2019 Excellence in Environmental Engineering and Science® Awards Competition Winner

Grand Prize - Research

When the Detour Turns Out to be a Shortcut: Partial Denitrification (PdN) - Anammox as Alternative Strategy for Mainstream Deammonification

Entrant: District of Columbia Water and Sewer Authority | Hampton Roads Sanitation District
Engineer in Charge: Christine DeBarbadillo, P.E. | Charles Bott, Ph.D., P.E., BCEE
Location: District of Columbia
Media Contact: Ahmed A-Omari, P.E.

Entrant Profile

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DC Water and HRSD provided environmental leadership to establish pathways toward sustainability and energy neutrality for 21st century wastewater treatment plants by developing cutting-edge process strategies that use energy efficient anammox bacteria integrated into the activated sludge process. These agencies brought together a team of experts to resolve scientific and engineering challenges to make this vision a reality. Keeping waterways clean is the catalyst for these extensive research efforts which leverage utility and university resources to advance water research while developing the next generation of environmental engineers and scientists.

Catholic University of America provided the support of Dr. Arash Massoudieh and Mr. Tri Le, a PhD candidate, who operated the nitrogen removal pilot at Blue Plains AWTP. The research focused on evaluation of suitable carbon sources and development of control strategies for partial denitrification – anammox applied in the activated sludge process.

George Washington University provided the support of Dr. Rumana Riffat and Ms. Priyanka Ali, a graduate student, who evaluated the cost savings associated with the partial denitrification-anammox approach and conducted experiments to evaluate the feasibility of using carbon generated from fermentation of primary sludge as an alternative to external carbon sources.

Virginia Tech provided the support of several students including Ms. Stephanie Klaus, a PhD candidate, and Mr. Cody Campolong who operated a 1,000 gallon per day pilot at the HRSD Chesapeake Elizabeth plant. As part of their research they designed and optimized a partial denitrification - anammox MBBR process that followed an activated sludge nitrogen removal process.

Project Description

Introduction

Development of mainstream deammonification processes represents a paradigm shift for wastewater treatment, offering an opportunity to achieve sustainable nitrogen removal, energy neutral or even energy positive facilities, and dramatic reductions in treatment costs. This clear driver, coupled with the success of deammonification processes for treatment of high-strength sidestreams, had academics and practitioners globally invested in applied collaborative research to apply deammonification to mainstream treatment. About eight years have passed since this widespread effort was initiated, and a range of technologies has been proposed. Although some success has been shown in pilot studies both by our team and other researchers, no clear transition towards full-scale implementation has been observed.

Biochemical reactions associated with nitrogen removal from wastewater are described by the nitrogen cycle. Short-cut nitrogen (N) removal processes rely on alternative, more efficient, routes through the nitrogen cycle that reduce energy, organic, and inorganic carbon requirements. Anaerobic ammonium oxidizing bacteria (AnAOB, or annamox) which convert ammonium and nitrite to nitrogen gas without consuming organic carbon are key to achieving these efficiencies. To successfully implement short-cut N removal in full-scale mainstream treatment systems, we must achieve reliable nitrite availability for AnAOB.

A great deal of research has focused on developing strategies to repress the growth of nitrite oxidizing bacteria (NOB) which compete against AnAOB for nitrite. While this "NOB out selection" route has been successful for sidestream systems, a major limitation for mainstream deammonification processes has been related to the difficulty of continuously repressing the NOB and the variability of the out-selection efficiency through seasonal operational changes. Short-cut N removal systems that use an alternative partial denitrification route (PdN - anammox) rather than relying only on NOB out-selection will likely provide more reliable nitrite availability and could accelerate full-scale implementation of these technologies. This project focused on development of PdN - anammox based concepts for achieving mainstream deammonification and the evaluation of this approach for full-scale implementation.

Comprehensive Approach to Problem Solving and Addressing Project Complexity

This project evaluated the potential of the PdN - anammox route for achieving reliable short-cut nitrogen removal. The key to success involved three major strategies to resolve the problem quickly, effectively and comprehensively:

1. Going back to first principles - this project focused on understanding the underlying principles of microbial selection. This was key for the development of simple and practical tools.
2. Thinking modular and holistically - develop a menu of tools that can be combined towards the most optimal global solution, considering different drivers and limitations.
3. Engaging the right minds and skill sets - To overcome the many technical and scientific challenges, DC Water, HRSD, and several universities including Catholic University, Virginia Tech and George Washington University, brought together engineers and scientists from around the world and drew upon the most current scientific techniques, with rapid results. The team identified several promising scientific and technical approaches to bring the vision to a reality.

Originality and Innovation

The key findings of this research are summarized in the following sections.

1. Nitrate residual concentration is a key factor for reliable partial denitrification
   • Controlling the PdN route was independent of the substrate availability (determined by COD/N ratio added) but it was solely dependent on the nitrate residual concentration (A&B). The PdN controller maintains a target nitrate residual concentration (> 1.5 mg N/L) in the bulk liquid using carbon.
   • This control maintains the capability of the biomass to perform full denitrification when the nitrate residual is low. This reduces the risk of effluent TN violations in case of process upsets. The PdN control manages the metabolism but not necessarily the species type, making implementation simple and flexible.
2. Evaluation of carbon sources and proof of principal
   • Average PdN selection efficiencies of 85±18% and 90±11% were observed within DC Water and HRSD pilots, respectively, while achieving effluent TIN levels below 5 mg N/L
3. Integration of PdN - anammox approach with NOB out-selection tools
   The tools for NOB out-selection were coupled with the PdN-Anammox approach integrated using two different process configurations:
   • Integrated single sludge system (DC Water)
     • TN removal → 30-50% under AvN control
     • 13-40% through PdN-Annamox; 0-45% through full denitrification.
   • Separate two-stage system (HRSD)
     • TN removal → 49% under AvN control
     • 35% through PdN-AnAOB
4. Sustainable and reliable mainstream deammonification concept development for Blue Plains implementation

Both systems were able to achieve effluent TN < 5 mg M/L

Quality and Expert Testimony

The development of the PdN – anammox concept is an example of how development of online process control approaches in wastewater treatment has allowed us to select and manage microbiology to achieve sustainable treatment goals. Translation of this knowledge to full-scale application is a crucial ongoing effort for both DC Water and HRSD. Full-scale implementation of these concepts at Blue Plains is anticipated to save from $3 to $6 million per year in operating costs. HRSD is preparing to implement PDN-anammox at the James River and York River treatment plants as part of the upgrades related to improving nitrogen removal performance and stability in support of the SWIFT program (Figure 6). The PdN – anammox route for achieving mainstream deammonification has wide application to other treatment facilities and different processes.

Contribution to Social and Economic Advancement

The project promotes cost-effective implementation of nutrient removal in WWTPs that will serve to protect the Chesapeake Bay, to keep rate payers cost low while achieving numerous environmental and quality-of-life benefits.

Conclusions and Significance

This project has resulted in multiple benefits with widespread impact on the engineering community including:

• Developing and proving a reliable alternative short-cut nitrogen removal pathway for achieving mainstream deammonification at full scale that can be applied to almost any existing nitrogen removal process configuration;
• Providing modular tools that combine developed control strategies to maximize success of mainstream deammonification;
• Successfully disseminated this information globally by publishing papers and actively sharing information through conference presentations, discussions and workshops.

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Blue Plains Advanced Wastewater Treatment Plant, Washington DC, is operated and owned by District of Columbia Water and Sewer Authority.	The James River plant upgrade will be configured with a post-denitrifying MBBR that will be configured to allow either conventional full denitrification with methanol or operation in PDN-anammox mode with polishing by conventional nitrification/denitrification zones of the MBBR.
District of Columbia Water and Sewer Authority Nitrogen Removal Pilot - Single Stage Mainstream Shortcut Nitrogen Removal Via Partial Nitrification and Partial Denitrification - Anammox.	Hampton Roads Sanitation District Nitrogen Removal Pilot at Chesapeake-Elizabeth Wastewater Treatment Plant – Showing first stage partial nitrification followed by partial denitrification- anammox in MBBR configuration [not shown].
Hampton Roads Sanitation District Nitrogen Removal Pilot at Chesapeake-Elizabeth Wastewater Treatment Plant – Showing Second stage partial denitrification-anammox in MBBR configuration.	DC Water Pilot Schematic and controller schemes in a single sludge process configuration
HRSD Pilot Schematic and controller schemes in two stage configurations.	Partial denitrification (PdN) – Anammox MBBR Performance with trials using Glycerol, Acetate, and Methanol at Chesapeake-Elizabeth Pilot. The results demonstrated the PdN capability using the various carbon sources using the developed control strategy to optimize PdN.
DC Water Nitrogen Research Team: Picture is featuring Tri Le [far right], PhD candidate from Catholic University, who supported this project through his research on the partial denitrification – anammox controls strategies.	HRSD Research Team: Picture is featuring Stephanie Klaus [3rd from left], PhD candidate from Virginia Tech, and Cody Campolong, master student from Virginia Tech, who supported this project through their research focus on partial denitrification-anammox in 2-stage configuration.

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