Regmi, Pusker

Dr. Regmi is a wastewater innovation leader at Brown and Caldwell. He is a board-certified environmental engineer named 40 Under 40 awardee in 2022 by The American Academy of Environmental Engineers & Scientists. Pusker is credited with pioneering advanced biological nutrient removal technologies. He is the author of over 50 peer-reviewed publications and has served as principal investigator for multiple Water Research Foundation projects. He is currently a vice-chair of the WEF research and innovation symposium and vice-chair of WEF Research and Innovation for Strengthening Engagement (RISE).

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