Coracero, Ariana

Ariana Coracero is a Research Engineer at the Los Angeles County Sanitation Districts. She holds a B.S. in Chemical Engineering from the University of California, Berkeley, and an M.S. in Environmental Engineering from California State University, Fullerton. Her research focuses on innovative biological nitrogen removal processes, including Partial Denitrification-Anammox (PdNA) for water reuse applications.

Titles from this speaker

Description: Assessing Nitrous Oxide Emissions from a Demonstration-Scale Membrane Bioreactor...

Assessing Nitrous Oxide Emissions from a Demonstration-Scale Membrane Bioreactor Process

Abstract

Introduction The Metropolitan Water District of Southern California (Metropolitan) and the Los Angeles County Sanitation Districts (Sanitation Districts) are collaboratively exploring water recycling possibilities through the Pure Water Southern California (PWSC) project. The full-scale endeavor would involve the construction of an Advanced Water Treatment Facility (AWTF) with a capacity of 150 million gallons per day (MGD) at the Sanitation Districts' A.K. Warren Water Resource Facility (Warren Facility) in Carson, CA, previously known as the Joint Water Pollution Control Plant. The AWTF would produce treated water for indirect potable reuse, with potential for direct potable reuse in the future. The Warren Facility, with a capacity of 400 MGD, currently operates as a high purity oxygen activated sludge (HPOAS) facility and discharges its treated effluent (non-nitrified secondary effluent) into the ocean. Metropolitan has established the Grace F. Napolitano PWSC Innovation Center (Napolitano Center) to formulate the design and operating criteria for the 150 MGD AWTF, while ensuring compliance with regulations. Within the Napolitano Center, a demonstration plant with a capacity of 0.5 MGD has been developed. The Napolitano Center's process train comprises a membrane bioreactor (MBR), followed by reverse osmosis membranes, and ultraviolet light with an advanced oxidation process. Nitrogen management is a pivotal aspect of the PWSC project. Consequently, the Napolitano Center's MBR process was designed with flexibility to accommodate different nitrogen removal configurations. The full-scale implementation of biological processes aimed at transforming or removing nitrogen may result in an increase in greenhouse gas (GHG) emissions from the Warren Facility. A specific concern revolves around nitrous oxide (N2O), primarily generated during nitrification and denitrification processes in wastewater treatment plants. N2O is a potent GHG, with the Intergovernmental Panel on Climate Change (IPCC) estimating its 100-year warming potential at 296 times that of CO2 (Ehhalt et al., 2001). Estimating, measuring, and, when necessary, mitigating GHG emissions that contribute to climate change are integral components of the broader sustainability and public health mission in wastewater treatment. The Sanitation Districts have demonstrated a strong commitment to sustainability, achieving carbon-negative status in both 2021 and 2022. Greenhouse Gas Emissions from Wastewater Treatment In the context of GHG emissions, wastewater treatment facilities play a relatively minor role in the overall emissions landscape. To provide perspective, in 2022, these facilities accounted for just 0.8% of the total US GHG emissions, equivalent to 41.8 million metric tons of carbon dioxide equivalents (MMT CO2eq). More specifically, wastewater treatment contributed 2.8% of the total US methane (CH4) emissions and 5.5% of the total N2O emissions (EPA, 2022). Despite their relatively modest overall contribution, there is considerable variability among individual facilities and processes. For instance, a 2010 study conducted by Ahn et al., which investigated N2O emissions from ten wastewater treatment plants, uncovered a wide range of emissions, from 0.0001 to 0.071 lb N2O/lb N-day for a given plant. In a more recent study by the IPCC, encompassing the ten plants studied by Ahn et al., along with an additional 20 facilities, emissions were reported in the range of 0.0003 to 0.071 lb N2O/lb N-day (IPCC, 2020). For the purpose of GHG inventorying, the IPCC and the United States Environmental Protection Agency (U.S. EPA) have established default emission factors for wastewater treatment plants based on available data, with values set at 0.016 and 0.015 lb N2O/lb N-day, respectively (IPCC 2019, U.S. EPA 2021). These default values are derived from the available data and, as such, they can result in substantial overestimation or underestimation of actual GHG emissions at an individual facility. Therefore, the accurate measurement of process emissions becomes essential in ensuring precise GHG inventorying and the evaluation of new treatment processes. Project Objective and Emissions Measurement Description To assess the potential N2O emissions resulting from the implementation of a large MBR process at the Warren Facility, emissions were measured from the Napolitano Center MBR process. In May of 2023, the system operated as a secondary MBR process, with a primary effluent feed flow of approximately 0.5 MGD and an average Total Kjeldahl nitrogen (TKN) concentration of 70 mg N/L (Figure 1). In this configuration, primary effluent was introduced into an anoxic tank to supply carbon for denitrification. Subsequently, this liquid was directed to the aerobic tank, where ammonia was nitrified to nitrate. The nitrified water was then recycled back to the anoxic tank for denitrification. These processes were then followed by membrane filtration conducted in separate membrane tanks. A fraction of the solids retained by the membranes was continuously returned to the front of the aeration tank. For emissions measurement, the anoxic and aerobic tanks were temporarily enclosed using scaffolding and plastic sheeting, which was connected to metal ductwork and an exhaust fan (Figure 2, Figure 3). One of two membrane tanks was also covered with plastic sheeting and connected to metal ductwork and an exhaust fan. Each tank was maintained under negative pressure during the emissions measurement process. Full enclosure of the tanks captured the emissions from the tank surface area and, as such, the resulting emission estimate would not be subject to the spatial variabilities that tend to affect studies that utilize other measurement techniques, such as probes or floating emissions capture systems. In the first two weeks of May 2023, gas-phase N2O emissions were monitored from the fully enclosed aerobic, anoxic, and MBR tanks using a calibrated Innova photoacoustic sensor (PAS) (Innova Air Tech, Denmark) configured to record data at two-minute intervals. Standards were run daily, and the lab analyzed 24 grab samples for comparison with the PAS data. Emissions were assessed over approximately 24-hour periods for each tank, involving four days of measurements for the aerobic tank, two days for the anoxic tank, and one day for the MBR tank. In the case of the aerobic tank, both steady-state and induced process upset emissions were recorded. The determination of emissions used the concentration (in parts per million, ppm) as recorded by the photoacoustic sensor and the measured gas velocity within the ductwork. Emission factors were calculated as the fraction of influent nitrogen lost as N2O and as the mass N2O emitted per MGD. Project Results As anticipated, under steady-state conditions, the aerobic tank exhibited the highest N2O emissions factor of 0.0008 lb N2O/ lb N. The average aeration rate of atmospheric air was 300 standard cubic feet per minute (scfm). In contrast, the anoxic tank and the MBR tank recorded emissions of 0.0004 lb N2O/ lb N, resulting in an overall process emission factor of 0.0016 lb N2O/ lb N (0.16%) or 0.96 lb N2O/MG. It's worth noting that during steady-state operation, the anoxic tank utilized low-intensity aeration at a rate of 100 scfm. Replacing this mixing method with mechanical mixing could reduce emissions from this tank by minimizing stripping. The MBR tank maintained an average air flow rate of 180 scfm. In the broader context, it's important to highlight some limitations in this study. The data collection suffered from limited temporal resolution, as it was conducted over a two-week period during a single season. Nevertheless, despite these limitations, the overall process emission factor of 0.0016 N2O-hr/ lb N-hr was an order of magnitude lower than the emission factors established by the EPA and IPCC, which are 0.015 and 0.016 N2O/ lb N, respectively (IPCC 2019, U.S. EPA 2021). This is particularly noteworthy, given the use of aeration mixing in the anoxic tank, which might have increased emissions from that specific tank. Additionally, it's worth noting that the overall emission value falls within the lower end of the range reported in the IPCC study of thirty facilities, where emissions ranged from 0.0003 to 0.071 lb N2O per lb N processed per day (IPCC, 2020).

This paper was presented at the WEF Residuals and Biosolids Conference, June 18-21, 2024.

SpeakerSpierling, Ruth

Presentation time

08:30:00

09:00:00

Session time

08:30:00

11:45:00

SessionGreenhouse Gas Emissions at Wastewater Treatment Plants

Session number11

Session locationOklahoma City Convention Center, Oklahoma City, Oklahoma

Topicdemonstration scale, Greenhouse Gases, Membrane bioreactor

Author(s)

Spierling, Ruth

Author(s)R. Spierling1, B. Mansell1, R. Tsai1, A. Coracero1, J. Lehman2, K. Melville2, A. Ronn2

Author affiliation(s)Los Angeles County Sanitation Districts 1; Los Angeles County Sanitation Districts 1; Los Angeles County Sanitation Districts 1; Los Angeles County Sanitation Districts 1; Metropolitan Water District of Southern California 2; Metropolitan Water District of Southern California 2; Metropolitan Water District of Southern California 2;

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Jun 2024

DOI10.2175/193864718825159421

Volume / Issue

Content sourceResiduals and Biosolids Conference

Word count11

Description: Carbon Efficient Tertiary Membrane Bioreactor with Partial Denitrification Anammox...

Carbon Efficient Tertiary Membrane Bioreactor with Partial Denitrification Anammox for Potable Reuse

Abstract

INTRODUCTION The Metropolitan Water District of Southern California and Los Angeles County Sanitation Districts (Sanitation Districts) are jointly implementing the Pure Water Southern California (Pure Water) program, which may include building an up to 150 million gallon per day (MGD) advanced water purification facility (AWPF) at the Sanitation Districts' A.K. Warren Water Resource Facility (Warren Facility). The Warren Facility is a 400 MGD high-purity oxygen activated sludge (HPOAS) plant that currently discharges non-nitrified secondary effluent to the ocean ([b]Figure 1[/b]). MOTIVATION Nitrogen management is a key component of Pure Water to meet MWD's nitrogen concentration targets in the purified product water. For the initial phases of Pure Water, the product water will primarily be used for indirect potable reuse (IPR), so the planned membrane bioreactor (MBR) will be configured for nitrification-only operation. For direct potable reuse (DPR) applications, which have lower product water nitrogen targets than IPR applications, the membrane bioreactor (MBR) will need to be configured to support denitrification prior to advanced treatment ([b]Figure 2[/b]) (Sanitation Districts, 2024). To avoid stranded assets when transitioning from IPR to DPR applications, the MBR will include a flexible design (Flex MBR) that allows for multiple operating modes, including using either primary or secondary effluent as the feed water and allowing for future operation to include denitrification. A significant challenge associated with conversion to denitrification is the need for supplemental carbon addition to support conventional nitrification-denitrification (NdN) in the Flex MBR. It is projected that 18,000 gal/day of carbon (MicroC® 2000, EOS, Inc.) will be needed to achieve effluent goals of complete nitrification and ≤ 19 mg NO₃⁻ N/L. To reduce external carbon requirements, two of eight available HPOAS reactors will be operated to achieve NdN. The viability of this innovative process (High-Purity Oxygen Ludzack-Ettinger process or HPOLE) was demonstrated at full scale (Pitt [i]et al[/i]., 2023) and implementation is projected to reduce carbon demand to 14,000 gal/day. Recently, partial denitrification-anammox (PdNA) ([b]Figure 3[/b]) has been demonstrated to significantly reduce carbon demand compared to NdN (Fofana [i]et al[/i]., 2022; Klaus [i]et al[/i]., 2023). Therefore, leveraging knowledge gained from two years of PdNA research at the Warren Facility (Sun [i]et al[/i]., 2024; Farrokh Shad [i]et al[/i]., 2025), the ability to transition Flex MBR process operation to PdNA was included in the full-scale design concept. Modeling projections indicated up to a 60% reduction in demand, however integration of PdNA with an MBR process had not yet been demonstrated in the industry. RESEARCH OBJECTIVE The objective of this study was to conduct pilot testing to validate the Flex MBR design concept and projected reduction in carbon demand by implementing PdNA. TECHNICAL APPROACH AND KEY FINDINGS The pilot was designed to be a scaled version of the full-scale concept described by Fitzgerald [i]et al[/i]. (2024) and is shown in [b]Figures 4 – 8[/b]. A detailed pilot equipment list is shown in [b]Table 1[/b]. Pilot operation and nitrogen removal performance were continuously monitored with online instrumentation and samples were collected twice per week for laboratory analysis. Anammox activity was confirmed by collecting media from the anoxic zones and batch testing the media to look for indications of annamox activity as described in [b]Figure 9[/b]. In November 2024, the pilot was started-up by seeding with suspended biomass from a demonstration-scale MBR described by Liu [i]et al[/i]. (2025) and operated for one year. At start-up, the system was operated in NdN mode and then virgin media was added to facilitate anammox growth and transition to PdNA. Anammox activity was established after approximately four months of operation. Benchmarked PdNA operating conditions are summarized in [b]Table 2[/b]. Benchmarked performance ([b]Figures 10–12[/b]) demonstrated that effluent water quality goals were consistently achieved ([b]Figure 10[/b]), with average effluent concentrations of <0.1 mg N/L for NH₄⁺ and 11.2 mg N/L for NO₃⁻. Overall, influent total inorganic nitrogen (TIN) loading was reduced by 76% at an observed carbon demand of 2.1 g COD per g TIN removed ([b]Figure 11[/b]), which is approximately 65% lower than the 6 g COD/g TIN reported by Liu [i]et al[/i]. (2025) during NdN testing at the Warren Facility using the same carbon source. Process evaluation indicated that 92% of the TIN removed between ANX 2 and ANX 6 was attributable to partial denitrification–anammox (PdNA), with anoxic NH₄⁺ removal accounting for 21% of the total nitrogen removed across all process tanks, including AER 1–AER 6, highlighting the aeration energy savings potential of PdNA. Anammox activity was further confirmed through ex-situ anoxic NH₄⁺ removal rate testing ([b]Figure 12[/b]). Collectively, these results indicate substantial operational and sustainability benefits for Pure Water, including estimated reductions in supplemental carbon demand from 14,000 to 5,000 gallons per day, annual carbon costs from $20M to $7M, and truck deliveries from approximately 1,400 to 500 per year, corresponding to a 72% reduction in associated greenhouse gas emissions ([b]Figure 13[/b]).

This paper was presented at WEFTEC 2026 in New Orleans, Louisiana.

SpeakerCoracero, Ariana

Presentation time

10:30:00

11:00:00

Session time

10:30:00

12:00:00

SessionAdvances in PdNA through Lab and Pilot Scale Research

Session locationErnest N. Morial Convention Center

TopicFacility Operations and Maintenance, Municipal Wastewater Treatment Design, Nutrients, Research and Innovation

Author(s)

Coracero, Ariana, Farrokh Shad, Mojtaba, Hsia, Patricia, Mansell, Bruce, Sun, Yewei, Danker, Bryce, Pitt, Paul, Khunjar, Wendell, LATIMER, Ron, Delgado, Joseph, Fitzgerald, Colin, Constantine, Timothy

Author(s)A. Coracero1, M. Farrokh Shad1, P. Hsia1, B. Mansell1, Y. Sun2, B. Danker2, P. Pitt2, W. Khunjar2, R. LATIMER2, J. Delgado1, C. Fitzgerald3, T. Constantine3

Author affiliation(s)LA County Sanitation District, 1LA County Sanitation District, 1LA County Sanitation District, 1Hazen and Sawyer, 2Hazen and Sawyer, 2Hazen and Sawyer, 2Hazen and Sawyer, 2Hazen and Sawyer, 2LA County Sanitation District, 1Jacobs, 3Jacobs, 3

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Sep 2026

DOI10.2175/193864718825160384

Volume / Issue

Content sourceWEFTEC

Word count13

Leveraging Glycerol-Driven and Primary-Effluent-Driven PdNA within Advanced Wastewater Treatment Facility

Abstract

Introduction The Los Angeles County Sanitation Districts (LACSD) and Metropolitan Water District of Southern California (MWD) have collaborated to evaluate the development of the Pure Water Southern California (PWSC) Program. The PWSC Program would implement a full-scale advanced water treatment facility (AWTF) to produce up to 150 million gallons per day (mgd) for indirect and potentially direct potable reuse. One of the AWTF options considered would include a new biological nutrient removal (BNR) facility followed by RO/UV/AOP. The new BNR facility would be constructed at the existing A.K. Warren Water Resource Facility (Warren Facility), which is a 400 mgd capacity high purity oxygen activated sludge facility. The AWTF and BNR upgrades are intended to achieve a nitrate <19 mg/L, prior to the RO/UV/AOP facility. Partial nitrification/denitrification/anammox (PANDA/PdNA) was identified by the PWSC team as a promising approach to intensify BNR, by facilitating reduction of supplemental carbon needs and potentially increasing TIN removal capacity, without increasing tank volume. This work summarizes findings from an ongoing multi-year pilot effort focused on validating the PANDA/PdNA concept within a large-scale reuse program. Specifically, the objectives were to: i) demonstrate the ability to achieve nutrient targets reliably by intensifying a tertiary MBBR and IFAS configuration with PANDA/PdNA; ii) validate carbon savings that can be achieved by implementing PANDA/PdNA; and iii) investigate the feasibility of incorporating primary effluent driven partial denitrification to further reduce projected operating costs associated with the PWSC Program. Methods Tertiary MBBR: A tertiary MBBR was configured as a step-feed BNR process, consisting of alternated aerobic and anoxic cells, with zone configuration and influent feed split (Figure 1). Both primary effluent (PE) and a glycerol-based supplemental carbon source (MicroC 2000) were used for supporting denitrification in anoxic zones. This flexible configuration allowed for performing both conventional BNR and PANDA/PdNA. Tertiary IFAS: The MBBR system was modified to include clarifiers to retain flocculant biomass. Additionally, a Solitax probe (Hach) was added in the last cell of the system to monitor the mixed liquor suspended solid concentration in the system. The first aerobic zone of Tertiary MBBR was converted to anoxic because the RAS feed was able to recycle sufficient NOx load into the that zone, negating the need for nitrification in that zone. Monitoring: Composite samples (24-hr) were used to monitor influent and effluent solids, organics and nutrients. Profile samples were grabbed from different cells across the system periodically to analyze for nitrogen species and organics (Hach TNT). Operational Modes: Three different operational modes were tested: 1) Hybrid conventional BNR mode in MBBR, during which both PE and glycerol were supplied to the system to perform full denitrification; 2) PANDA/PdNA mode in MBBR, during which both PE and glycerol were supplied to the system to perform partial denitrification and anoxic ammonia removal via anammox; and 3) PANDA/PdNA mode in IFAS (on-going), during which suspended biomass is retained in the system by using a clarifier. Results and Discussion Hybrid BNR Mode: The system operated in this mode from July 2022 to April 2023. Findings were reported in Sun et al., 2023. Briefly, both the ammonia target of 1 mg/L and the NOx target of 16 mg/L were achieved during hybrid BNR mode operation, confirming that a conventional BNR option could reliably achieve nutrient targets. MBBR PANDA Mode: The MBBR system was transitioned to PANDA/PdNA mode in May 2023 and operated until October 2023. Key findings are as follows:

*The system was able to reliably achieve the effluent ammonia and NOx targets of 1 mg/L and 16 mg/L, respectively (Figure 2). It was also possible to further decrease effluent TIN as low as ~ 9 mg/L, without increasing total system volume (Figure 2).

*Carbon usage was tracked during different phases of operation (Table 1). During the hybrid BNR and PANDA phases, approximately 7 to 9% of the total flow was comprised of PE. The COD addition/N removal ratio reduced from ~3.9 lb sCOD/lb NOx during hybrid BNR phase to ~1.2 lb sCOD/lb NOx during the PANDA/PdNA phase. This reduction was due to enhanced anammox activity and represents greater than 70% savings in supplemental carbon needs.

*Investigation into PdNA activity within the system revealed that partial denitrification was likely driven by both PE (first anoxic) and glycerol (second anoxic), with PE driven PdNA accounting for 3 to 7 mgN/L anoxic ammonia removal (Figure 3) and glycerol driven PdNA accounting for up to 9.4 mgN/L anoxic ammonia removal (Table 1). Batch tests confirmed that PE and internally stored carbon could be used to successfully drive partial denitrification if sufficient control of carbon, nitrate and ammonia is provided (Figure 4). PANDA/PdNA in IFAS Mode: In November 2023, the system was transitioned to operate in IFAS PANDA/PdNA mode. The IFAS phase of operation will be completed in mid-2024, the results of which and lessons learned will be presented during the conference.

The Los Angeles County Sanitation Districts are exploring nitrogen removal options to address potential reuse and regulatory drivers. A tertiary step-feed moving bed biofilm reactor (tMBBR) configuration was evaluated as an approach. The tMBBR configuration was successfully pilot tested and demonstrated the ability to meet nitrogen removal targets. It was also found that by leveraging glycerol-driven and PE-driven PdNA, aeration energy and carbon savings can be ~28% and up to 70%, respectively.

SpeakerSun, Yewei

Presentation time

11:00:00

11:30:00

Session time

10:30:00

12:00:00

SessionAnoxic Reactor Design for Low Energy BNR

Session number520

Session locationRoom 335

TopicEnergy Production, Conservation, and Management, Facility Operations and Maintenance, Intermediate Level, Municipal Wastewater Treatment Design, Nutrients

Author(s)

Sun, Yewei, Mansell, Bruce, Coracero, Ariana, Farrokh Shad, Mojtaba, Tsai, Raymond, Pitt, Paul, Khunjar, Wendell, Latimer, Ron, Danker, Bryce, Sun, Yian

Author(s)Y. Sun1, B.O. Mansell2, A.K. Coracero3, M. Farrokh Shad2, R. Tsai4, P.A. Pitt5, W. Khunjar6, R.J. Latimer7, B. Danker8, Y. Sun5, M. Farrokh Shad2

Author affiliation(s)1Hazen and Sawyer, VA, 2LA County Sanitation District, CA, 3Los Angeles County Sanitation Districts, CA, 4LACSD, CA, 5Hazen and Sawyer, CA, 6Hazen & Sawyer PC, VA, 7Hazen and Sawyer, GA, 8Hazen, CA

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2024

DOI10.2175/193864718825159618

Volume / Issue

Content sourceWEFTEC

Word count11

Partial Denitrification-Anammox Treatment of Reverse Osmosis Concentrate

Abstract

INTRODUCTION AND OBJECTIVES The A.K. Warren Water Resource Facility (Warren Facility) is owned and operated by the Los Angeles County Sanitation Districts (LACSD). The facility has an average daily dry-weather flow capacity of 400 million gallons per day (mgd) and employs a high-purity oxygen activated sludge (HPOAS) process (Figure 1). Non-nitrified secondary effluent (SE) is chlorinated and discharged to the ocean. LACSD has been investigating nitrogen management options that may be implemented at the Warren Facility to address two drivers: (1) effluent reuse for the Pure Water Southern California (PWSC) program which will produce 150 mgd of purified water and (2) total inorganic nitrogen (TIN) load reduction for ocean discharge. PWSC processes that will be implemented are shown in Figure 2. Implementing nitrification-denitrification (NdN) within PWSC is projected to result in a net reduction in the TIN load discharged to the ocean (~ 49%) relative to continued operation with HPOAS. However, LACSD is proactively investigating alternative approaches to enhance load reduction beyond that achieved by implementing PWSC. Outside of conventional strategies to increase nitrogen removal, the elevated mass of nitrate in the reverse osmosis concentrate (ROC) provides a unique opportunity to reduce ocean nitrogen discharge. While uncommon, approaches considered to denitrify ROC typically incorporate biofilms and high levels of carbon dosing. This paper presents a novel approach developed by LACSD that leverages the nitrate-rich ROC and ammonia-rich HPOAS secondary effluent (SE) (Figure 2, Streams 5 and 7) utilizing a carbon efficient partial denitrification-anammox (PdNA) process. In this approach, ROC and SE would be blended at a target NH4-N/NOx-N ratio in a reactor and supplemental carbon added to drive PdNA (Figure 3). The objectives of this study were to (1) conduct proof-of-concept testing of the ROC/SE Blend PdNA process and (2) develop design criteria that can be used for planning level full-scale process sizing and cost estimation. PILOT SYSTEM AND RESULTS The ROC/SE Blend PdNA pilot system included a batch blend tank, feed pump, single-stage PdNA moving-bed biofilm reactor (MBBR), and supplemental carbon (MicroC 2000) dosing system (Figure 4, Table 1). Supplemental phosphorous (H3PO4) was added directly to the batch blend tank. Seeded MBBR media was taken from an existing mainstream PdNA pilot system that has been in operation at the Warren Facility for over a year (Sun et al., 2024). ROC was produced at the PWSC Grace F. Napolitano Innovation Center (NIC) 0.5 mgd reverse osmosis facility. However, ROC was not always available during testing due to facility shutdowns. Therefore, for part of the study, reactor feed was prepared by spiking SE with NaNO3 or by spiking NaNO3 and NaCl to target the desired NH4-INTRODUCTION AND OBJECTIVES
The A.K. Warren Water Resource Facility (Warren Facility) is owned and operated by the Los Angeles County Sanitation Districts (LACSD). The facility has an average daily dry-weather flow capacity of 400 million gallons per day (mgd) and employs a high-purity oxygen activated sludge (HPOAS) process (Figure 1). Non-nitrified secondary effluent (SE) is chlorinated and discharged to the ocean. LACSD has been investigating nitrogen management options that may be implemented at the Warren Facility to address two drivers: (1) effluent reuse for the Pure Water Southern California (PWSC) program which will produce 150 mgd of purified water and (2) total inorganic nitrogen (TIN) load reduction for ocean discharge. PWSC processes that will be implemented are shown in Figure 2.

Implementing nitrification-denitrification (NdN) within PWSC is projected to result in a net reduction in the TIN load discharged to the ocean (~ 49%) relative to continued operation with HPOAS. However, LACSD is proactively investigating alternative approaches to enhance load reduction beyond that achieved by implementing PWSC. Outside of conventional strategies to increase nitrogen removal, the elevated mass of nitrate in the reverse osmosis concentrate (ROC) provides a unique opportunity to reduce ocean nitrogen discharge. While uncommon, approaches considered to denitrify ROC typically incorporate biofilms and high levels of carbon dosing. This paper presents a novel approach developed by LACSD that leverages the nitrate-rich ROC and ammonia-rich HPOAS secondary effluent (SE) (Figure 2, Streams 5 and 7) utilizing a carbon efficient partial denitrification-anammox (PdNA) process. In this approach, ROC and SE would be blended at a target NH4-N/NOx-N ratio in a reactor and supplemental carbon added to drive PdNA (Figure 3).

The objectives of this study were to (1) conduct proof-of-concept testing of the ROC/SE Blend PdNA process and (2) develop design criteria that can be used for planning level full-scale process sizing and cost estimation.

PILOT SYSTEM AND RESULTS
The ROC/SE Blend PdNA pilot system included a batch blend tank, feed pump, single-stage PdNA moving-bed biofilm reactor (MBBR), and supplemental carbon (MicroC 2000) dosing system (Figure 4, Table 1). Supplemental phosphorous (H3PO4) was added directly to the batch blend tank. Seeded MBBR media was taken from an existing mainstream PdNA pilot system that has been in operation at the Warren Facility for over a year (Sun et al., 2024). ROC was produced at the PWSC Grace F. Napolitano Innovation Center (NIC) 0.5 mgd reverse osmosis facility. However, ROC was not always available during testing due to facility shutdowns. Therefore, for part of the study, reactor feed was prepared by spiking SE with NaNO3 or by spiking NaNO3 and NaCl to target the desired NH4-N/NOx-N ratio and TDS concentration at similar concentrations to the ROC produced at NIC. Analysis of TIN removal performance data normalized to account for carbon dose did not indicate a statistically significant difference in performance based on TDS concentration.

The pilot system was started up in April 2024 and operated for approximately 5 months. Average conditions over a four-month period of stable operation (May to September 2024) are shown in Table 2. Influent TIN and NH4-N/NOx-N ratio, nitrogen loading rates, and supplemental carbon dose are shown in Figures 5, 6, and 7, respectively. Average influent TIN, NH4-N/NOx-N ratio, and supplemental carbon dose were 74 ± 4 mg N/L, 0.45 ± 0.10 g/g, and 1.9 ± 0.45 g COD added/g TIN influent, respectively. Average influent TIN, NOx, and NH4 loading were 0.55 ± 0.05, 0.38 ± 0.05, and 0.17 ± 0.03 g N/m2-day, respectively.

Performance results are summarized in Table 3. Average TIN, TIN removed via PdNA, NOx, and NH4 removals were 57 ± 16%, 63 ± 14%, 57 ± 15%, and 61 ± 29%, respectively. Corresponding average surface area removal rates were 0.31 ± 0.09 (TIN), 0.22 ± 0.06 (NOx), and 0.10 ± 0.04 (NH4) g N/m2-day. Supplemental carbon dose varied between 0.9 — 2.7 g COD added/g TIN influent and had a significant impact on performance (Figures 8 — 10). As carbon dosing increased or decreased over this range, a corresponding increase or decrease in TIN, NOx, and NH4 removal was observed. TIN, NOx, and NH4 removals ranged between 28 to 84%, 27 to 90%, and 17 to 99%, respectively.

PdN efficiency averaged 55 ± 15% and supplemental carbon demand averaged 3.5 ±0.59 g COD added/g TIN removed. Both parameters generally improved from start-up to the end of the study (Figure 11) and over the last month of stable operation averaged 65 ± 9% and 3.1 ± 0.45 g COD added/g TIN removed. The average PdN efficiency observed in this study is within the range reported in the literature for single-stage PdNA MBBR reactors with glycerol addition: 43 ± 29% g COD/g N (Macmanus et al., 2022) and 88 ± 13% g COD/g N (Klaus et al., 2023). However, the average carbon demand observed was ~ 1 g COD/g N higher, but notably lower than the 5 — 6 g COD/g N removed for glycerol driven FdN observed by Liu et al., 2025.

Planning level cost estimates (AACE Class 5) for full-scale implementation were developed to benchmark against previously evaluated concepts (LACSD 2024). Preliminary estimates suggest that ROC PdNA may be a financially viable approach. The presentation will provide a detailed overview of the pilot system.

This paper was presented at WEFTEC 2025, held September 27-October 1, 2025 in Chicago, Illinois.

Presentation time

10:30:00

10:45:00

Session time

10:30:00

12:00:00

SessionInnovations in Membrane Treatment for Reuse

Session locationMcCormick Place, Chicago, Illinois, USA

TopicAdvanced Water Treatment and Reuse

Author(s)

Mansell, Bruce, Coracero, Ariana, Deco, Rachel, Hsia, Patricia, Le, Tri, Fitzgerald, Colin, Constantine, Timothy, Sun, Yewei, Khunjar, Wendell, Danker, Bryce, Pitt, Paul

Author(s)B. Mansell1, A. Coracero1, R. Deco1, P. Hsia1, T. Le3, C. Fitzgerald3, T. Constantine3, Y. Sun4, W. Khunjar4, B. Danker4, P. Pitt4

Author affiliation(s)LA County Sanitation District1, City of San Mateo2, Jacobs3

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2025

DOI10.2175/193864718825159935

Volume / Issue

Content sourceWEFTEC

Word count8

Description: Primary Effluent- and Glycerol-Driven PdNA for Large-Scale Potable Reuse: Maximizing...

Primary Effluent- and Glycerol-Driven PdNA for Large-Scale Potable Reuse: Maximizing Benefits from MBBR to IFAS Transition

Abstract

Introduction
The Los Angeles County Sanitation Districts (LACSD) and Metropolitan Water District of Southern California (MWD) have partnered to implement a full-scale advanced water treatment facility (AWTF) for reuse. One of the AWTF options considered was a new biological nutrient removal (BNR) facility followed by RO/UV/AOP. The BNR upgrades are intended to achieve a nitrate goal of <19 mg N/L, prior to RO/UV/AOP.

A promising approach identified to intensify BNR performance is Partial Nitrification/Denitrification/Anammox (PdNA). PdNA can reduce supplemental carbon requirements and enhance Total Inorganic Nitrogen (TIN) removal capacity without increasing tank volume. The ongoing multi-year pilot study summarized here explores PdNA application for a large-scale reuse program.

The study objectives are: i) to demonstrate reliable nutrient target achievement by intensifying a tertiary Moving Bed Biofilm Reactor (MBBR) and Integrated Fixed-film Activated Sludge (IFAS) configuration with PdNA, ii) to validate the carbon and aeration energy savings achieved through primary effluent-driven and glycerol-driven PdNA, and iii) to assess the benefits and considerations of incorporating suspended-phase biomass and provide insights for future full-scale PdNA design in membrane bioreactor systems.

Methods
Tertiary MBBR: The tertiary MBBR was a step-feed BNR process with alternating aerobic and anoxic zones (Figure 1). Both primary effluent (PE) and glycerol (MicroC 2000) were used to support denitrification in the anoxic zones, allowing for conventional BNR and PdNA processes.

Tertiary IFAS: The MBBR system was modified to include flocculant biomass retaining clarifiers (Figure 2 and 3). The first aerobic zone was converted to an anoxic zone, with RAS recycling NOx for pre-anoxic partial denitrification. PE was the primary carbon source for Anx1, but glycerol was used when necessary. Operational periods with and without PE are labeled in Figures 4, 5, and 6.

Monitoring and System Control: 24-hour composite samples were used to monitor influent and effluent solids, organics, and nutrients, while periodic grab samples from different system cells were analyzed for nitrogen species and organics. Nitrification and aeration were monitored with NOx and DO probes in each aerobic cell. In the IFAS system, a Solitax probe tracked MLSS concentration. Control loops were used for glycerol feeding based on NOx and DO readings. The NOx/NH3 ratio was controlled by adjusting SE step feed flowrates based on NH3 and NOx probe readings.

Operational Phases:
- Hybrid NdN Mode in MBBR: Both PE and glycerol were supplied to the system for full denitrification.
- Hybrid PdNA Mode in MBBR: Both PE and glycerol were provided to perform PdN and anoxic ammonia removal via anammox.
- PdNA Mode in IFAS: Suspended biomass was retained using a clarifier, and only glycerol (no PE) was supplied to perform PdNA.
- Hybrid PdNA Mode in IFAS: Suspended biomass was retained, and both PE and glycerol were supplied to the system.

Results and Discussion
System Performance: During steady-state operation (August to October 2023), the system consistently met the effluent 1 mg/L NHx limit and the 16 mg/L TIN limit (Figure 4). The transition from MBBR to IFAS mode occurred early November 2023 to April 2024, in which suspended solids began accumulating in the system (Figure 5). Despite operational challenges, the system maintained stable effluent NH3 levels throughout this period. However, during transition, effluent TIN levels temporarily rose above 20 mg/L due to fluctuating MLSS concentrations (Figure 4). Once MLSS stabilized at 2,000 mg/L (Figure 5), effluent TIN gradually decreased to less than 16 mg/L, with effluent NH3 consistently remaining below 1 mg/L (Figure 4).

PdNA Efficiency and Anammox Activity: Anoxic ammonia removal (AAR, g/m2/d), commonly used as a proxy for anammox activity during the PdNA process, is presented in Figure 6. In Anx2, ammonia removal was solely driven by glycerol-fed PdNA, while in Anx1, it was either driven by PE or by glycerol. The AAR driven by PE increased from approximately 0.21 g/m2/d during the steady-state hybrid MBBR operation (August to October 2023) to 0.37 g/m2/d during the steady-state hybrid IFAS operation (June to July 2024). Glycerol-driven AAR rates were comparable between MBBR and IFAS steady-state operations. However, Anx2 required lower bulk NHx and NO2 concentrations to maintain similar removal rates during IFAS mode (Figure 7), due to an increased anammox activity rate, as shown in ex-situ activity tests (Table 1). The bulk NHx concentration of <0.5 mgN/L in Anx2 also eliminated the need for Aer2 in the IFAS system.

Activity Migration into Suspended Phase: IFAS differs from MBBR in the incorporation of suspended biomass, which may facilitate the denitrifier migration from the biofilm phase to the suspended phase, freeing media space for slow-growing anammox bacteria. During the IFAS transition period, elevated effluent TIN levels were observed due to unstable MLSS concentrations (Figure 4). The reduction in ARR alongside MLSS reduction from December 2023 to March 2024 (Figure 6) suggested denitrifiers migrated to the suspended phase. The rise in effluent ammonia concentration (Figure 4) and 7/29/2024 biomass loss (Figure 5) suggests nitrifiers may have also migrated to the suspended phase. This was confirmed by ex-situ batch nitrification act

This paper was presented at WEFTEC 2025, held September 27-October 1, 2025 in Chicago, Illinois.

Presentation time

09:00:00

09:30:00

Session time

08:30:00

10:00:00

SessionPdNA: Insights into Pilot and Full-scale Implementations

Session locationMcCormick Place, Chicago, Illinois, USA

TopicLiquid Stream Treatment Technology - Secondary & Tertiary Treatment

Author(s)

Farrokh Shad, Mojtaba, Sun, Yewei, Mansell, Bruce, Hsia, Patricia, Danker, Bryce, Coracero, Ariana, Khunjar, Wendell, Sun, Yian, Pitt, Paul, Latimer, Ron

Author(s)M. Farrokh Shad1, Y. Sun2, B. Mansell1, P. Hsia1, B. Danker2, A. Coracero1, W. Khunjar2, Y. Sun2, P. Pitt2, R. Latimer2

Author affiliation(s)LA County Sanitation District1, Hazen and Sawyer2

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2025

DOI10.2175/193864718825159969

Volume / Issue

Content sourceWEFTEC

Word count17