Regmi, Pusker

Dr. Regmi is a wastewater innovation leader at Brown and Caldwell. Pusker is credited with pioneering advanced biological nutrient removal technologies. His research contributions are published in leading water journals, and he is a frequent presenter at prominent WEF and IWA conferences globally. In leadership roles, Pusker chairs the WEF Research and Innovation Symposium and acts as vice-chair for their Research and Innovation Community. He's also a member of the IWA Nutrient Removal and Recovery Specialist Group's management committee. His expertise extends to serving as a principal investigator on multiple Water Research Foundation projects and as a co-author of SWAN's Digital Twin Readiness Guide.

Titles from this speaker

Description: A Full-Scale Demonstration of SND, Post Denitrification With Internally Stored...

A Full-Scale Demonstration of SND, Post Denitrification With Internally Stored Carbon and Anammox Potential For Energy and Carbon-Efficient BNR

Abstract

Introduction
Availability and transformation of organic carbon at different stages in the activated sludge process impact the efficiency of biological nitrogen (N) and phosphorus (P) removal. Conventional biological nutrient removal (BNR) flowsheets often do not take full advantage of influent carbon and favorable influent carbon-to-nitrogen (C/N) and carbon-to-phosphorus (C/P) ratios for N and P removal. The reasons for the inefficiency of conventional BNR are rigid design guidelines without adequate considerations for local conditions, suboptimal operational strategies based on limited anecdotes, lack of understanding of carbon transformations at different redox conditions, gaps in the knowledge of bio-P, including selection factors for desired microbial community members, and inappropriate use of large safety factors resulting from a lack of process understanding. To this end, the main research objectives of this study were to: - Maximize influent carbon utilization for N and P removal rather than aerobic oxidation; - Integrate biological P removal and simultaneous nitrification and denitrification (SND) for energy and carbon efficient complete nutrient removal; and - Test potential for partial denitrification anammox (PdNA) in mainstream application for N polishing (with and without supplemental carbon).
Methodology The 26 mgd Seneca Water Resource Recovery Facility (WRRF) employs a 5-stage Bardenpho process, secondary clarifiers, and filters to meet stringent nutrient limits (< TN of 4 mgN/L, TP of 0.27 mgP/L). One of the five process trains was converted in Spring 2021 to a test train which involved the following changes: - Internal mixed liquor recycle (IMLR) reduced from 400% to 200% of the influent flow; - Ammonia-based aeration control (ABAC) control to maintain controlled dissolved oxygen (DO) levels in all aerated zones, including reaeration zone (Ammonia setpoint of 1.5 mg/L at the end of the aerobic zone; minimum DO setpoint of 0.2, maximum DO setpoint of 1.5 mg/L); - Methanol addition discontinued in the post-anoxic zone; and - Decreasing the size of post anoxic zone volume from 17% to 9% of the reactor basin. It is important to note that the plant does not have a primary clarifier, and the test train does not have dedicated clarifiers (combined return activated sludge [RAS]). Therefore, any microbial adaptation resulting from the operational conditions of the test train would impact the rest of the plant and vice-versa. The experimental plan included: - Reactor profiling for ammonia, OP, nitrate, and nitrite by taking two grab samples (morning and afternoon) every week; - Influent and effluent monitoring of carbon, nitrogen, phosphorus species; - Batch testing to determine the specific denitrification rates (without supplemental carbon), which involved collecting samples from the end of the aerated zone (just before the post-anoxic zone); - Monitoring airflow in the test train and the rest of the trains; - Collecting DNA samples for microbial population analysis; and - Collecting Polyhydroxyalkanoates (PHA) samples to understand the fate of carbon transformations for post anoxic denitrification (PHA analysis to be performed per Oehmen et al., 2005).
Results and Discussion Effluent quality The test train produced excellent effluent quality, as seen in Figure 1, without the use of supplemental chemicals. Based on weekly profiles, the average test train effluent ammonia was less than 0.2 mgN/L, TIN was 1.9 mgN/L, and OP was less than 0.2 mgP/L. Aluminum sulfate is dosed slightly downstream before the secondary clarifiers for additional phosphorus removal. SND and post-anoxic denitrification were responsible for enhanced nitrogen removal in the test train. The high degree of P uptake at low DO conditions resulted in very low effluent P levels. SND and aeration savings The low DO operation (~0.3 mg/L) achieved by ABAC resulted in significant aeration savings; about 30% less airflow was measured in the test train compared to the other trains operated at higher constant DO (~1.5 mg/L), which is presented in Figure 2. In addition, the low DO operation resulted in conditions favorable for SND, which removed an average of 5 mgN/L in the test train's aerated zones, as seen in Figure 3. Post-denitrification The test train removed > 4 mgN/L via denitrification in the post-anoxic zones without supplemental carbon and achieved similar effluent nitrate concentrations compared to the other trains, which do require supplemental carbon. The specific denitrification rate (SDNR) test results indicated that the low DO conditions resulted in high rates (Figure 4). These rates are much higher than the denitrification attributed to endogenous respiration, as seen in Figure 4. More efficient utilization of internally stored carbon may have resulted in more carbon availability for post-denitrification at low DO conditions.
Anammox potential The test train at the Seneca WRRF has demonstrated the ability to meet nutrient removal requirements without chemical addition. However, it appears that there is further opportunity to remove more N via the anammox pathway in the post-anoxic zone. The internally stored carbon-driven post-denitrification nitrite accumulation due to partial denitrification, likely aided by the shorter hydraulic retention time (HRT) of the post-anoxic zone (Figure 5). Further anoxic ammonia removal without the use of methanol at the Seneca WRRF would increase the treatment capacity and may be desired in the future. In the full paper, the findings from the following ongoing efforts will also be presented: 1. Anammox potential batch testing using the samples from the end of the aerated zone (to show that internally stored carbon generated nitrite is viable for anammox activity); 2. PHA profiling from the test reactor; and 3. Microbial analysis via 16S rRNA amplicon sequencing.
Conclusion - Optimization of ammonia-based aeration control (ABAC) resulted in low dissolved oxygen (DO) operation (<0.3 mgO2/L on average, saving > 30% in aeration energy), leading to significant simultaneous nitrification/denitrification (SND) (~60% nitrogen [N] removal in the low DO zones). - Low DO operation was compatible with biological P uptake, resulting in low effluent orthophosphate (OP) (< 0.2 mgP/L). - Reduction in internal mixed liquor recycle from 400% to 200% saved on pumping energy. - The efficient use of internally stored carbon in the low DO SND zone led to the carbon availability for denitrification in the post anoxic zone (> 4 mgN/L removed) without supplemental carbon. - Post denitrification rate as high as 2.7 mgN/gVSS/h was observed, which was significantly higher than what is expected from endogenous respiration. - The internally stored carbon driven post denitrification resulted in some nitrite accumulation (~0.8 mgN/L) via the partial denitrification pathway, which could be favorable for further N polishing via anammox - The demonstration train achieved effluent total inorganic nitrogen (TIN) < 2 mgN/L and OP < 0.2 mgP/L without supplemental carbon and metal salts addition.

The 4-stage Bardenpho train (with a small anaerobic selector) demonstrated efficient BNR (TIN < 2 mgN/L and OP < 0.2 mgP/L) without supplemental carbon and metal salts addition via low DO operation and use of internally stored carbon. Significant aeration savings ~30%, SND ~60% and 50% reduction in internal recycle pumping were realized. The efficient use of internally stored carbon in the low DO SND zone led to the carbon availability for denitrification (at 2.7 mgN/gVSS/h) in the post-anoxic z

SpeakerRegmi, Pusker

Presentation time

09:30:00

09:55:00

Session time

08:30:00

10:00:00

TopicAdvanced Level, Municipal Wastewater Treatment Design, Nutrients

Author(s)

Regmi, Pusker

Author(s)P. Regmi1; M. Johnson2; C.K. Nguyen3; A.A. Al-Omari4; G. Wells5; B. Yeakle3; P. Regmi1

Author affiliation(s)Brown and Caldwell, MD1; WSSC Water2; Washington Suburban Sanitary Commision, MD3; VA4 ; Northwestern University Library, IL5

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2022

DOI10.2175/193864718825158546

Volume / Issue

Content sourceWEFTEC

Word count20

Beyond Energy Savings: A Deep Dive into Carbon Efficiency of Low DO BNR

Abstract

The Seneca Water Resource Recovery Facility (WRRF) uses a 5-stage Bardenpho process for nutrient removal, meeting strict regulations (< 0.2 mgN/L, Total Inorganic Nitrogen (TIN) < 2.0 mgN/L, and orthophosphate < 0.2 mgP/L. This success was attributed to simultaneous nitrification-denitrification (SND) and post-anoxic denitrification, facilitated by ABAC's regulation of dissolved oxygen (DO) levels. The test train achieved significant aeration savings and utilized internally stored carbon for post-denitrification under low DO conditions, eliminating the need for supplemental carbon. Analysis revealed that glycogen, more than polyhydroxyalkanoates (PHA), likely played a major role in this, aligning with the high abundance of glycogen-accumulating organisms (GAO), particularly Competibacter, and Tetrasphaera, the dominant phosphate-accumulating organism (PAO) observed. This system's efficiency suggests an innovative approach to carbon management for enhanced nutrient removal in wastewater treatment.

DO was maintained at ~0.3 mg/L, lower than the usual ~1.5 mg/L. Low DO operation resulted in average effluent ammonia <0.2 mgN/L, <TIN of 1.5 mgN/L, and orthophosphate <0.2 mgP/L, without supplemental chemicals. High P uptake occurred even under low DO conditions, with enhanced nitrogen removal attributed to SND and post-anoxic denitrification. Moreover, specific denitrification rate tests showed higher rates at low DO, indicating efficient utilization of internally stored carbon.

SpeakerRegmi, Pusker

Presentation time

09:30:00

09:50:00

Session time

08:30:00

10:00:00

SessionLow Carbon BNR Fundamentals and Controls

Session locationRoom S502 - Level 5

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

Author(s)

Regmi, Pusker

Author(s)P. Regmi 1; M. Johnson 2 ; C. Nguyen 3; A. Al-Omari 4; G. Wells 5; B. Yeakle 6; P. Regmi 1;

Author affiliation(s)Brown and Caldwell 1; WSSC Water 2 ; WSSC Water 3; Brown and Caldwell 4; Northwestern University 5; WSSC Water 6; Brown and Caldwell 1;

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2023

DOI10.2175/193864718825159064

Volume / Issue

Content sourceWEFTEC

Word count14

Digital Twin: A Path To Efficient and Intuitive Water System Operations

Abstract

Introduction
Water utilities and the water industry see the promise of Digital Twin to increase operational efficiency, increase cost savings, and improve their overall business objectives but have challenges in understanding what digital twins are, what they can do, and how to implement them. The smart water network forum (SWAN) Digital Twin Holistic Architecture workgroup is leveraging the industry's first Digital Twin Architecture and establishing a common language and approach to Digital Twins. This group has assembled a panel of experts from global water leaders from utilities, solution providers, engineering firms, and academia to develop a Digital Twin white paper to bring clarity and further guide the industry. This white paper will cover core concepts and case studies to aid utilities in defining their path to implementing a Digital Twin. The objectives of the white paper include: a) Educate the water industry on the fundamentals of Digital Twin b) Update current knowledge c) Showcase practical applications- success sorties and lessons learned d) Provide outlooks and recommendations for utilities The main goal of this paper is to provide a summary of the white paper to the audience that is keenly looking forward to the guidance and clarification around digital twins for water systems operation.
Methodology
The white paper will be divided into core concepts and case studies. The case studies will support the proposed ideas in core concepts with real-life success stories. Following core concepts will be discussed:
1. Future of Digital Twins for water
2. Consolidated Digital Twin architecture for water
3. How do I get started with (operational) Digital Twins?
4. How do I progress with Digital Twins? Table 1 shows a global list of utilities/firms providing real-life case studies of implementing Digital Twin for the operations of their water systems.
Discussion
The use of models to understand and predict water systems' performance has been practiced with great success for many decades. However, it is crucial to distinguish Digital Twin from conventional models to highlight the new paradigm enabled by the recent digital revolution (see Figure 1). Consequently, the SWAN Digital Twin Architecture Subgroup developed a new architecture (see Figure 2) that conveys the different components that comprise a Digital Twin in a water/wastewater system from the physical system to the user experience. The main objective of a holistic architecture for utilities and the entire ecosystem is to build secure and connected technology platforms that enable incremental build-out of technology in support of immediate and long-term outcomes. However, there should be a focus on early use cases that provide a clear return on investment (ROI) while building a technical architecture. Furthermore, Digital twin architecture should support operators of the water systems to make more informed decisions that optimize performance and create actionable results. The roadmap of Digital Twin will benefit from a measure of success at each stage followed by a re-assessment for steps to be taken in the next stage. This pragmatic and agile approach is necessary to incorporate knowledge and experience gained from internal and external sources.
Relevance to the industry
To meet the sustainability objectives, the operation of water systems is expected to become more resilient and efficient. To this end, rapid digitalization in the water sector is seen as an imminent enabler. The innovation around digital technologies is expected to accelerate as costs continue to decline as suggested by Wright's law â€“ 'For every cumulative doubling of units produced, costs will fall by a constant percentage.' Consequently, the convergence of affordable digital technologies such as the internet of things (IoT), artificial intelligence (AI), and software analytics gives rise to robust digital water solutions that are easy to use and intuitive, enabling self-diagnosis and unsupervised corrective actions. Therefore, Digital Twin is a logical next step for the industry to adopt. SWAN Digital Twin white paper will be a crucial accelerator for the wider adoption of Digital Twin across disciplines for efficient water system operations.

Utilities of all sizes face unprecedented challenges from increased cost, greater customer expectations, talent management, and knowledge retention. These challenges create overwhelming complexities to operate water throughout its lifecycle. Digital Twins offer a promise to revolutionize the way utilities are managed, yet there hasn't been any guide for utilities to best leverage this technology into a common environment where utility personnel are fully supported. SWAN Digital Twin Readiness Gu

SpeakerRegmi, Pusker

Presentation time

10:35:00

10:50:00

Session time

10:30:00

12:00:00

TopicAdvanced Level, Asset Management, Utility Management and Leadership

Author(s)

Regmi, Pusker

Author(s)Pusker Regmi1; Michael Karl2; Chengzi Chew3

Author affiliation(s)Brown and Caldwell, Walnut Creek, CA1; DHI, Hørsholm, Denmark2

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2022

DOI10.2175/193864718825158555

Volume / Issue

Content sourceWEFTEC

Word count12

Description: From theory to practice: Continuous flow aerobic granulation using external...

From theory to practice: Continuous flow aerobic granulation using external selectors in full-scale US facilities

Abstract

Work is ongoing to develop robust protocols for SARS-CoV-2 quantification. However, to fully realize the potential of wastewater-based epidemiology, additional methods must be developed to normalize the SARS-CoV-2 concentrations to population equivalence. It is well known that wastewater concentrations vary significantly with wet weather flow, thus a normalization technique must account for variations in wastewater strength. Wastewater concentrations under dry weather will also change with transient populations, and this is especially important for a college town or business community with commuter activity. Biomarkers can be used to determine the number of individuals contributing fecal matter to a sewershed. Ideally, biomarkers are specific to human waste, stable in wastewater, and consistently shed at known rates.

The use of hydrocyclone based wasting provided densification of activated sludge, resulting in rapid improvements of settleability (SVI from 200 mL/g to 90 mL/g within weeks of implementation). Solids retention time (SRT) for the granules fraction was two times more than the flocculent fraction. Longer granules (SRT) preferentially selected PAOs and nitrifiers in the underflow of the hydrocyclone. Consequently, carbon-efficient N and P removal was achieved at influent COD: N ratio of 6:1 without adding external chemicals.

SpeakerRegmi, Pusker

Presentation time

13:45:00

14:00:00

Session time

13:30:00

14:30:00

SessionKnowledge Development Forum: The Plot Thickens Part II - Future of Granular Sludge

Session number505

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

Author(s)

Pusker Regmi

Author(s)P. Regmi1; B. Sturm3; J. Jimenez1; I. Avila2;

Author affiliation(s)Brown and Caldwell, Walnut Creek, CA1Metro Wastewater Reclamation District, CO2The University of Kansas, Lawrence, KS3Metro Wastewater Reclamation District4

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2021

DOI10.2175/193864718825158147

Volume / Issue

Content sourceWEFTEC

Word count16

Description: Full-Scale Demonstration of Continuous AvN Control: What Did We Learn for BNR...

Full-Scale Demonstration of Continuous AvN Control: What Did We Learn for BNR Optimization?

Abstract

The main purpose of this study is to demonstrate applicability of AvN control to reduce energy and chemical requirements for a carbon starved 15.7 MGD BNR system at Pueblo, CO required to meet nitrogen and phosphorus limits. The intermittent AvN control has been demonstrated for efficient shortcut nitrogen removal (Regmi et al., 2014 and Regmi et al., 2015) at a pilot-scale. Consequently, there has been a desire to implement AvN at full-scale systems. However, implementation of intermittent aeration with existing aeration system is not trivial and would require major modifications. Hence, in this study a simpler and more practical alternative based on continuous aeration AvN control as an add-on to the existing DO control is tested at full-scale to achieve BNR goals (TIN < 15 mg/L, TP < 1 mg/L as annual average). At Pueblo wasting is performed via hydrocyclone which has resulted in densification (Regmi et al., 2019). Therefore, a unique opportunity was presented to evaluate two very promising intensification technologies – densification with external selector (hydrocyclone) with the AvN control in concert. This paper includes insights from a comprehensive science-based investigation to shed light on i) Aeration savings ii) nitrification rates iii) anoxic P uptake iv) impact of densification on low DO operation as result of AvN control.

SpeakerRegmi, Pusker

Presentation time

09:10:00

09:30:00

Session time

08:30:00

10:30:00

SessionOptimizing Energy Through Advanced Aeration Control

Session number508

TopicEnergy Production, Conservation, and Management, Facility Operations and Maintenance, Intelligent Water, Municipal Wastewater Treatment Design

Author(s)

S. MurthyB. WettJ. JimenezP. RegmiP. Regmi

Author(s)S. Murthy1; B. Wett2; J. Jimenez3; P. Regmi4; P. Regmi4;

Author affiliation(s)DC Water1; ARAconsult, Tirol2; Brown And Caldwell, FL3; , VA4

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2020

DOI10.2175/193864718825157479

Volume / Issue

Content sourceWEFTEC

Word count14

Description: Model-based Investigation of the Fate and Transport of Internal and External Carbon...

Model-based Investigation of the Fate and Transport of Internal and External Carbon Sources to Drive Partial deNitrification (PdN)-based Nitrogen Removal Processes

Abstract

This paper was presented at WEFTEC 2023 in Chicago, IL.

SpeakerAl-Omari, Ahmed

Presentation time

11:30:00

11:45:00

Session time

10:30:00

12:00:00

SessionPushing the Boundaries of Our Biological Models

Session locationRoom S404a - Level 4

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

Author(s)

Al-Omari, Ahmed

Author(s)A. Al-Omari 1; P. Regmi 2 ; T. Wadhawan 3; M.L. Bachmann 4; K. Bauhs 5; J.A. Jimenez 7; I. Takacs 8; CB Bott 4; A. Al-Omari 1;

Author affiliation(s)Brown and Caldwell 1; HRSD 2 ; Dynamita 3; HRSD 4; Dynamita 5; Dynamita 7; Dynamita 8; Dynamita 4; Brown and Caldwell 1;

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2023

DOI10.2175/193864718825159193

Volume / Issue

Content sourceWEFTEC

Word count22

Tale of Two WRRFs: Optimizing Internal Carbon for Meeting Low Nutrient Limits

Abstract

Introduction This investigation draws on comparative analyses from two neighboring WRRFs employing the 5-stage Bardenpho process. WSSC Water operates three other BNR facilities, encouraging sharing of valuable insights and strategies for broader use in the water resource recovery community. Accordingly, this paper delineates: 1) Operational approaches that leverage high Carbon-to-Nitrogen (C/N) ratio (~12) to enhance nutrient removal efficiency. 2) A comparative analysis of Nitrogen (N) and Phosphorus (P) removal mechanisms in two WRRFs sharing similar configurations but different operational approaches. 3) A conceptual framework to evaluate and optimize simultaneous nitrification-denitrification (SND), pre-anoxic, and post-anoxic denitrification through endogenous respiration and internally stored carbon. Methods Both WRRFs are in Montgomery County, MD, and eventually discharge into the Chesapeake Bay. The stringent nutrient limits are TN < 4 mg/L and TP < 0.27 mg/L annually. Fig. 1 shows the side-by-side comparison of BNR trains from the two facilities. Table 1 shows the key operational differences. The experimental plan included: - Reactor profiling for ammonia, orthophosphate, nitrate, and nitrite with morning and afternoon grabs; - Influent and effluent monitoring of carbon, N, and P species; - Batch testing to determine specific denitrification rates without supplemental carbon, sampling just before the post-anoxic zone; - Tracking airflow; - Collecting DNA samples for microbial analysis; and - Collecting Polyhydroxyalkanoates (PHA) and glycogen samples to understand carbon transformations in post-anoxic denitrification. Results and Discussion The Seneca WRRF has successfully implemented ammonia-based aeration control (ABAC) for about one year. Both facilities achieve excellent nutrient removal. The 90th percentile values are 2.5 mgN/L for TN and 0.18 mgP/L for TP at Seneca, while Damascus reported 2.1 mgN/L for TN and 0.13 mgP/L for TP. Notably, these outcomes are achieved without supplemental carbon. Furthermore, Seneca's ABAC system reduces aeration demand by 20% due to low dissolved oxygen (DO) operation compared to Damascus, which operates at high DO (Fig. 2). N Removal: SND represents the primary N removal mechanism, accounting for 69% of TN elimination at Seneca and 55% at Damascus (Fig. 3). Given the operational conditions-ABAC at Seneca and high DO at Damascus-the superior SND performance at Seneca aligns with expectations. Surprisingly, Damascus also exhibits substantial SND activity despite the higher DO. Both facilities demonstrate comparable pre-anoxic zone contributions to N removal. Nonetheless, Damascus depends more on post-anoxic denitrification, achieving 7.0 mgN/L vs. 3.5 mgN/L at Seneca, contributing to exceptional effluent TIN levels (Fig. 4). The post-anoxic zone makes up 20% of Damascus's total volume, double Seneca's 9% (Table 1). The maximum specific denitrification rates were also slightly higher at Damascus than at Seneca (Fig. 5). Additionally, denitrification rates in the absence of external carbon sources, measured at the end of the main aerobic zone-indicative of internal carbon storage-were higher at Damascus by ~0.3 mgN/gVSS/hr compared to Seneca. These measurements exceed the baseline endogenous denitrification rate of 0.35 mgN/gVSS/hr, suggesting a not-so-trivial role for internally stored carbon in the denitrification process. P Removal: Seneca and Damascus use both biological and chemical P removal to meet strict TP limits. Aluminum sulfate (alum) is added before the secondary clarifiers to precipitate residual P. Seneca relies more on bioP and uses half as much alum per million gallons per day (MGD) compared to Damascus (Fig. 6). Notably, recent operational shifts at both aim to reduce the alum dose (Seneca: 15 gallons of alum/MGD; Damascus: 35 gallons of alum/MGD). Enhanced P release in Seneca's pre-anoxic zone suggests more effective bioP activity than Damascus (Fig. 6). Additionally, a notable re-release of P is observed in Seneca's post-anoxic zone, likely due to a long SRT of ~25 days, which may lead to the decay of phosphorus-accumulating organisms. Despite a similar SRT, such a re-release is not evident at Damascus, potentially due to the inhibitory effects of high alum dosing on bioP processes (Fig. 7). With a strategic reduction in SRT and alum use, Seneca and Damascus are expected to rely on bioP to achieve the low TP limits. Particle Size Distribution and Settling: The extended SRT and high organic content of the influent contribute to a low anaerobic Food-to-Microorganism (F/M) ratio at both Seneca (1.8 gBOD/MLSS/d) and Damascus (1.4 gBOD/MLSS/d), which falls below the optimal ratio of 2.4 gBOD/MLSS/d recommended for favorable settling. Despite this, settling performance at both facilities remains commendably effective. Image analyses reveal a higher incidence of filamentous bacteria at Seneca than at Damascus; however, Seneca's biomass particles are larger (Fig. 8). Given that the lower SVI at Damascus than at Seneca, it can be inferred that filament abundance may significantly impact sludge settleability more than particle size.

Meeting stringent nutrient limits increases operational costs for WRRFs due to high energy demands for aeration and the need for supplemental chemicals. Traditional BNR processes can exacerbate costs through inefficient carbon management. This study compares two WRRFs using the 5-stage Bardenpho process, revealing strategies to optimize BNR and reduce external chemical reliance via SND and post-denitrification driven by internally stored carbon.

SpeakerRegmi, Pusker

Presentation time

09:30:00

10:00:00

Session time

08:30:00

10:00:00

SessionInternal Stored Carbon for Nutrient Removal

Session number309

Session locationRoom 243

TopicAdvanced Level, Nutrients, Research and Innovation

Author(s)

Regmi, Pusker, Nguyen, Caroline, Bauhs, Kayla, Yeakle, Brad, Marinelli, Michael, Rowe, Allen

Author(s)P. Regmi1, C.K. Nguyen2, K. Bauhs3, B.C. Yeakle4, M. Marinelli5, A. Rowe6

Author affiliation(s)1Brown and Caldwell, MD, 2WSSC Water, MD, 3Brown and Caldwell, TN, 4WSSC, MD, 5Washington Suburban Sanitary Commision, MD, 6Washington suburban sanitary commission, MD

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2024

DOI10.2175/193864718825159579

Volume / Issue

Content sourceWEFTEC

Word count13

Towards Sustainable WRRFs: Exploring the Potential of Internally Stored Carbon for Efficient BNR

Abstract

Introduction Water resource recovery facilities (WRRFs) may rely on external carbon sources like methanol for denitrification. However, carbon may be stored within the biomass to be used later in the biological nutrient removal (BNR) process for denitrification either post-anoxically or via simultaneous nitrification-denitrification (SND) and may reduce these external carbon requirements. Evidence of internally stored carbon (ISC) denitrification has been observed at full-scale (Bauhs et al., 2022; Regmi et al., 2023), although to a limited extent. 5-stage BNR facilities that are the focus of this analysis include the Seneca WRRF and Damascus WRRF (Washington Suburban Sanitary Commission [WSSC]), and the Virginia Initiative Plant (VIP) and Nansemond Treatment Plant (NTP) (Hampton Roads Sanitation District [HRSD]). Seneca and Damascus show indications of ISC denitrification: low to no methanol addition and yet 4-7 mg N/L of post-anoxic nitrate reduction. Similarly, profiles at VIP attribute 33% of post-anoxic N removal to ISC. NTP serves as a reference facility with no ISC denitrification. This analysis presents a framework for further implementation of ISC denitrification, drawing on an extensive literature review and observations from full-scale WRRFs. Operational Factors Several factors have been theorized to contribute to ISC denitrification at the WSSC and HRSD facilities. High selector F/M and influent C/N: High food-to-microorganism (F/M) ratios promote substrate storage in selector zones, as is the case for densified systems (Sturm 2020). The F/M at VIP far exceeds the recommended value of 2.4 g BOD/g MLSS/d for anaerobic selectors (Jenkins et al., 2003). All three ISC denitrifying facilities have high influent carbon-to-nitrogen (C/N) ratios above 12. Low IMLR: Lower internal mixed liquor recycle (IMLR) rates promote deeper anaerobic conditions upfront in the process for better carbon storage. IMLR rates at Seneca were reduced from 400% to 200%, and Figure 1 shows the significantly lower batch test post-anoxic ISC denitrification rates for the 400% IMLR rate. Low DO: This results in less oxidation of ISC prior to denitrification. Implementation of ABAC at Seneca (averaging 0.3 mg/L DO) improved SND and reduced post-anoxic methanol addition (Regmi et al, 2023). Batch tests at HRSD showed longer aerobic HRT led to lower ISC denitrification rates (Bauhs et al., 2022). Bio-P performance: Sources have identified PHA (Carvalho et al., 2007; Qin et al., 2005) and/or glycogen (Coats et al., 2011; Vocks et al., 2005; Winkler et al., 2011) as the likely form of ISC for denitrification, both of which are forms of carbon in the metabolism of organisms involved in bio-P. Batch testing of HRSD biomass showed a positive correlation of ISC denitrification rates with P uptake rates (Bauhs et al., 2022). Plug flow reactor configuration: The high substrate gradient may enable access to this carbon source. The post-anoxic zone configuration at VIP is equivalent to over 30 continuously stirred tank reactors (CSTRs) in series, compared to facilities like NTP with 3 CSTRs. Figure 2 shows an aerial of the post-anoxic zones at all four facilities. Benefits There are many benefits to implementation of ISC, as follows:

*Chemical Savings: Elimination of external carbon reduces chemical costs. Furthermore, less external carbon addition lowers sludge production and associated solids handling costs.

*Energy Savings: Lower IMLR reduces associated pumping energy while low DO operation leads to significant aeration energy savings.

*Settleability Improvements: Use of a selector zone to promote carbon storage is similar to biological selection factors for densification, so promoting ISC could improve settleability.

*Simplification of Process: Pre-anoxic zones could ultimately be eliminated (use an anaerobic/oxic/anoxic process as in Coats et al. (2023)). Furthermore, pending SND performance, the post-anoxic zone could be as well. Discussion Several knowledge gaps still remain, which if addressed could significantly increase implementation of ISC denitrification. First, how resilient is ISC for N removal? Responses to variation in WRRF loading or other process upsets is not yet understood. For instance, Figure 3 shows the inconsistency in methanol dose at VIP over many seasons. The viability of operating without a 'backup' system (i.e. external carbon addition) should be explored. Next, while several factors may promote ISC denitrification, which factors are the highest priority and what level of control do they offer? Table 1 summarizes these factors for each of the four full-scale facilities, but notably for Damascus, most are absent. Clearly some aspects of operation/configuration may be more important than others, or haven't yet been identified. Some, like ABAC for low DO, may be relatively straightforward. Others, like boosting C/N, may require more guidance. Related to the somewhat surprising observations of low methanol use at Damascus, there arises another question-does reduction of methanol itself promote ISC denitrification? In other words, there could be some interference of methylotrophs with ISC denitrifying organisms (Bauhs 2021). Nitrate concentrations in these systems are not limiting; nevertheless, cease of external carbon feed could trigger a microbial population shift.

Evidence of internally stored carbon (ISC) denitrification has been observed at multiple of Washington Suburban Sanitary Commission's and Hampton Road Sanitation District's Water Resource Recovery Facilities (WRRFs), where minimal post-anoxic methanol addition is required to meet effluent total nitrogen limits. A framework for further implementation of ISC denitrification based on results from these WRRFs is presented, including key factors, benefits, and knowledge gaps.

SpeakerBauhs, Kayla

Presentation time

08:30:00

09:00:00

Session time

08:30:00

10:00:00

SessionInternal Stored Carbon for Nutrient Removal

Session number309

Session locationRoom 243

TopicAdvanced Level, Nutrients, Research and Innovation

Author(s)