recover vivianite in a fraction of the digestate to produce low P BLOOM rather than the whole biosolids treatment train. Future testing will explore recovery efficiencies of P and vivianite to confirm feasibility and setup a path towards pilot testing approaches.

Introduction: Ultraviolet LED technologies have progressed to the point where full-scale implementation is now on the horizon. The work outlined in this study is part of WRF project 5173 which investigates the feasibility of UV LEDs at different magnitudes of flow and water qualities. A 280nm, 100 GPM, closed-channel UV LED unit was installed in a wastewater facility in Nova Scotia, Canada to compare to a conventional open-channel UV disinfection system. This project represents the first ever installation of UV LEDs for wastewater disinfection at this scale and provides foundational data for understanding how UV LEDs scale as a technology. In addition, the practical experience gained during the installation process of this technology is valuable to consultants and utilities who may be considering the use of UV LEDs in the future. Project Background: Data was collected over a 4-month period before the installation of the full-scale UV LED system using the UV auditing approach. The UV auditing approach has been developed by Dalhousie University and provides an understanding of the delivered fluence for full-scale UV disinfection by leveraging bench-scale inactivation curves (Rauch et al., 2022). This approach has successfully demonstrated that UV LEDs can outperform conventional, mercury-based 254nm disinfection for some wastewater matrices (MacIsaac et al., 2023). UV auditing is also useful for utilities in understanding how LEDs will perform when considering mercury-free disinfection technologies. The LED reactor used for this work (shown in Figure 1) was manufactured by AquiSense Technologies and is a closed channel design with a 100 gallon per minute (GPM) capacity and was conducted over the Fall of 2023. The flow capacity of the LED unit represents approximately 10% of the average daily flow of the wastewater facility that it has been installed at. This installation marks the largest commissioning of a UV LED wastewater disinfection reactor anywhere in the world. Pre-installation data is shown in Figure 2 and was collected during the Summer of 2023. The average UV transmittance measured at the facility during this sampling period was 53% with an average power consumption of 35 KW. The disinfection results indicate that 280nm UV LEDs performed comparably to conventional 254nm low-pressure system and can provide sufficient pathogen inactivation when used at the full-scale. Additional Project Phases: The second phase of this work involves stress testing the UV LED reactor to define the range of performance in terms of power output, flow rate and UV transmittance. This work was conducted over a 4-week period in early 2024 and involved operating the reactor at a flow rate of 100 and 200 GPM, as well as power outputs ranging from 50-100%, and variable UVT during the sampling period. The final phase of this work involves the comparison between the UV LED reactor with the conventional, open channel, low-pressure UV system that is already installed at the facility. This work covers a 6-month period with twice weekly sampling of the inlet and outlet of both treatment trains. A scale analysis concludes this work by collecting samples of internal surfaces at the end of the six-month sampling period. This work identifies the differences in fouling mechanisms between each of the UV light sources. UV LEDs do not generate heat on the emitting side of the light source and therefore, are not expected to form inorganic scales in the same way that conventional mercury lamps do. This work provides foundational information for both consultants and utilities when considering approaches for testing the feasibility of using UV LEDs in wastewater facilities. UV LEDs have shown to be comparable in performance to conventional systems while avoiding several of the environmental, human health, and safety issues related to mercury-based UV disinfection. In closing, the tasks conducted in this work help achieve the goals in understanding UV LED implementation as defined in WRF 5173.

Background Water resource recovery facilities (WRRFs) around the world are constantly faced with significant challenges 1, 2. It is estimated that WRRFs are operating at an average of 81% of their design capacity, while 15% of systems are at or have exceeded that threshold3. As the most prevalent biological nutrient removal (BNR) process, any improvements to conventional activated sludge (CAS) processes are highly desirable in our industry4. However, upgrading CAS trains is costly and alternative technologies often tend to be more energy-intensive, expensive1, and time consuming to install, commission, and operate. Thus, the use of physical selectors (e.g., hydrocyclones) for biomass densification has emerged as a front-runner for increasing secondary clarifier capacity and improving nutrient removal. Objective and Approach Despite the many studies exploring the advantages of densified activated sludge (DAS) systems compared to CAS systems, DAS impacts on microbial communities and fecal indicator bacteria (FIB) are unknown2, 5. In 2023, the Water Research Foundation funded a tailored collaboration with the Metro Water Recovery (MWR) in Denver. The collaboration aimed to investigate FIB removal and disinfection kinetics. This study focused on CAS and DAS treatment trains at three North American full-scale operating WRRFs (Figure 1). The WRF project aims to: A) Compare E. coli concentrations over a 15-month period and investigate factors influencing differences (e.g., granulation size distribution, floc/granule mass fraction, floc/granule aSRT, microscopy, COD, Turbidity, TSS, NH3, pH, Temperature, Color, UV-254, TKN, TP, TOC). B) Determine how changes in Secondary Effluent (SE) properties between DAS and CAS affect disinfection efficacy using chlorine, peracetic acid (PAA), performic acid (PFA) and ultraviolet disinfection (UV) seasonally (n=12), with the same water quality parameters listed in Objective A. C) Assess impacts of operational variables on DAS and provide utilities with recommendations. These can include how to utilize modeling and statistics to improve performance using demand and decay values and mechanistic disinfection efficacy models D) Determine if additional analyses (e.g., protozoa counts, granule sieving analyses) provide operational value to utilities adopting DAS. Results Data collected for one year at the MWR Hite Treatment Facility highlights the statistically significant difference in E. coli concentrations between the CAS and the DAS trains (Figure 2). This could be explained by a variety of variables that have not yet been evaluated. FIB counts may be impacted by the predator protozoan community5, but this has yet to be supported by data (Figure 3). While percent mass fraction (Figure 4) and seasonality (Figure 5) have been hypothesized to impact DAS E. coli counts6, this has not been shown by the preliminary data collected, which highlights the importance of a more detailed study to explain the differences observed . Summary DAS is able to be implemented with low capital cost while increasing the capacity of CAS systems. However, there is little data on how SE from DAS systems impact downstream disinfection processes. This WRF project will evaluate the impact DAS systems have on disinfection processes compared to CAS systems. Data collection and testing for this project will begin in April 2024.

Introduction Intensification is a new term describing upgrades at WWTP's which increases treatment capacity in existing tankage. Waste Activated Sludge (WAS) using hydrocyclones increase process throughput, provide more stable performance via the selection of dense sludge aggregates with improved settling rates and promotes enhanced biological phosphorus removal (EBPR). Increased density leads to improved settling characteristics, preventing loss of biomass and subsequent treatment disruption, especially during wet weather scenarios. There are over 50 installations worldwide using the WAS hydrocyclone technology (inDENSETM), however none have been installed at STP's with an operating SRT between 2 and 2.5 days and warm operating conditions (25oC - 35oC). The purpose of this project was to verify if WAS hydrocyclone technology could improve sludge settleability operating under warm operating conditions, thereby demonstrating a higher flow could be treated with the existing infrastructure. Project Background Ajman Sewerage Private Company Limited (ASPCL) was founded in 2002 and was granted by the Government of Ajman Emirate (United Arab Emirates) a Concession Contract to Finance, Build, Own, Operate, Maintain and Transfer its main wastewater infrastructure. ASPCL shareholders are the Government of Ajman, Besix and Veolia. ASPCL appointed Moalajah as its Operator. The infrastructure constructed by ASPCL since its inception includes: 950 km of network, 220,000 properties connected (a connection rate of 92%), 35 pumping stations, and a centralised wastewater treatment plant (Ajman Sewerage Biorefinery) that treated the wastewater and produced more than 15 GWh of electricity in 2023. Ajman Sewerage Biorefinery WWTP was developed in two main phases (Phase 1 and Phase 2), which can treat a combined maximum volume of 137 MLD. Phase 2 of Ajman WWTP was commissioned in January 2017. Phase 2 consists of two aeration tanks and four rectangular clarifiers. Due to the increase in flows to Ajman WWTP, ASPCL investigated an option to increase the capacity of Phase 2 from 40 MLD to 60 MLD. Due to poor sludge settleability the maximum capacity of Phase 2 was 45 MLD was unable to be reached. As an interim solution, ASPCL investigated if WAS hydrocyclone technology could improve the poor sludge settleability and increase the plant capacity. As part of the full-scale implementation, four (4) inDENSE skids were installed. Each hydrocyclone treats 10 m3/hr, resulting in a total capacity of 200 m3/hr. A new higher capacity of pump (i.e. 200 m3/hr, 2.1 ~2.4 bar operating pressure) was installed. Figure 1 shows an inDENSE skid, the influent manifold piping, overflow piping collecting in the effluent waste and underflow collection pipe which returns the heavier biomass back to the system. Figure 2 shows a process flow diagram of Ajman WWTP (Phase 2) with inDENSE System implementation. The hydrocyclone skids were installed and commissioned in October 2022 with minimal impact to the operating plant. Figure 3 shows the hydrocyclone skids installed at Phase 2, Ajman WWTP. Full Scale Demonstration Results The hydrocyclones at Phase 2, Ajman WWTP started up in November 2022. Figure 4 shows changes in the mixed liquor SVI since the hydrocyclones were commissioned. Prior to hydrocyclones, the mixed liquor SVI varied significantly between 50 to 250 mL/g. Since the hydrocyclones started up, SVI improved significantly averaging around 80 mL/g and remained below 100 mL/g. Figure 5 presents the changes in solids loading rates (SLR) after the installation of the hydrocyclones. Solids loading rate (SLR) is a key parameter used to assess the capacity of secondary clarifiers. Higher SLR indicates higher flows can be conveyed without impacting the effluent quality. Since the hydrocyclones have been in operation, the SLRs have increased from 3.8 kg/m2/hr to 5.8 kg/m2/hr while maintaining the effluent quality target. Figure 6 presents the MLSS concentration trends since the hydrocyclones were commissioned. It should be noted that increasing the MLSS was not intentional. The early increase of the MLSS from Feb to May was mostly due to insufficient wasting due to frequent clogging of the cyclones (e.g. issue with the inlet screens). One key project objective was to see how much more flow could be treated in Phase 2 while maintaining effluent compliance. Since the hydrocyclones have been in operation, the influent flow rates to Phase 2 have gradually increased from 40 MLD and reached 58 MLD within 6 months operations of hydrocyclones. It is to be noted that the limitation to 58 MLD does not come from the clarifiers (settleability) but from the downstream disc filters capacity. It was believed that the biological treatment capacity could be increased above 58 MLD if more disc filters were added. Table 1 summarizes the impact of hydrocyclone operation at Phase 2, Ajman WWTP. Since the hydrocyclones are in operation, the capacity of Phase 2 has been increased by approximately 45% as the SVI improved significantly. This resulted in significant CAPEX and OPEX savings for Ajman WWTP. Conclusions The long term hydrocyclone operation at Phase 2 demonstrated that the improved SVI resulted in treating more flow in the existing secondary treatment infrastructure without major capital expenditure. The outcomes of the lessons learned from the long term hydrocyclone operation from Phase 2 will be incorporated into a Phase 3 upgrade.

Introduction As population growth, urbanization, and climate change intensify pressures on water resources, utilities are faced with an increased urgency for advanced water treatment (AWT) solutions and a need to enhance resilience against evolving climatic conditions. Concurrently, wastewater resource recovery facilities (WRRFs) are faced with increasingly stringent nutrient discharge limits that surpass the capabilities of conventional treatment methods. Consequently, utilities are compelled to adopt innovative approaches to address the quality and quantity of water supplies while ensuring regulatory compliance and sustainability. In this work, we highlight case studies of two forward-thinking utilities, distinguished by geographical contexts and unique drivers, yet united by a commitment to advance climate change adaptation strategies, achieve ultra-low nutrient limits, and integrate holistic one water initiatives. Metro Water Recovery (Denver, CO): Upcoming Colorado water quality regulations are set to impose stringent stream standards, notably 2.01 mg/L for total nitrogen (TN) and 0.10 mg/L for total phosphorus (P) on WRRFs, including Metro Water Recovery's Robert W. Hite Treatment Facility (RHWTF) and Northern Treatment Plant (NTP). AWT technologies like carbon-based advanced treatment (CBAT) schemes (e.g., coagulation/flocculation/sedimentation (floc/sed), ozone (O3), biofiltration (BAF), and granular activated carbon (GAC)) may address stringent nutrient limits while also aligning with Direct Potable Reuse (DPR) requirements. A study was initiated to: 1) assess the treatability of dissolved organic carbon (DOC), dissolved organic nitrogen (DON), and soluble non-reactive phosphorus (sNRP) using CBAT technologies; and 2) discern the capabilities of CBAT in concurrently achieving nutrient limits and DPR compliance. Evaluation of nutrient removal through tertiary CBAT processes spanned full-scale applications (floc/sed at NTP and BAF/floc/sed at RHWTF's Denver Water Recycling Plant (DWRP)) and pilot-scale (O3 only, BAF only, and O3/BAF at RHWTF), supplemented by bench-scale floc/sed (jar testing) and GAC evaluations (rapid small-scale column tests). Parameters such as O3 dose and empty bed contact times aligned with potable reuse standards. While full-scale floc/sed/filtration at NTP (Figure 1; Figure 2) and DWRP (Figure 3, Figure 4) (~20 mg/L alum) effectively managed particulate P and sNRP removal, it did not meet DOC and DON targets for Direct Potable Reuse (DPR) applications. CBAT testing showed potential for control of DOC and DON, albeit with the need for multiple potentially costly unit processes. The GAC runtime (up to 3,500 Bed Volumes for DOC and DON targets) was notably extended through enhanced upstream treatment. While floc/sed processes achieved comparable DOC and DON removal rates (up to 40% each) at the expense of elevated coagulant doses (80 mg/L Ferric chloride), O3/BAF treatments realized a modest 26% reduction in DON. Future pilot efforts aim to assess the efficacy of a comprehensive CBAT treatment train, inclusive of tertiary denitrifying BAF, to fulfill TN requirements and optimize DPR suitability. AWT Utility (Midwest): A midwest AWT utility has seen significant population growth in recent years and is estimated to double by 2040. Rapid growth and a desire improve the health of the receiving water body have urged the utility to consider alternative water supplies. Subsequently, the utility commissioned a CBAT pilot consisting of O3, two-stage BAF, GAC, and UV advanced oxidation process (UVAOP). The objective of this study was to pilot CBAT technologies to demonstrate the ability of AWT process trains to produce high quality finished water that meets stringent water quality targets. This study utilized a multi-barrier scheme of O3/two-stage BAF (aerobic/anoxic) to meet low TN limits. Filters were operated in several phases (Table 1) until effluent quality targets were met (TOC < 3 mg/L, TN < 2 mg/L, contaminants of emerging concern (CECs)- meet MCLs) and steady-state was achieved. Select operational parameters were varied during each phase and the resulting water quality surrounding the first anoxic BAF (BAF 3) is shown in Figure 8. Table 2 shows the effluent DO, nitrate (NO3-N) concentrations and corresponding % NO3-N removal achieved across each anoxic BAF. Results indicate that when supplemental carbon and upstream feed DO levels were controlled, anoxic BAF 1 established and maintained anoxic conditions and achieved NO3-N removals up to 60% with anoxic BAF 2 acting as a polishing biofilter (%NO3-N removal ~30%). When supplemental carbon and upstream DO quenching chemical doses were reduced, anoxic BAF 1 turned into a sacrificial BAF, consuming excess DO and displaying poor nitrate removals (~15%), while anoxic BAF 2 became the dominant anoxic biofilter (> 60% NO3-N removal). Piloting efforts demonstrate how a modified CBAT train may simultaneously meet low TN targets (< 2 mg/L) and produce high quality product water. Conclusion Case studies at Metro Water Recovery and a midwest AWT utility demonstrate CBAT's potential for improving finished water quality for reuse and meeting ultra-low nutrient discharge requirements. Project findings provide first guidance on how WRRFs can adjust operational setpoints using CBAT process infrastructure to meet DPR or discharge water quality requirements in ecologically sensitive and drought-prone watersheds.

Background Air is potentially an important exposure pathway for antibiotic resistance genes (ARGs) and bacteria (ARBs) in some environments (1). However, most studies on environmental antibiotic resistance focus on water, leaving air as an understudied matrix (2, 3). There is more to learn about the sources, nature and human health risks of the airborne antibiotic resistance (as reviewed in 4). Specifically, most studies focus on air as an isolated matrix, overlooking the interrelationships with antibiotic resistance in the other surrounding environmental matrices such as water, soil, animals, or insects (5). WWTPs are a source of ARG emissions to the atmosphere (3), and understanding the concentrations of and therefore potential exposure to ARBs via bioaerosols at wastewater treatment plants (WWTPs) is of particular interest given the immediate hazard posed. Moreover, the ARB methicillin resistant Staphylococcus aureus (MRSA) is not only a major cause of hospital-acquired infections, but also community-acquired infections (6). This antibiotic resistant opportunistic pathogen can be transmitted to humans through humans, fomites, and, most importantly for the present study, air (7). Objectives The objectives of this study were to a) detect the presence of methicillin resistant Staphylococcus aureus in air from the grit chamber and UV room of a WWTP, b) compare the concentrations of select ARGs in water and bioaerosols at these locations and b) study the resistome, microbiome, and mobilome of air samples in comparison to paired wastewater influent and effluent samples. A combination of culturing, qPCR, and metagenomic sequencing were used in this study. Methodology Samples were collected from two locations (grit and UV chamber) at a tertiary WWTP. The treatment train includes bar screens, grit chamber, primary clarification, trickling filtration, secondary clarification, aeration basins for nitrification, final clarifiers, pressure filtration, and UV disinfection. Air samples were collected in replicates using the stationary Electrostatic Bioaerosol Sampler (SEBS, 8) at 20 L/min. Samplers were operated for 7.5 hours and samples were collected on five days at each site in fall 2022. Paired composite water samples (influent and effluent) were collected at the time of air sampling. Air and water samples were split for biomolecular (qPCR and metagenomics on total samples) and cultivation-based analyses (heterotrophs via TSA and MRSA via CHROMAgar MRSA). All of the colonies growing on TSA were also analyzed via qPCR for select ARGs. Results Similar concentrations of cultivable bacteria (reported as CFUs/m3) were observed for air samples collected from the grit chamber and UV-effluent site (paired Wilcoxon test, p= 0.4). While CFUs were measurable on most days (N=4/5) in air samples from UV disinfection room, the paired disinfected water samples (N=2/5) did not necessarily show growth on TSA. To understand the potential hazard posed by the cultivable bacteria, ARGs were quantified in the colonies collected from the TSA agar plates. For air samples, the colonies collected from TSA plates contained qacE genes, encoding for quaternary ammonium compound resistance, at both sites in most of the samples (N=4/5, 80%). The genes sul1, blaTEM, and tet(G) were detected in only one sample, encoding for sulfonamide, beta lactam, and tetracycline resistance. In water samples, all of the four targeted ARGs were detected and quantified in four of the influent samples. These ARGs were generally not detected in effluent water samples. One antibiotic resistant pathogen was cultivated in the present study: MRSA. MRSA was detected on four days at the grit-chamber and two days in air samples at the UV-effluent. MRSA was not previously reported in air sampled using different techniques at a WWTP from a study conducted in Poland (9). MRSA was detected on four days in the wastewater influent samples and in none of the effluent samples. For samples analyzed via direct biomolecular analysis, bacterial 16S rRNA was detected in all samples. As expected, sul1 was detected in all influent and effluent samples, it was detected only in three air samples (Fig. 1). The three ARGs detected via metagenomics analysis in the air were tet(K), mdtB and muxB encoding for tetracycline, aminocoumarin, and multidrug resistance (Table 1). mdtB and tet(K) were detected in both air and water paired samples. The ARGs detected in air represent a very small portion of the ARGs observed in the paired wastewater where hundreds of ARGs were annotated in each sample. Significance Protecting public health of utility operators requires considering the potential hazards posed by various pathogen exposure routes. These data presented will help answer some questions about the relationship between bioaerosols and wastewater at two stages of treatment.

INTRODUCTION Concerns related to the formation of disinfection byproducts (DBPs) during chlorine disinfection of wastewater and other safety concerns regarding chlorine operation initiated a great interest in alternative chemical disinfectants. For example, peracetic acid (PAA) received significant attention due to its minimal aquatic toxicity and efficacy in reducing regulated fecal indicator bacteria (FIB) (Antonelli et al., 2006; Manoli et al., 2019; WEF, 2020). The generally low efficacy of PAA in inactivating viruses in wastewater along with the ongoing discussions about revision of the United States Environmental Protection Agency Ambient Water Quality Criteria to include a viral indicator (Dunkin et al., 2017), led to a strong interest in another peracid, performic acid (PFA), which its bacterial and viral inactivation capacity usually outperforms PAA (Ragazzo et al., 2020). The objective of this study was to establish efficacy of PFA as a disinfectant compared to PAA and sodium hypochlorite for secondary effluent wastewater applications. The inactivation of indigenous FIB by PFA has been evaluated and compared with PAA and sodium hypochlorite under identical conditions. The disinfection data were interpreted using the concept of integral CT (ICT) and modeled by an ICT-based double-exponential microbial inactivation kinetic model to develop ICT-response data. This abstract presents the initial results of the Water Research Foundation Project #5219 titled 'Performic Acid Disinfection in Wastewater Effluent and CSOs In Context of Disinfection By-Products and Future Ambient Water Quality Criteria for Viruses', with the participation of more than 10 wastewater treatment plants (WWTPs) across the United States and Canada. Similar experiments with the ones presented herein for the first WWTP will be performed for all participating utilities, thus the results of this project may have a significant impact on disinfection practices in North America. Additional to FIB experiments, disinfection tests on viral indicators inactivation and DBPs formation will also be performed in the framework of this project. METHODS Secondary effluent wastewater was collected from a WWTP in ON, Canada (activated sludge-based processes). Its basic water quality characteristics were: pH=7.6, TSS=7.7 mg/L, BOD=10.8 mg/L, COD=13.5 mg/L, TN=18.6 mg/L, and TP=0.4 mg/L. Disinfection bench tests were performed in 2 L of wastewater at 2 disinfectant concentrations (1 and 2 mg/L for PFA and chlorine; 2 and 3 mg/L for PAA). Samples were collected at 6 contact times (0, 1, 3, 5, 10 and 30 min) and analyzed for disinfectant concentration (Chemetrics and Hach methods) and E. coli, fecal coliforms, total coliforms and enterococci (standard membrane filtration methods) (GAP EnviroMicrobial Services, London, ON, Canada). RESULTS The residual disinfectant concentration data were used to calculate exposure to chemical disinfectant (i.e., integral CT) by fitting initial demand (D, mg/L) and decay (k, 1/min) (Eq. 1): ICT=((C0-D)/k)∙(1-e^(-k∙t))(1) where ICT is the integral estimate of the time-dependant residual disinfectant concentration (mg min/L), C0 is the initial concentration of disinfectant (mg/L) and t is the contact time (min). The FIB inactivation data were plotted as a function of integral CT (Figures 1-4) and modeled by a double-exponential inactivation kinetic model in the domain of ICT (Eq. 2): N=N0∙(1-β)∙e^(-kd∙ICT^m )+N0∙(β)∙e^(-kp∙ICT)(2) where N0 and N are the initial and after treatment concentration of bacteria (CFU/100 mL), β is the fraction of particle-associated bacteria, m is a parameter that describes initial resistance of bacteria to disinfectant, and kd and kp are the ICT-based inactivation rate constants for dispersed (free) and particle-associated bacteria, in (L/(mg min))m and L/(mg min), respectively. PFA exhibited the highest inactivation efficiency for all studied indigenous FIB, followed by chlorine and PAA (Figures 1-4). For example, model-predicted integral CT requirements for 1-log reduction of total coliforms and enterococci were determined as 3-4 mg min/L, 8-10 mg min/L and 40-45 mg min/L for PFA, chlorine and PAA respectively (Figures 3 and 4). Based on model predictions, to achieve a 2-log reduction of both commonly regulated E. coli and fecal coliforms, PFA required ~10 times lower ICT than both PAA and chlorine (Figures 1 and 2). We also present an advanced disinfectant dosing control strategy that accounts for changes in wastewater quality and quantity, together with the hydrodynamics of the contact chamber. Bench test results of PFA (Eqs. 1 and 2) were integrated into a process model to evaluate four dosing strategies, namely, flow pacing, constant ICT, constant ICT advanced demand, and constant ICT advanced demand/decay. Figure 5 and Table 1 show that the advanced control strategy achieves consistent performance and optimizes disinfectant dosage. CONCLUSIONS Results show that PFA was superior to both PAA and chlorine. Although the PFA pricing estimates are currently higher than that of hypochlorite, the lower ICT requirements of PFA may result in a competitive cost compared to chlorine. This indicates the need for site-specific testing to better understand disinfection efficiency and cost benefits of PFA as a wastewater disinfectant.

Common phosphate minerals in wastewater treatment plants such as struvite (MAP, MgNH4PO4*6H2O), calcium phosphates such as amorphous calcium phosphate (ACP, Ca3(PO4)2), and iron salt precipitates such as vivianite (Fe3(PO4)2*8H2O) have been recognized as a maintenance and operational nuisance for their tendency to scale and deposit within anaerobic digesters, in pipe bends, and on dewatering equipment downstream of anaerobic digesters. Precipitation of these minerals occur if the concentrations of the ionic constituents exceed the solubility product (Ksp) of the solid which is measured as scaling tendency (ST) or scaling index (SI). The solubility of these precipitates is dependent on factors such as pH, temperature, other competing ions, and nucleation sites. Chemical thermodynamic modeling could be used in evaluating the parameters that contribute to scaling and, thereby, safeguard process equipment from scaling-induced damage, improve treatment efficiency, and regulate phosphorus sequestration to produce nutrient rich biosolids. In this study two commercially available models were evaluated: (i) Visual MINTEQ Version 4.0 and (ii) OLI Studio. The model inputs were gathered at a pilot-scale experimental setup at Hampton Roads Sanitation District's (HRSD) Atlantic Treatment Plant (ATP), Virginia Beach, VA. The pilot evaluates the impact of aeration, mixing, and chemical addition of thermally hydrolyzed pretreated, anaerobically digested solids on scaling tendency. Critical parameters such as pH, temperature, alkalinity, orthophosphate (OP), ammonia (NH3), and major cations and anions concentrations were measured as model inputs. The solids formed during these evaluations were characterized by X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM)/Energy Dispersive X-Ray Spectroscopy (EDS), and Raman Spectroscopy analysis to validate prediction by the two models. The pilot set up at ATP consists of four tanks (Figure 1). Each tank is 11 feet tall and can hold up to about 63 gallons of digestate. The tanks are operated as daily batch fed continuously stirred tank reactors maintained by pump recirculation at a 3-day solids retention time (SRT). The tanks are aerated with fine bubble diffuser membranes which can be operated at constant or intermittent air flow rates, via dissolved oxygen (DO) or pH set points. Chemical injection lines will be added to measure the effects of calcium hydroxide [Ca(OH)2] and magnesium hydroxide [Mg(OH)2] at varying dosages. The modelling process was based on the pilot influent solution compositions depicted in Table 1 of anaerobic digestate. In both modeling programs, anaerobically digested solids at a temperature of 30 degrees C, a pH of 7.4, and initial parameters from Table 1 were analyzed to determine the pilot influent potential precipitate formation. Figure 2 represents the fractions of solids predicted to form at equilibrium in Visual MINTEQ and Figure 3 displays similar results produced from OLI, both in mg/L. The two model predictions are closely related, listing siderite, struvite, and calcite as the top three controlling precipitates, respectively. This is a prediction of what is forming currently in the digesters, prior to manipulation in the pilot from aeration or chemical addition. A pH sweep from 7 to 8.5 as well as a temperature sweep from 20 degrees C to 40 degrees C were also analyzed in both modeling programs to understand the effects of aeration within the pilot on pH, biological activity, and how the solubility of scaling precipitates were affected. These results, as well as future work that includes modeling the effects of chemical addition in the pilot, will be presented. Precipitate Characterization was conducted in a contract laboratory for XRD, SEM/EDS, and Raman Spectroscopy to determine precipitate identification. The major peaks in XRD patterns produced likely matched with struvite. Further testing will be completed and presented to validate the solids predicted to form by the models. The presentation will showcase the outcomes derived from each model, offering insights into their respective abilities to predict the potential precipitation of controlling solids. The precipitate characterization analysis will also be compared to determine the validity of results and to further optimize both modeling software.

Introduction Coastal regions globally are experiencing the growing manifestation of the effects of climate change, where the intensified frequency and severity of storm events, along with the rise of sea levels, pose escalating threats to communities, infrastructure, and ecosystems. It is in this context that nature-based solutions, often referred to as 'green infrastructure,' have emerged as sustainable and adaptive measures to counter the multifarious challenges arising from coastal vulnerability. The challenges and lessons learned from three living shoreline projects from around the country includes: Lister Park Project (LPP) on the south shore of Long Island, NY; Clover Island Shoreline Restoration Project (CISRP) at the Port of Kennewick along the Columbia River in Kennewick, WA; and Miami-Dade County (MDC) Living Shoreline Project in southeast Florida. Objectives This presentation will gain insight on lessons learned from three nature-based solutions projects in three separate geographies and environments. Seamlessly integrating flood protection, habitat restoration, and public access along the Mill River waterfront, the LPP addresses multifaceted impacts of climate change with a focus on community engagement. Simultaneously, the CISRP aims to overcome ecological challenges from historical waste concrete deposition, emphasizing biodiversity and shoreline stabilization through the creation of a strategically designed submerged bank for juvenile salmon. The MDC Living Shoreline Project initiative seeks to navigate regulatory complexities, developing a Living Shorelines Guidance Document for nature-based solutions. Status Construction of the LPP was completed in December 2023, the CISRP was completed in May 2023, Methodology The LPP integrates living shorelines-a nature-based design alternative employing a blend of green and grey solutions to combat erosion while concurrently promoting the restoration of vital ecosystems along a tidal river. This 5,500 LF living shoreline was meticulously designed to encompass a variety of riverbank conditions, serve as a buffer against both routine and extreme flooding events, thereby protecting the community and its assets. The CISRP confronts substantive ecological challenges stemming from the deposition of concrete waste along its shoreline. This has precipitated adverse effects on the habitat for federally listed species including juvenile salmon, which necessitated prompt and comprehensive restoration initiatives. The project's objective is to surmount these challenges through the systematic creation of a strategically designed submerged bank tailored to the precise requirements of juvenile salmon. Concurrently, the project addresses the stabilization of the shoreline, mitigating the effects of concrete deposition, and the establishment of riparian habitats fostering biodiversity. The MDC Living Shoreline Project involves the development of a guidance document poised to assist public and private entities in securing funding opportunities, navigating regulatory complexities, and incentivizing living shoreline creation through time and cost savings. Despite the recognized ecological benefits of living shorelines, challenges arise from perceived regulatory complexities. MDC, having undertaken multiple living shorelines projects on public lands, faces concerns over onerous regulations, prompting calls for changes in relevant acts and codes. Findings and Significance For the Lister Park Project, the design team encountered challenges necessitating adaptive solutions, such as the potential impact on existing utilities, change in conditions, and constraints of budgetary allocations precipitating iterative adaptations throughout the design and construction process. Additionally, existing conditions from when the living shoreline was surveyed to when construction began drastically changed due to the continual shoreline erosion. The CISRP stands as a testament for ecological sustainability, envisioning harmonious coexistence between industrial progress and environmental conservation on Clover Island. The MDC Living Shoreline provides a valuable resource for stakeholders involved in shoreline development and conservation within the county. These three projects emphasize the significance of adaptive strategies, tailored designs, and regulatory considerations in effectively implementing nature-based solutions to combat the multifaceted challenges of coastal vulnerability.

Introduction: UV disinfection systems have gained popularity in wastewater disinfection applications as they can inactivate microorganisms while avoiding the injection of a chemical and any risk of a high disinfectant demand or disinfection byproducts. UV disinfection process design must account for UV Transmittance (UVT) which is a critical parameter that characterizes the ability of UV photons to pass through water and reach a microbiological target. Monitoring of UVT is achieved by online or benchtop readings, but online data can be skewed by sensor drifting or water quality impacts. Black & Veatch worked with two wastewater facilities where UVTs <55% were observed and employed machine learning to analyze correlations between measured UVT and various water quality parameters including carbonaceous biological oxygen demand (CBOD) and total organic carbon (TOC). UVT prediction allows for historical data to be verified whether the sensor was reading correctly or for optimization of UV system operation. Materials and methods: This study collected UVT and additional water quality data from each respective treatment facility secondary effluent at various sample collections intervals over the last 5 years. UVT was collected with online and benchtop instruments while other water quality data were collected via analytical methods accepted by 40 CFR criteria. Data cleaning and analysis was performed in R using various open-source packages and algorithms. Results and discussion: Review of Industry Guidance. Although there is no EPA requirement of a minimum design UVT for wastewater disinfection, guidelines have been followed in various states. The 2012 NWRI Guidelines set minimum allowable UVTs for wastewater applications based on the type of upstream treatment with a 55% minimum for applications with media filtration (REF2). In addition, 10 States standards recommends UV disinfection in wastewater be limited to effluent UVTs greater than 65% (REF3). However, UV disinfection has been implemented in states across the US with UVTs of 55% or lower, where various benchtop and full-scale data supports viable inactivation of microbes relevant to each projects operating permit. This study considered two facilities which are known to produce lower UVTs than conventional nitrifying treatment, Pure Oxygen Activated Sludge and Trickling Filter, from projects in Michigan and California, respectively. Machine Learning Techniques. Machine learning consists of algorithms and statistical models to analyze and draw inferences from patterns in data and can be utilized for various applications relevant to water treatment. This study reviews industry accepted techniques for employing machine learning for numerical predictions models based on multivariate regression and provides an in-depth review of the two algorithms employed in this work, Random Forests (RF) and Support Vector Regression (SVR). Case Study 1. A pure oxygen activated sludge treatment facility in Michigan undergoing a disinfection system evaluation was analyzed to consider UV disinfection to replace previous disinfection systems using sodium hypochlorite and ozone. Black & Veatch implemented an online UVT probe for a period of 12 months where the plant experienced various low UVT trends (<50%) that were impacted by ferric chloride addition, expected industrial source discharges, and sensor drifting. RF and SVR machine learning algorithms were employed to predict UVT based on CBOD, Solids and Temperature. Model results were successful in predicting UVT with an R mean squared value (RMSE) of 0.84 and 0.83, respectively (Figures 2 and 3). To mitigate the impact of excessive drifting of the online UVT probe, the model was further refined to predict periods where the UVT probe may have drifted out of calibration. Outcomes of these predictions could help promote instrument calibration or ensure historical data is accurate and whether or not it should be included in further analysis for process design of a UV disinfection system. Case Study 2. A regional wastewater facility in California undergoing a plant upgrade to employ UV disinfection for Title 22 non-potable reuse was also evaluated. As a part of process design and commissioning of the new Title 22 UV disinfection system, Black & Veatch analyzed 2+ years of water quality data where UVTs less than 50% were observed, which has been documented for trickling filter secondary effluent (REF4). Upstream trickling filter backwashing events were thought to have especially produced organic loads which impacted the UVT sensor and may have altered data collection after the system upset had already passed. TOC and TSS data were used to train the RF and SVR models to predict UVT across the monitoring period, with the SVR achieving a higher success in prediction with an RSME of 0.86 (Figures 5 and 6). Conclusions: 1.Applications where UVT is <55% can be managed contrary to some guidance and provide effective disinfection. 2.Machine Learning can verify analyzer trends to identify correct/incorrect historical data and ensure appropriate process design. 3.Machine Learning can be integrated with control approaches to accelerate response of UV disinfection systems based on anticipated water quality. 4.Multivariate water quality constituent regression could be paired with UV validation equations to predict performance and improve understanding of disinfection operations.

Aging septic tank systems used for the treatment of residential/commercial wastewater were determined to leak and negatively impact groundwater and nearshore water bodies over time by releasing nitrogen and phosphorus into the environment. To reduce these impacts, the State of Florida enacted Senate Bill 712, the 'Clean Waterways Act' (Chapter 2020-150, Laws of Florida). This new law requires a wide range of water quality protection provisions aimed at minimizing impacts from known nutrient pollution sources and includes changes to the Florida Department of Agriculture and Consumer Services Basin Management Action Plan program. The law covers both permitted point source contributors, including National Pollutant Discharge Elimination System permitted discharge points and non-point source contributors like agriculture and residential septic systems. In response to this bill and community outcry to clean the Indian River Lagoon, one of the most biodiverse estuaries in the Northern Hemisphere that is home to more than 4,300 species of plants and animals, Brevard County passed a referendum to fund the Save Our Indian River Lagoon Program (expected to exceed $160 million) which includes the elimination of septic tanks located in areas adjacent to the lagoon. This presentation focuses on the technology selection and design optimization to be used for the elimination of septic systems and conveyance of wastewater to existing wastewater treatment facilities in three areas adjacent to the Indian River Lagoon known as South Merritt Island, North Merritt Island, and Little Hollywood, and the selection of the best collection system technology. Brevard County first evaluated three technologies for the septic to sewer conversions including gravity, vacuum, and low pressure. Gravity sewers are defined as gravity mains with lift stations located to minimize deep excavations in Florida's high-water table. Vacuum technology consists of a vacuum main connected to valve pits that serve multiple residents and is driven by one or more vacuum pump stations. Low pressure consists of grinder pumps located on individual private property energized by the property owner's electrical connections that pump wastewater through low-pressure laterals to mains that convey the wastewater. Rather than selecting a 'preferred' technology across all three areas, County staff and Wade Trim completed an evaluation to select the optimal technology that will bring the highest value to the program. The three areas were divided into subareas and each subarea's specific characteristics were considered. A rating system was developed that considered geography, parcel density, operation and maintenance, capital cost, etc., and impacts on private property owners and weighted the importance of each. Brevard County recognized that private property owners are the most impacted stakeholder in septic-to-sewer conversion projects and made resolving private property challenges a priority in the technology evaluation and selection process. Although private property owners benefit from the removal of the septic system and a potential property value increase from the connection to a centralized sewer system, this benefit can quickly be dismissed if the system technology does not 'fit' with their property conditions. Deep parcels, or parcels with elevations lower than the right-of-way struggle in vacuum and gravity collection systems. Sparsely populated subareas often push the cost-per-connection figures to unaffordable levels for vacuum technology. Florida law mandates on-site grinder pumps to be operated and maintained by the governing body requiring private property owners to allow constant access of municipal staff onto their property. The balance of private property impacts to technology costs, and the impacts of area characteristics (geography, parcel density, etc.) led to a combination of collection system technologies being selected throughout the three areas to maximize the value of Brevard County's infrastructure investment and garner buy-in by the residential/commercial property owner. Learning Objectives: No. 1 — Attendees will understand wastewater collection technologies and how private property characteristics impact, and are impacted, by the wastewater collection technology that serves them. No. 2 — Attendees will understand how to optimize collection system technology selection based on property and area characteristics such as geography, population density, right-of-way conditions, etc.

Purpose: Struvite (MgNH4PO4*6H2O) and other precipitates have long posed persistent maintenance and operational challenges at wastewater treatment plants. These precipitates can be enhanced at plants that utilize biological phosphorus removal and can precipitate within anaerobic digesters and on final dewatering equipment which causes damage and decreases efficiency. Struvite can be sequestered as nutrient rich biosolids if properly controlled to remain in the cake. In a digested solids storage tank (DSST) that is in between anaerobic digestion and final dewatering, precipitation can be controlled by manipulating variables such as mixing, aeration of digestate to achieve a shorter solids retention time (SRT) version of post aerobic digestion (PAD) and by chemical addition. Optimizing this via batch and pilot testing can control nuisance struvite formation, increase phosphorus in the cake and achieve additional volatile solids reduction (VSR). This research will review findings from batch and pilot scale tests and discuss the nature of these precipitates. Objectives include determining the mechanism that provides optimal phosphorus removal, ammonia removal, and analyzing the precipitated solids of interest. The presentation will discuss results across batch, pilot, and full-scales and the lessons learned of each. Motivation and Background: The Atlantic Treatment Plant (ATP) in Virginia Beach, VA, operated by the Hampton Roads Sanitation District's (HRSD) is a high-rate facility with an A/O process configuration. In solids handling, a Cambi Thermal Hydrolysis Process (THP) is utilized prior to anaerobic digestion. ATP is actively engaged in efforts to control formation of scaling precipitates and nuisance struvite for optimal operational efficiency. Precipitate formation is determined predominantly by the solids solubility product (Ksp) and the saturation in solution and can be controlled by pH [1]. Manipulation of pH via CO2 stripping from aeration has successfully been shown to control solubility reactions [2, 3]. Increasing the saturation index via chemical addition can also control precipitation reactions and improve cake dryness with an SRT of a few hours [4]. Likewise, PAD has been shown to achieve ammonia removal and additional VSR at a 5-6 day SRT [5]. Based on these findings, a pilot scale set up (Figure 1) will run at an SRT of 3 days to provide benefits from PAD, but with a longer reaction time that may be more beneficial for phosphorus sequestration. Various mixing, aeration rates, and chemical addition will be manipulated to determine the optimal operation conditions on phosphorus sequestration in the class A biosolids. Pilot Design and Operation: The pilot set up at ATP consists of four tanks. Each tank has a volume of about 63 gallons. Simulating the DSST, the tanks are operated as daily batch fed continuously stirred tank reactors maintained by pump recirculation with a 3-day SRT. The tanks are aerated with fine bubble diffuser membranes which can be operated at constant or intermittent air flow rates, or via Dissolved Oxygen (DO) or pH set points. Preliminary operation has included mixing and aerating the four tanks at a constant airflow rate of 5 LPM, while recording online measurements of DO, pH (Figure 2), and temperature, which has been maintained between 22 and 38 degrees C. At this operation, about 50% OP removal and 10% COD degradation across the pilot has been measured with minimal NH3 removal. Future plans include operating at higher aeration rates, DO control setpoints, the potential establishment of partial nitrification/nitritation, and the addition of Ca(OH)2 or Mg(OH)2 at various dosages. Preliminary mixing operations conducted under suboxic conditions without the use of chemical addition results in a sustained OP removal by about half across the pilot. This suggests value in this continued effort. Batch Testing: The following test was conducted on a Phipps and Bird Jar Tester at a continuous mixing speed of 300 rpm. Five jars of digestate consisting of a control with no chemical addition, two jars dosed with a carbide lime slurry at Ca2+ + Mg2+/P ratios of 0.5:1 and 1:1, and two jars dosed with thioguard, at the same Ca2+ + Mg2+/P ratios. Chemical dose was injected as a spike at time zero of the test. Analytical measurement of OP-P and pH were determined daily via spectrophotometry (HACH TNTplus UHR mg-PO4-P/L and pH meter) (Figure 3). The pH of the digestate sample was about 7.4 and increased up to a maximum of 8.7 within 24 hours likely due to CO2 stripping from the mixing intensity. OP removal in the control condition was measured as 68%. The addition of chemical helped to increase OP removal as high as 95%. The digestate pH increasing towards alkaline within the first test day showed the greatest impact on OP removal rate. The higher Ca2+ + Mg2+/P molar ratio tested of 1:1 for both the chemicals had higher OP removal rates than those dosed at lower ratios of 0.5:1. Thioguard compared to the carbide lime slurry overall had a slightly more significant effect on OP removal. The pH decrease measured after 24 hours may be due to struvite's production of hydrogen ions in the formation reaction, however, future plans of repeat experiments and X-Ray Diffraction for precipitate analysis will further determine this.