Pace, Gregory

Greg is a licensed Professional Engineer in the Commonwealth of Virginia, with over 10 years experience with advanced BNR/ENR wastewater processes. Greg works on a wide range of wastewater projects, including operational support, wastewater treatment optimization, nutrient removal studies, energy efficiency evaluations, and wastewater resource recovery facility design.

Titles from this speaker

Description: Full-scale Mainstream Deammonification via Partial...

Full-scale Mainstream Deammonification via Partial Nitrification-Denitrification-Anammox

Abstract

Introduction Partial nitrification/denitrification coupled with anaerobic ammonia oxidation (PdNA, PANDA) process has the potential to result in capacity, chemical and energy savings at water resource recovery facilities (WRRFs). In this process, ammonia oxidation is controlled to achieve a specific NO3/NH3 ratio. Partial denitrification driven by supplemental carbon addition (e.g., methanol) is then used to stably generate NO2--N accumulation. Anaerobic ammonia oxidizers can then remove both nitrite and ammonia to achieve effluent NH3 and TN limits. Successful PdNA/PANDA has been documented in pilot and full-scale. This work documents advancement and implementation of PANDA at the Fairfax County Noman M. Cole Pollution Control Plant (NCPCP) to achieve TN limits less than 3 mg/L. Specifically, the work will discuss full-scale results demonstrating effective anoxic ammonia removal via the PANDA mode of operation Materials and methods Full-scale reactor setup. The full-scale MBBR system was commissioned in 2013 and is comprised of six trains, five of which are currently equipped with fixed-film media and ancillary equipment. Each train includes two anoxic denitrification cells (approximately 2.4 MG in total volume) in series followed by a single re-aeration cell (approximately 0.6 MG in volume). The anoxic denitrification cells are equipped with mixers and flat screens for media retention. The re-aeration cells are equipped with medium bubble aeration diffusers and cylindrical screens. All cells are equipped with K1 media, which provide the surface area necessary for attached growth of nitrifying and denitrifying bacteria. Methanol dosing was controlled via feed-back nitrate paced addition. Ammonia and nitrate for the tertiary MBBR PANDA demonstration was provided via process control adjustments to the secondary process, including changes to step-feed configuration, DO and airflow setpoints, load paced equalization and methanol feeding. Results and discussion Full-scale results — Full-scale demonstration testing of PANDA mode commenced in Q3 of 2022 and is ongoing. Results indicated:

*Anoxic ammonia removal between 1 and 2.0 mg/L has been observed since startup and the full-scale facility has been able to maintain weekly effluent ammonia concentration below 0.5 mg/L, monthly effluent TN concentrations of between 2 and 4 mg/L and an average annual effluent TN of 2.9 during the past 12 months of operation (2023).

*Unit methanol use at the facility has decreased by approximately 20% and unit energy demand at the facility has decreased by approximately 5% relative to 2021-2022 plant operations since operating in PANDA mode.

*Full-scale demonstration has confirmed that partial denitrification/anammox is sensitive to the NO3/NH3 ratio in the MBBR influent. Optimal performance (greater than 90% anoxic ammonia removal, COD to Nitrate removed less than 4.0 and influent ammonia above 1.1 mg/L) has been observed at NO3/NH3 ratio of 3.1 to 5.1.

*The FFX NCPCP has historically observed intermittent spikes in secondary effluent ammonia concentration. Potential causes of these spikes may be attributed to load peaking and/or suppressive compounds in the wastewater. A recent ammonia spike resulted in secondary effluent ammonia of 3.6 mgNH3-N/L to the MBBR. The PANDA mode of operation reduced 2.7 mgNH3-N/L to achieve a MBBR effluent ammonia of 0.9 mgNH3-N/L and MBBR effluent TIN of 2.5 mgTIN/L at a NO3/NH3 ratio of 1.5.

*NCPCP operators have easily shifted from PANDA to conventional mode of treatment when necessary to manage outside factors that might interfere with normal operations. Cumulatively, this work is the first to effectively demonstrate full-scale deammonification via PANDA while meeting stringent nutrient limits. Ongoing efforts are focused on optimizing the NO3/NH3 ratio, stabilize phosphorus removal while continuing to reduce energy and methanol associated with nutrient removal at the NCPCP.

This paper was presented at the WEFTEC 2024 conference in New Orleans, LA October 5-9.

SpeakerPace, Gregory

Presentation time

09:30:00

10:00:00

Session time

08:30:00

10:00:00

SessionProgression of PdNA: Development to Full-Scale

Session number504

Session locationRoom 240

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

Author(s)

Pace, Gregory, Khunjar, Wendell, Sun, Yewei, Wang, Jiefu, Wang, Zhiwu, Chitrakar, Sajana, Rasel, Munshi Md

Author(s)G.J. Pace1, W. Khunjar2, Y. Sun3, J. Wang4, Z. Wang4, S. Chitrakar5, M. Rasel5

Author affiliation(s)1Hazen and Sawyer, 2Hazen & Sawyer, 3Hazen and Sawyer, 4Virginia Tech, 5Noman M Cole Jr Pollution Control Center, 5City of Springfield

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2024

DOI10.2175/193864718825159719

Volume / Issue

Content sourceWEFTEC

Word count7

Full-scale Mainstream Deammonification via Partial Nitrification-Denitrification-Anammox

Abstract

Partial nitrification/denitrification coupled with anaerobic ammonia oxidation (PdNA, PANDA) process has the potential to result in capacity, chemical and energy savings at water resource recovery facilities (WRRFs). In this process, ammonia oxidation is controlled to achieve a specific NO3/NH3 ratio. Partial denitrification driven by supplemental carbon addition (e.g., methanol) is then used to stably generate NO2 - -N accumulation. Anaerobic ammonia oxidizers can then remove both nitrite and ammonia to achieve effluent NH3 and TN limits. Successful PdNA/PANDA has been documented in pilot and full-scale. This work documents advancement and implementation of PANDA at the Fairfax County Noman M. Cole Pollution Control Plant (NCPCP) to achieve TN limits less than 3 mg/L. Specifically, the work will discuss: 1) Pilot scale results that verified the feasibility of performing nitrogen removal in a tertiary MBBR configured for PANDA, 2) Full-scale results demonstrating effective anoxic ammonia removal via the PANDA mode of operation

This work documents advancement and implementation of Partial Nitrification Denitrification Anammox (PANDA) at the Fairfax County Noman M. Cole Pollution Control Plant (NCPCP) to achieve TN limits less than 3 mg/L. Specifically, the work will discuss: 1) Pilot scale results that verified the feasibility of performing nitrogen removal in a tertiary MBBR configured for PANDA, 2) Full-scale results demonstrating effective anoxic ammonia removal via the PANDA mode of operation

SpeakerPace, Gregory

Presentation time

14:00:00

14:30:00

Session time

13:30:00

15:00:00

SessionLessons Learned from Early PdNA Implementation

Session locationRoom S504a - Level 5

TopicIntermediate Level, Nutrients, Research and Innovation

Author(s)

Pace, Gregory

Author(s)G.J. Pace 1; W. Khunjar 2 ; Y. Sun 3; J. J. WANG 4; Z. Wang 4; S. Chitrakar 5; G.J. Pace 1;

Author affiliation(s)4; 5; 1;

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2023

DOI10.2175/193864718825159088

Volume / Issue

Content sourceWEFTEC

Word count7

Description: Long-Term Performance of Pilot-Scale Aerobic Granular Sludge at the Noman M. Cole...

Long-Term Performance of Pilot-Scale Aerobic Granular Sludge at the Noman M. Cole Pollution Control Plant

Abstract

The Fairfax County Noman M. Cole Pollution Control Plant (NCPCP) is a 67 million gallon per day (MGD) facility that employs primary, secondary and tertiary treatment to meet effluent total nitrogen (TN) and total phosphorus (TP) limits of 3.0 mg N/L and 0.18 mg P/L, respectively. Currently, nitrogen removal is performed via step-feed biological nutrient removal (BNR) and a tertiary denitrifying moving bed bioreactor (MBBR) supplemented with methanol. Phosphorus control is achieved via ferric chloride addition, tertiary clarification and filtration. In consideration for expansion of the facility from 67 to 80 MGD, the AquaNereda® Aerobic Granular Sludge (AGS) process was identified as a promising treatment alternative. The AquaNereda process consolidates infrastructure by performing secondary BNR and solids separation in the same tankage. The process has been implemented at full-scale in Europe, South America and Africa; however, there are only two full-scale facilities in operation in the USA. A 9-month piloting effort was therefore conducted to understand performance of the AquaNereda® process at NCPCP.

This presentation will discuss the findings from a 9-month AquaNereda® Aerobic Granular Sludge piloting effort conducted to understand performance of the AquaNereda® process at the Fairfax County Noman M. Cole Pollution Control Plant (NCPCP) in Fairfax County, VA.

SpeakerPace, Gregory

Presentation time

11:15:00

11:30:00

Session time

11:00:00

12:00:00

SessionKnowledge Development Forum: The Plot Thickens Part I - Current State of Granular Sludge

Session number203

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

Author(s)

Gregory Pace

Author(s)G.J. Pace1; W. Khunjar1; K. Sveum2; A. Pathak1; E. Manning1; P. Le Bel1; J. Donati1; M. Ali3; J. Wilkinson4; T. Reid5; D. Gravagno5; E. Price5;

Author affiliation(s)Hazen and Sawyer, Fairfax, VA1Loudoun Water2Fairfax County3Timmons Group4Aqua-Aerobic Systems Inc5

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2021

DOI10.2175/193864718825158040

Volume / Issue

Content sourceWEFTEC

Word count16

Description: Mechanistic Understanding of the Kinetic Difference Between the Methanol and...

Mechanistic Understanding of the Kinetic Difference Between the Methanol and Glycerol-driven Partial Denitrification Anammox in Low Nitrogen Polishing Moving Bed Biofilm Reactors

Abstract

Introduction Partial denitrification coupled with anaerobic ammonia oxidation (PdNA) process has been identified as a promising approach to intensify biological nutrient removal systems to increase total nitrogen removal capacity while reducing chemical and energy demand (Campolong, 2019; Le et al., 2019; Zhang et al., 2020). Understanding how operational factors impact PdNA is necessary to extract optimal performance at water resource recovery facilities (WRRFs) regardless of the configuration employed. For example, work performed previously (Campolong, 2019; Le et al., 2019) has shown that PdNA is impacted by multiple factors including the type of carbon utilized e.g., methanol, glycerol, acetate, etc.). This prior work hypothesized that partial denitrification results due to two main mechanisms, i) rate differential between heterotrophic nitrate and nitrite reduction due to different substrate availability and carbon sources, ii) nitrite sink due to anammox activity (Al-Omari et al., 2021). This current study provides insights into understanding how these different mechanisms may dictate partial denitrification in a low nitrogen polishing environment. Data from long term operation (417 days) of two pilot-scale MBBR treatment trains treating secondary effluent from the Noman M. Cole Jr. Pollution Control Plant (NCPCP) was used to develop a mechanistic understanding of methanol versus glycerol driven PdNA performance with a view to informing how to scale PdNA into other WRRFs. This work also provides a framework for informing design practices as related to stimulating stable PdNA. Materials and methods Reactor setup and operation: Two parallel MBBR treatment trains dosed with methanol and glycerol, respectively, were operated on site at NCPCP. In each treatment train, two 14 L working volume anoxic MBBRs filled with K1 media at a volumetric fraction of 45% were connected in series, followed by an 8 L working volume reaeration reactor filled with K1 media at a volumetric fraction of 32% (configuration simulated full-scale MBBR trains at NCPCP). K1 media with established biofilms of heterotrophs and nitrifiers from the full-scale MBBR train were used to seed the pilots. The pilots were operated for 417 days with a focus on demonstrating the ability to achieve effluent nutrient limits while reducing supplemental carbon needs. A description of performance is provided in (Sun, 2022; WANG, 2022). Model development: Kinetic analysis of PdNA was investigated by developing expressions describe denitratation (NO3--N â†’ NO2--N) and denitritation (NO2--N â†’ N2) (Glass and Silverstein, 1998). The specific nitrate uptake rate of denitratation culture (qDenitra.) can be expressed as Equation 1 according to Activated Sludge Model NO. 1 (Henze et al., 2000). Similarly, the specific nitrite uptake rate of denitritation culture (qDenitri.) can also be expressed as Equation 2. Equation 3 shows the specific nitrite uptake rate of anammox (AMX) bacteria (Bi et al., 2015). qAMX/qDenitri., qAMX/qDenitra. and qDenitra/qDenitri. as shown in Equations 4, 5 and 6 were used to compare effects of conditions on specific substrate uptake rates with a view to identifying which process might govern performance. All the kinetic parameters used in the investigation are listed in Table 1. Results and discussion Pilot results: Methanol-driven PdNA achieved an effluent TIN concentration of 2.6 +/- 0.6 mg/L and observed an average of 1.3 mg/L anoxic NH4+-N removal. Glycerol-driven PdNA achieved an effluent TIN concentration of 2.7 +/- 1.0 mg/L and observed an average of 1.3 mg/L anoxic NH4+-N removal. Results confirmed it was possible to achieve nutrient targets while also reducing supplemental carbon by 20 to 30% relative to conventional BNR. Nitrite sink by AMX governed PdNA performance in methanol fed train: Data from pilot operation were overlaid on heat maps plotting specific utilization rate ratios of denitratation, denitritation and AMX (Figures 1, 2 and 3). Results indicated that the in situ anammox substrate utilization rate (qAMX) was likely greater than the denitritation utilization rate (qDenitri) for the entire 372 days of operation period. Additionally, it was observed that anammox substrate utilization and denitratation utilization rates were similar i.e., qAMX/qDenitra ~ 1. Collectively, these results suggest that heterotrophic denitritation was outcompeted by anammox for nitrite in the methanol system. This implies that nitrite sink from anammox governed PdNA performance. Rate differential for heterotrophic denitratation versus denitritation governed PdNA performance in glycerol fed train: In contrast to the methanol train, pilot data from the glyercol train suggested that qAMX was less than qDenitri for the majority of pilot operation. Further, it was observed that qAMX was less than qDenitra while qDenitra. was greater than qDenitri. This data implies that the rate differential for heterotrophic nitrate and nitrite reduction dictated PdN performance in the glycerol train. Significance of Results The approach described in this paper can be used to help improve our understanding of existing PdNA systems to help clarify how different conditions may impact which mechanisms dictate performance.

This study explores using methanol and glycerol as carbon sources in partial denitrification coupled with anammox (PdNA) in tertiary moving bed biofilm reactors (MBBRs). Over 371 days, two MBBR trains were tested. Both achieved effluent total inorganic nitrogen (TIN) below 3 mg/L, with methanol being more cost-effective for nitrogen removal. Anammox (AMX) played a key role in nitrite sink, guiding future full-scale PdNA applications for improved efficiency and cost savings.

SpeakerWang, Jiefu

Presentation time

16:30:00

17:00:00

Session time

15:30:00

17:00:00

SessionEnhancing Nitrogen Removal: Insights Into Carbon Sources and Mechanisms

Session number420

Session locationRoom 340

TopicAdvanced Level, Facility Operations and Maintenance, Municipal Wastewater Treatment Design, Nutrients, Research and Innovation

Author(s)

Wang, Jiefu, Chitrakar, Sajana, McGrath, Michael, Sun, Yewei, Khunjar, Wendell, Pace, Gregory, Wang, Zhiwu

Author(s)J. Wang1, S. Chitrakar2, M.J. McGrath3, Y. Sun4, W. Khunjar5, G.J. Pace6, Z. Wang1

Author affiliation(s)1Virginia Tech, VA, 2Noman M Cole Jr Pollution Control Center, VA, 3Fairfax County Government, VA, 4Hazen and Sawyer, VA, 5Hazen & Sawyer PC, VA, 6Hazen and Sawyer, DC

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2024

DOI10.2175/193864718825159506

Volume / Issue

Content sourceWEFTEC

Word count23

Unlocking Resource Intensification through Full-Scale Densification and PdNA

Abstract

ABSTRACT
The Fairfax County Noman M. Cole Pollution Control Plant (NCPCP) is a 67 MGD facility using primary, secondary, and tertiary treatment to meet effluent limits of 3.0 mg N/L for total nitrogen (TN) and 0.18 mg P/L for total phosphorus (TP). Historically, nitrogen removal relied on secondary step-feed activated sludge tanks (ASTs) and a tertiary denitrifying moving bed biofilm reactor (MBBR) with methanol, operated in conventional modes with high resource demands for units, methanol, and energy. In the past three years, Fairfax County has implemented process intensification by introducing full-scale Densified Activated Sludge (DAS) in the secondary BNR system without external selectors like hydrocyclones and Partial Denitrification Anammox (PdNA) in the tertiary MBBR. DAS has lowered the Sludge Volume Index (SVI), reducing the need for ASTs and clarifiers while maintaining nitrification. PANDA has cut carbon and energy use without affecting effluent quality. These innovations have improved both efficiency and sustainability in the county's wastewater treatment operations.

INTRODUCTION | BACKGROUND
Densified Activated Sludge (DAS) and Partial Denitrification/Anammox (PdNA) are two examples of resource intensification processes have the potential to result in capacity, chemical and energy savings at water resource recovery facilities (WRRFs). In the DAS process, the ability to provide sufficient biological selection by operating at specific feast-to-famine (F/F) ratios that have been shown to be crucial for achieving sludge densification and aerobic granulation (Sun et al., 2021). The proper F/F ratio in the secondary is controlled via step-feed ratio and SRT control. The step-feed ratio is modified to increase flow to the upfront passes of the Activated Sludge Tanks (ASTs) to provide more feast condition and SRT/MLSS is maintained at reasonable levels for nitrification while preventing long-SRT forming filamentous microogranisms (Kent et al., 2018). Both operational parameters increase kinetic selective pressure and improve sludge volume index (SVI) in the ASTs. Successful Densification has been documented at full-scale. In the PdNA process, Partial ammonia oxidation is controlled to achieve a specific NO3/NH3 ratio (Wang et al., 2024). Partial denitrification driven by supplemental carbon addition (e.g., methanol) is then used to stably generate NO2--N. Anammox can then remove both nitrite and ammonia to achieve effluent NH3 and TN limits. Successful PdNA has been documented in pilot and full-scale.

METHODOLOY
Secondary AST Setup
The AST system (Figure 1) includes three large (~4.9 MG each) and six small ASTs (~1.7 MG each). The large ASTs operate in densification mode with a six-pass step-feed flow, where five passes receive primary effluent (PE) (Figure 2). Alternating anoxic and aerobic zones are equipped with mixers, diffusers, DO probes, and airflow control valves. PE flow, DO, and airflow are regulated by operator setpoints. Supplemental carbon is fed via flow-paced methanol dosing. SRT and MLSS are managed by adjusting the waste activated sludge (WAS) rate and basins in service. Densification was achieved through step-feed and wasting rate adjustments without hydrocyclones.
Tertiary MBBR Setup
The MBBR system (Figure 1) consists of six trains, five with fixed-film media. Each train has two anoxic denitrification cells (~2.4 MG total) and one re-aeration cell (~0.6 MG). Anoxic cells use mixers and flat screens; re-aeration cells have medium bubble diffusers and cylindrical screens. K1 media support anammox, denitrifying, and nitrifying bacteria. Methanol dosing is nitrate-paced, and influent NO3/NH3 ratios are maintained through secondary process adjustments, including step-feed, DO, airflow, load-paced equalization, and methanol feed adjustments.

RESULTS
Fairfax County has been deploying PdNA since Q3 of 2022 and coupled DAS with PdNA since Q2 2023. Results have indicated the following:
DAS in Secondary ASTs
- Historically, SVI fluctuated between 110—140 mL/g due to low kinetic selective pressure, which was addressed by adjusting step-feed distribution and reducing MLSS.
- Increasing step-feed to Passes A and C reduced SVI from over 100mL/g to ~80mL/g (Figure 3a). Lowering MLSS during stable summer flow further reduced SVI from ~110mL/g to 70mL/g (Figure 3b).
- Higher upfront step-feed and reduced MLSS raised the F/M ratio, enhancing feast-to-famine conditions and improving sludge settleability.
- SVI was negatively correlated with particles >212 µm (Figure 4), indicating that more granules under improved feast-to-famine conditions enhanced settleability.

PdNA in Tertiary MBBRs
- The facility consistently maintained effluent ammonia below 0.5 mg/L (Figure 5), with PdNA achieving anoxic ammonia removal of 1—2 mg/L (Figure 6).
- Monthly effluent TN ranged from 2—4 mg/L, averaging 2.8 mg/L over 28 months (08/22—12/24) (Figure 7).
- Optimized PdNA reduced methanol use by ~20% (Figure 8) and energy demand by ~5% compared to 2021—2022 operations.

Cumulatively, this work is the first to effectively demonstrate full-scale Densification with mainstream deammonification via PdNA while meeting stringent nutrient limits. This paper will discuss operational lessons learned and considerations to continuously support DAS/PdNA operation at NCPCP moving forward.

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

Presentation time

16:30:00

16:45:00

Session time

15:30:00

17:00:00

SessionFull-Scale Shortcut Nitrogen Removal

Session locationMcCormick Place, Chicago, Illinois, USA

TopicLiquid Stream Treatment Technology - Secondary & Tertiary Treatment

Author(s)

Pace, Gregory, Sun, Yewei, Khunjar, Wendell, Manning, Elizabeth, Chitrakar, Sajana, Rasel, Munshi Md