Innovative Nutrient
Removal Technologies:
CASE STUDIES OF INTENSIFIED OR ENHANCED TREATMENT
¦
svEPA
U.S. Environmental Protection Agency
Office of Water
Office of Wastewater Management, Water Infrastructure Division
Sustainable Communities and Infrastructure Branch
EPA 830-R-01-001 August 2021
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EPA 830-R-01 -001 -2021
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Innovative Nutrient Removal Technologies: Case
Studies of Intensified or Enhanced Treatment
Prepared by:
Faycal (Phil) Zahreddine, MSEnvEng
Smiti Nepal, P.E.
US. Environmental Protection Agency
Office of Wastewater Management Office of Water
Washington, D.C.
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Notice
This document was produced by the U.S. Environmental Protection Agency (EPA). It has been subjected
to EPA's peer and administrative review and has been approved for publication. Mention of trade names,
technologies and processes, or commercial products does not constitute endorsement or
recommendation for use.
The facility operating information and related analyses in this document are based on data received from
the facilities featured in this document. While EPA has reviewed and evaluated this data, EPA does not
assume responsibility for the accuracy of the data used in the analyses. Neither the data used in this
report nor the technology evaluations provided here nor the conclusions or results reported in this
document substitute for site-specific analysis needed when considering the use of these technologies at
other facilities.
Technology performance and variability in effluent concentrations, particularly for nutrient removal, is
affected by site-specific factors such as process design, wet weather flow, variability in influent flow and
concentrations, process control capabilities, presence of biological inhibitors or toxics, presence of
equalization tanks, sidestreams, and many other factors. In addition, a plant's actual flow and nutrient
loading relative to the design capacity could be a significant factor that impacts performance. As such, the
information in this report can be viewed as a guide based on the investigated plants' actual full-scale
operation over 36 months but should not be used to translate performance or variability to other plants
without careful consideration of the plant's site-specific conditions.
This document is intended to be solely informational and does not impose legally binding requirements on
EPA or other U.S. federal agencies, states, local, or tribal governments; or members of the public.
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Foreword
The Office of Wastewater Management supports communities' consideration and adoption of innovative
and alternative technologies as part of their infrastructure investments for a resilient, clean, and safe
water future. This document provides information on the performance and reliability of several innovative
nutrient removal technologies available for municipal wastewater treatment facilities. Specifically, the
publication shares information on innovative technologies or approaches for achieving nitrogen and/or
phosphorus targets in municipal wastewater treatment plant effluents, evaluates performance and
reliability in meeting permit limits, and shares the lessons learned in implementing such technologies.
In the last few years, there has been an increased interest in innovative nutrient removal technologies.
This interest is driven by many factors including nutrient pollution impacts on water quality, the need to
renew aging infrastructure, and the emergence of new and highly sustainable treatment approaches and
practices. These innovations offer significant advantages in terms of treatment performance and resource
management efficiency. We at EPA have seen many water resource recovery facilities (WRRFs) lead the
way towards a more sustainable and climate resilient future through the adoption of innovative and
alternative technologies and solutions.
As communities evaluate infrastructure investment options, there is an opportunity to integrate resource
recovery solutions in areas such as nutrient removal and recovery, water reuse, energy recovery, and
carbon management; to deliver triple bottom line benefits (i.e., economic, social, environmental) to
WRRFs and their communities. Innovative technologies introduced over the last few years have the
potential to significantly transform and intensify treatment approaches to nutrient removal. Innovative
processes or approaches, when properly designed and operated, can achieve reliable nutrient removal at
a lower carbon and economic footprint, and often with a smaller physical footprint as well. They can help
wastewater treatment facilities reduce their energy demands, costs, chemical usage, or solids production
while reliably meeting discharge permit limits. An additional significant benefit of some of these innovative
technologies is that they can also result in a net gain of treatment capacity.
Introduction and wider adoption of new wastewater treatment technologies can be challenging in the
North American marketplace and require collaborative efforts by all industry stakeholders in addressing
barriers to wider deployment. These barriers can be technical, regulatory, or economic. The risks involved
are often borne by innovators and early technology adopters. Measures that can reduce the risk involved
in new technology applications include increased transparency of information, provision of independent
technology evaluations, and development of new mechanisms for sharing risk more broadly. In order to
facilitate the consideration and adoption of such technologies, the Office of Wastewater Management
works to provide objective resources on innovative and alternative technologies to the public in response
to emerging needs and trends in the sector.
This report includes detailed assessments of several innovative nutrient removal technologies. The
assessments are based on actual operational data over a three-year period and under specific operating
conditions. It is our hope that this report will be useful to utilities and regulators in informing decision-
making related to innovative technology capability and choices as well as in informing the implementation
of water quality standards and discharge permits.
Andrew D. Sawyers
Director, Office of Wastewater Management
Office of Water
U.S. EPA
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Acknowledgement
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This study was completed by the EPA Office of Water, Office of Wastewater Management. Participation
of managers and staff from the six case study facilities who provided data and participated in discussions
with the study authors, and their review and concurrence with their case study write-ups, was valuable
and much appreciated. In addition to providing operational data, the facility managers and in some cases
their consultants provided information on plant process treatment trains and diagrams, operational
procedures, design criteria, and operational difficulties encountered. Following completion of the case
study performance and statistical analyses, draft case studies were developed and provided to facility
managers for review, comments, and concurrence. Final drafts were then reviewed by external experts in
nutrient removal prior to finalizing and publishing this report.
Contributions of facility managers and staff and external peer reviewers of this study are recognized
below:
Facility
Representative
AlexRenew Advanced Water Resource Recovery
Facility, City of Alexandria, Virginia
Hari Santha, Felicia Glapion
Westside Regional Wastewater Treatment Plant.
District of West Kelowna. British Columbia.
Canada
Bryan Mazda. Angela Lambrecht
F. Wayne Hill Water Resource Center,
City of Buford, Georgia
Pierce Freeman, Gayathri Mohan, J.C. Lan,
Robert Harris
City of Kingsley Wastewater Treatment Facility.
City of Kingsley. Iowa
Steve Jantz
South Durham Water Reclamation Facility,
City of Durham, North Carolina
Charles Cocker
Hillsborough Wastewater Treatment Plant
Hillsborough. Town of Hillsborough. North
Carolina
Jeff Mahagan
External Peer Reviewers:
Charles B. Bott, Ph.D., P.E., BCEE
Hampton Roads Sanitation District
Virginia Beach, VA 23455
H David Stensel, Ph.D., P.E., BCEE, WEF Fellow
University of Washington
Mercer Island, WA 98040
Heng Zhang, Ph.D., BCEEM
Independent consultant
Cicero, IL 60804
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Table of Contents
CHAPTER 1.0 Project Background and Approach 1-1
1.1 Introduction 1-1
1.2 The Need for Innovation 1-1
1.3 Conventional and Innovative Nutrient Removal 1-2
1.4 Proj ect Background 1-4
1.5 Participating Facilities and Plant Data 1-5
1.6 Operational Performance 1-6
1.7 Statistical Analysis 1-7
1.7.1 Summary Statistics and Probability Plots 1-7
1.7.2 Data Set Statistical Manipulations 1-8
1.7.3 Variability 1-8
1.7.4 Reliability 1-9
1.8 Report, Data, and Analysis General Limitations 1-10
REFERENCES 1-11
CHAPTER 2.0 AlexRenew Advanced Resource Recovery Facility - Alexandria, Virginia
Mainstream Biological Nitrogen Removal and Sidestream Deammonification Process
(DEMON®) for Centrate Nitrogen Removal - Case Study 2-1
2.1 Background 2-1
2.2 Plant Processes 2-2
2.3 Conventional Nitrogen Removal Technology 2-5
2.4 Deammonification 2-6
2.5 DEMON® Sidestream Deammonification Process at AWRRF 2-7
2.6 Detailed Statistical Analysis - Plant Effluent Concentrations 2-8
2.7 Process Performance - DEMON® Sidestream Deammonification at AWRRF 2-14
2.8 Impact of DEMON® Sidestream Deammonification Process and Other Upgrades on
AWRRF Plant Performance 2-18
REFERENCES 2-23
CHAPTER 3.0 The Westside Regional Wastewater Treatment Plant - Sidestream
Enhanced Biological Phosphorus Removal (S2EBPR) - Case Study 3-1
3.1 Background 3-1
3.2 Plant Processes 3-1
3.3 Conventional Enhanced Biological Phosphorus Removal Technology 3-2
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3.4 Sidestream Enhanced Biological Phosphorus Removal (S2EBPR) 3-4
3.5 Sidestream Enhanced Biological Phosphorus Removal (S2EBPR) at WRWTP 3-5
3.6 Detailed Statistical Analysis - Plant Effluent Concentrations 3-6
3.7 Process Performance - Mainstream EBPR at WRWTP 3-11
REFERENCES 3-14
CHAPTER 4.0 The Kingsley Wastewater Treatment Facility - Enhanced Nitrification -
Submerged Attached Growth Reactor (SAGR®) - Case Study 4-1
4.1 Background 4-1
4.2 Plant Processes 4-1
4.3 Nitrification 4-3
4.4 Submerged Attached Growth Reactor (SAGR®) at KWTF 4-4
4.5 Detailed Statistical Analysis - Plant Effluent Concentrations 4-8
4.6 Process Performance - Submerged Attached Growth Reactor (SAGR®) at KWTF.. 4-12
REFERENCES 4-14
CHAPTER 5.0 The F. Wayne Hill Water Resources Center (FWHWRC) - Gwinnett
County, GA - Enhanced Nutrient Recovery through WASSTRIP® Phosphorus Stripping
and Ostara Pearl® Nutrient Recovery - Case Study 5-1
5.1 Background 5-1
5.2 Plant Processes 5-2
5.3 Conventional Enhanced Biological Phosphorus Removal Technology 5-5
5.4 Phosphorus Recovery 5-7
5.5 The WASSTRIP® Process 5-7
5.6 The Pearl® Process 5-8
5.7 The WASSTRIP® and Pearl® Processes at FWHWRC 5-8
5.8 Detailed Statistical Analysis - Plant Effluent Concentrations 5-9
5.9 WASSTRIP® and Ostara Pearl® Process Performance & Lessons Learned 5-13
REFERENCES 5-18
CHAPTER 6.0 South Durham Water Reclamation Facility - Durham, North Carolina
Mainstream Biological Nitrogen Removal and Sidestream Deammonification Process
(ANITA Mox®) for Centrate Nitrogen Removal - Case Study 6-1
6.1 Background 6-1
6.2 Plant Processes 6-1
6.3 Conventional Nitrogen Removal Technology 6-4
6.4 Deammonification 6-4
6.5 ANITA Mox® Sidestream Deammonification Process at SDWRF 6-6
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6.6 Detailed Statistical Analysis - Plant Effluent Concentrations 6-7
6.7 Process Performance - ANITA Mox® Sidestream Deammonification at SDWRF ... 6-13
REFERENCES 6-17
CHAPTER 7.0 Town of Hillsborough Wastewater Treatment Plant 7-1
7.1 B ackground 7-1
7.2 Plant Processes 7-1
7.3 Conventional Nitrogen Removal Technology 7-3
7.4 Five-Stage BNR Modifications at HWWTP 7-5
7.5 Detailed Statistical Analysis - Plant Effluent Concentrations 7-6
7.6 Process Performance and Lessons Learned - Five-Stage BNR Modifications at
HWWTP 7-13
REFERENCES 7-16
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Tables
Table 1-1. Participating Facilities and Technologies Implemented 1-5
Table 2-1. Design and Average Raw Influent Concentrations and Loads, and Percent of Design for
the AWRRF from January 2015 to December 2017 2-4
Table 2-2. NPDES Limits - January 2015 - December 2017 at AWRRF 2-5
Table 2-3. Summary Statistics for Final Effluent Ammonia Nitrogen for AWRRF from January 2015
to December 2017 2-12
Table 2-4. Summary Statistics for Final Effluent NOx-N for AWRRF from January 2015 to
December 2017 2-12
Table 2-5. Summary Statistics for Final Effluent Total Nitrogen for AWRRF from January 2015 to
December 2017 2-12
Table 2-6. Summary Statistics for Final Effluent ON for AWRRF from January 2015 to December
2017 2-13
Table 2-7. Design Parameters for DEMON® Sidestream Deammonification at AWRRF 2-15
Table 3-1. Current Discharge Limits as of January 1, 2014 atWRWTP 3-2
Table 3-2. EBPR Reliability at Various EBPR Facilities 3-3
Table 3-3. Summary Statistics for Final Effluent TP and OP for WRWTP 3-9
Table 3-4. S2EBPR-Enhanced BNR Reliability atWRWTP 3-13
Table 4-1. Design and Average Raw Influent Concentrations and Percent of Design Loads
for the KWTF from January 2015 to December 2017 4-2
Table 4-2. NPDES Permit Limits - January 2015 - December 2017 at KWTF 4-3
Table 4-3. Gravel Media Composition 4-6
Table 4-4. Summary Statistics for Final Effluent Ammonia Nitrogen for KWTF 4-12
Table 5-1. Design and Average Raw Influent Concentrations and Percent of Design Loads
for the FWHWRC from January 2015 to December 2017 5-4
Table 5-2. NPDES Limits - January 2015 - December 2017 at FWHWRC 5-5
Table 5-3. EBPR Reliability at Various EBPR Facilities 5-6
Table 5-4. Summary Statistics for Final Effluent Total Phosphorus for FWHWRC 5-12
Table 5-5. Ostara Pearl® Production Data 5-14
Table 6-1. Design and Average Raw Influent Concentrations and Percent of Design Loads
for the SDWRF from January 2015 to December 2017 6-3
Table 6-2. NPDES Limits - January 2015 - December 2017 at SDWRF 6-3
Table 6-3. Influent Design Values for the Anita Mox MBBR Process at SDWRF 6-7
Table 6-4. Summary Statistics for Final Effluent Ammonia Nitrogen for SDWRF 6-11
Table 6-5. Summary Statistics for Final Effluent NOx-N for SDWRF 6-11
Table 6-6. Summary Statistics for Final Effluent Total Nitrogen for SDWRF 6-11
Table 6-7. Summary Statistics for Final Effluent ON for SDWRF 6-12
Table 7-1. Design and Average Raw Influent Concentrations and Percent of Design Loads
for the HWWTP from January 2015 to December 2017 7-2
Table 7-2. NPDES Limits - January 2015 - December 2017 at HWWTP 7-3
Table 7-3. Summary Statistics for Final Effluent Ammonia Nitrogen for HWWTP 7-10
Table 7-4. Summary Statistics for Final Effluent NOx-N for HWWTP 7-10
Table 7-5. Summary Statistics for Final Effluent Total Nitrogen for HWWTP 7-11
Table 7-6. Summary Statistics for Final Effluent ON for HWWTP 7-11
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Table 7-7. Comparison of Zone Volumes and Detention Times Before and After Modifications to the
Original Design 7-
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Figures
Figure 2-1. Liquid Treatment Process Train 2-3
Figure 2-2. Solids Treatment Process Train 2-4
Figure 2-3. Nitrogen Transformations 2-7
Figure 2-4. Schematic of Deammonification Reactor at AWRRF 2-8
Figure 2-5. 12-Month Rolling Average Time Series Plot for Plant Effluent TN Load 2-9
Figure 2-6. 30-Day Rolling Average Time Series Plot 2-10
Figure 2-7. Probability Plots for AWRRF from January 2015 - December 2017 - (A) Daily Data;
(B) 30-day Rolling Average; (C) Monthly Average; (D) 12-Month Rolling Average 2-11
Figure 2-8. Probability Summary for AWRRF 2-14
Figure 2-9. (A) Ammonia and Total Nitrogen Removal and Ammonia Loading of Sidestream
Deammonification Process (B) Monthly Average Temperature of the Sidestream
Deammonification Reactor 2-16
Figure 2-10. Monthly Average Plant Effluent TN Concentrations 2-19
Figure 2-11. Average Monthly BNR Aeration 2-20
Figure 2-12. Average Monthly Methanol Use 2-21
Figure 3-1. Schematic of S2EBPR Reactor and BNR System at WRWTP 3-6
Figure 3-2. (A) Daily Times Series Plot, (B) 30-Day Rolling Average, and (C) 12-month Rolling
Average Time Series Plots for WRWTP 3-8
Figure 3-3. Probability Plots for WRWTP (A) Daily Data; (B) 12-Month Rolling Average 3-9
Figure 3-4. Probability Summary for WRWTP Effluent TP and OP 3-10
Figure 3-5. Bioreactor Layout at WRWTP 3-11
Figure 3-6. Cumulative Probability Plot for Bioreactor Effluent OP at WRWTP 3-12
Figure 3-7. Bioreactor Effluent Ortho-P Concentrations at WRWTP 3-13
Figure 4-1. Wastewater Flow Scheme at KWTF 4-2
Figure 4-2. (A) Schematic of SAGR Reactor (B) Cut-away with air distribution 4-5
Figure 4-3. Lagoon Upgrades and SAGR Layout at KWTF 4-8
Figure 4-4. (A) Daily and (B) Monthly Average, and (C) 30-Day Rolling Average Time Series Plots
for Effluent Ammonia at KWTF 4-10
Figure 4-5. Probability Plots for KWTF (A) Daily Data; (B) Monthly Average 4-11
Figure 4-6. Probability Summary for KWTF 4-12
Figure 5-1. Liquid and Solids Treatment Process Train at FWHWRC 5-2
Figure 5-2. Liquid and Solids Treatment Process Train at FWHWRC 5-9
Figure 5-3. (A) Daily and (B) 30-Day Rolling Average Time Series Plots for Effluent TP at
FWHWRC 5-10
Figure 5-4. Probability Plots for FWHWRC-(A) Daily Data; (B) 30-day Rolling Average;
(C) Weekly Average; (D) Monthly Average 5-11
Figure 5-5. Probability Summary for FWHWRC 5-12
Figure 5-6. Orthophosphate Percent Recovery 5-13
Figure 5-7. Monthly Average Bioreactor OP Effluent 5-14
Figure 5-8. Monthly Average Alum and Ferric Chloride Dosage before and after OSTARA Startup ....5-16
Figure 5-9. Sludge Cake Percent Total Solids - Monthly Average 5-17
Figure 6-1. Liquid and Solids Treatment Process Train at SDWRF 6-2
Figure 6-2. Nitrogen Transformations 6-5
Figure 6-3. ANITA Mox® MBBR Model 6-6
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Figure 6-4. 12-month Rolling Average Time Series Plot for TN 6-8
Figure 6-5. 30-Day Rolling Average Time Series Plot 6-9
Figure 6-6. Probability Plots for SDWRF - (A) Daily Data; (B) 30-day Rolling Average; (C)
Monthly Average; (D) 12 Month Rolling Average 6-10
Figure 6-7. Probability Summary for SDWRF 6-13
Figure 6-8. Simplified Flow Diagram of SDWRF Deammonification System 6-14
Figure 6-9. Monthly Average Ammonia Percent Removal for Sidestream Reactors 1 and 2 6-15
Figure 1-1. Solids and Liquid Treatment Process Trains at HWWTP Before BNR Upgrades 7-2
Figure 7-2. Modified Ludzack-Ettinger Process 7-4
Figure 7-3. 5-Stage Bardenpho Process 7-5
Figure 7-4. HWWTP 5-Stage BNR Configuration 7-6
Figure 7-5. 12-Month Rolling Average Time Series Plot for TN 7-7
Figure 7-6. 30-Day Rolling Average Time Series Plot 7-8
Figure 7-7. Effluent TN Individual Sample Time Series Plot 7-8
Figure 7-8. Probability Plots for HWWTP - (A) Daily Data; (B) 30-day Rolling Average; (C)
Monthly Average; (D) 12-Month Rolling Average 7-9
Figure 7-9. Probability Summary for HWWTP 7-12
Figure 7-10. Initial BNR Performance in 2014 7-13
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A20
ABAC
AWRRF
Anammox
AOB
BAC
BNR
BOD
BPR
BRB
cBOD
cBODs
COD
CoV
CPT
CV
C/P
DO
EBPR
EPA
EPRI
FE
FWHWRC
GAO
GMF
HDPE
HWWTP
HRT
IDNR
IF AS
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KWTF
MBBR
MGD
ML
MLE
N
ND
NdN
NH3-N
NH4-N
NO2-N
Acronyms and Abbreviations
Anaerobi c/anoxi c/aerobi c
Ammonia-based aeration control
AlexRenew (Alexandria Renew Enterprises) Advanced Water Resource Recovery
Facility
Anaerobic ammonium oxidation
Ammonia oxidizing bacteria
Biological activated carbon
Biological nutrient removal
Biochemical oxygen demand
Biological phosphorus removal
Biological reactor basin
Carbonaceous biochemical oxygen demand
Five-dav carbonaceous biochemical oxygen demand
Chemical oxygen demand
Coefficient of variation
Centrate pre-treatment
Coefficient of variation
Carbon to phosphorus ratio
Dissolved oxygen
Enhanced biological phosphorus removal
United States Environmental Protection Agency
Electric Power Research Institute
Final effluent
F. Wayne Hill Water Resource Center
Glycogen accumulating organism
Granular Media Filtration
High density polyethylene
Hillsborough Wastewater Treatment Plant
Hydraulic retention time
Iowa Department of Natural Resources
Integrated Fixed Film Activated Sludge
Ion exchange
Kingsley Wastewater Treatment Facility
Moving bed biofilm reactor
Million gallons per day
Mixed Liquor
Modified Ludzack-Ettinger
Nitrogen
Not detected
Nitrification and denitrification
Ammonia species (as nitrogen)
Ammonium (as nitrogen)
Nitrite (as nitrogen)
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N03-N
Nitrate (as nitrogen)
NOB
Nitrite oxidizing bacteria
NOx-N
Nitrate plus nitrite as nitrogen
NPDES
National Pollutant Discharge Elimination System
NRCY
Internal nitrified recycle
OHO
Ordinary heterotrophic organism
ON
Organic nitrogen (total)
ORP
Oxidation-reduction potential
Ortho-P
Orthophosphate
P
Phosphorus
PAO
Polyphosphate accumulating organism
qPCR
Quantitative polymerase chain reaction
PHA
Poly-P-hydroxyalkanoate
PHB
Poly-P-hydroxybutyrate
PO4-P
Phosphate (as phosphorus)
PS
Primary sludge
RAS
Return activated sludge
rbCOD
Readily biodegradable chemical oxygen demand
RO
Reverse osmosis
SAGR®
Submerged Attached Growth Reactor
S2EBPR
Sidestream enhanced biological phosphorus removal
SBR
Sequencing batch reactor
SCADA
Supervisory control and data acquisition
SDWRF
South Durham Water Reclamation Facility
SRT
Solids retention time
TKN
Total Kjeldahl nitrogen
TN
Total nitrogen
TP
Total phosphorus
TPSs
Technology performance statistics
TSS
Total suspended solids
UV
Ultraviolet
VFA
Volatile fatty acid
WAS
Waste activated sludge
WERF
Water Environment Research Foundation
WRWTP
Westside Regional Wastewater Treatment Plant
WRF
The Water Research Foundation
WRRF
Water resource recovery facility
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CHAPTER 1.0
Project Background and Approach
1.1 Introduction
The U.S. Environmental Protection Agency (EPA) completed a project that developed six
detailed case studies of recent innovations in municipal nutrient removal treatment. The project
included five facilities in the U.S. and one in Canada. The facilities implemented innovative
technologies or process enhancements designed to significantly intensify treatment orenhance
the removal of total nitrogen (TN) or total phosphorus (TP), with one of the facilities evaluated
for ammonia nitrogen treatment only. Treatment intensification has been defined as any system
that significantly outperforms conventional designs, and performance could be defined using
effluent quality, energy consumption, or capital expenditures (Sturm, 2016).
Technologies that result in treatment intensification have also been described as those that
provide reduction in treatment tank volume or footprint compared to those with established
designs.
The focus of the analysis in this project centered on assessing the performance of the selected
processes over a three-year period, including assessing their impact on mainstream treatment
performance and statistical variability of plant effluent nutrient concentrations. Each case study
presents a detailed technical description of the innovative process, an analysis of process
performance, an assessment of the process train consistency in meeting permit limits, and the
lessons learned by the facility in implementing the process and addressing operational
difficulties.
Wastewater treatment facilities are subject to real conditions that impact performance and
variability in effluent concentrations. These conditions include seasonal challenges such as lower
temperatures, wet weather high flow events, changes in influent characteristics, unavoidable
imperfections that are present in every design or operation, mechanical problems, and impacts of
toxic discharges into the sewer collection system that impact plant process performance, among
others. As such, providing detailed assessments of innovative nutrient removal technologies over
a three-year period based on sufficient actual operational data can be quite useful to utilities and
regulators in informing decision-making related to innovative technology capability and choices,
as well as in informing the implementation of water quality standards and development of
discharge permits.
1.2 The Need for Innovation
The water and wastewater industry is facing significant challenges in its ability to maintain safe
and sustainable water resources. These challenges include decreased availability and quality of
water resources, population growth, emerging contaminants, aging infrastructure, and impacts of
climate change related to precipitation, temperature, and flooding. Other challenges include
changing workforce dynamics and the need to enhance workforce retention, recruitment, and
development. In addition, challenges related to costs associated with meeting water quality
objectives, coupled with declining water consumption and associated decline in water revenue at
some facilities, are resulting in significant economic challenges for utilities.
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In addition, the industry has been transforming from one of known challenges that can be
addressed by well-established wastewater engineering solutions, to one with a variety of
uncertainties such as in how to project future water use, climate change impacts, and the
technical capacity necessary for decision making. These uncertainties will likely require a suite
of strategies to mitigate and master the most probable and consequential trends and associated
risks. Utility responses to uncertainties, risks, costs, and innovative opportunities will help shape
public perceptions of water utilities and their leaders, and in turn, shape the state of the industry.
In the face of uncertainty, research and information sharing are critical to industry adaptation to
uncertainties and, ultimately, success (Hughes et al., 2013).
The water and wastewater industry is also realizing that utility sustainability is dependent on the
ability to explore, evaluate, and implement innovative technologies and practices (Ries and
Murthy, 2014). Water and wastewater utilities have historically been more conservative in
accepting new ideas and technologies, in part due to traditional procurement practices intended
to manage risk and organizational structures resistant to new business practices. Over the last ten
years, however, many utilities have begun to take ownership of solution development to key
challenges. These utilities are implementing innovation programs focused on accelerating the
development of innovative technologies.
Third party process assessments of innovative technologies, such as the assessments in this
document, can be of value to many utilities exploring innovative technologies. The assessments
provide potential technology adopters information that may not otherwise be obtained with their
own resources and that can be useful in better assessing potential risks and benefits in adopting
these technologies.
Optimizing existing technologies and introducing new ones can both be effective in mitigating
the costs of wastewater treatment for the wastewater industry; however, the introduction of new
technologies faces significant obstacles in the North American marketplace. The risks involved
with these innovation introductions mean that many municipalities will not participate in initial
technology adoption, waiting instead for others to be first. Recommended measures that will
reduce the risk involved in new technology applications have been identified, such as increased
transparency of information, provision of independent evaluations of technologies, and
mechanisms for sharing risk more broadly (Parker, 2011).
1.3 Conventional and Innovative Nutrient Removal
Nutrient control has been required at some municipal treatment plants for many years. In the last
few years, there has been an increased interest amongst industry stakeholders in innovative
nutrient removal technologies. This interest is driven by a number of factors. These include the
need to renew aging infrastructure originally constructed in response to the 1972 Clean Water
Act, the emergence of new and highly sustainable treatment approaches and practices, a
paradigm shift in the industry's view that wastewater is a resource and not a waste, and
increasingly stringent effluent nutrient standards implemented across the U.S. to mitigate
eutrophication by managing nitrogen and/or phosphorus. Many States have adopted or are now
planning to adopt nutrient criteria into their water quality standards and are considering
lowering nutrient limits in renewing discharge permits. Many more plants may soon be required
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to construct new nutrient control facilities or upgrade their existing facilities to consistently meet
lower effluent limits. This has increased interest in information on innovative cost- effective
technologies or approaches for achieving lower total nitrogen and/or total phosphorus levels in
municipal wastewater treatment plant effluents as well as in a need to evaluate novel
technologies or operating strategies and define their performance and reliability in meeting
permit limits.
Conventional nitrogen removal practiced over the last 40 years involves the microorganism-
mediated autotrophic oxidation of ammonia to nitrite then to nitrate under aerobic conditions in a
two-step process called nitrification. This process is followed by heterotrophic reduction of
nitrate to nitrite then to nitrogen gas in the presence of an organic carbon source and the absence
of dissolved oxygen (DO) in a process called denitrification. Nitrification is an aerobic process
requiring energy-intensive and costly aeration and additional aeration volume to maintain
required DO levels; it may require the addition of chemicals such as caustic or sodium
bicarbonate to maintain desired alkalinity levels. Denitrification requires an adequate amount of
carbon, often beyond what is available in the incoming wastewater in order to achieve low total
nitrogen limits. Both processes result in sludge production which requires subsequent processing
prior to beneficial use or disposal.
Conventional phosphorus removal is achieved by chemical phosphorus precipitation and/or by
biological phosphorus removal. Chemical phosphorus precipitation requires the addition of
chemicals in the form of metal salts. This process results in significant additional sludge
production particularly when very low phosphorus limits need to be met. Also, metal salts react
with and consume natural alkalinity in the wastewater. Biological phosphorus removal (BPR)
relies on consumption of readily biodegradable chemical oxygen demand (rbCOD) and
anaerobic release of phosphate followed by aerobic phosphate uptake by polyphosphate
accumulating organisms (PAOs). Plants using BPR typically include dedicated anaerobic zones
followed by aerobic zones with DO generally greater than or equal to 1.0 mg/1.
Over the last decade, a number of highly sustainable processes used for nutrient removal or
approaches for enhancing existing nutrient removal processes have been introduced to the
market, but the rate of introduction and adoption by facilities has been generally slow. In some
cases, these innovative processes or approaches can achieve reliable nutrient removal at a lower
carbon and economic footprint, often with a smaller physical footprint, thereby helping
wastewater treatment facilities in reducing their energy demands, costs, chemical usage, and
solids production while reliably meeting their permit limits. In some cases, technologies (such as
deammonification) have been implemented under specific favorable sidestream conditions but
may not yet be ready for deployment under mainstream full plant flow and varying wastewater
influent characteristics and conditions. In other cases, innovative technologies or approaches
may not be integral to the mainstream process (e.g., sidestream phosphorus stripping, granular
sludge applications) but have a significant positive impact on nutrient removal efficacy and
required resources such as aeration energy or carbon addition. An additional significant benefit
of some of these innovative technologies is that they can, in some cases, also result in a net gain
of treatment capacity.
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It should be noted that many technical publications can be found in the literature drawing
conclusions or making claims about the capabilities of specific technologies in reaching low
nutrient concentrations. While many of these publications are accurate and useful, claims of
technology performance should be viewed with a degree of caution unless supported by plant
design and operational information, along with statistical analysis of data from longer-term
operating periods. Presentation of performance data without stating its statistical characteristics
could be misleading to utilities making infrastructure decisions to comply with nutrient permit
limits and prevents the comprehensive comparison of data among various studies (Bott et al.,
2011).
1.4 Project Background
This project continues previous EPA efforts to share information on municipal wastewater
treatment technologies in the area of nutrient removal. The scope and approach of this project
was influenced by two previous studies that presented information on the performance of
nutrient removal processes. The first was a two-volume EPA report titled "Municipal Nutrient
Removal Technologies Reference Document" published in 2008. The report was developed to
provide information to assist local decision-makers and regional and state regulators in planning
cost-effective nutrient removal projects for municipal wastewater treatment facilities (Kang et
al., 2008). The report included performance data and a statistical evaluation of 40 treatment
alternatives in service at the time and 30 full-scale treatment facilities achieving various levels of
nutrient removal. The statistical analysis evaluated the variability of effluent concentrations
based on mostly one-year data sets and included various percentiles (i.e., 50th, 92nd, 98th, and
99.7th percentiles) of nutrient concentration data sets. The report also included information on
capital as well as operations and maintenance costs associated with the various technologies and
facilities.
The second project was conducted by the Water Environment Research Foundation (WERF, now
the Water Research Foundation) through its nutrients research challenge program and in
cooperation with the Water Environment Federation (WEF) and resulted in a publication entitled
"Nutrient Management Volume II: Removal Technology Performance & Reliability". The
project was influenced by the EPA study mentioned above and included a comprehensive
evaluation of multiple nutrient removal plants designed and operated to meet very low effluent
TN and TP concentrations, several as low as 3.0 mg/1 TN and 0.1 mg/1 TP. The study focused on
determining the TN and TP effluent concentrations achieved by the processes investigated. The
investigation also focused on the ability of nitrification technologies to meet low maximum daily
limits for ammonia. Three years of operational data from 22 exemplary plants were analyzed
using a consistent statistical approach that considered both process reliability and the permit
limits applied. Technology Performance Statistics (TPS) were defined as three separate values
representing the ideal, median, and reliably achievable performance. Also, monthly average 95th
percentiles of effluent data were used to compare the plants in terms of their ability to achieve
the 3.0 mg/1 TN or 0.1 mg/1 TP criteria. Maximum day statistics were used to stratify the ability
of plants to meet low maximum day permit levels. The project focused on maximizing what can
be learned from existing technologies to provide a database that will inform key decision makers
about proper choices for both technologies and rational bases for statistical permit writing
(Parker et al., 2011).
1-4
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This EPA study focuses on innovative nutrient removal treatment processes or process
enhancements designed to significantly intensify treatment or enhance the removal of TN or TP
from municipal wastewaters. The study presents detailedtechnical descriptions of the innovative
processes, an analysis of process performance, an assessment of the process train reliability in
meeting permit limits, and the lessons learned by thefacility in implementing the process and
addressing operational difficulties encountered. The study also presents the benefits of each
innovative technology compared to applicable conventional technologies.
1.5 Participating Facilities and Plant Data
At the start of the project, EPA developed an initial list of 18 candidate facilities. These facilities
had relatively recently implemented innovative nutrient removal technologies or process
enhancements that intensified treatment or significantly improved existing process performance.
EPA reviewed published information on the facility projects to determine if the innovations have
been in operation at full scale and for how long, and to get an initial understanding of the
benefits resulting from their deployment. EPA selected a short list of six of these facilities and
contacted facility managers to assess their interest in participating in this project and inquire
about data availability. The main considerations used in selecting the six facilities were the
expected technology benefits, availability of a minimum of three years of operating data, the
challenges addressed by the facility, and lessons learned in implementing the technology that
could be useful to this report's intended audience. All six facilities expressed their interest in
participating in the project and providing facility data. Table 1-1 provides a list of the facilities
and the technologies implemented.
Table 1-1. Participating Facilities and Technologies Implemented
Facility
Innovative Process or Enhancement
AlexRenew Advanced Water Resource
Recovery Facility, City of Alexandria,
Virginia
DEMON® Sidestream Deammonification
Westside Regional Wastewater Treatment
Plant, District of West Kelowna, British
Columbia, Canada
Sidestream Enhanced Biological Phosphorus
Removal (S2EBPR)
F. Wayne Hill Water Resource Center,
City of Buford, Georgia
WAS STRIP® Stripping and Ostara Pearl®
Phosphorus Recovery
City of Kingsley Wastewater Treatment
Facility, City of Kingsley, Iowa
Submerged Attached Growth Reactor
(SAGR®) Nitrification
South Durham Water Reclamation Facility,
City of Durham, North Carolina
ANITAMOX® Sidestream Deammonification
Hillsborough Wastewater Treatment Plant,
Town of Hillsborough, North Carolina
Low Nitrogen BNR Enhancement
Modification
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For the six selected case study facilities, 36 months of final effluent data and innovative process
operational data provided by the participating facilities were analyzed and subjected to a detailed
statistical analysis. For plants analyzed for nitrogen removal, nitrogen species concentrations
evaluated included TN, ammonia nitrogen (NH3-N), nitrate plus nitrite nitrogen (NOx-N), and
organic nitrogen (ON). ON as referred to in this report means total organic nitrogen. In some
cases, data for some species (e.g., ON) was not available. The nitrogen species(i.e., NH3,N02,
NO3, ON) referred to in this report indicate the chemical forms using the molecular weight of
only the nitrogen atoms (e.g., NH3-N) and not the molecular weight of the entire ammonia
molecule (in the case of ammonia, 1 nitrogen atom and 3 hydrogen atoms). For plants analyzed
for phosphorus removal, TP and orthophosphate (OP) were considered.
To ensure consistency in data representation and usability in statistical analyses, EPA reviewed
all data received from the case study facilities prior to analysis. Effluent values for each
constituent reported as non-detectable, zero, or as the minimum detection limit were replaced
with half of the minimum detection limit. EPA used all data provided by the case study facilities
in the analyses with no exclusions.
1.6 Operational Performance
This study assessed the performance of the innovative process as well as the performance and
variability of plant effluent concentrations of the nutrient treated. The study also assessed each
plant's ability to consistently meet its nutrient limit for the nutrient investigated.
Depending on operational data and process control information provided by each plant, an
attempt was made to identify the factors that impacted the performance of the innovative process
investigated. In addition to reviewing available process control data, this included correlating
nutrient effluent concentrations with other operational parameters as well comparing actual
influent loading and characteristics to design criteria. For the sidestream processes, the study also
investigated the impact of the sidestream process on the mainstream nutrient removal process,
including the impact on mainstream process stability.
It should be noted that technology performance and variability in effluent concentrations,
particularly for nutrient removal, is affected by site-specific factors such as process design, wet
weather flow, variability in influent flow and concentrations, process control capabilities,
presence of biological inhibitors or toxics, presence of equalization tanks, sidestreams, and many
other factors. In addition, a plant's actual flow and nutrient loading relative to the design
capacity could be a significant factor that impacts performance as it can reflect the degree of
stress placed on the plant, particularly relative to biological treatment processes when looking to
achieve very low nutrient limits. As such, the information in this report can be viewed as a guide
based on the investigated plants' actual full-scale operation over 36 months but should not be
used to translate performance or variability to other plants without careful consideration of the
plant's site-specific conditions.
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1.7 Statistical Analysis
1.7.1 Summary Statistics and Probability Plots
The use of probability values that relate to permit compliance is very useful in evaluating process
performance under an appropriate set of averaging conditions. A statistical analysis was
conducted on the complete sets of 3-year final effluent data from each facility. In some cases, the
effluent concentrations from the innovative process were statistically assessed as well. Summary
statistics were calculated for the full final effluent data set. These included the mean, geometric
mean, standard deviation, coefficient of variance (CoV), skew, minimum, and maximum. Time
series data plots were prepared showing the individual data points (e.g., daily concentrations)
with the plots also generally showing the facility's discharge limits and median values.
To better assess performance and variability of effluent concentrations and the ability of each
facility to meet permit limits, a set of percentile statistics was calculated from the data sets
including the Technology Performance Statistics (TPSs) evaluated by Neethling et al. (2009) to
represent the lowest (3.84th percentile), median (50th percentile), and reliably achievable
technology performance (95th percentile). The calculated set of percentile statistics for this
project includes the 3.84th, 50th, 90th, 95th, and 99th percentiles. A percentile represents the
probability that a data value is less than or equal to the stated concentration. As an example, a
95th percentile effluent concentration of 4 mg/1 TN calculated from a data set indicates that 95
percent of the data points are below 4 mg/1 and as such, the probability of meeting a 4 mg/1
effluent concentration is 95 percent.
Log-transformed probability plots were then developed using the approach presented by Bott et
al. (2011) by ranking the effluent concentration data in Microsoft Excel then calculating the
corresponding Weibull probability (P) values by dividing P by (n+1), with n being the number of
data points in the set. The concentration values were plotted versus the probability (less than or
equal to) using SigmaPlot 14.0 (Systat Software, Inc.) with the y-axis converted to a log scale to
reflect the lognormal transformation, and the x-axis plotted using the normal distribution
probability scale. Other statistical calculations were done using Microsoft Excel.
The TPSs evaluated were used in checking performance in relation to desired effluent limits and
their specific averaging periods. The 14-day TPS (3.84th percentile) representing an ideal
performance sustained over only 14 days is useful in assessing best possible short-term
performance. It is minimally influenced by various factors affecting facility and operational
performance variability including influent variability, seasonal variations and loading conditions,
the full impact of process control corrections, equipment failures, and occasional industrial
discharges. As such, it does not reflect reliable sustained performance. The TPS-50 percent
(median) isuseful in looking at the performance on an annual basis but does not provide a
statistical assessment of performance on a monthly basis. The TPS-95 percent (95th percentile) is
often used as a measure of reliable maximum month performance but the appropriate reliable
performance percentile should be selected depending on the facility risk of tolerance given
existing plant infrastructure, equipment redundancy, and other facility factors. Other statistics
such as a 30-dayrolling average could be used in assessing performance consistency in meeting a
monthly or an annual average under conditions experienced over a longer time period such as 3
years.
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In using the probability plots, the appropriate percentile probability to be used in assessing
reliable performance should be selected taking into account a number of considerations such as
the technology itself, the averaging period used in a plant's National Pollutant Discharge
Elimination System (NPDES) permit, and risk tolerance. Additionally, the use of specific
percentiles in assessing performance should be considered withan understanding of the
associated implications in terms of the resulting frequency of permit violations. For example,
the 95th percentile for a daily average limit is exceeded 91 times (5 percent x 365 days x 5 years)
in a 5-year NPDES permit, while the 95th percentile for a monthly average limit is exceeded 3
times (5 percent x 12 months x 5 years) in a 5-year NPDES permit.
1.7.2 Data Set Statistical Manipulations
For each facility, a series of data manipulations were conducted based on daily values, 30-day
rolling average values, monthly average values, and 12-month rolling average (rolling annual
average) values. In most cases, weekly values were also analyzed. A rolling average is a moving
average calculated as explained below. For each of these value categories, the manipulations
included the summary statistics, percentile calculations (probabilities), and probability plots
described above as well as time series plots showing effluent parameter concentrations versus the
data category (e.g., daily, monthly, etc.).
The calculation of rolling averages was done by taking the mean of the data points in the initial
averaging period to calculate the initial rolling average and then shifting forward by one data
point to calculate the next rolling average. For example, the first 30-day rolling average was
calculated by averaging the first 30 consecutive daily data points (such as effluent
concentrations). The next 30-day average will exclude the previous average's first day data point
and add the data point for the next day following the initial 30-day period. Each 30-day average
was plotted on the 30th day. As such, the rolling average plotted date represents the plotted date
and the previous 29 days. With three years of data generally provided for each plant and one leap
year period in 2016, 1096 daily data points will be subject to the above manipulations if
complete daily data is provided,
It should be noted that some plants did not collect daily samples. So, for example, a plant that
only collects samples three times a week would generally have 12 data points included in a 30-
day rolling average. When 30-day rolling averages were calculated, the averages span gaps in the
data. As a result, the rolling average represents a true rolling average of daily data within a 30-
day period and not a 30 data point rolling average.
1.7.3 Variability
Variations in effluent quality from nutrient removal processes are the result of various internal
and external factors. These could include variations in influent characteristics, environmental
conditions such as temperature, presence of toxics or inhibitors in the influent, and process
operational parameters and other factors inherent to the treatment process. In many cases, causes
of effluent variability may not be explained by analyzing available data. However, determining
variability in effluent concentrations is an important consideration in designing nutrient removal
facilities as well as in the development of discharge permit limits. Variability measures allow
designers assessing technology options for a particular facility to include appropriate levels of
1-8
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conservatism in their design in light of permit effluent concentrations and averaging periods.
Effluent variability measures also allow the development of appropriate effluent limits taking
into consideration effluent variability as well as receiving water flows and constituent
concentrations variability.
Several statistical parameters have been used for assessing variability of effluent concentrations
including the variance, standard deviation, CoV, and TPSs. TPSs are used to assess variability in
this report, as they provide a precise and practical measure of the capability of a nutrient
removal treatment to meet an effluent limit in specific numerical terms particularly at low
concentrations where variability is expected to be higher. The 95th percentile, for example, can
be useful in evaluating the ability tomeet monthly permit limits. It is also useful in informing
process design to ensure permit compliance.
The ratio between the 3.84th, 50th, and 95th percentiles can also be used to represent the
variability of performance. For example, the ratio of the 95th to 50th percentile can be used to
assess the ability of a technology to meet monthly limits compared to annual values. Comparing
a particular ratio for different technologies provides a measure of the stability of a particular
process compared to another.
1.7.4 Reliability
The reliability of a treatment plant or a treatment process may be defined as the probability of
adequate performance for a specified period of time under specific conditions, or, in terms of
treatment plant performance, the percent of time that effluent concentrations meet specified
permit requirements. Because of the variations in effluent quality, treatment plants must be
designed to produce an average effluent concentration below the permit requirements. The
question is: what value should be used for process design to be assured that constituent
concentrations in the effluent will be equal to or less than a specified limit with a specified
degree of reliability? (Tchobanoglous et al., 2003)
Two approaches have been used to estimate the design value needed to meet prescribed
standards. One approach developed by Niku et al. (1979, 1981) involves the use of a coefficient
of reliability (COR) in relating design values to the standards that must be achieved on a
probability basis. Another graphical probability approach for setting the required effluent value
at a specified reliability level was described by Tchobanoglous et al. (2003). As nutrient removal
as well as many wastewater treatment and other environmental processes are often log-normally
distributed, the use of a plotted ideal log-normal distribution line can be practical and may
eliminate the need to conduct multiple calculations to determine reliability under different
conditions of effluent variability and permit averaging periods as long as log-normal data
distribution is valid.
In addition to the individual data points on the case study probability plots in this report, a
colored line representing the ideal log-normal distribution was drawn as done by Bott et al.
(2011) based on log-normally transforming the data set, determining the expected probabilities
by computing the log-normal Z (=LOGNORMDIST(x, mean of ln(x), std. dev. of ln(x) in Excel)
1-9
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using the log-transformed mean and standard deviation. The expected normal probability
associated with the Z values (=NORMSDIST(x) function in Excel) were then calculated. The
log-normally transformed data were then plotted as a red line versus the expected log-normal
probability in each of the probability plots. The reliability in meeting a given effluent
concentration can be determined simply by following the red line and reading the percentile on
the x-axis as long as the log-normal distribution is valid. While the plotted red lines are not used
in describing process performance in this report, we included them in this report for use by
practitioners who may be interested in assessing the reliability associated with any given
concentration using the ideal log-normal distribution red line in cases where the data is well
fitted to the log-normal distribution.
1.8 Report, Data, and Analysis General Limitations
Facility and operational data used in this study were provided by the participating facilities.
While considerable effort was conducted by EPA in evaluating the data and discussing it with
facility managers, EPA does not assume responsibility for the quality of the data or any issues or
circumstances associated with the collection or analysis of the data.
As noted in Section 1.7.2, some plants did not collect daily samples. Also, some facilities did not
have a complete data set of influent flow or influent and effluent nutrients species
concentrations. In other cases, mainstream biological nutrient removal (BNR) process data or
sidestream process operational data was incomplete. Where applicable, this was noted in the
case studies and for the most part, did not significantly impact the performance evaluations.
It is important to recognize that infrastructure conditions, operational procedures, and site-
specific conditions under which the data for this project were collected significantly impact
treatment performance and the technology performance statistics and related analyses. These
conditions include internal factors such as process design, process control capabilities, presence
of equalization tanks and onsite solids processing including anaerobic digesters, sidestreams, and
construction. They also include external conditions such as wet weather flow, ambient
temperature, and industrial discharges. As such, while the performance analysis in this study
provides a clear picture of the achieved treatment associated with the technologies evaluated at
these facilities, the results cannot be directly translated and should be used with significant
judgement in relating them to performance at other facilities, taking into consideration site-
specific conditions and the factors mentioned above.
The mention of trade names, vendors, or products in this report does not represent an actual or
presumed endorsement, preference, or acceptance by EPA or the Federal Government. Stated
results, conclusions, usage, or practices do not necessarily represent EPA views or policies.
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REFERENCES
Bott, C., Parker, D. 2011. "Nutrient Management Volume II: Removal Technology Performance
& Reliability". Water Environment Research Foundation. NUTRlR06k. Alexandria, VA.
Hughes, J., and M. Tiger. 2013. "Steering Innovation in Water Utility Finance and Management:
Summary Report". Project #4506. Denver, Colo: Water Research Foundation.
Kang, S.J., Olmstead, K., Takacs, K., Collins, J. 2008. "Municipal Nutrient Removal
Technologies Reference Document", EPA 832-R-08-006, report prepared for EPA by Tetra
Tech.
Neethling, J.B., Stensel, D., Parker, D., Bott, C., Murthy, S., Clark, D., 2009. "What is the Limit
of Technology (LOT)? A Rational and Quantitative Approach". Proceedings of the Water
Environment Federation Annual Technical Conference and Exhibition, pp. 5917-5930.
Niku, S., Schroeder, E., and Samaniego, F. (1079). "Performance of Activated Sludge Processes
and Reliability-Based Design". Journal Water Pollution Control Federation, vol. 51, p.2841.
Niku, S., Schroeder, E., Tchobanoglous, G., and Samaniego, F. (1981). "Performance of
Activated Sludge Processes: Reliability, Stability, and Variability". U.S. Environmental
Protection Agency, EPA Grant No. R805097-01, pp. 1-124.
Parker, D. 2011. "Introduction of New Process Technology into the Wastewater Treatment
Sector." Water Environment Research, 83: 483-497.
Parker, D., Bott, C., Jimenez, J., Miller, M., Murthy, S., Neethling, J.B., Pramanik, A.,
Zahreddine, P. 2011. "WEF/WERF Cooperative Study of Nutrient Removal Plants: Achievable
Technology Performance Statistics for Low Effluent Limits". Proceedings of the Water
Environment Federation/International Water Association Nutrient Recovery and Management
Conference, January 2011.
Ries, M., and Murthy, S. 2014. "Water Utility R&D: Establishing Metrics to Justify the
Investment". Proceedings of the Water Environment Federation Utility Management Conference.
Savannah, GA.
Sturm, B. 2016. "State of Knowledge and Workshop Report: Intensification of Resource
Recovery (IR2) Forum". Project #4506. Denver, Colo: Water Research Foundation. Project #
TIRR1R15. Alexandria, Virginia. Water Environment Research Foundation.
Tchobanoglous, G., Burton, F. L., Stensel, H. D., & Metcalf & Eddy. (2003). "Wastewater
Engineering: Treatment and Reuse". Boston: McGraw-Hill.
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CHAPTER 2.0
AlexRenew Advanced Resource Recovery Facility - Alexandria, Virginia
Mainstream Biological Nitrogen Removal and Sidestream
Deammonification Process (DEMON®) for Centrate Nitrogen Removal -
Case Study
2.1 Background
The Alexandria Renew Enterprises (AlexRenew) Advanced Water Resource Recovery Facility
(AWRRF) is a 54 million gallons per day (MGD) wastewater treatment facility located in
Alexandria, Virginia. The facilitycurrently serves more than 300,000 people in the City of
Alexandria and adjacent portions of Fairfax County. The plant discharges into Hunting Creek, a
tributary of the Potomac River and subsequently the Chesapeake Bay.
To meet an annual average Total Nitrogen (TN) concentration goal of 8 mg/1, the facility was
upgraded in 2002 to include replacement of its rotating biological contactors with a suspended
growth activated sludge system and an upgraded tertiary treatment process to removetotal
suspended solids (TSS) and Total Phosphorus (TP) using inclined-plate settling tanks and deep-
bed sand filters.
In 2005 Virginia's Department of Natural Resources enacted new regulations to reduce nutrient
levels in the Chesapeake Bay, which included setting nutrient load caps on wastewater treatment
plant nutrient discharges. The facility was required to meet a maximum TN waste load allocation
of 493,381 lb/yr and a TP average monthly concentration limit of 0.18 mg/1 and average weekly
limit of 0.27 mg/1. The facility initiated a nitrogen removal enhancement program in 2009,
which included addition of anoxic volume to the existing biological reactors, expansion of the
methanol addition system, and construction of a centrate pretreatment facility and a nutrient load
management facility. The certificate-to-operate,following completion of all the construction
activities, was obtained in August of 2016. Starting January 2017, the annual average TN permit
limit was lowered to 3.0 mg/1, with the same load cap.
Since May 2015 the facility has been operating a centrate pre-treatment system using the
DEMON® sidestream deammonification process to remove nitrogen from the centrate that
results from dewatering anaerobically digested sludge. Prior to the upgrade, this stream
comprised as much as 20 percent of the total nitrogen load entering the biological reactors.
Cost comparisons with mainstream treatment by other investigators revealed that sidestream
treatment using the deammonification pathway can be as much as three times lower in cost per
pound of nitrogen removed ($0.93/lb of nitrogen removed for deammonification compared with
$2.66/lb of nitrogen removed for mainstream treatment) when capital and operating costs were
considered (Bilyk et al., 2017). However, actual savings will vary depending on the process
used, existing facility infrastructure, influent characteristics, process control efficiency, and other
factors.
2-1
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2.2 Plant Processes
Liquid treatment processes at the AWRRF are shown in Figure 2-1. Preliminary treatment
includes three-inch coarse screening, Vi inch fine screening, and vortex grit removal. Primary
treatment occurs in eight settling tanks. Primary effluent flows into the biological treatment
process consisting of six biological reactors and six secondary settling tanks. Primary sludge
from the bottom of the primary settling tanks is pumped to gravity sludge thickeners.
The primary effluent can also be diverted to a nutrient load management facility, which is
essentially a load equalization facility used to balance the diurnal ammonia-nitrogen loading to
the biological reactors during periods of above-average ammonia nitrogen loading. The diverted
flow is held in storage and then pumped back to the biological reactors during below-average
loading periods. In this manner, the ammonia-nitrogen loading to the biological reactors is
balanced and spikes are avoided.
The biological reactors also receive flow from the centrate pre-treatment facility. This facility is
designed to treat ammonia-rich dewatering centrate and remove most of the associated ammonia
load prior to re-introduction of the recycle stream to the main plant flow ahead of the biological
system. The biological reactor system can be operated in parallel (Modified Ludzack-Ettinger
(MLE) mode) or in series (step-feed mode). While the system was designed with the step feed
BNR configuration, it has relied on the addition of methanol to the last anoxic zone when and as
needed to achieve the new effluent requirements.
Ferric chloride is added in the secondary settling tanks for phosphorus removal. Solids from the
bottom of the settling tanks are returned to the biological reactor basins as return activated sludge
(RAS), and a portion of the solids is diverted to the solids handling system as waste activated
sludge (WAS).
Effluent from the secondary settling tanks flows to a tertiary settling process consisting of eight
tanks. Each tank is sub-divided into a rapid mix tank where a coagulant (normally alum or
alternatively, ferric chloride) is added to the water and thoroughly mixed, a gentle mix
flocculation tank, and an inclined plate settling tank for floe gravity settling to further remove
suspended solids and phosphorus. This is followed by effluent settling in a filtration system of
twenty-two sand gravity filters. Final treatment includes a UV disinfection system in six parallel
channels containing low-pressure low-intensity UV lamps. Effluent then enters a post-aeration
system to increase the dissolved oxygen (DO) concentration prior to discharge to Hunting Creek.
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Row
Wostewater / /
Coarse
Screens
9 O J
Primary
Settling Tank
Centrate
Pre-Treotment
Fine Flow
Screens Grit Removal Measurement
Dewatering
Centrate
33% 33% J 33%
V Mr . - | * |,| ¦
6RB1. BRB2 BRB3
Waste Activated Sludge
Primary
Sludge
Nutrient Management Facility
Iff?
Supplemental Carbon
t Secondary Settling Tanks
BRB4jr BRBS
Biological Reactor Basins
BR86
Wf
legend
ss Existing Processes
State-of-the-Arl
Nutrient Removal
Improvements
WBG021313I42107W0C
Figure 2-1. Liquid Treatment Process Train
Solids treatment processes at AWRRF are shown in Figure 2-2. The solids handling system
includes gravity thickening of primary and tertiary sludge followed by pumping the thickened
sludge to the thickened sludge equalization tanks. Waste activated sludge is stored in raw sludge
blending tanks and pumped to four thickening centrifuges. Thickened sludge is transferred to
sludge equalization tanks where it is blended with the gravity-thickened sludge and pumped to a
pre-pasteurization process where the sludge is screened and then pumped through heat
exchangers to be heated to a temperature of 70 °C for at least 30 minutes. The sludge is then
cooled and sent to four mesophilic anaerobic digesters. After digestion, the sludge is pumped to
equalization tanks. Digester gas is returned to the digesters for mixing and excess gas is utilized
for operation of the steam boilers or burned in the waste gas flares.
Three dewatering centrifuge trains are used to dewater digested sludge to a dewatered sludge
cake of approximately 27 percent total solids content. Polymer is added to the sludge to aid the
liquid/solid separation process. The centrate is stored in dewatering centrate tanks and pumped to
the centrate pre-treatment facility.
Rapid Mix and
Flocculation Tanks
Tertiary Gravity Filters UV Disinfection
Settling Tanks
Post-Aeration
Final Effluent Flow
Measurement Weir
Plant
Effluent
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Waste Activated (
Sludge
Polymer
Primary / (
Sludge
Tertiary
Sludge
Sludge
Screening
Gravity
Thickeners
~
(
Pre-Pasteurization
Process
WBG021313142107WDC
Anaerobic
Digesters
Blending Tanks
Blending Tanks
Pdymer
SB
Thickening
Centrifuges
w
Thickened Sludge
Equalization Tanks
Polymer
Thickening
Centrifuges
Pdymer
Lime
¦=i^
Q ass A
Biosdids
Equalization Tanks
Dewatering
Centrate to
Cen Irate
Pre-Treatment
Dewatering
Centrifuges
to
~ Land
Application
Figure 2-2. Solids Treatment Process Train
Table 2-1. Design and Average Raw Influent Concentrations and Loads, and Percent of
Design for the AYVRRF from January 2015 to December 2017
Parameter
Raw Influent Design
Average
Raw
Influent
Percent
of
Design1
(Annual Average)
(Maximum Month)
Flow (MGD)
54
70
32.9
61
cBODs (Ibs/d)
84,600
110,000
72,438
85.6
TSS (lbs/d)
110,000
154,000
85,060
77.3
Ammonia (lbs/d)
N/A
N/A
7,134
N/A
TKN (lbs/d)
15,800
19,000
12,896
81.6
TP (lbs/d)
2,600
3,640
1,756
67.5
Temperature (°C)
20
14
21.1
N/A
Note:
1. Percent of design values, except for flow, are based on average annual values for the analysis period for
influent design loads (lbs./day) and actual influent loads (lbs./day).
N/A: Data not available or applicable.
2-4
-------
Table 2-2. NPDES Limits - January 2015 - December 2017 at AWRRF
Parameter
Monthly
Average
(mg/L)
Monthly
Average
(kg/day)
Weekly
Average
(mg/L)
Weekly
Average
(kg/day)
Annual
Load
(lb/yr)
Annual
Average
(mg/L)
Jan 2015 -
Dec 2016
Jan - Dec 2017
cBODs
5
1,000
8
1,600
N/A
N/A
TSS
6
1,200
9
1,800
N/A
N/A
Ammonia
(Apr. - Oct.)
1
200
4.4
900
N/A
N/A
Ammonia
(Nov.- Jan.)
8.4
N/A
10.0
N/A
N/A
N/A
Ammonia
(Feb. - Mar.)
6.9
N/A
8.5
N/A
N/A
N/A
TN
N/A
N/A
N/A
N/A
493,381
N/A
TN
N/A
N/A
N/A
N/A
N/A
3.0
Temperature
N/A
N/A
N/A
N/A
N/A
N/A
Note:
1. N/A: Data not available or applicable.
2.3 Conventional Nitrogen Removal Technology
Nitrogen removal in most wastewater treatment facilities (also known as water resource recovery
facilities - WRRFs) is achieved biologically through conventional biological nitrogen removal
using nitrification and denitrification processes, with nitrification consuming as much as half the
power required for aeration based on typical wastewater carbon to nitrogen ratios (COD/TKN).
Nitrification and denitrification occur in two-steps in which autotrophic and heterotrophic
bacteria sequentially convert ammonia to nitrogen gas. The first step, nitrification, is aerobic
whereby ammonium (NH4+) is oxidized to nitrite (NO2") by ammonia oxidizing bacteria (AOBs),
and nitrite is converted to nitrate by nitrite oxidizing bacteria (NOBs).
The second step is anoxic whereby nitrate (NO3") is converted to nitrite and then to nitrogen gas
by ordinary heterotrophic bacteria (OHOs). In the first step, ammonia conversion consumes
oxygen and alkalinity. In the second, no oxygen is consumed, and alkalinity is produced.
Additionally, since this reaction is by heterotrophic bacteria, sufficient carbon is needed in the
plant influent COD to achieve a minimum BOD:TKN ratio of about four to five or a minimum
COD:TKN ratio between nine and ten. Where plant influent carbon is not adequate,
supplemental degradable soluble COD needs to be added, typically at a COD:NOx-N removed
ratio in the range of approximately 3.5-8, with the ratio using methanol addition being at about
3.5.
Energy consumption by public water and wastewater services is about 0.5 percent of total U.S.
primary energy and 2 percent of its end-use electricity (Twomey and Webber, 2011, EPRI,
2013).
Energy consumption by wastewater treatment facilities and drinking water systems can amount
2-5
-------
to up to one third of a municipality's total energy bill (EPA, 2009). Typically, at an activated
sludge wastewater treatment facility, 40-70 percent of the energy used is for aeration (WEF,
1997).Plants using biological nitrogen removal are at the higher end of this range.
In plants that use anaerobic digestion for sludge stabilization and reduction, volatile solids are
destroyed resulting in the release of significant amounts of ammonia nitrogen, typically
amounting to between 15- 20 percent of the plant nitrogen load in many cases, but may be as
high as 40-50 percent in some cases depending on the type of sludge stabilization used and the
associated degree of volatile solids destruction achieved as well as other factors such as whether
other solids are co-digested and whether primary treatment is used. In plants where sludge is
dewatered intermittently, this sidestream ammonia load may significantly affect the stability of
mainstream biological nutrient removal processes and cause diurnal spikes in effluent ammonia
or total nitrogen levels. As such, effective approaches to treating this sidestream load has become
an increasingly important treatment objective due to potential cost savings and the positive
impact on the mainstream nutrient removal process.
2.4 Deammonification
Several processes have been used over the last decade to treat high ammonia sidestreams
generally relying on using biomass for treatment in varying configurations, process control
approaches, and control of process parameters such as hydraulic retention times (HRT) and
ammonia concentration. However, the discovery in the 1990s (Mulder et al., 1995) of a group of
microorganisms known as the anammox (anaerobic ammonium oxidation) bacteria that can
convert ammonia and nitrite directly to nitrogen gas has significantly enhanced the attractiveness
of sidestream nutrient removal processes due to aeration energy savings, reduced external carbon
demand, and reduced sludge production. This is possible as the anammox are anaerobic,
autotrophic and the reaction has low biomass yield and only produces small amounts of nitrate.
The deammonification process involves partial nitritation (conversion of ammonia to nitrite) and
anaerobic ammonia oxidation. It requires a 50 percent mix of ammonia and nitrite for the
anammox bacteria to oxidize ammonia under anoxic conditions using nitrite. The process has
been established and used successfully for sidestream treatment at a number of wastewater
facilities inthe U.S. and overseas. Deammonification is an ideal process for dewatering
sidestreams because centrate or filtrate resulting from dewatering of anaerobically digested
sludge is warm in temperature and high in ammonia concentration (around 1,000 mg/1 or above
in most cases) which inhibits nitrite oxidizing bacteria (NOBs) that compete for nitrite for
aerobic nitrite oxidation (nitratation). Centrate also has low carbon content which inhibits
heterotrophic bacteriafrom outcompeting the anammox for the available nitrite. Research and
testing for stable mainstream deammonification continue but the process has not been used at full
scale in the U.S. yet, mainly since full-scale repression of NOBs in mainstream processes is
difficult to consistently achieve. Current deammonification systems for sidestream treatment
include sequencing batch reactor (SBR) processes, an up-flow granular bed process, a moving
bed biofilm reactor (MBBR) process, and a hybrid suspended and attached growth process. The
process known as Integrated Fixed Film Activated Sludge (IFAS) has also been tested for
sidestream treatment.
2-6
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Figure 2-3. Nitrogen Transformations (WERF, 2014)
Deammonification can result in significant savings compared to conventional nitrification-
denitrification biological nitrogen removal. This can theoretically amount to 60 percent or more
reduction in oxygen demand and associated aeration energy and near complete elimination of
costly supplemental carbon addition. As mentioned in section 2.1 above, cost comparisons with
mainstream treatment revealed that sidestream treatment using the deammonification pathway
could be as much as three times lower in cost per pound of nitrogen removed compared with
mainstream conventional biological nitrogen removal. However, actual savings will vary
depending on the process used, existing facility infrastructure, influent characteristics, process
control efficiency, and other factors. At AWRRF, based on Table 2-1 and assuming about 35
percent BOD removal with primary treatment, the BOD:TKN ratio is less than 4.0 and thus
supplemental carbon would be needed. Since the cost per pound of nitrogen removed in the
mainstream is related to adding carbon for denitrification in addition to more energy for aeration
for full nitrification, sidestream deammonification processes are particularly advantageous when
there isa carbon limitation as the anammox bacteria do not use carbon.
2.5 DEMON® Sidestream Deammonification Process at AWRRF
Centrate from dewatering anaerobically digested sludge at AWRRF is stored in centrate tanks
and pumped to the centrate pre-treatment facility. This facility uses the DEMON® sidestream
deammonification system which is based on a SBR process with the use of hydrocylones for
sludge wasting with return of anammox granules to maintain the anammox bacteria in the
reactor. The SBR system operates on a fill/react/settle/decant cycle. Theprocess cycles pumps,
mixers, and blowers on and off multiple times per hour and includes instrumentation to measure
DO, pH, temperature, nitrate nitrogen, and ammonia nitrogen. Decanters remove a portion
(approximately 5-10 percent at AWRRF) of the settled reactor contents at the end of each batch
to free up reactor volume for the next cycle. The clarified supernatant is discharged into the
primary settling effluent channel where it blends with the main plant flow ahead of the biological
reactor basins. The facility has been operating in DEMON® mode since May 2015. DEMON®
SBR is typically designed with a volumetric ammonium loading rate near 0.7 kg/m3-day.
Ammonium and total inorganic nitrogen removal efficiencies of 90-95 percent and 80- 85
percent, respectively, have been reported for full-scale systems at loading rates ranging from
kg/m3-day (Bowden et al., 2015). A process schematic for the centrate pretreatment facility is
presented in Figure 2-4.
2-7
-------
Hydrocyclone
To Biological Reactor Basins
Supplemental
Carbon
Day Tank
Metering
Pump
Odor Control
To the
Biological
Reactor
Basins
Drain
Pumps
To Biological
Reactor
Basins
Figure 2-4. Schematic of Deammonification Reactor at AWRRF (Yin and Sanjines, 2017)
The facility uses two full scale SBRs sized to treat all the dewatering centrate produced at
AlexRenew at design annual average flow. A third small-scale reactor is available for testing and
can also be used to grow and store biomass if needed. The centrate from the centrate storage
tanks is pumped to the centrate pre-treatment (CPT) facility which operates in the DEMON®
mode. The mixed liquor inside the reactor is aerated by flat panel diffusers mounted on the
reactor floor and is kept homogeneously mixed by top-mounted mixers. All reactors are
equipped with heat exchangers to cool the contents of the reactor to avoid excessively high
temperatures (over 35 °C) which could inhibit the process. Since the anammox bacteria are slow-
growing, a portion of the reactor contents is circulated through the hydrocyclones which allows
the wasting of lighter weight organisms such as AOBs, NOBs, and heterotrophs while keeping
the heavier anammox granules and circulating them back to the reactor and increasing their
solids retention time (SRT).
2.6 Detailed Statistical Analysis - Plant Effluent Concentrations
Facility operating data from January 2015 to December 2017 were analyzed. Figures 2-5 through
2-8 and Tables 2-3 through 2-6 provide a summary of the statistical analysis performed for the
AWRRF facility in Alexandria, Virginia. As explained below, the data shows that the facility
consistently met the final effluent treatment objectives for total nitrogen and ammonia shown in
Table 2-2 throughout the analysis period.
Figure 2-5 shows the rolling 12-month average TN concentrations and discharge loadings, and the
plant's consistency in meeting the concentration and loading limits from month to month. For 2015
through 2016, the annual average TN discharge waste load allocation was 493,381 lbs/yr TN at
actual flow. As of January 2017, the facility was required to meet an annual
2-8
-------
average TN discharge limit of 3.0 mg/1. The actual annual average effluent TN concentration for
2017 was 2.61 mg/1. Additionally, for 2015 and 2016, Figure 2-5 shows that the plant effluent was
also consistently well below its maximum TN load limit of 493,381 lbs/day.
7.00
6.50
6.00
5.50
5.00
ao
E 4.50
4.00
3.50
3.00
2.50
2.00
Dec-14
TN Maxal
ow
abl
e load be
ore
D«
:cember 3
1,
101
6: 493,38
1 lb
s/v
ear
—
m
~—
•
*-U
-«
-9-
m
—1
ra
pi
r»
• <
—
-tr
k
—
TN Annual Average Limit as of
anuary 1, 2017 : 3 mg/1
-Ar
A
—<
t—
— -<
—i
r"Tl
A
-k
4-
-
-¦
r*-
500000
400000
600000
(O
CD
s-
300000 ~
200000
100000
J u 1-15
Jan-16
Aug-16
Mar-17
Sep-17
~ TN 12-month Rolling Avg (mg/1)
• TN Load 12-month Rolling Avg (lbs/year)
TN concentration limit
•TN load limit (lbs/year)
Figure 2-5.12-Month Rolling Average Time Series Plot for Plant Effluent TN Load
AWRRF's NPDES discharge permit for the 3-year analysis period included weekly average
ammonia limits of 4.4 mg/1 (April - October), 10 mg/1 (November - January), and 8.5 mg/1
(February - March). The permit also included monthly average ammonia limits of 1.0 mg/1
(April - October), 8.4 mg/1 (November - January), and 6.9 mg/1 (February - March). In addition,
the permit included weekly and monthly ammonia loading limits of 900 kg/day and 200 kg/day,
respectively for the periods between April and October.
The weekly average plant effluent ammonia concentrations over the 3-year data set period were
as follows: 0.07 mg/1 (April - October), 0.17 mg/1 (November - January), and 0.35 mg/1
(February - March). The monthly average ammonia concentrations calculated from the daily
data for these intervals over the 3-year data set period were as follows: 0.08 mg/1 (April -
October), 0.16 mg/1 (November - January), and 0.37 mg/1 (February - March). Similarly, the
2-9
-------
weekly and monthly average ammonia loadings discharged in the effluent between April and
October over the 3-year period were 15.24 kg/day and 34.76 kg/day, respectively. In all
these cases, the facility was well within the permit requirements for ammonia.
Figure 2-6 shows the 30-day rolling average time series plot for nutrient species effluent
concentrations at AWRRF. For the 3-year analysis period, the median 30-day rolling average TN
concentration was 2.83 mg/1 with a maximum value of 5.12 mg/1. The median 30-day rolling
average concentration was 0.085 mg/1 for ammonia and 1.94 mg/1 for NOx-N, with maximum
values of 0.793 mg/1 NFb-N and 3.53 mg/1 Nox-N. During the analysis period before DEMON
startup (January 2015 - May 2015), the median NOx-N value was 2.87 mg/1 and the maximum
value was 7.61 mg/1. After DEMON startup (June 2015 - December 2017), the median NOx-N
value was 1.78 mg/1, and the maximum value was 5.11 mg/1.
10
o.oi
12/27/2014 7/15/2015 1/31/2016 8/18/2016 3/6/2017 9/22/2017 4/10/2018
x NHs -B-NHs Median • NOx —NOx Median
~ TN —TN Median • ON —ON-Median
Figure 2-6. 30-Day Rolling Average Time Series Plot
Figures 2-7 A through D include cumulative probability plots for AWRRF's daily, 30-day rolling
average, monthly average, and 12-month rolling average data sets. A percentile value on the x-
axis represents the probability that the value is less than or equal to the stated corresponding
concentration on the plot's y-axis. Figure 2-7A shows that a significant part of the effluent TKN
was comprised of organic nitrogen and that most of the effluent TN was due to effluent nitrate.
Organic nitrogen concentrations were calculated as the difference between TKN and NH3
nitrogen.
2-10
-------
Daily N Species
• nh3
ON
• NOx
— Log Normal Values
~ TN
¦ cn mo
¦ O CO O 0)0 0)
O CD
5)0)
O) CD
% values less than or equal to indicated values
30 Day Rolling Avg N Species
NHa
NOx
TN
ON
Log Normal Values
-1—i—i 1—i r~
o •*— O CN
—i 1 1—r~
0)0 CD LO
% values less than or equal to indicated values
B
Monthly Averages N Species
—I—I—I 1 1 1-
¦ o ^ « •
H o o o
•
NHs
•
NOx
TN
A
TKN
¦
ON
Log Normal Values
¦ O CO O 0)0 O)
12-month Rolling Average
nh3
NOx
TN
TKN
ON
¦ Log Normal Values
-------
Table 2-3. Summary Statistics for Final Effluent Ammonia Nitrogen for AWRRF from
January 2015 to December 2017
NH3-N
NH3-N
NH3-N
NH3-N
NH3-N
Daily
Data
Weekly
Data
30-day Rolling
Average
Monthly
Average
12-Month Rolling
Average
n
1,096
156
1,067
36
25
Mean
0.15
0.15
0.15
0.15
0.14
Geometric Mean
0.06
0.08
0.10
0.10
0.14
Standard Dev.
0.31
0.19
0.15
0.15
0.03
CV
2.10
1.29
1.01
0.99
0.21
Skew
4.77
2.46
2.03
1.87
-0.08
Minimum
0.03
0.03
0.03
0.03
0.10
Maximum
3.30
1.00
0.79
0.69
0.19
Table 2-4. Summary Statistics for Final Effluent NOx-N for AWRRF from January 2015 to
December 2017
NOx-N
Daily
Data
NOx-N
Weekly
Data
NOx-N
30-day Rolling
Average
NOx-N
Monthly
Average
NOx-N
12-Month
Rolling Average
n
1,096
156
1,067
36
25
Mean
2.09
2.07
2.08
2.09
1.98
Geometric Mean
1.92
1.95
1.99
2.00
1.95
Standard Dev.
0.87
0.73
0.62
0.64
0.38
CV
0.42
0.35
0.30
0.31
0.19
Skew
1.11
0.78
0.49
0.58
0.90
Minimum
0.46
0.79
1.06
1.21
1.62
Maximum
7.61
4.51
3.53
3.41
2.81
Table 2-5. Summary Statistics for Final Effluent Total Nitrogen for AWRRF from January
2015 to December 2017
TN
Daily
Data
TN
Weekly
Data
TN
30-day Rolling
Average
TN
Monthly
Average
TN
12-Month Rolling
Average
n
1,096
156
1,067
36
25
Mean
3.02
3.00
3.01
3.02
2.90
Geometric
Mean
2.87
2.90
2.93
2.94
2.87
Standard Dev.
1.00
0.84
0.70
0.72
0.43
CV
0.33
0.28
0.23
0.24
0.15
Skew
1.20
1.01
0.71
0.79
0.85
Minimum
1.22
1.62
1.86
2.00
2.49
Maximum
8.73
6.21
5.12
4.93
3.81
2-12
-------
Table 2-6. Summary Statistics for Final Effluent ON for AWRRF from January 2015 to
December 2017
ON Daily
Data
ON Weekly
Data
ON 30-day
Rolling Average
ON Monthly
Average
ON 12-Month
Rolling Average
n
1,096
156
1,067
36
25
Mean
0.79
0.79
0.79
0.79
0.78
Geometric
Mean
0.77
0.78
0.78
0.78
0.78
Standard Dev.
0.14
0.10
0.08
0.08
0.02
CV
0.18
0.13
0.10
0.10
0.03
Skew
0.73
0.90
1.06
1.12
0.92
Minimum
0.35
0.58
0.63
0.67
0.75
Maximum
1.38
1.21
1.04
1.04
0.83
Figure 2-8 provides a probability summary for the nitrogen species at the 3.84, 50, 90, 95, and
99th percentiles for the various data sets (i.e., daily, weekly, 30-day rolling, monthly, and
annual). The monthly average ammonia concentrations associated with the 3.84, 50, 90, 95, and
99 percentiles were 0.025, 0.089, 0.352, 0.390, and 0.587 mg/1, respectively, all well below the
discharge permit monthly average limits of 1.0 mg/1 (April - October), 8.4 mg/1 (November -
January), and 6.9 mg/1 (February - March). Similarly, the weekly average ammonia
concentrations associated with the 3.84, 50, 90, 95, and 99th percentiles were 0.025 mg/1, 0.057
mg/1, 0.372 mg/1, 0.566 mg/1, and 0.887 mg/1, respectively, all well below the discharge permit
monthly average limits of 4.4 mg/1 (April - October), 10.0 mg/1 (November - January), and 8.5
mg/1 (February - March).
Figure 2-8 also highlights the process variability for TN and NFb-N. Comparing the daily data
median (50th) percentile of 2.82 mg/1 for TN to the 95th percentile of 4.92 mg/1, the 95th /50th was
about 1.74. Calculating this ratio for the period when the 3 mg/1 TN limit was effective (January
- December 2017), the ratio was lower at 1.57 demonstrating lower variability.
2-13
-------
Daily
Weekly
30-day Rolling
Monthly Averages
Annual Averages
3.84
(14d)
50
90
95
99
Probability
7.0
6.0
5.0
«"• ¦ ¦¦»
00 4.0
£
" ~ "
3.0
z
h
2.0
1.0
0.0
II I I
3.84 50 90 95 99
(14d)
Probability
Daily
Weekly
30-day Rolling
Monthly Averages
Annual Averages
Figure 2-8. Probability Summary for AWRRF
2.7 Process Performance - DEMON® Sidestreain Deammonification at AWRRF
As shown in section 2.5 and figure 2-4 above, the centrate pre-treatment (CPT) facility at
AWRRF uses the DEMON® sidestream deammonification system which is based on a SBR
process to reduce the ammonia loading to the bioreactors. The system was chosen as a
preferred option to treat the ammonia load compared to treatment in the mainstream BNR
system, due to reduction of aeration and supplemental carbon requirements
2-14
-------
which result in cost savings. Sidestream deammonification also results in reduction in alkalinity
requirements compared to conventional nitrification-deni trifieation.
The SBR operational sequence includes a fill/react initial step in anoxic mode with the mixer
running until the pH reaches a maximum setpoint or until a set time has passed (usually about 10
minutes). The mixer is then turned off and the aeration is turned on until the pH reaches a
minimum setpoint or until a set time has passed (usually about 10 minutes). The anoxic and
aerobic cycles are repeated until the end of the fill/react step (generally about 7 hours). A settle
step is then started with the mixer and the aeration turned off (generally 15 to 30 minutes). A
decant step is then initiated to remove the top layer in the SBR to a desired minimum operating
level. The facility is operated remotely by a supervisory control and data acquisition (SCADA)
system. Main process control parameters include pH, DO, ammonia, nitrate, and reactor level.
The design values for the process are shown in Table 2-7.
Table 2-7. Design Parameters for DEMON® Sidestream Deammonification at AWRRF
Parameter
Design Value
Reactor Dimensions
46 ft x 56 ft x 21 ft depth
(14 m x 17 m x 6 m)
Reactor Volume
400,000 gal (1,500 m3)
Reactor Unit Loading
0.0036 lb NH3-N/gal-day
(0.43 kg NH3-N/m3-day)
Loading Per Reactor
1,400 lb/day
(636 kg NH3-N/day)
Average Centrate Concentration
1,200 mg/1
Centrate Flow per Reactor
140,000 gpd
Ammonia Removal
85%
Total Nitrogen Removal
80%
The process was put in service in May 2015. The CPT system was designed with two sets of
SBR reactors and associated equipment/instrumentation, with each reactor sized to treat all the
dewatering centrate produced at AlexRenew at design annual average flow rates. Based on
centrate production and the volume of each SBR reactor, only one of the two reactors was
needed for the process. It was seeded with imported Annamox and initially operated at a low
ammonia loading rate which was gradually increased over the following 12 months as the
process became more stable. Figure 2-9A shows the operational performance of the sidestream
deammonification reactor through December 2017 while Figure 2-9B shows the reactor's
monthly average temperature. Figure 2-9A plots monthly average reactor nitrogen loading rates
as well as ammonia nitrogen and total nitrogen removal values calculated from daily data
provided by AWRRF. The facility was able to reach its target ammonia loading rate of 0.43 kg
NH3-N/m3-day in August 2016 and operate at average monthly loading rates as high as 0.67 kg
NH3-N/m3-day at times thereafter. Ammonia removal rates after July 2016 were achieved
consistently except for a period between July and September 2017 when wasting rates were
inadvertently set too high resulting in loss of biomass from the reactor. This was corrected,
however it impacted ammonia and total nitrogen removal rates and it took over 3 months for the
system to completely recover due to the very slow anammox growing rates.
2-15
-------
¦ NHs % Removal (Avg. Monthly Data)
¦ TN % Removal (Avg. Monthly Data)
Reactor Ammonia Loading Rates (Avg. Monthly Data)(kg N/m3/day)
A
~ Monthly average of reactor maximum daily temperature (Deg C)
40
25 i 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
# $> ~ 0 <> ,<\
^ cf ^ ^ ^ <§- ^ ^ ^ of ^
B
Figure 2-9. (A) Ammonia and Total Nitrogen Removal and Ammonia Loading of
Sidestream Deammonification Process (B) Monthly Average Temperature of the
Sidestream Deammonification Reactor
2-16
-------
During the time period investigated (May 2015 - December 2017), the facility faced a number of
operational challenges which reduced deammonification activity, some of which are explained
below. These included problems with centrate quality, micronutrients deficiency, over-aeration,
floating granules, pH probe issues, and others. In addition to monitoring DO, pH, temperature,
and fill/react/settle/decant cycle periods, reactor nitrite was monitored to assess process stability.
Nitrite is a significant parameter as the electron acceptor in the conversion by anammox in the
deammonification process. Testing at other facilities has shown that concentrations as low as 4.8
mg/1 nitrite nitrogen result in decreased anammox activity (Wett, 2007).
Nitrite concentration control was a significant challenge during the reactor startup. Operational
data provided by AWRRF showed that the nitrite concentration in the DEMON® reactor
exceeded the target concentration of 2 mg/1 during startup and throughout the first year of
operation and was as high as 18 mg/1 on occasions. About three weeks after startup, it was
discovered that high solids in the centrate generated during centrifuge startup and shutdown
periods inhibited AOB and anammox resulting in lower ammonia and TN removal rates. This
problem was addressed by diverting dirty centrate away from the CPT system.
Reactor performance deteriorated again about eight weeks later with higher reactor nitrite
concentrations even at low ammonia loading rates (below 0.15 kg N/m3 /d). A scan of
micronutrients was conducted on influent centrate and reactor mixed liquor to evaluate and
compare to threshold values reported in the literature; however, results were inconclusive. In late
July 2015, a micronutrient solution was added to the reactor, which immediately lowered the
reactor nitrite concentration and allowed a quick increase of influent ammonia loading to 0.4 kg
N/m3/d within one week. In early September 2015, reactor nitrite spiked again and was
attributed to over-aeration. As a result, ammonia loading was lowered again to stabilize nitrite.
The ammonia loading was then increased but at a very slow rate. After addressing other
challenges mentioned below, influent ammonia loading was raised and exceeded the design
target of 0.43 kg N/m3/d in November 2016.
Another challenge encountered during startup was floating granules in the CPT reactor during
the reactor nitrite spike periods. This posed a risk of losing anammox bacteria from the reactor
and was thought to be caused by excessive polymer in the centrate. The excessive polymer may
have coated the granules possibly causing them to trap nitrogen gas and cause floating granules.
To address this issue, plant operations staff reduced the polymer dose in the dewatering process
by about 30 percent without impacting biosolids cake dryness; however, this did not address the
problem. Staff then observed that when nitrite concentrations were high, significantly higher
bubble formation occurred which is expected in the deammonification reaction due to nitrogen
gas formation when conditions are favorable. Operations staff reported that the floating
granules problem was subsequently addressed by maintaining low nitrite concentrations which
limited nitrogen gas production during the settling and decanting phases and by keeping theses
phases reasonably short.
Additionally, dark solids and foam were observed in the DEMON® reactor for several weeksafter
startup. After investigating potential causes, AWRRF determined that this was due to large
amounts of solids in the centrate during centrifuge startup and stoppage, which escaped the
2-17
-------
centrate storage tanks that fed the CPT facility. This was determined to be due to difficulties in
cleaning the bottom of the centrate receiving tank. As a result, AWRRF implemented operating
procedures to periodically drain the bottom of the centrate tanks.
Hydrocyclone operation is very important in the DEMON® process since they result in retaining
anammox granules within the reactor and facilitate wasting of undesired species such as AOB,
NOB, and heterotrophs out of the system. AWRRF staff addressed a problem related to clogging
of the recycle pumps that feed the hydrocyclones resulting in damage of the pumps and casings.
This was determined to be caused by rags and other debris escaping the sludge screening system
ahead of the sludge pre-pasteurization process mentioned above and ending up in the centrate
and not settling in the centrate receiving tank. A strainer was installed by AWRRF staff on the
centrate feed line to resolve this problem; however, frequent strainer cleanings were required as a
result.
It should also be noted that quantitative polymerase chain reaction (qPCR) analyses were
conducted during the DEMON® startup phase to quantify AOB, anammox and NOB abundance
(Yin et al., 2018). During initial reactor startup, AOB were present in high abundance and NOB
were low. However, after June 2015, AOB decreased significantly coupled with quick
accumulation of Nitrospira spp. This coincided with the incidents of dirty centrate entering the
reactor and micronutrient deficiency mentioned above. After micronutrient addition, a sample in
late September 2015 showed low NOB presence. In early 2016, the AOB population was back to
desired levels but then decreased again in March and April and were reduced to very low levels
in summer 2016. In April 2016, hydrocyclone operation hours were reduced and hydrocyclone
overflow decreased. This caused an increase of reactor mixed liquor TSS. Concurrently, CPT
reactor nitrite concentration reliably dropped below 5 mg/1 despite the process upset periods.
These observations matched with reduced anammox fractions observed in the period, which is
believed to be associated with increased presence of heterotrophs. It was concluded that while
the qPCR analysis showed decreased anammox and AOB populations during the periods of poor
centrate quality and reduced hydrocyclone overflow, their microbial activities were higher
thereby preventing nitrogen removal from being negatively affected (Yin et al., 2018).
2.8 Impact of DEMON® Sidestream Deammonification Process and Other Upgrades on
AWRRF Plant Performance
Figure 2-10 shows the monthly average plant effluent TN concentrations from January 2014
through December 2017. The graph clearly shows the significant reduction in plant effluent
concentrations since the startup of the CPT facility in May 2015. Monthly average effluent TN
concentrations from January 2014 through April 2015 were 4.00 mg/1 compared to 2.87 mg/1
from May 2015 through December 2017, the period since startup of the CPT facility. The 95th
and 50th percentile monthly average TN concentration for these two periods were 6.08, 4.00 and
3.82, 2.74 mg/1, respectively. The ratio of the 95th to 50th percentiles for these two periods were
1.59 and 1.46, indicating more stable TN removal at AWRRF after startup of the CPT facility.
2-18
-------
Plant Effluent Monthly Average TN
"7 nn
6.00
O ?
+-»
5 OO ^
b-UU m <5
~ i/l
^ 4.00 1
aa 1 _ 1
£_
H 3 00 11
2.00
1.00
nnn ill
c
i:
t
Jan-14
Mar-
14
May-
14Jul-
14 Sep-
14
Nov-14
Jan-15
Mar-15
May-
15Jul-
15 Sep-
15
Nov-15
Jan-16
Mar-16
May-
16Jul-
16 Sep-
16
Nov-16
Jan-17
Mar-17
Figure 2-10. Monthly Average Plant Effluent TN Concentrations
While AWRRF believes that the CPT facility's impact on improving the plant's overall nitrogen
removal as well as on reducing mainstream aeration requirements and methanol addition is
significant, the facility did implement a number of additional mainstream BNR process
enhancements which were placed in service in 2016 to further reduce costly aeration
requirements and methanol consumption. These enhancements included implementation of
ammonia-based aeration control (ABAC), automated methanol dosing, and primary effluent flow
and load equalization to reduce fluctuations in the carbon to nitrogen ratio of the bioreactor
influent.
In implementing ABAC, a target ammonia concentration range at the end of each biological
reactor is set and the ammonia concentration is measured. The plant's supervisory control and
data acquisition (SCADA) system automatically adjusts the DO set points in the biological
reactor to maintain the ammonia at the target range. If the ammonia concentration is less than the
ammonia low end setpoint, the DO setpoint is decreased; if the ammonia concentration is greater
than the ammonia high end setpoint, the DO setpoint is increased. SCADA also automatically
turns swing zones on and off to maintain the ammonia at the target range. This process control
approach can result in significant reduction in aeration energy.
Figure 2-11 below shows the monthly average aeration flow from the blowers to the biological
reactors. Comparing the monthly average air use values between the periods of January 2014
through April 2015 and May 2015 through December 2017 (i.e., before and after CPT facility
startup) shows a reduction in aeration flow of 28 percent. It is worth noting that for 2017, the
lower air and associated lower energy use were accomplished while meeting the more stringent
final effluent total nitrogen annual limit of 3 mg/1 starting in January 2017.
2-19
-------
u
N*
S»
V
S
&
X'
,0
s-1
Figure 2-11. Average Monthly BNR Aeration
Automated methanol dosing in the mainstream BNR system was initiated in October 2016 and is
controlled through the SCADA system. The methanol dose setpoint is automatically determined
using an operator-adjustable lookup table that increases the dose in proportion to the NOx
concentration measurement in the influent to the last post-anoxic biological reactor basin (BRB).
The methanol dosing is also interlocked with oxidation-reduction potential (ORP) readings in the
last BRB. If the ORP readings indicate anaerobic conditions, methanol pumps are turned off and
air is turned on just upstream of the post-anoxic BRB. Figure 2-12 shows monthly methanol use
for January 2014 through December 2017. Comparing average monthly methanol use before
(January 2014 through September 2016) and after automated dosing was initiated (October 2016
through December 2017) shows a significant reduction in methanol use of 46 percent. This was
accomplished while meeting the lower annual average TN effluent limit of 3 mg/1 starting in
January 2017.
2-20
-------
Monthly Methanol Use
60,000
50,000
c
o
< 40,000
c
o
30,000
c 20,000
ro
_c
§. 10,000
T-l
C
in m
tH
C i
in id
i—i *—i
1"*i
Figure 2-12. Average Monthly Methanol Use
It should be noted that the treatment system upgrades at VVRRF to reduce energy and chemicals
consumption described above were done as part of an overall treatment strategy that included
efforts to redirect the nitrogen removal pathways in the mainstream biological reactors from the
conventional nitrification-denitrification to the more efficient nitritation-anammox
(deammonification) while maintaining the ability to nitrify and denitrify as needed to meet TN
effluent limits. As mentioned in Section 2.4, full-scale repression of NOBs in mainstream
processes is difficult to consistently achieve. This is generally due to lower wastewater
temperatures and substrate concentrations as compared to sidestream conditions and requires an
operational strategy that focuses on these limitations. Based on previous research and testing, the
success of mainstream deammonification is thought to depend, to a large extent, on the control of
two crucial parameters for NOB repression and prevention of nitrate formation: competition
between AOB and NOB for oxygen and competition between anammox and NOB for nitrite
(Wettetal., 2013).
The AWRRF BNR system mainstream deammonification upgrades focused on creating the
particular environmental conditions necessary to suppress NOB activity and increase
deammonification rates. In addition to implementation of ABAC and automated methanol
dosage described above, the implementation strategy at AWRRF included planned operational
actions such as the following:
1. Aeration process control to create conditions in the biological reactor basins (BRBs)
that are favorable for nitritation/denitritation/deammonification.
2. Hydrocyclones on the waste-activated sludge (WAS) flow stream to separate the
anammox granules and keep them in the system while wasting NOBs and other
smaller particles and improving sludge settleability by keeping larger particles in the
system.
3. Seeding anammox bacteria from the centrate pre-treatment (CPT) facility to augment
the anammox population and increase its activity in the mainstream process.
2-21
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4. Primary effluent flow/load equalization to diminish fluctuations in the carbon to
nitrogen (C:N) ratio of the bioreactor feed, aeration demand, and methanol dosage
requirements.
System testing, tuning and optimization has been ongoing to test implementation of mainstream
deammonification at AWRRF. A complete description of this strategy and related upgrades is
provided by Sanjines et al. (2019).
2-22
-------
REFERENCES
Bilyk, K., Khunjar, W., Pace, G., Worley-Morse, T, Cocker, C., Lobdell, S., Taylor, R., Gasper,
B., Pitt, P. (2017). Lessons Learned about Deammonification from Design, Startup and
Operation of an ANITA™ Mox System. Proceedings of the Water Environment Federation
Nutrient Symposium 2017, 253-263.
Bowden, G., Tsuchihashi, R., and H. D. Stensel. (2015.) "Technologies for Sidestream Nitrogen
Removal", WERF NUTRIR06w. London: IWA Publishing.
EPRI (Electric Power Research Institute). 2013. Electricity Use and Management in the
Municipal Water Supply and Wastewater Industries. Technical Report 3002001433. Palo Alto,
Calif.: EPRI.
Mulder, A., Van de Graff, A.A., Robertson, L.A., and Kuenen, J.G. 1995. Anaerobic ammonium
oxidation discovered in a denitrifying fluidized bed reactor. FEMS Microbiol Ecology 16, 177-
184.
Sanjines, P., Santha, H., King-Mcrae, K., Constantine, T., Willoughby, A. 2019. "AlexRenew's
Experience with Aeration Controls for Shortcut Nitrogen Removal". WEF Nutrient Removal and
Recovery Symposium 2019. Minneapolis, MN.
Twomey, Kelly M., and Michael E. Webber. 2011. "Evaluating the Energy Intensity of the U.S.
Public Water Supply". Proceedings of the ASME 2011 5th International Conference on Energy
Sustainability, ES2011- 54165. 1735-48.
U.S. EPA. 2009. "Clean Energy Lead by Example Guide: Strategies, resources, and Action Steps
for State Program". Washington, DC: US Environmental Protection Agency.
Yin, H., and Sanjines, P. "18-Month Operation of Sidestream Deammonification - Ready for
Mainstream Anammox Seeding?". WEFTEC 2017.
Yin, H., Chandran, K., Li, Z., Reck, K., 2018. "Sidestream Deammonification Startup - Process
Controls". Proceedings of the 2018 Water Environment Federation Annual Technical
Conference and Exhibition, pp 5318-5328.
WEF (1997). "Energy Conservation in Wastewater Treatment Facilities". Manual of Practice No.
MFD-2. Alexandria, VA.
WERF Nutrient Challenge (2014). "Deammonification,". Water Environment Research
Foundation (WERF), Ed. J.B. Neethling, Accessed 03/04/2019, http://www.werf.org (now
http ://waterrf. org)
WERF. 2011. "Nutrient Management Volume III: Development of Nutrient Permitting
Frameworks". NUTRIR06k. Water Environment Research Foundation. Alexandria, VA.
2-23
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Wett, B. et. al. "Key Parameters for Control of DEMON Deammonification Process". Water
Practice, November 2007.
Wett, B., Omari, A., Podmirseg, S.M., Han, M., Akintayo, O., Gomez Brandon, M., Murthy, S.,
Bott, C., Hell, M., Takacs, I., Nyhuis, G., O'Shaughnessy, M. (2013). "Going for Mainstream
Deammonification from Bench to Full Scale for Maximized Resource Efficiency". Water Sci.
Technol. 68, 283-289.
2-24
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CHAPTER 3.0
The Westside Regional Wastewater Treatment Plant - Sidestream
Enhanced Biological Phosphorus Removal (S2EBPR) - Case Study
3.1 Background
The Westside Regional Wastewater Treatment Plant (WRWTP) is a tertiary treatment plant
located in the District of West Kelowna, British Columbia, Canada. It is operated by the
Regional District of Central Okanagan and receives wastewater from the Districts of West
Kelowna and Peachland and from the Westbank First Nation Reserves #9 and #10. Its purpose is
to serve the sewered areas of Westbank and Shannon Lake. WRWTP underwent three
expansions in 1995, 2006, and 2012 with a final resulting capacity of 3.8 MGD (16,800 m3/day).
The 2012 expansions included a new headworks building with 6 mm perforated plate mechanical
screens, fermenter retrofits, additional bioreactors, clarifiers, and fabric filters. Additional UV
banks as well as biosolids dewatering centrifuges were also included.
3.2 Plant Processes
Preliminary treatment of influent wastewater includes coarse bar screening, perforated plate
mechanical screens, and vortex grit removal. Primary settling occurs in three rectangular
clarifiers.
Primary effluent is then treated in a BNR facility designed to remove both nitrogen and
phosphorus in addition to BOD. The BNR facility is operated in the Westbank process mode but
with only a portion of the fermentate (from a primary sludge fermenter) added to the anerobic
zone, and primary effluent is introduced into the mainstream anoxic zone (none to the pre-anoxic
zone or anaerobic zone) along with the rest of the fermentate.
Effluent from the bioreactors is settled in the secondary clarifiers for clarification. Alum can be
added ahead of the secondary clarifiers for chemical phosphorus removal when needed. Clarified
secondary effluent is treated in AquaDisk® 10-micron cloth membrane filters prior to ultraviolet
(UV) disinfection and discharge into Okanagan Lake.
Primary sludge solids are treated in fermenting tanks for generating volatile fatty acids (VFAs)
which are fed to the sidestream reactor and to the mainstream anoxic zone for phosphorus
release. Waste activated sludge (WAS) is thickened in dissolved air flotation units and then
mixed with fermented primary sludge prior to centrifuge dewatering. Dewatered sludge cake is
hauled offsite to a land application site.
3-1
-------
Table 3-1. Current Discharge Limits as of January 1, 2014 at WRWTP
Parameter
Daily Max
(mg/L)
Annual Average
(mg/L)
BOD5
10
N/A
cBODs
N/A
N/A
TSS
10
N/A
TN (mg/1)
10
6
TP (mg/1)
2.0
0.2
Temperature (°C)
N/A
N/A
Note: N/A: Data not available or applicable
3.3 Conventional Enhanced Biological Phosphorus Removal Technology
Enhanced biological phosphorus removal (EBPR) in wastewater treatment is accomplished by
encouraging the growth of phosphate accumulating organisms (PAOs). PAOs are heterotrophic
bacteria that occur naturally in the environment and in aerobic activated sludge. The growth of
PAOs is encouraged by cycling them between anaerobic and aerobic conditions. In the presence
of oxygen (i.e., aerobic conditions), PAOs obtain energy from stored food and uptake large
amounts of phosphorus into their cells, which they store as polyphosphates. These
polyphosphates contain high-energy bonds and function like energy storage batteries.
In the absence of oxygen (i.e., anaerobic conditions), PAOs can break the polyphosphate bonds
resulting in the release of orthophosphate and use the resulting energy to uptake easily
biodegradable compounds, namely short chain volatile fatty acids (VFAs). PAOs polymerize and
store the VFAs in their cells as intermediate products known as poly-P-hydroxy-alkanoates
(PHAs), of which the most common is poly-P-hydroxy-butyrate (PHB). When oxygen becomes
available again (i.e., aerobic conditions), they can metabolize the PHAs to generate energy and
uptake phosphorus (in the form of phosphate) and store the excess amount. (Randall et al.,
2010).
In general, it was traditionally accepted that phosphorus could only be removed in conventional
plants when the wastewater characteristics were favorable with a COD:TP ratio of at least 37:1
or a BOD:TP ratio about 18:1, with some of the COD consisting of short chain VFAs. More
COD may be required if the process also involves denitrification of nitrate (Kobylinski et al.,
2008). At wastewater treatment facilities where this ratio is low, external sources of carbon such
as methanol, ethanol, or proprietary carbon products can be added. In some cases, carbon-rich
waste products such as molasses, sugar wastes or others may also be used. Additionally, many
plants have elected to ferment their primary sludge. This often requires measures to limit odors
and to ensure stable and consistent performance.
Other microorganisms besides PAOs exhibit a similar metabolism as PAO. For example,
Glycogen Accumulating Organisms (GAOs) are similar to PAOs in terms of being able to store
readily biodegradable organic matter such as VFAs as PHA in the anaerobic phase (Zeng et al.,
3-2
-------
2003). GAOs do not contribute to phosphorus removal as their metabolism does not involve
anaerobic phosphorus release and subsequent aerobic (or anoxic) phosphorus uptake (Lopez-
Vazquez et al., 2007). Therefore, in terms of biological phosphorus removal, GAOs are seen as
competitors of PAOs for substrate and, as such, a main cause of process deterioration, or even
failure, of EBPR systems (Thomas et al., 2003). Temperature has been identified as having a
potential significant impact on the PAO-GAO competition. At temperatures greater than 25 °C,
GAOs can outcompete PAOs for organic carbon (Law et al., 2016).
EBPR is considered a sustainable approach to removing phosphorus from wastewater. However,
the process can in some cases be unstable particularly at low influent rbCOD/TP ratios and
where other wastewater constituents such as dissolved oxygen or nitrate interfere with the
anaerobic phosphorus release. To address such difficulties, particularly where low phosphorus
limits are in place, many facilities install backup chemical systems and incur the cost of using
chemical phosphorus removal as a backup to EBPR.
Generally speaking, the reliability of a nutrient removal process in meeting particular effluent
targets varies from plant to plant and depends on various site-specific factors including
wastewater characteristics, design, specific process configurations, operational conditions, and
control parameters. In a detailed study of the long-term performance of EBPR facilities
(Neethling, 2005), five EBPR facilities of various process designs, wastewater characteristics,
operation, and other factors were evaluated over a three-year period to determine the biological
phosphorus removal efficiency as well as their consistency (termed reliability in the study) of
producing effluent concentrations at or below a given treatment goal. Table 3-2 shows the range
of frequencies with which the plants achieved effluent orthophosphate (OP) concentrations of
0.5 mg/1, 1.0 mg/1, and 2.0 mg/1. The table also shows the concentrations achieved in 50
percent and 90 percent of the samples as well as the ratio between the 90th and the 50th
percentiles (90 percent/50 percent) effluent OP concentrations. The values show that EBPR
reliability is significantly reduced withlower desired effluent phosphorus concentrations
particularly at lower discharge levels. Moreover, EBPR effluent concentration variability is
significant as evidenced in the wide reliability range observed (90 percent/50 percent ratio
range of 2 - 24) for the five facilities indicating relatively unstable performance.
Table 3-2. EBPR Reliability at Various EBPR Facilities (Adapted from Neethling et al.,
2005)
Effluent Concentration &
Percentile
Reliability Range for Five
EBPR Facilities
Reliability Average
OP< 0.5 mg/1
24% - 95%
68%
OP< 1 mg/1
64% - 99%
82%
OP < 2 mg/1
85% - 100%
93%
50% (Geometric Mean)
0.05 - 0.76 mg/1
0.26 mg/1
90%
0.2 - 2.5 mg/1
1.6 mg/1
90%/50%
2.0-24.0
11.5
3-3
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3.4 Sidestream Enhanced Biological Phosphorus Removal (S2EBPR)
An earlier study conducted to quantify key processes in full-scale sidestream hydrolysis tanks at
two treatment plants concluded that sidestream EBPR is a promising configuration that in a
number of cases will have advantages to the conventional mainstream EBPR process, especially
when sufficient VFA is not available in the mainstream wastewater (Vollertsen et al., 2006).
While many previous research observations showed that fermentation of return activated sludge
(RAS) or a portion of the mixed liquor could help in producing low effluent phosphorus, it was
assumed that the fermentation-produced VFAs were sustaining the growth of the much-
researched PAO, Candidatus Accumulibacter, found mostly in conventional BNR plants
(Barnard et al., 2017).
Candidatus Accumulibacter is able to store large amounts of polyphosphate (poly-P) aerobically
after taking up organic substrates anaerobically, unlike ordinary heterotrophic organisms.
Accumulibacter PAOs take up VFAs anaerobically and store them as PHAs, with energy
obtained from hydrolysis of intracellular poly-P andreducing power from glycolysis of
intracellular glycogen. Besides Accumulibacter, Tetrasphaera-related organisms are also
putative PAOs present in a higher abundance than Accumulibacter in full-scale EBPR systems.
Tetrasphaera-related PAOs can take up polyphosphate aerobically and store it intracellularly as
poly-P, while assimilating different organic substrates (such as glucose and amino acids) under
anaerobic conditions (Marques et al.,2017). Recent research showed that other PAOs may
contribute to biological phosphorus removal and that Tetrasphaera can contribute and provide
stability to the enhanced biological removal process (Nguyen et al., 2011; Barnard et al., 2017).
An alternative approach for improving EBPR process stability, eliminating the need for costly
external carbon addition, and minimizing chemical usage includes implementation of a
sidestream anaerobic biological solids hydrolysis and fermentation reactor. The reactor would
involve sidestream RAS or mixed liquor hydrolysis and fermentation and has been named
sidestream EBPR (S2EBPR). Recent full-scale and lab-scale testing performed on S2EBPR
showed that it can be implemented in multiple configurations that can beused in a variety of
wastewater treatment facilities, including those that do not utilize primary clarifiers (Tooker et
al., 2018).
A study published by the Water Research Foundation (Gu et al., 2019) was conducted to
elucidate the fundamental mechanisms involved in the S2EBPR process and to develop criteria
for effective design and operation of the process. The study included a survey of operational
information from a number of full-scale S2EBPR facilities, simulated sidestream reactor batch
testing, full-scale pilot testing with side-by-side S2EBPR and conventional EBPR processes, and
development of an improved biological process model for S2EBPR. The study concluded that a
properly designed S2EBPR process allows the continuous generation of in-situ VFAs from RAS
that have more complex composition than those in the conventional EBPR influent and that
results in multiple advantages that enable more robust and stable EBPR performance over a
wider range of wastewater characteristics and process configurations. The study found that
GAOs, generally considered as undesirable with aerobic phosphorus uptake, were generally
found at lower abundances in S2EBPR facilities than those in conventional EBPR facilities. The
study also found that PAOs can outcompete GAOs with extended anaerobic conditions due to the
ability of PAOs to sequentially utilize polyphosphates and glycogen for maintenance prior to
3-4
-------
their delayed decay, while GAOs' decay occurred relatively quickly following the initial
consumption of glycogen. The study also mentioned that itis possible that enrichment of specific
types of PAOs, such as those that can obtain energy via fermentation such as Tetrasphaera,
occurs in the sidestream reactor of an S2EBPR system. The study concluded that additional
research on the role of Tetrasphaera or other PAOs that are capable of fermentation is needed to
better understand their role in the S2EBPR process (Gu et al., 2019).
3.5 Sidestream Enhanced Biological Phosphorus Removal (S2EBPR) at WRWTP
The configuration of the BNR facility at WRWTP is similar to that of the Westbank process
(The term "Westbank" here refers to the Westbank process and not the Westbank First Nation
Reserves mentioned on page 3-1). A typical Westbank process has a small pre-anoxic zone
followed by an anaerobic zone, a mainstream anoxic zone, and a large aerobic zone. The pre-
anoxic zone minimizes DO and nitrates entering the anaerobic portion. Primary effluent is
divided among the pre-anoxic zone (to denitrify the RAS), the anaerobic zone (to provide some
VFAs for phosphorus removal), and the second anoxic zone (to stimulate denitrification). VFAs
obtained from fermentation of sludge (typically primary sludge) are passed to the anaerobic
zone. However, at WRWTP, only a portion of the fermentate is added to the anerobic zone, and
primary effluent is introduced into the mainstream anoxic zone #1 (none to the pre-anoxic zone
or anaerobic zone) along with the rest of the fermentate as explained below.
As shown in Figure 3-1, 100 percent of the RAS at WRWTP is first passed through the small
pre-anoxic zone (HRT of less than 20 minutes). This is followed by sidestream treatment of the
RAS in the anaerobic S2EBPR zone (HRT of 1 to 4 hours) where a portion of the fermentate
from a primary sludge fermenter is added. Primary effluent is introduced into the mainstream
anoxic zone #1 along with the rest of the fermentate. A benefit of a S2EBPR system
configuration where 100 percent of RAS is blended with a source of supplemental carbon (e.g.,
primary sludge fermenter overflow) in a sidestream reactor, compared to other S2EBPR
configurations, is that the addition of fermentate to the S2EBPR reactor significantly shortens
the HRT to 1-4 hours compared to a HRT of 16 hours or higher in other S2EBPR
configurations. An additional benefit is that a portion of the fermentate can also be used for
denitrification (Gu et al., 2018). At WRWTP, Alum is added upstream of the secondary
clarifiers as a safety factor when needed for additional phosphorus removal.
3-5
-------
VFwmentef/
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£
%
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i
£
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£
i
2
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-------
The 95th percentile daily TP of 0.26 mg/1 shown on Figure 3-4 is 173 percent of the median value
(0.15mg/l) indicating a significant degree in variability. However, based on the above, and
comparing the maximum 30-day rolling average TP concentration of 0.17 mg/1 for the entire
analysis periodto the 0.2 mg/1 annual average shows that the treatment objective was consistently
met on a rolling 30-day basis. Additionally, in looking at Table 3-3 and Figure 3-2B, it is clear
that maximum values for the 30-day rolling average (0.30 mg/1) and 12-month rolling average
(0.18 mg/1) are approximately equal to their respective (99 percent) probability.
x TP
Median
• OP
-*-Max Daily TP Limit
Annual Average TP Limit
CL
m
E. 0.5
V)
aj
'u
01
G.
«/>
a.
Dec-14
Jul-15
Jan-16
Aug-16
Feb-17
Sep-17
A* - Daily Plant Effluent Concentrations
* Points not shown on the graph: TP and OP concentrations were 1.8 and 1.57 mg/1, respectively,
on July 21, 2015, and 1.50 and 1.42 mg/1, respectively, on July 22, 2015. Max Daily TP limit is
2.0 mg/L.
3-7
-------
0.45
0.4
0.35
< 0.3
O.
00
£,0.25
-------
A B
Figure 3-3. Probability Plots for WRWTP (A) Daily Data; (B) 12-Month Rolling Average
Table 3-3. Summary Statistics for Final Effluent TP and OP for WRWTP
TP Daily
Data
TP Rolling 30-
day Average
TP Monthly
Averages
TP 12-month Rolling
Average
n
1094
1067
36
25
Mean
0.17
0.17
0.17
0.17
Geometric
Mean
0.16
0.16
0.16
0.17
Standard Dev.
0.10
0.04
0.04
0.01
CV
0.58
0.22
0.22
0.05
Skew
9.89
0.97
1.01
-0.44
Minimum
0.08
0.10
0.12
0.16
Maximum
1.80
0.30
0.29
0.18
OP Daily
Data
OP Rolling
30-day Average
OP Monthly
Averages
OP 12-month Rolling
Average
n
1095
1067
36
25
Mean
0.09
0.09
0.09
0.10
Geometric
Mean
0.08
0.09
0.09
0.10
Standard Dev.
0.01
0.03
0.03
0.01
CV
0.10
0.34
0.34
0.10
Skew
11.06
1.07
1.12
-0.84
Minimum
0.01
0.03
0.04
0.08
Maximum
1.57
0.21
0.20
0.11
3-9
-------
0.45
0.40
0.35
0.30
0.25
E
"—'0.20
a.
0.15
0.10
0.05
0.00
0.35
0.30
0.25
feS 0.20
e,
q_ 0.15
o
o.io
0.05
0.00
3.84
(14d)
Daily
30-day Rolling
Monthly Averages
12-Month Rolling
50
90
95
99
Probability
Daily
30-day Rolling
Monthly Averages
12-Month Rolling
3.84
(14d)
50
90
95
99
Probability
Figure 3-4. Probability Summary for WRWTP Effluent TP and OP
3-10
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3.7 Process Performance - Mainstream EBPR at WRWTP
The BNR facility at WRWTP includes 6 bioreactors operated in the Westbank process mode but
with only a portion of the fermentate added to the anerobic zone, and primary effluent is
introduced into the mainstream anoxic zone (none to the pre-anoxic zone or anaerobic zone)
along with the rest of the fermentate. One hundred percent of the RAS is passed through a
small pre-anoxic reactor with an HRT of about less than 20 minutes. This is followed by
sidestream treatment of the RAS in the anaerobic S2EBPR zone where a portion of the
fermentate from a primary sludge fermenter is added, with an actual flow HRT of
approximately 80 minutes. Primary effluent is introduced into the first mainstream anoxic zone
along with rest of the fermentate. As shown in Figure 3-5, bioreactors 1 and 2 include 3 anoxic
zones while bioreactors 3 through 6 include only two; however, the total volume of the anoxic
zones in each reactor is approximately the same. Under normal flow conditions, only 4
bioreactors are in service.
BIOREACTORS# 1 and 2
Alum sf R«qu'ir«'i
Pre-
Anaerobic
AlWtttC »1
Anc*ic#2
Anoxic *3
Aerobic #1
1 Aerobe «2
Aerobic »3
Anowc
CM
190 m1)
(30 m')
(30 m5)
(235 m1)
(235 m'l
(235 m5)
Gel
190 mlJ
(5m1]
Ferrntrter VFA'l
I
Nitrrfitd Rft-Cyeia Flow
Jr
SicendifV
Clarjfiar
bioreactors # 3 through 6
RAS
1 Pre-
Artaefobic
Arietta *1
.fWWHic *2
Awobic *1
Aerobic *2
Aerobe «3
Arrowc
OI
(WSm'j
mSm'l
1230 ro'l
(230 m')
(230 m*!
Cei
ESSrv1!
, ESm')
f
F«rm»fit»r VFA4i
Alum «f Required
G3»rifi«r
Figure 3-5. Bioreactor Layout at WRWTP
Each bioreactor is dedicated to one clarifier with individual RAS pumps, each with VFD control.
A RAS collection well collects RAS from all clarifiers and is believed to result in a significant
reduction in the nitrate concentration and in variability of the RAS total solids concentration fed
to the bioreactors. The RAS pre-anoxic cell further reduces RAS nitrate to very low levels,
3-11
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typically, below 0.5 mg/1, thereby minimizing negative impacts on the anaerobic S2EBPR zone.
This also allows less fermentate addition to the anaerobic zones and more fermentate available to
the mainstream anoxic zone. Since additional VFA addition to the anoxic zone may potentially
increase OP removal to levels that negatively impact nitrification in the aerobic zone, OP levels
in the 1st aerobic zone are carefully monitored; fermenter supernatant flow to the anerobic zone
is reduced if needed to ensure that sufficient OP remains to support the growth of nitrifiers and
ensure compliance with total nitrogen effluent limits.
100
% values less than or equal to indicated value
Figure 3-6. Cumulative Probability Plot for Bioreactor Effluent OP at WRWTP
Figure 3-6 shows the cumulative probability plot for bioreactor daily effluent OP concentrations
before alum addition for the 3-year analysis period. As shown on this graph, the 90th percentile
concentration was 0.11 mg/1 OP, significantly lower than the average 90th percentile
concentration of 1.6 mg/1 reported in Table 3-3 for five conventional EBPR processes. This
indicates that S2EBPR can result in significant improved performance compared to conventional
EBPR. Additionally, Table 3-4 below shows that the ratio of the 90th to the 50th percentile
bioreactor effluent OP concentrations at WRWTP was 2.2, which is significantly lower than the
corresponding average ratio of 11.5 reported in Table 3-3 for the conventional EBPR processes.
This indicates that S2EBPR can result in significantly improved phosphorus removal process
stability and reliability. Table 3-4 also shows the frequency in meeting bioreactor effluent Ortho-
P concentrations of 2.0 mg/1, 1 mg/1, and 0.5 mg/1 (100 percent, 100 percent, and 99.8 percent
respectively) before alum addition, all significantly higher than those reported in Table 3-2 for
the conventional biological phosphorus removal facilities.
3-12
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Table 3-4. S2EBPR-Enhanced BNR Reliability at WRWTP
Effluent Concentration &
Reliability
Percentile
OP< 0.2 mg/1
96.8%
OP< 0.5 mg/1
99.8%
OP < 1 mg/1
100%
OP< 2 mg/1
100%
50% (Geometric Mean)
0.05 mg/1
90%
0.11 mg/1
90%/50%
2.2
Finally, it should be noted that WRWTP staff monitor bioreactor effluent orthophosphate and
TP to ensure that the optimal levels of phosphorus removal are being achieved. As the plant at
times experiences uncontrollable conditions including high influent flows and spikes of influent
phosphorus, staff typically add alum to the bioreactor effluent ahead of the secondary clarifiers
as a safety factor to ensure that the daily maximum and annual average TP limits shown in Table
3-1 are consistently met. Figure 3-7 shows that the bioreactor effluent orthophosphate
concentrations before alum addition were consistently low. Daily data for the three-year analysis
period shows that 90 percent of the samples were below 0.11 mg/1 TP and 50 percent of the
samples were at or below 0.05 mg/1. However, as Figure 3-7 shows, there were occasions where
bioreactor effluent orthophosphate concentrations were above desired levels, necessitating the
use of alum addition to ensure TP limits are not exceeded. It should be noted that the
recirculation of alum in the RAS may also have played a positive role in improving overall
phosphorus removal.
Figure 3-7. Bioreactor Effluent Ortho-P Concentrations at WRWTP
3-13
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REFERENCES
Barnard, J., Dunlap, P., and Steichen, M. (2017). "Rethinking the Mechanism of Biological
Phosphorus Removal". Water Environment Research. 89. 2043-2054.
Gu, A., Tooker, N., Onnis-Hayden, A., Wang, D., Li, G., Srinivasan, V., and Takacs, I.
"Optimization and Design of a Side-Stream EBPR Process as a Sustainable Approach for
Achieving Stable and Efficient Phosphorus Removal." Project No. U1R13/4869. Water Research
Foundation, 2019.
Kobylinski, E., Van Durme, G., Barnard, J., Massart, N., and Koh S-H. (2008). "How Biological
Phosphorus Removal is inhibited by Collection System Corrosion and Odor Control Practices" -
WEFTEC 2008.
Lopez-Vazquez, C., Hooijmans, Brdjanovic, D., Gijzen, H., and van Loosdrecht, M. (2007).
"Occurrence of Glycogen Accumulating Organisms (GAO) at Full-Scale Enhanced Biological
Phosphorus Removal (EBPR) Wastewater Treatment Plants". IWA Nutrient Removal
Conference 2007.
Law, Y., Kirkegaard, R., Cokro, A., Liu, X., Arumugam, K., Xie, C., Stokholm-Bjerregaard, M.,
Drautz-Moses, D., Nielsen, P., Wuertz, S., and Williams R. (2016). "Integrative Microbial
Community Analysis Reveals Full-Scale Enhanced Biological Phosphorus Removal under
Tropical Conditions". Scientific Reports 6:25719. DOI:10.1038/srep25719.
Marques, R., Santos, J., Nguyen, H., Carvalho, G., Noronha, J.P., Nielsen, P.H., Reis, M.A. and
Oehmen, A. (2017). "Metabolism and Ecological Niche of Tetrasphaera and Ca. Accumulibacter
in Enhanced Biological Phosphorus Removal". Water Research, 122, pp.159-171.
Neethling, J.B., Bakke, B., Benisch, M., Gu, A., Stephens, H., Stensel, H.D., Moore, R. (2005).
"Factors Influencing the Reliability of Enhanced Biological Phosphorus Removal". Report No.
01CTS3. Water Environment Research Foundation, Alexandria, VA.
Nguyen, H., Hansen, V., Nielsen, J., and Nielsen, P. (201 1). "High Diversity and Abundance of
Putative Polyphosphate-Accumulating Tetrasphaera-Ktlattd Bacteria in Activated Sludge
Systems". FEMS Microbiol Ecol 76 (201 1) 256-267.
Randall, C., Branard, J., Stensil, D., and Brown, J. "Nutrient Control Design Manual". U.S.
Environmental Protection Agency, Washington, DC, EPA/600/R-10/100, 2010.
Thomas, M., Wright, P., Blackall, L., Urbain, V., Keller, J. (2003). "Optimization ofNoosaBNR
Plant to Improve Performance and Reduce Operating Costs". Water Sci. Technol., 47 (12), 141.
Tooker, N., Guangyu, L., Srinivasan, V., Barnard, J., Bott, C., Dombrowski, P., Schauer, P.,
Menniti, A, Shaw, A, Stinson, B., Stevens, G., Dunlap, P., Takacs, L, Phillips, H., Anal la, H.,
Russell, A, Lambrecht, A, McQuarrie, J., Avila, L, Omnis-Hayden, A., and Gu, A. (2018).
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"Side-stream EBPR Practices and Fundamentals - Rethinking and Reforming the Enhanced
Biological Phosphorus Removal Process". WEF Nutrient Removal and Recovery Conference
2018.
Vollertsen, J., Petersen, G., Borregaard, V.R. (2006). "Hydrolysis and Fermentation of Activated
Sludge to Enhance Biological Phosphorus Removal". Water Science & Technology, 53(12),
pp. 5 5-64.
Zeng, R., van Loosdrecht, M., Yuan, Z., Keller, J. (2003). "Metabolic Model for Glycogen
Accumulating Organisms in Anaerobic/Aerobic Activated Sludge Systems". Biotechnol.
Bioeng., 81(1), 92.
3-15
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CHAPTER 4.0
The Kingsley Wastewater Treatment Facility - Enhanced Nitrification -
Submerged Attached Growth Reactor (SAGR®) - Case Study
4.1 Background
The City of Kingsley Wastewater Treatment Facility (KWTF) is a 0.13 MGD average dry
weather flow facility located in Plymouth County, Iowa and discharges to the West Fork of the
Little Sioux River. Prior to 2013, the City anticipated significant growth over a 20-year planning
period and was expecting its new NPDES permit to include low single digit ammonia limits
which could not be met with their existing lagoon treatment system, particularly during
prolonged periods of low water temperatures.
Original lagoon treatment at KWTF consisted of a two-cell aerated lagoon system. Following an
alternatives analysis, the City opted for upgrading the existing lagoons and retrofitting its
treatment system using a Submerged Attached Growth Reactor (SAGR®) system provided by
Nelson Environmental Inc. (now Nexom) of Winnipeg, Manitoba, Canada. In the summer of
2013, construction began on the facility upgrade. New lower NPDES ammonia effluent limits
became effective after construction of the SAGR facility.
4.2 Plant Processes
Current wastewater treatment processes at KWTF include two aerated lagoon cells with fine
bubble aeration in cells 1 and 2 and an unaerated setting zone in cell 2 which was isolated using
a baffle curtain. The total depth of the aerated lagoon is nine feet, and the water depth is six feet.
Lagoon effluent flows into a four-cell horizontal flow SAGR treatment system for nitrification,
and an ultraviolet (UV) treatment system for disinfection prior to discharge. Figure 4-1 shows
the facility's flow scheme including the SAGR system.
A lagoon fine bubble diffused aeration system was installed as part of the upgrade to achieve
improved year-round BOD and TSS removal, provide stability, and optimize the SAGR process
design for year-round nitrification (ammonia removal). Since the Iowa wastewater design
standards did not specifically address the SAGR process, the Iowa Department of Natural
Resources (IDNR) worked with the facility and its consultant to approve SAGR as an acceptable
alternative technology. This involved developing alternative design criteria which included
lagoon BOD treatment requirements, SAGR BOD and TSS loading requirements, minimum
DO, minimum HRT, and SAGR media, liner, and insulation requirements.
4-1
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Kingsley Wastewater
Treatment Facility
Figure 4-1. Wastewater Flow Scheme at KWTF
Table 4-1. Design and Average Raw Influent Concentrations and Percent of Design Loads
for the KWTF from January 2015 to December 2017
Parameter
Raw Influent
Design
Average Raw Influent
Percent of Design
Average Flow (MGD)
0.131 (Dry Weather)
0.1501
(Avg. for Analysis
Period)
N/A
0.30 (Wet Weather)
cBODs (lbs/day)
262
N/A
N/A
TSS (lbs/day)
300
57.31
19.1
Ammonia (mg/1)
N/A
N/A
N/A
TKN (mg/1)
45
N/A
N/A
TP (mg/1)
N/A
N/A
N/A
Temperature (°C)
0.5-202
N/A
N/A
Note:
1. Based on limited facility data.
2. Temperature is expected lagoon temperature, not influent temperature.
N/A: Data not available or applicable
4-2
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Table 4-2. NPDES Permit Limits - January 2015 - December 2017 at KWTF
Daily
Daily
7-Day
7-Day
30-Day
30-Day
Parameter
Maximum
Maximum
Average
Average
Average
Average
(mg/1)
(lbs/day)
(mg/1)
(lbs/day)
(mg/1)
(lbs/day)
cBODs
N/A
N/A
40
63
25
100
TSS
N/A
N/A
30
75
45
113
Ammonia
(January)
20.8
50.8
N/A
N/A
11.9
20.3
Ammonia
(February)
9.5
22.2
N/A
N/A
9.5
22.2
Ammonia
(March)
4.7
10.6
N/A
N/A
4.7
10.6
Ammonia
(April)
5.2
12.3
N/A
N/A
4.4
7.8
Ammonia
(May)
3.7
8.6
N/A
N/A
3.7
6.7
Ammonia
(June)
3.7
8.6
N/A
N/A
2.6
4.7
Ammonia
(July)
3.7
8.6
N/A
N/A
2.6
4.4
Ammonia
(August)
3.1
7.1
N/A
N/A
2.4
4.0
Ammonia
(September)
3.3
7.3
N/A
N/A
2.9
5.3
Ammonia
(October)
3.3
7.3
N/A
N/A
3.3
7.3
Ammonia
(November)
3.2
7.2
N/A
N/A
3.2
7.2
Ammonia
(December)
4.5
10.4
N/A
N/A
4.5
10.4
Note:
N/A: Not applicable.
4.3 Nitrification
In many watersheds, ammonia loading to receiving waters can be a significant cause of
eutrophication and/or toxicity as ammonia can be toxic to certain fish and other aquatic species,
even at very low concentrations in some cases.
The main effective and most widely used approach for ammonia removal is the process of
nitrification, which involves biological oxidation of ammonia nitrogen to nitrate nitrogen under
aerobic conditions. Biological oxidation of ammonia is carried out by nitrification organisms
4-3
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(nitrifiers) and occurs in two steps. In the first step, an autotrophic group of ammonia-oxidizing
bacteria (AOB) produce nitrite nitrogen ions as an intermediate product (Metcalf and Eddy,
2014). In the second step, another group of autotrophic microorganisms known as nitrite
oxidizing bacteria (NOB) oxidize nitrite-nitrogen to nitrate nitrogen (Metcalf and Eddy, 2003).
The nitrification process has been shown to be strongly dependent on temperature and generally
occurs over a range of approximately 4-45 °C, with about 35 °C optimum for Nitrosomonas and
35-42 °C optimum for Nitrobacter. Maximum specific growth rate values for Nitrosomonas
agree reasonably with the van't Hoff-Arrhenius equation, which predicts the doubling of growth
rates with each 10 °C increment in temperature (EPA, 1993). Nitrification activity is significantly
reduced with colder water temperatures, particularly below 8 °C. Nitrifiers are very slow-
growing microorganisms, and their growth can be inhibited by various other environmental
conditions including DO, pH, alkalinity, and the presence of toxic or inhibitory compounds. In
adverse conditions, nitrifier growth rates can significantly slow down or even cease leading to
nitrifier washout from the treatment system.
When passive treatment systems such as some lagoons are used for nitrification, limited control
may be available for consistent performance and control of important parameters such as DO
and SRT. When lagoons are used for nitrificationtreatment in cold climates, wastewater
temperatures can reach as low as 1 °C for prolonged periods. This can significantly inhibit
nitrifiers and ammonia removal. However, there is evidence that attached growth nitrification
processes can achieve important rates of ammonia removal at temperatures as low as 4 °C
(Delatolla et.al., 2009). Facultative or partially aerated lagoons can be upgraded to activated
lagoons by converting the lined earthen basins to aeration basins and adding secondary
clarifiers and a return activated sludge system. In addition to conversion to an activated sludge
system, lagoon retrofits for ammonia removal can be accomplished by post-lagoon polishing,
in-lagoon polishing, and other systems. Fixed film (attached-growth) processes, such as
trickling filters, biotowers, and rotating biological contactors (RBCs) may be used to remove
ammonia as well as BOD if required. A combinationof fixed film and suspended growth
processes can also be used.
4.4 Submerged Attached Growth Reactor (SAGR®) at KWTF
As mentioned in section 4.2, the original aerated lagoon system at KWTF was upgraded and
retrofitted with a SAGR in 2013. A schematic of a typical SAGR reactor is included in
Figures 4-2 A and B.
4-4
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B
Figure 4-2. (A) Schematic of SAGR Reactor (B) Cut-away with air distribution
(Both Schematics Courtesy of Nexom)
The SAGR® process by Nexom is a patented tertiary wastewater process that can provide
nitrification during prolonged periods of cold-water temperature. The process can be
implemented for nitrification following aerated or facultative lagoons. It consists of an aerated
flow-through aggregate (gravel) bed with a horizontal distribution structure at the front end of
the system to distribute the influent flow across the width of the cell. A linear aeration system
with coarse bubble diffusers is used to provide oxygen to the sub-surface flow and enhance
4-5
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sludge digestion. The submerged aggregate provides the necessary surface area for growth of
nitrifying biomass within the bed. The aggregate gradation was selected to balance bacterial
growth area with hydraulic flow through the pore spaces. As the lagoon effluent flows
horizontally through the bed, the high-DO environment encourages nitrifying bacterial growth on
the aggregate surface area. A horizontal effluent collection chamber at the end of the treatment
zone collects the treated effluent and channels it to the discharge structure.
SAGR aggregate bed depths vary generally from four feet to twelve feet. A layer of mulch,
compost, chipped rubber tires, woodchips or other insulating material is placed on the surface of
each SAGR cell as an insulation layer and for prevention of aggregate bed freezing. Since the
Iowa Wastewater Facilities Design Standards did not specifically address the SAGR process, the
Iowa Department of Natural Resources (IDNR) performed a technology analysis in order for
KWTF to proceed with the project. Based on the IDNR review, the SAGR system was approved
as an acceptable alternative technology after satisfying specific concerns by IDNR. The City of
Kingsley then proceeded with one of the first installations in Iowa using the SAGR technology
designed in accordance with the IDNR guidelines to meet the ammonia discharge limits listed in
Table 4-2 above.
The aggregate (gravel) bed at KWTF consists of eight feet of wetted gravel media with one foot
of mulch over the gravel. The aggregate gradation (Table 4-3) is selected to balance the bacterial
growth area with hydraulic flow through the pore spaces. Aeration is provided throughout the
floor of the reactor to maintain desired aerobic conditions required for nitrification. Based on
IDNR requirements, SAGR aggregate media at KWTF was required to meet the following
requirements:
Table 4-3. Gravel Media Composition
Sieve Analysis
1 Percent
Sieve Size
__
Passing
|<><>
1"
So-|oo
_
30-X0
_
|o-;, o
_
i)-:
_
0-1
Sizing of the bed is based on TKN loading rates to provide year-roundnitrification needed to
consistently meet ammonia discharge permit requirements. According to Nexom, the SAGR is
generally designed to not exceed 0.52 lbs TKN/day per 1000 ft3 of aggregate for systems with
water temperatures below 1 °C and effluent ammonia requirements of <2 mg/1. An important
design consideration for a SAGR system is the organic loading rate.
SAGR beds are designed with a minimum of two cells, with each cell including two zones in
series. A shallow buried header connects blowers to the SAGR laterals. Aeration is provided
through high density polyethylene (HDPE) laterals located in the top layer of the insulating
4-6
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mulch. HDPE drop legs provide aeration to the individual diffuser lines. Influent distribution and
effluent collection chambers prevent short-circuiting in the bed which is sized to enable full
cBOD polishing as well as full nitrification at cold temperatures.
The SAGR's patented step-feed process at KWTF prebuilds and stores nitrifying bacteria in
October while the water is still warm so that they are already in place to compensate for the slow
nitrifier growth rate at cold water temperatures in the winter. When the water temperature is
warm (>12 °C), most of the ammonia removal happens in the first zone. But as the water
temperature drops, nitrifier activity slows down and more ammonia reaches the second zone for
treatment. During fall before temperature drops to below 53 °F, the first zone is bypassed, and
the entire influent runs only through the secondary zone (step feed operation). After
approximately one month, the influent is sent back to the first zone (regular operation). Through
this patented operational strategy, nitrifiers are grown in both zones of SAGR. The increase in
the population of nitrifiers compensates for reduced biomass kinetics in low temperature and
enables SAGR to provide effective ammonia removal during the winter. This step feeding is
critical for optimizing cold temperature nitrification. Aeration remains in operation even for the
zones that are not directly receiving lagoon effluent. This allows for enhanced aerobic solids
digestion and minimization of any long-term fouling effects. Flow distribution is important to
ensure true horizontal flow throughout the aggregate media.
Figure 4-3 below shows a layout of the upgraded lagoon system cells 1 and 2 as well as the
added four SAGR cells at KWTF.
4-7
-------
Figure 4-3. Lagoon Upgrades and SAGR Layout at KWTF
(Courtesy of Nexoni)
4.5 Detailed Statistical Analysis - Plant Effluent Concentrations
The facility's performance based on operating data from January 2015 to December 2017 was
analyzed. Figures 4-4 (A through C), 4-5, and 4-6 and Table 4-3 provide a summary of the
statistical analysis performed for the KWTF facility. The facility has daily maximum and 30-day
4-8
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average effluent ammonia concentration and mass loading limits as shown in Table 4-2 and is
required to collect a 24-hr composite sample once a week for effluent ammonia (with a minimum
of five samples in one calendar month during each 3-month period from March 15 to November
15). Daily maximum and 30-day average ammonia concentration limits vary on a monthly basis
from highs in January of 20.8 and 11.9 mg/1, respectively, to lows in August of 3.1 and 2.4 mg/1,
respectively. Daily maximum and 30-day ammonia loading limits vary on a monthly basis from
highs in January of 50.8 and 20.3 lbs/day, respectively, to lows in August of 7.1 and 4.0 lbs/day,
respectively.
Figure 4-4 A shows that the facility produced low effluent ammonia concentrations even
duringcold weather months with plant effluent daily ammonia concentrations consistently
below the detection limit of 0.2 mg/1 except for six days during the entire 3-year period (See
Section 4.6).The daily median ammonia value was below detection limit.
Figure 4-4 (B and C) shows the monthly average and 30-day rolling average effluent ammonia
concentrations at KWTF. Comparing the 30-day rolling average concentrations to the 30-day
ammonia discharge limits in Table 4-2 shows that the facility can consistently meet its 30-day
treatment objective. The monthly average and 30-day rolling average ammonia concentrations
were all below 1.5 mg/1 with a median concentration below the detection limit of 0.2 mg/1.
u>
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mm
H
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Daily Effluent Ammonia Time Series Plot for KWTF
4-9
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0.010
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X
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vVV
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12/27/14 7/15/15 1/31/16 8/18/16 3/6/17 9/22/17 4/10/18
B
Monthly Average Effluent Ammonia Concentrations Time Series Plot
10.00 -=
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12/27/2014 7/15/2015 1/31/2016 8/18/2016 3/6/2017 9/22/2017 4/10/2018
30-Day Rolling Average Effluent Ammonia Time Series Plot
Figure 4-4. (A) Daily and (B) Monthly Average, and (C) 30-Day Rolling Average Time
Series Plots for Effluent Ammonia at KWTF
Figure 4-5 A and B represents the cumulative probability plots for daily and monthly average
effluent ammonia concentrations. Figure 4-5 A and Table 4-3 show that the overall daily
effluent 95th percentile ammonia concentration was below the detection limit of 0.2 mg/1 (shown
on the graph as 0.1 mg/1, half of the detection limit). The 99th percentile daily ammonia
concentration was 5.28 mg/1. The median performance (50th percentile) was also below the
detection limit. Comparing the 95th percentile concentration to the median indicates consistent
4-10
-------
achievement of low levels of ammonia at low concentrations. It should be noted that the various
technology performance statistics (TPSs) evaluated in this report are affected by various
wastewater, site, and technology-specific conditions and upset events. They are used in this
report for describing technology performance at the facility. They can also be useful in informing
the design of the process at other facilities by taking into consideration site-specific
characteristics of each facility, its permit averaging period and permit limit, and how each TPS
relates to permit exceedances. For example, a 95th percentile concentration, if used on a daily
maximum basis, would be exceeded 91 times in a 5-year permit period while a 99th percentile
concentration would be exceeded 18 times. In comparison, a 95th percentile concentration used
on a monthly maximum basis would result in three exceedances in a 5-year permit period.
Figure 4-5 B shows that the effluent monthly average 95th percentile ammonia concentration for
the three-year period was 1.11 mg/1 while the 99th percentile was 1.15 mg/1, both well below the
30-day permit limits in Table 4-2. The median (50th percentile) monthly ammonia concentration
was below the detection limit of 0.2 mg/1.
Daily N Species
NH3 Log Normal Values
CM LO t- CM LO
o o
—1 r~
cm o
~1 1 1 r~
LO h- O 0)0 O) CO
O) CO O) O)
% values less than or equal to indicated values
Monthly Averages N Species
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•
• ^
•
• nh3
Log Normal Values
CM O LO
O) O) O) CO
O) CO O) O)
> values less than or equal to indicated values
B
Figure 4-5. Probability Plots for KWTF (A) Daily Data; (B) Monthly Average
4-11
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Table 4-4. Summary Statistics for Final Effluent Ammonia Nitrogen for KWTF
Individual
Sample
Data
NH3-N
Weekly
Data
NH3-N 30-
day Rolling
Average
NH3-N
Monthly
Average
NH3-N 12-
Month
Rolling
Average
n
154
154
1,067
36
25
Mean
0.189
0.189
0.189
0.178
0.188
Geometric
Mean
0.111
0.111
0.129
0.127
0.184
Standard Dev.
0.608
0.608
0.286
0.248
0.039
CV
3.225
3.225
1.509
1.390
0.204
Skew
8.012
8.012
3.577
3.592
-0.963
Minimum
0.100
0.100
0.100
0.100
0.112
Maximum
5.500
5.500
1.450
1.180
0.236
Figure 4-6. Probability Summary for KWTF
4.6 Process Performance - Submerged Attached Growth Reactor (SAGR®) at KWTF
According to the KWTF facility operator, the SAGR process is simple to operate and maintain,
with minimal moving parts in the system such as the blowers supplying oxygen to the process
and the aerated lagoons at KWTF. Generally, routine actions include performing a system
inspection, collecting water samples, and occasionally changing lubricating oil. Dissolved
oxygen and pH are measured once a week. Approximately every six months, the filters in the
blower units are changed. Twice a year, the operator implements the SAGR step feed procedure
by fully opening and fully closing separate valves.
4-12
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Other actions include adjusting SAGR influent valves periodically and adding ammonium sulfate
to SAGR influent in the fall as needed if influent ammonia levels entering the SAGR cells are
very low. The facility operator also reported an incident where sulfuric acid was used to clear
mineral deposits in air diffusers of a SAGR cell.
SAGR effluent ammonia data was analyzed for the 3-year period of January 2015 to December
2017 along with plant effluent ammonia concentrations. For the entire dataset received from the
facility, the SAGR effluent concentrations were mostly the same as the plant effluent
concentrations. For the instances where plant effluent ammonia data (after UV disinfection) was
not available, the SAGR reactor effluent concentration was used. As shown in Table 4-2, the
daily maximum effluent ammonia discharge limit varies on a monthly basis from a high of 20.8
mg/1 in January to a low of 3.1 mg/1 in August. Average monthly high and low air temperatures
in Kinsley, Iowa are approximately 27 °F and 8 °F, respectively, in January and 81 °F and 61 °F,
respectively, in August (source: NOAA). During the entire 3-year period, the facility consistently
met its effluent daily maximum ammonia discharge limit except for 2 occasions out of 154 as
explained below (the facility is required to sample its effluent for ammonia once per week). This
is significant given the susceptibility of nitrification to extreme cold temperatures and other
factors such as the potential presence of inhibiting constituents in the facility influent.
These excursions occurred as follows:
• June 2, 2015: Effluent ammonia concentration was 5.50 mg/1; Daily maximum limit is 3.7
mg/1. SAGR operating data do not seem to explain this effluent ammonia concentration. The
facility attributed this value to likely inappropriate sampling.
• November 29, 2016: Effluent ammonia concentration was 5.1 mg/1; Daily maximum limit is
3.2 mg/1. The facility reported that in order to ensure sufficient and consistent winter
nitrification during extreme cold weather and sufficient winter month biomass growth in
SAGR while the wastewater was still relatively warm, the facility supplemented lagoon
effluent ammonia by adding ammonium sulfate during the SAGR step feed procedure with
the dosing rate based on splitting the influent flow between zones 1 and 2. However, the
entire flow was passed through the two zones in series resulting in the higher effluent
ammonia concentration on 11/29/2016. This was quickly corrected and reported by the
operator.
On a 30-day basis, the maximum effluent 30-day ammonia limit varies on a monthly basis from
a high of 11.9 mg/1 in January to a low of 2.4 mg/1 in August. The actual effluent monthly
average ammonia concentrations were consistently below these limits with a maximum of 1.18
mg/1 in June 2015 and a minimum concentration below the detection limit of 0.2 mg/1 in 32 of
the 36 months periods.
4-13
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REFERENCES
Delatolla, R., Tufenkji, N., Comeau, Y., Gadbois, A., Lamarre, D., and Berk, D. (2009). "Kinetic
Analysis of Attached Growth Nitrification in Cold Climates". Water Science &
Technology 60(5): 1173-84 • February 2009.
NOAA, National Climatic Data Center. NOAA's 1981-2010 Climate Normals. Accessed August 18, 2021.
https://www.currentresults.coin/Weather/Iowa/average-annual-teinperatures.php
Tchobanoglous, G., H. D Stensel, R. Tsuchihashi, and F. L. Burton. (2014). "Wastewater
Engineering: Treatment and Resource Recovery". 5th ed. Met calf and Eddy, Inc., McGraw-Hill
Education.
U.S. EPA (1993). "Nitrogen Control Manual". EPA/625/R-93/010. Washington, DC.
4-14
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CHAPTER 5.0
The F. Wayne Hill Water Resources Center (FWHWRC) - Gwinnett
County, GA - Enhanced Nutrient Recovery through WASSTRIP®
Phosphorus Stripping and Ostara Pearl® Nutrient Recovery - Case Study
5.1 Background
The F. Wayne Hill Water Resources Center (FWHWRC) plant is a 60 MGD advanced treatment
facility located near the City of Buford, Georgia and operated by the Gwinnet County
Department of Water Resources. Advanced tertiary effluent from FWHWRC is discharged
primarily to Lake Lanier which serves as a recreational resource as well as an important water
supply for the Atlanta metropolitan area. A portion of the effluent is also occasionally discharged
to another water reclamation facility where the two effluents are combined and discharged to
Chattahoochee River.
Enhanced biological phosphorus removal (EBPR) and chemical phosphorus precipitation trim
are used at the FWHWRC to meet a monthly average total phosphorus (TP) limit of 0.08 mg/1.
The facility's solids processing system includes anaerobic digestion of combined primary sludge
and waste activated sludge (WAS). The facility also receives combined primary sludge and
WAS from the 22 MGD Yellow River Water Reclamation Facility which significantly increases
the phosphorus and TKN load handled at FWHWRC.
In 2009, Gwinnett County initiated the addition of magnesium hydroxide (Mg(OH)2) into its
collection system to control odor and corrosion. This addition significantly reduced the need for
alkalinity adjustment at the plant and resulted in phosphorus precipitation from the digested
sludge centrate, which decreased phosphorus recycle to the liquid treatment train and provided
stability to the EBPR process. However, the phosphorus precipitated as struvite accumulated in
centrate drain lines, the dewatering centrifuges, and in the digestion facility; it negatively
impacted sludge dewatering capacity. With the facility experiencing increasing incidents of
undesirable struvite precipitation necessitating significant maintenance efforts and resulting in
negative process impacts, Gwinnett County began piloting struvite precipitation phosphorus
recovery technologies in 2011. Based on the pilot results and in comparing a phosphorus
recovery process versus phosphorus removal via chemical coagulant addition, Gwinnett County
chose to pursue a nutrient recovery process for phosphorus recovery and controlling its
phosphorus recycle loads at FWHWRC.
In 2015, FWHWRC implemented the WASSTRIP® process, which strips phosphorus from
WAS, and the OSTARA Pearl® process for phosphorus and nitrogen recovery and the creation
of a slow-release fertilizer (Crystal Green) under controlled conditions.This allowed combining
of dewatered sludge centrate with phosphorus and magnesium-rich filtrate from sludge
thickening to feed the Pearl® process, thereby increasing Crystal Greenproduction and
phosphorus recovery and further reducing struvite precipitation in undesired locations at the
plant.
5-1
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5.2 Plant Processes
Liquid and solids treatment processes at FWHWRC are shown in Figure 5-1.
Preliminary treatment is comprised of influent screening and grit removal. Seven individual
trains are used, each train employing a center-flow perforated plate band screen and a stirred
vortex grit removal tank. Primary treatment occurs in ten rectangular primary clarifiers, with
primary sludge pumped to the WASSTRIP tank (described below) and subsequently to the
plant's solids handling system. Fermentation of primary sludge occurs naturally in the 5-7 ft
blankets maintained in the clarifiers. This helps with generation of more volatile fatty acids
(VFAs) that are beneficially used subsequently in the bioreactors where EBPR is implemented
Scum thickening and removal equipment are used to concentrate the scum for disposal in the
facility's anaerobic digesters.
Primary effluent flows into a biological treatment system consisting of ten plug-flow biological
reactors to achieve BOD removal, nitrification, denitrification, and EBPR. These are followed by
ten circular clarifiers for solids separation. Sludge is wasted from the secondary clarifiers and is
pumped back to the front of the bioreactors as return activated sludge (RAS). The effluent from
the secondary clarifiers flows to a secondary effluent collection box, from which flow can be
routed to equalization or to the two downstream tertiary treatment processes.
5-2
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Eight 20 million-gallon circular tanks are used for storage and flow equalization. Five of the
tanks are for flow equalization, three are for emergency storage, and one is dedicated for off-
specification flow. Primary effluent is equalized diurnally to maintain a more consistent flow and
loading to the bioreactors. Secondary effluent flow can also be equalized to maintain consistent
flows to tertiary treatment.
The biological treatment system at FWHWRC is operated in the Anaerobic/Anoxic/Aerobic
(A20) mode. Low energy mixers are installed in the anoxic and anaerobic zones to maintain
mixed liquor solids in suspension. Anaerobic zones allow for BOD reduction and phosphorus
release. After secondary treatment, secondary effluent flow is split into two treatment trains. The
first treatment train is rated for 20 MGD and includes solids contact clarifiers, recarbonation
clarifiers, and granular media filtration (GMF). Alum is added right before the secondary
clarifiers to provide chemical phosphorus polishing. The solids contact clarification includes four
circular clarifiers for coagulation and flocculation of solids with ferric chloride. Previously used
recarbonation clarifiers serve as an additional flow-through point to settle solids. The effluent
then flows to multi-media dual-bed type gravity filters which are backwashed for periodic
cleaning. The second treatment train is rated for 40 MGD and includes chemical coagulation,
flocculation, clarification, and membrane ultrafiltration. This train also allows for ferric chloride
addition to the secondary effluent. Chemical sludge is handled in the solids treatment facility as
described below. Effluent from the chemical clarifiers flows to the tertiary membrane system for
further treatment. The tertiary ultrafiltration membrane facility uses hollow fiber membranes and
is comprised of 16 parallel treatment trains.
The effluent from both trains is combined prior to pre-ozone treatment which consists of ozone
generators, sidestream ozone dissolution, contactors, and off-gassing system. The purpose of the
pre-ozone system is to meet the immediate oxidation demand of the GMF and membrane
effluent and also to convert recalcitrant organic compounds to bioavailable organic compounds
prior to treatment in the biological activated carbon (BAC) process. This is operated as a
biological process and is not used for organic pollutant adsorption. As such, activated carbon is
not removed and reactivated.
Effluent then flows to the post-ozone system which operates similarly to the pre-ozone system.
The primary purpose of the post-ozone system is disinfection of the BAC effluent, as much of
the oxidation demand is satisfied by the pre-ozone system. The effluent pump station provides
effluent pumping conveyance to Lake Lanier and the Chattahoochee River.
Solids treatment processes at the FWHWRC are also shown in Figure 5-1. Solids handling
includes a primary sludge and WAS stripping, co-thickening using rotary drum thickeners,
chemical sludge gravity thickeners, egg-shaped anaerobic digesters, and dewatering centrifuges.
The existing facility also includes a co-generation system which includesa fats, oil, and grease
(FOG) and high strength waste (HSW) receiving station.
Primary sludge and WAS are combined in the WASSTRIP tank for phosphorus (and
magnesium) release prior to thickening and subsequent anaerobic digestion. Digested sludge is
transferred to sludge storage tanks and is then sent to the centrifuges for dewatering. Chemical
sludge from the tertiary treatment train is thickened by gravity and then blended with digested
5-3
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sludge in the pipeline as material is being sent to the dewatering centrifuges. Dewatered cake is
loaded onto trucks and hauled to a landfill and used as fill and cover material. Anaerobic digester
gas handling consists of compressors, storage tanks, waste gas burners (flares), hydrogen sulfide
and siloxane removal, and an engine generator that operates using the cleaned digester gas. The
heat from the engine generator is recovered and utilized in the digester heating process, and the
energy generated is used as electricity within the plant.
The nutrient recovery facility at FWHWRC uses the Ostara Pearl® process to recover
phosphorus, minimize nuisance struvite formation in solids handling unit processes, and
minimize phosphorus recycle loading to the head of the facility, while facilitating the production
of inorganic struvite pellets that are beneficially used as a slow-release fertilizer. Equalized
filtrate and centrate are pumped from thickening and centrifuge dewatering equalization tanks to
the nutrient recovery facility.
The Ostara process has two Pearl® 2000 reactors, where optimal pH conditions are maintained
using caustic addition to induce struvite precipitation. The struvite pellets are dewatered, dried,
classified based on pellet size, and transferred to the storage silos. The finished product is bagged
in one-ton super sacks and stored onsite for pickup for final use as fertilizer, labeled as Crystal
Green®.
Table 5-1. Design and Average Raw Influent Concentrations and Percent of Design
Loads for the FWHWRC from January 2015 to December 2017
Parameter
Raw Influent Design
Average
Raw
Influent
Percent
of
Design1
(Annual Average)
(Maximum Month)
Flow (MGD)
50
60
32.2
64
cBODs (lbs/d)
109,671
131,065
61,515
56
TSS (lbs/d)
188,901
226,681
140,138
74
Ammonia (lbs/d)
13,761
16,513
8,536
62
TKN (lbs/d)
20,016
24,019
11,841
59
TP (lbs/d)
3,962
4,754
2,431
61
\Tote:
1- Percent of design values, except for flow, are based on average annual values for the analysis
period for influent design loads (lbs./day) and actual influent loads (lbs./day).
5-4
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Table 5-2. NPDES Limits - January 2015 - December 2017 at FWHWRC
Parameter
Monthly
Monthly
Weekly
Weekly
Average
Average
Average
Average
(mg/1)
(Kg/day)
(mg/1)
(Kg/day)
COD
18
2729
27
3412
TSS
3
455
4.5
569
Ammonia (mg/1)
0.4
61
0.6
76
TP (mg/1)
0.08
12
0.19
242
\Tote:
1. The weekly average is based on FWHWRC design for a monthly phosphorus limit of 0.13
mg/1
5.3 Conventional Enhanced Biological Phosphorus Removal Technology
Enhanced biological phosphorus removal (EBPR) in wastewater treatment is accomplished by
encouraging the growth of polyphosphate accumulating organisms (PAOs). PAOs are
heterotrophic bacteria that occur naturally in the environment and in aerobic activated
sludge. The growth of PAOs is encouraged by cycling them between anaerobic and aerobic
conditions. In the presence of oxygen (i.e., aerobic conditions), PAOs obtain energy from stored
food and uptake large amounts of phosphorus into their cells, which they store as
polyphosphates. These polyphosphates contain high-energy bonds and function like energy
storage batteries.
In the absence of oxygen (i.e., anaerobic conditions), PAOs can break the polyphosphate bonds
resulting in the release of orthophosphate and use the resulting energy to uptake easily
biodegradable compounds, namely short-chain volatile fatty acids (VFAs). PAOs polymerize and
store the VFAs in their cells as intermediate products known as poly-P-hydroxy- alkanoates
(PHAs), of which the most common is poly-P-hydroxy-butyrate (PHB). When oxygen becomes
available again (i.e., aerobic conditions), they can metabolize the PHAs to generate energy and
uptake phosphorus (in the form of phosphate) and store the excess amount (Randall et al.,
2010).
In general, it was traditionally accepted that phosphorus could only be removed in conventional
plants when the wastewater characteristics were favorable with a COD:TP ratio of at least 37:1
or a BOD:TP ratio of about 18:1, with some of the COD consisting of short chain VFAs. More
COD may be required if the process also involves denitrification of nitrate (Kobylinski et al.,
2008). At wastewater treatment facilities where this ratio is low, external sources of carbon such
as methanol, ethanol, or proprietary carbon products could be added, and in some cases, carbon-
rich waste products such as molasses, sugar wastes, or others may also be used. Additionally,
many plants have elected to ferment their primary sludge. However, this often requires measures
to limit odors and to ensure stable and consistent performance.
5-5
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Other microorganisms besides PAOs exhibit a similar metabolism. For example, Glycogen
Accumulating Organisms (GAOs) are similar to PAOs in terms of being able to store readily
biodegradable organic matter such as VFAs as poly-|3-hydroxyalkanoate (PHA) in the anaerobic
phase (Zeng et al., 2003). GAOs do not contribute to phosphorus removal as their metabolism
does not involve anaerobic phosphorus release and subsequent aerobic (or anoxic) phosphorus
uptake (Lopez-Vazquez et al., 2007). Therefore, in terms of biological phosphorus removal,
GAOs are seen as competitors of PAOs for substrate and a main cause of process deterioration or
even failure of EBPR systems (Thomas et al., 2003). Temperature has been identified as having a
potentially significant impact on the PAO-GAO competition. At temperatures greater than 25°C,
GAOs can outcompete PAOs for organic carbon (Law et al., 2016).
EBPR is considered a sustainable approach to removing phosphorus from wastewater. However,
the process can in some cases be unstable particularly at low influent rbCOD/TP ratios and
where other wastewater constituents such as dissolved oxygen or nitrate interfere with the
anaerobic phosphorus release. To address such difficulties, particularly where low phosphorus
limits are in place, many facilities incorporate added chemical polishing and incur the cost of
using chemical phosphorus removal as a backup to EBPR.
In a detailed study of the long-term performance of EBPR facilities (Neethling, 2005), five
EBPR facilities of various process designs, wastewater characteristics, operation, and other
factors were evaluated over a three-year period to determine the biological phosphorus removal
efficiency as well as their consistency of producing effluent concentrations (termed reliability in
the study) at or below a given treatment goal. Table 5-3 shows the range of frequencies with
which the plants achieved effluent orthophosphate (OP) concentrations of 0.5 mg/1, 1.0 mg/1,
and 2.0 mg/1.
Table 5-3. EBPR Reliability at Various EBPR Facilities
(Adapted from Neethling et al., 2005)
Effluent Concentration &
Percentile
Reliability Range for Five
EBPR Facilities
Reliability Average
OP< 0.5 mg/1
24% - 95%
68%
OP< 1 mg/1
64% - 99%
82%
OP < 2 mg/1
85% - 100%
93%
50% (Geometric Mean)
0.05 - 0.76 mg/1
0.26 mg/1
90%
0.2-2.5 mg/1
1.6 mg/1
90%/50%
2.0-24.0
11.5
The table also shows the 90th and the 50th percentile concentrations achieved as well as the ratio
between the 90th and the 50th percentile (90 percent/50 percent) effluent OP concentrations. The
values showthat EBPR reliability is significantly reduced with lower desired effluent
phosphorus concentrations particularly at lower discharge levels. Moreover, EBPR effluent
concentration
5-6
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variability is significant as evidenced in the wide reliability range observed (90 percent/50
percent ratiorange of 2 - 24) for the five facilities indicating relatively unstable performance.
5.4 Phosphorus Recovery
Nutrient removal from wastewater represents a significant resource demand for water resource
recovery facilities (WRRFs). This can include costs related to consumption of electricity, organic
carbon, chemicals, and sludge production, utilization, or disposal. Development of effective and
economically feasible nutrient removal options is highly desirable to utilities. This is particularly
the case for phosphorus removal as conventional BPR can be unstable and, if the BPR sludge is
anaerobically digested and dewatered, can result in the recycleof significant phosphorus loads
back into the mainstream processes thereby requiring additional treatment. The other
conventional phosphorus removal alternative is chemical phosphorus removal which involves
costly chemical addition and produces significant amounts of chemical sludge, particularly for
phosphorus removal to low effluent discharge concentrations. From a resource recovery
perspective, phosphate rock is a non-renewable resource and current global reserves may be
depleted in 50-100 years (Cordell, Drangert, & White, 2009).
Extractive phosphorus recovery represents an alternative potentially attractive strategy for
managing a portion of the phosphorus treated at many WRRFs. The approach generally involves
using energy and resources to accumulate phosphorus and produce a nutrient product that has
value in a secondary market and, if resold, can also potentially help plants offset operating costs
(WERF, 2015). The attractiveness of a phosphorus recovery process to a WRRF generally
depends on several factors including the loading and concentration in the influent nutrient
stream, nutrient recovery efficiency, cost competitiveness with conventional treatment
technology, quality of return flow to the plant's mainstream processes, and product quality and
purity.
5.5 The WASSTRIP® Process
The waste activated sludge stripping to recover internal phosphate (WASSTRIP®) process is a
patented process designed to release phosphates, magnesium, and potassium produced in an
EBPR process prior to anaerobic digestion. The process complements and enhances other
nutrient recovery processes such as Ostara's Pearl® process described below by providing
magnesium and increasing struvite formation through the additional phosphorus made available.
WASSTRIP anaerobically reacts primary sludge (PS) with EBPR waste activated sludge
resulting in phosphorus release from PAOs. Under WASSTRIP's anaerobic conditions, PAOs
in the EBPR sludge readily release stored phosphate, along with magnesium and potassium
counter ions. The primary sludge and WAS are then thickened and the filtrate is blended with
dewatering centrate orfiltrate typically high in ammonia thus allowing increased phosphorus
recovery by providing a feed stream with a higher phosphorus content to a nutrient recovery
facility. The WASSTRIP process HRT depends on factors including the phosphorus content in
the WAS as well as VFA availability to PAOs to allow phosphorus release. VFA availability is
typically from WAS fermentation but can be added if needed, such as from aprimary sludge
fermenter, to enhance phosphorus release and reduce WASSTRIP HRT.
5-7
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In addition, WASSTRIP can provide other benefits. WASSTRIP controls undesirable struvite
precipitation in the solids treatment train by lowering the concentration and bioavailability of OP
and magnesium in the digester, two of the major ingredients essential for formation of inorganic
precipitates such as struvite and Newberyite (Fabiyi et al., 2016). Such undesired struvite
formation in downstream solids handling processes can disrupt operations andis costly to
remove and maintain. Another benefit observed by a number of facilities that use EBPR for
phosphorus removal is a reduction in the volume of the produced dewatered biosolids cake due
to improved dewatering. Additionally, WASSTRIP can in some cases benefit certain facilities
that land apply their biosolids by reducing biosolids phosphorus content and potentially
increasing availability of sites for land application.
5.6 The Pearl® Process
The Pearl® process is a patented nutrient recovery process by Ostara that recovers phosphorus
from nutrient-rich wastewater filtrate and/or centrate through the controlled precipitation of
struvite. The Pearl reactor is an up-flow fluidized bed reactor designed to maximize nutrient
recovery and production of a high-quality fertilizer. The process includes optimized reactor
geometry, flow management, and process control of chemical addition such as soluble
magnesium for ionic concentration adjustment and sodium hydroxide for pH adjustment. The
influent and chemicals are introduced at the bottom of the reactor, where struvite crystal
formation begins. Treated effluent is discharged from the top of the reactor and returned to the
mainstream for further treatment. A portion of treated effluent is returned to the bottom of the
reactor for product size control and as needed for influent flow variations. The product is
dewatered, dried, sorted by size, and bagged or optionally stored in silos as high-purity struvite
pellets prior to distribution and sale directly from the facility as a slow-release fertilizer branded
Crystal Green®.
5.7 The WASSTRIP® and Pearl® Processes at FWHWRC
Nutrient recovery at FWHWRC is accomplished by using the WASSTRIP® process and the
Pearl® process to mitigate nuisance struvite formation in solids handling unit processes and to
minimize phosphorus recycle to the head of the facility, while facilitating the production of
inorganic struvite pellets that are beneficially used as a slow-release fertilizer. FWHWRC began
adding magnesium hydroxide into the collection system in 2009 to control odor and corrosion.
As a result, P precipitation from the digester centrate decreased P recycle loads returned to the
bioreactors allowing for the stabilization of the EBPR process. However, this precipitation
restricted flow in the centrate drain lines and reduced centrifuge dewatering capacity. After
evaluating several alternatives, the facility selected the OSTARA Pearl® nutrient recovery
process with WASSTRIP® process phosphorus stripping. The main project components
included WASSTRIP, centrate and filtrate equalization tanks, transfer pumps, Ostara Pearl
nutrient recovery reactors and chemical feed systems, product handling system, and process
control. A process flow diagram is provided in Figure 5-2.
5-8
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Liquid Treatment
Drains / Overflows
Figure 5-2. Liquid and Solids Treatment Process Train at FWHWRC
(Adapted from Latimer et al., 2017)
Primary sludge (PS) and WAS are pumped to the WASSTRIP tank and blended in a constant
level tank, and the blended sludge is mixed with a large bubble mixing system and allowed to
react anaerobically for at least 6 hours. From there, combined sludge from the WASSTRIP
process is thickened in rotary drum thickeners (RDTs). The filtrate, rich in phosphate and
magnesium, is stored in an equalization tank and fed along with flow from centrate equalization
tanks to the nutrient recovery facility. The equalization tanks were designed to allow heavy
solids to settle and automatically drain and washdown. Filtrate and centrate equalization tanks, as
well as one swing tank are 500,000 gallons each.
In order to reduce the potential for struvite accumulation in centrate lines, the facility installed
PVC centrate pipes with removable sections in the centrifuge dewatering building as well as
parallel HDPE centrate pipes into the recovery facility. In addition, an acid feed loop was
installed to allow cleaning of the feed pipes as needed.
The Ostara process consists of two Pearl ® 2000 reactors with space for a third reactor in the
future. Each reactor has a nominal capacity of 4,400 pounds of daily struvite production. Optimal
reactor pH conditions are maintained using caustic addition to induce struvite precipitation at a
target pH of 7.8. The struvite pellets are dewatered, dried, classified based on pellet size, and
transferred to the storage silos. The finished product is bagged in one-ton sacks and stored onsite
for pickup and final use as fertilizer, labeled as Crystal Green ®.
5.8 Detailed Statistical Analysis - Plant Effluent Concentrations
Facility operating data from January 2015 to December 2017 were analyzed. Figures 5-3 through
5-5 and Table 5-3 provide a summary of the statistical analysis performed for the FWHWRC. As
5-9
-------
explained below, the data shows that the facility consistently met the final effluent treatment
objectives for total Phosphorus shown in Table 5-2 throughout the analysis period.
10
to
QJ
u
OJ
a.
fcTj
a.
0,1
x TP
-^TP Median
-¦-TP Monthly Avg Limit
-o-TP Weekiy Avg Limit
0.01
Dec-14 Jul-15
Jan-16
Aug-16 Feb-17 Sep-17
Mar-18
a,
(JO
E
J 0.1
"O
-------
Figures 5-4 A through D include cumulative probability plots for FWHWRC's daily, 30-day
rolling average, weekly average, and monthly average data sets. A percentile value on the x-axis
represents the probability that the value is less than or equal to the stated corresponding
concentration on the plot's y-axis. Figure 5-4 C shows that the weekly average 99 percentile TP
concentration was 0.08 mg/1. All 156 weekly average effluent concentrations reported were
below the weekly average discharge limit with a maximum value of 0.11 mg/1. Similarly, on a
monthly basis, Figure 5-4 D shows that the monthly average 99 percentile TP concentration was
0.06 mg/1. All 36 monthly average effluent concentrations reported were below the TP monthly
average discharge limit of 0.08 mg/1, with a maximum value of 0.065 mg/1.
A
B
C
D
Figure 5-4. Probability Plots for FWHWRC-
(A) Daily Data; (B) 30-day Rolling Average; (C) Weekly Average; (D) Monthly Average
5-11
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Figure 5-5 provides a probability summary for TP effluent concentrations at the 3.84, 50, 90, 95,
and 99 percentiles for the various data sets (daily, 30-day rolling, weekly average, monthly
average, and annual average). Based on the three-year data set, the daily average concentration at
the95th percentile (as an example) is 0.07 mg/1 TP, while at the 50th percentile (median), the
concentration is 0.03 mg/1.
Figure 5-5 also can highlight the variability for TP concentrations. Comparing the daily data 14-
day (3.84th) percentile of 0.02 mg/1 for TP to the 95th percentile of 0.07 mg/1, the 95 percent/3.84
percent is about 3.5 demonstrating low variability.
Table 5-4. Summary Statistics for Final Effluent Total Phosphorus for FWHWRC
TP Daily
Data
TP Rolling
30-day
Average
TP Weekly
Averages
TP
Monthly
Averages
TP
Annual
Average
n
1,081
1,067
156
36
25
Mean
0.04
0.04
0.04
0.04
0.04
Geometric Mean
0.03
0.04
0.03
0.04
0.04
Standard Dev.
0.02
0.01
0.01
0.01
0.00
CV
0.57
0.27
0.38
0.28
0.13
Skew
8.61
0.69
1.58
0.73
-0.44
Minimum
0.02
0.02
0.02
0.02
0.03
Maximum
0.47
0.07
0.11
0.06
0.05
Figure 5-5. Probability Summary for FWHWRC
5-12
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5.9 WASSTRIP® and Ostara Pearl® Process Performance & Lessons Learned
As mentioned in Section 5.7, The FWHWRC facility implemented the OSTARA Pearl® nutrient
recovery process with WASSTRIP® process phosphorus stripping. The OSTARA Pearl®
facility came online on July 6, 2015. Figure 5-6 shows the OP percent recovery in each of the
two reactors of the OSTARA Pearl facility. The percent recovery values ranged from about 40
percent to 83 percent. The initial lower OP recovery values before December 2016 were
attributed to a number of operational factors as explained below. Additionally, the facility
reported lower initial total phosphorus recovery due to struvite fines production and loss to the
overflow. Struvite fines as small particulates, generally described as less than 0.5 millimeters, are
spontaneously precipitated in supersaturated conditions.
Figure 5-6. Orthophosphate Percent Recovery
In order to address the initial low percent OP removal and the fines production problem, the
facility implemented various modifications in the operational pH setpoint and in the product
harvesting procedure. This work included optimizing the type, frequency, and mode of seeding,
and routine replacement of pH probes every six months. The facility also implemented periodic
citric acid cleaning to prevent struvite clogging of pumps and pipes. Additionally, since the
WASSTRIP RDT thickening facility operates seven days a week while centrifuge dewatering
does not occur
5-13
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on weekends, procedures were implemented to ensure centrate tanks are full ahead of the
weekend so as to maintain desired filtrate-to-centrate ratios in the feed to the Ostara facility.
Table 5-5 shows the average daily gross and net production of the fertilizer product at the Ostara
facility during the analysis period of January 2015 through December 2017. The process during
this period was operating at well less than the nominal capacity of a single reactor. As shown, the
facility was able to increase net daily production in 2016 and to almost 1,700 pounds per day in
2017 due to operational enhancements as plant operators gained further experience with
operating the nutrient recovery facility and its process-specific requirements.
Table 5-5. Ostara Pearl® Production Data
Operating Period
Average Daily Gross
Production*, lb/d
Average Daily Net
Production*, lb/d
Startup - Dec 2015
1,416
601
2016
1,116
800
2017
1,978
1,682
* Average daily production values reported by FWHWRC.
Figure 5-7 shows the bioreactor effluent OP concentrations before and after Ostara Pearl process
startup. As mentioned previously, FWHWRC utilizes EBPR and chemical polishing to meet a
low effluent total phosphorus limit of 0.08 mg/1.
Methods of nutrient recovery such as the use of the Ostara Pearl® process through controlled
harvesting of struvite normally can help in the reduction of phosphorus recycle loadings to the
mainstream BNR process, thereby improving biological phosphorus removal performance and
reducing the need for supplemental chemical phosphorus removal. However, as shown in Figure
5-7, the BNR facility experienced an initial increase in effluent OP concentrations in the effluent
from the BNR reactors.
< Monthly Average Bioreactor OP Effluent (mg/L)
Figure 5-7. Monthly Average Bioreactor OP Effluent
5-14
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FWHWRC indicated that the initial performance of the nutrient recovery facility startup had a
negative impact on mainstream EBPR performance due to the facility's low recovery of
particulate TP after its startup. Based on a strong correlation observed between the reduction in
EBPR performance, stability, and the facility's reduced TP recovery, the EBPR performance was
attributed by FWHWRC mainly to the struvite fines loss after startupof the nutrient recovery
facility. The loss of struvite fines is a significant issue since it can dissolve upon return to the
head of the plant thereby increasing the phosphorus load to the biological reactors and resulting
in higher bioreactor effluent concentrations. This resulted in the sudden breakthrough of OP in
the reactor effluent, with average monthly OP concentrations fluctuating between approximately
0.4 mg/1 and 1.1 mg/1 between February 2016 to August 2017as shown in Figure 5-7. These
periodic episodes of reduced EBPR performance in turn resulted in increased reliance on metal
salt addition to the bioreactor effluent and upstream of the tertiary treatment train as explained
below.
In order to address this problem, the facility implemented a 7-month field optimization effort in
2017 to improve EBPR performance and reduce metal salt addition, especially during periods of
reduced nutrient recovery performance. This effort focused on better understanding of the impact
of several operational variables on EBPR performance in the bioreactors including the impact of
the internal nitrified recycle (NRCY) operation and the bioreactor configuration that would be
less susceptible to upset conditions. Results of the testing showed that higher DO from NRCY
streams, higher nitrate back to the anoxic zone, along with back mixing when they entered
anaerobic zones, negatively impacted phosphorus release. They also showed that higher
secondary clarifier sludge blankets may have resulted in secondary phosphorus release.
Additionally, testing showed that RAS short-circuiting and back mixing of flow from aerated
zones to unaerated zones also negatively impacted performance.
Based on the data collected in the optimization effort and available historical efforts, changes in
the bioreactor configuration and in the zone receiving NRCY were implemented on all
bioreactors. This was done to allow proper anaerobic conditions for EBPR and maximize anoxic
volume for denitrification. Additional secondary clarifier sludge blanket control measures were
also implemented. As a result of these measures, EBPR performance improved significantly
starting in August 2017 as shown in Figure 5-7. Alum addition also improved as shown below,
However, the main driver for the reduced alum addition at the secondary process was to
maximize the bioavailability of OP in the WAS, and a subsequent increase of ferric dosing at the
tertiary processes was implemented to remove any OP remaining in the BNR effluent.
Facility staff also realized that while implementing these measures would improve performance,
limited periodic EBPR upsets are likely to occur in the future, and an additional treatment step
for the recycle stream from the nutrient recovery facility may be needed. A complete description
of the optimization effort, including testing and results, are illustrated in the paper by Mohan et
al., 2018.
Figure 5-8 shows the alum addition to the secondary clarifiers and the Ferric chloride addition at
the tertiary process before and after OSTARA start up in July 2015. Notwithstanding periodic
fluctuations in Alum addition experienced in the months following startup of the Ostara facility,
5-15
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the monthly average alum addition after OSTARA startup (July 2015 through December 2017)
was lower by approximately 60 percent compared to the period between January 2013 through
July 2015.
» Monthly Average Alum Dosage (mg/L) » Monthly Aver eg e Ferrt Dosage
70.00
6Q.00
50.00
40.00
30.00
20.00
10.00
0.00
Figure 5-8. Monthly Average Alum and Ferric Chloride Dosage before and after OSTARA
Startup
An additional benefit observed since startup of the Nutrient recovery facility in July 2015 along
with using the WASSTRIP process is a significant increase in dewatered sludge solids content
resulting in reduced volumes of dewatered sludge produced, associated sludge hauling, and
landfilling costs. Figure 5-9 shows the average monthly solids content of the dewatered sludge
cake from January 2013 through December 2017. As shown, the sludge cake percent total solids
(percent TS) increased from an average monthly value of 22.2 percent from January 2013
through June 2015 to an average of 23.7 percent after startup of the Ostara process in July 2015.
Research has shown that biological phosphorus removal plants may experience higher
monovalent to divalent (M/D) cation ratios in their anaerobic digestion due to release of
phosphate and potassium under anaerobic conditions and complexation and precipitation of
calcium phosphate and magnesium phosphate species. The resulting increase in M/D cation
ratios contribute to poor floe formation and subsequent poor dewatering performance (Higgins et
al., 2014). As such, the addition of a process such as WASSTRIP to release and redirect the
phosphorus and potassium prior to digestion results in an improvement in the dewatering
properties.
Before OSTARA
Startup
After
OSTARA
Startup
rara£r^;3-onra£r^'3"orinj£r^;b-
±
o n
n ft" ^ & o
5 5 i/i
~ n ra ^ 0" o
^ > w -z.
5-16
-------
Month
Figure 5-9. Sludge Cake Percent Total Solids - Monthly Average
5-17
-------
REFERENCES
Cordell, D., Drangert, J. O., & White, S. (2009). "The Story of Phosphorus: Global food security
and food for thought". Global Environmental Change, 19(2): 292-305.
Fabiyi, M, et al. "Modeling & Operational Case Study of a Full-scale Phosphorus Recovery
System Coupled with WASSTRIP®: Factors to Consider in Model Development & Insights for
Optimal P Recovery". WEFTEC 2016.
Higgins, M., Bott, C., & Beightol, S. (2014). "Does Bio-P Impact Dewatering after Anaerobic
Digestion? Yes, and not in a good way!". Proceedings of the Water Environment Federation.
2014. 1-11. 10.2175/193864714816196826.
Kobylinski, E., Van Durme, G., Barnard, J., Massart, N., and Koh S-H. (2008). "How Biological
Phosphorus Removal is inhibited by Collection System Corrosion and Odor Control Practices" -
WEFTEC 2008.
Latimer, R., Hardy, S., McCallum, E., Brown, B., Kilby, K., Lan, J.C., Richards, T. "Nutrient
Recovery at the F. Wayne Hill Water Resources Center: Experience and lessons learned after 18
months". WEF Nutrient Symposium, 2017.
Law, Y., Kirkegaard, R., Cokro, A., Liu, X., Arumugam, K., Xie, C., Stokholm-Bjerregaard,
M., Drautz-Moses, D., Nielsen, P., Wuertz, S., and Williams R. (2016). "Integrative Microbial
Community Analysis Reveals Full-Scale Enhanced Biological Phosphorus Removal under
Tropical Conditions". Scientific Reports 6:25719. DOI:10.1038/srep25719.
Mohan, G.R., Lan, J.C., Latimer, R., Lynch, M., Pitt, P. 2018. "Nutrient Recovery Performance
and the Optimization of Biological Phosphorus Removal at the F. Wayne Hill Water Resources
Center". Proceedings of the Water Environment Federation Nutrient Removal and Recovery
Conference 2018.
Neethling, J.B., Bakke, B., Benisch, M., Gu, A., Stephens, H., Stensel, H.D., Moore, R., 2005.
"Factors Influencing the Reliability of Enhanced Biological Phosphorus Removal". Report
01CTS3. Water Environment Research Foundation, Alexandria, VA.
Randall, C., Branard, J., Stensil, D., and Brown, J. "Nutrient Control Design Manual". U.S.
Environmental Protection Agency, Washington, DC, EPA/600/R-10/100, 2010.
Thomas, M., Wright, P., Blackall, L., Urbain, V., Keller, J. (2003). "Optimization ofNoosaBNR
Plant to Improve Performance and Reduce Operating Costs". Water Sci. Technol., 47 (12), 141.
WERF. 2015. "Towards a Renewable Future: Assessing Resource Recovery as a Viable
Treatment Alternative. Case Studies of Facilities Employing Extractive Nutrient Recovery
Technologies". NTRYlR12b. Water Environment Research Foundation (WERF). Alexandria,
VA.
5-18
-------
Zeng, R., van Loosdrecht, M., Yuan, Z., Keller, J. (2003). "Metabolic Model for Glycogen
Accumulating Organisms in Anaerobic/Aerobic Activated Sludge Systems". Biotechnol.
Bioeng., 81(1), 92.
5-19
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CHAPTER 6.0
South Durham Water Reclamation Facility - Durham, North Carolina
Mainstream Biological Nitrogen Removal and Sidestream
Deammonification Process (ANITA Mox®) for Centrate Nitrogen Removal
- Case Study
6.1 Background
The South Durham Water Reclamation Facility (SDWRF) is a 20 MGD design flow wastewater
treatment facility located in the City of Durham, North Carolina. The facility currently treats an
average flow of approximately 10 MGD and discharges to Jordan Lake in Cary, North Carolina.
Currently, the facility operates under an annual average total nitrogen (TN) load limit of 334,705
lb/yr, which translates to an equivalent TN discharge limit of approximately 5.5 mg/1 at design
flow. The TN loading limit may be reduced to 185,345 lb/yr in the near future to comply with the
total maximum daily load limits in the Jordan Lake Watershed. This translates to a mass
equivalent TN discharge limit of approximately 3.0 mg/1 TN at design flow.
In 2011, the city completed a wastewater master planning effort that evaluated different
treatment alternatives for meeting a total nitrogen (TN) limit of 3 mg/1 and a total phosphorus
(TP) limit of 0.23 mg/1 at its design flow expected in the near future to comply with total
maximum daily load limits in the Jordan Lake Watershed which serves as a source of drinking
water in theregion.
SDWRF uses anaerobic digesters to process the plant's sludge. Digested sludge is dewatered
using belt filter presses and the filtrate sidestream amounts to approximately 20 percent of the
load to the BNR process. As part of the master planning study, several mainstream and
sidestream treatment alternatives were evaluated to enable the plant to meet its expected TN
limits. Sidestream treatment using the ANITA Mox® deammonification process for sidestream
nitrogen removal was recommended. Cost comparisons with mainstreamtreatment revealed
sidestream treatment using the deammonification pathway to be three times lower in cost per
pound of nitrogen removed ($0.93/lb N removed for deammonification compared with $2.66/lb
N removed for mainstream treatment) when capital and operating costswere considered (Bilyk
etal.,2017).
6.2 Plant Processes
Liquid and solids treatment processes at SDWRF are shown in Figure 6-1. The major treatment
processes at the facility include screening, influent pumping, grit removal, primary clarification,
five-stage biological nutrient removal, secondary clarification, alum precipitation for chemical
Phosphorus precipitation trim, filtration, ultraviolet (UV) disinfection, solids thickening,
anaerobic digestion, belt filter press dewatering, and sidestream ANITA Mox®
Deammonification.
Flow enters the plant at the influent pump station where it passes through two bar screens and is
then pumped up to four grit collectors before flowing to primary settling tanks. Scum and grit are
collected and transported to a landfill. Primary sludge is sent to the anaerobic digesters for
6-1
-------
treatment. Primary effluent flows to a modified 5-stage Bardenpho BNR system to treat the
wastewater for nitrogen and phosphorus removal, which is equipped with the ability to feed
carbon though the plant currently does not require carbon addition. Secondary effluent is settled
in secondary clarifiers and then passed through dual media filters. Filtered effluent undergoes
UV disinfection and is post-aerated prior to discharge.
Carbon C*rb«n Alum Alum
Figure 6-1. Liquid and Solids Treatment Process Train at SDWRF (Bilyk et al., 2017)
Waste activated sludge (WAS) is thickened through gravity thickeners and then through gravity
belt thickener. It is then mixed with primary sludge before entering the anaerobic digesters.
Digested sludge is dewatered with belt filter presses, and the dewatered cake is placed in a sludge
storage pad prior to transportation to land application sites. Sand drying beds are available but
are not in service. Biogas produced in the anaerobic digesters is utilized to run two engine-driven
blowers. The dewatering filtrate is fed to a sidestream ANITA Mox® deammonification facility
for ammonia and total nitrogen load reduction, and the effluent from the deammonification
facility isreturned to the head of the plant.
6-2
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Table 6-1. Design and Average Raw Influent Concentrations and Percent of Design Loads
for the SDWRF from January 2015 to December 2017
Parameter
Raw Influent Design
Average Raw
Influent
Percent of
Design1
(Annual Average)
(Maximum
Month)
Flow (MGD)
15.4
NA
10.602
68.8
BOD (lbs/d)
33,907
44,439
27,401
80.81
TSS (lbs/d)
30,182
43,411
26,716
88.52
Ammonia (lbs/d)
NA
NA
2,431
NA
TKN (lbs/d)
3,622
4,739
3,359
92.74
TP (lbs/d)
861
1,130
425
49.36
Temperature (°C)
NA
NA
NA
NA
Note:
1- Percent of design values, except for flow, are based on average annual values for the analysis
period for influent design loads (lbs./day) and actual influent loads (lbs./day).
1- N/A: Data not available or applicable.
2- Raw influent flow data available from 1/1/2015 through 8/1/2016 only
Table 6-2. NPDES Limits - January 2015 - December 2017 at SDWRF
Parameter
Monthly
Average (mg/1)
Weekly
Average (mg/1)
Annual Load (Lbs/yr)
BODs (Apr - Oct)
5.0
7.5
N/A
BOD5 (Nov -
Mar)
7.0
10.5
N/A
TSS
30.0
45.0
N/A
Ammonia
(Apr. - Oct.)
1.0
3.0
N/A
Ammonia
(Nov.-Mar.)
2.0
6.0
N/A
TN
N/A
N/A
334,705 (Current)
185,345 (Future expected)
TP
N/A
N/A
14,053
Temperature (°C)
N/A
N/A
N/A
\Tote:
N/A: Data not available or applicable.
6-3
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6.3 Conventional Nitrogen Removal Technology
Nitrogen removal in most wastewater treatment facilities (also known as water resource recovery
facilities - WRRFs) is achieved biologically through conventional biological nitrogen removal
using nitrification and denitrification (NdN) processes, with nitrification consuming as much as
half the power required for aeration based on typical wastewater carbon to nitrogen ratios
(COD/TKN). NdN is a two-step process in which autotrophic and heterotrophic bacteria
sequentially convert ammonia to nitrogen gas. The first step, nitrification, is aerobic whereby
ammonium (NH4+) is oxidized to nitrite (NO2") by ammonia oxidizing bacteria (AOBs), and
nitrite is converted to nitrate by nitrite oxidizing bacteria (NOBs). The second step,
denitrification, is anoxic whereby nitrate (NO3") is converted N02" then to nitrogen gas by
ordinary heterotrophic organisms (OHOs). In the first step, ammonia conversion consumes
oxygen and alkalinity. In the second, no oxygen is consumed, and alkalinity is produced.
Additionally, since the denitrification reaction is conducted by heterotrophic bacteria, sufficient
carbon is needed from the wastewater COD or by external chemical carbon addition to achieve a
COD:TKN ratio of about ten or more depending on the carbon source type.
Energy consumption by public water and wastewater services consumes about 0.5 percent of
total U.S.primary energy and 2 percent of its end-use electricity (Twomey and Webber 2011,
EPRI 2013).
Energy consumption by wastewater treatment facilities and drinking water systems can amount
to up to one third of a municipality's total energy bill (EPA, 2009). Typically, at an activated
sludge wastewater treatment facility, 40-70 percent of the energy used is for aeration (WEF,
1997). Plants using conventional biological nitrogen removal are at the higher end of this range.
In plants that use anaerobic digestion for sludge stabilization and reduction, volatile solids are
destroyed resulting in the release of significant amounts of ammonia nitrogen, typically
amounting to between 15-20 percent of the plant's influent nitrogen load in many cases. This
may behigher depending on the type of digesters used and the associated degree of volatile
solids destruction achieved, as well as other factors such as whether other solids are co-digested
and whether primary treatment is used. In plants where sludge is dewatered intermittently or if
the dewatering process is not operating properly, this sidestream ammonia load may
significantly affect the stability of mainstream biological nutrient removal processes and cause
diurnal spikesin effluent ammonia or total nitrogen levels. As such, cost-effective approaches to
treating this sidestream load has become an increasingly important treatment objective due to
potential cost savings and the positive impact on the mainstream nutrient removal process.
6.4 Deammonification
Several processes have been used over the last decade to treat high ammonia sidestreams,
generally relying on using biomass for treatment in varying configurations, process control
approaches, and operational variables including hydraulic retention times (HRT), temperature,
and ammonia concentration. However, the discovery of a group of microorganisms known as the
anammox (anaerobic ammonia oxidation) bacteria that can convert ammonia and nitrite directly
to nitrogen gas published in the 1990s (Mulder et al.,1995) has significantly enhanced the
attractiveness of sidestream nutrient removal processes. This is due to aeration energy savings,
reduced external carbon demand, reduced alkalinity demand, and reduced sludge production as
6-4
-------
the anammox are anaerobic, autotrophic, and the reaction has low biomass yield and only
produces small amounts of nitrate.
The deammonification process involves partial nitrification (conversion of ammonia to nitrite)
and anaerobic ammonia oxidation. It requires approximately a 50 percent mix of ammonia and
nitrite for the anammox bacteria to oxidize ammonia under anoxic conditions using nitrite. The
processhas been established and used successfully for sidestream treatment at a number of
wastewater facilities in the US and overseas. Deammonification is an ideal process for
dewatering sidestreams because centrate or filtrate resulting from dewatering of anaerobically
digested sludge is warm in temperature and high in ammonia concentration (around 1,000 mg/1
or above in most cases). The higher temperature allows the anammox to grow within a
reasonable volumeand sludge retention time (SRT) and the higher ammonia concentrations are
believed to inhibit nitrite oxidizing bacteria (NOBs) that compete for nitrite for aerobic nitrite
oxidation (nitrification). Centrate also has low carbon content which inhibits heterotrophic
bacteria from outcompeting the anammox for the available nitrite for anerobic denitrification.
Research and testing for stable mainstream deammonification continue but the process has not
been used at fullscale in the United States yet. This is mainly due to the difficulty of consistent
full-scale repression of NOBs in mainstream processes as well as the need for retention of the
anammox due to their slower growth rates.
Current deammonification systems for sidestream treatment include sequencing batch reactor
(SBR) processes, an up-flow granular bed process, a moving bed biofilm reactor (MBBR)
process, an Integrated Fixed Film Activated Sludge (IFAS) process for sidestream treatment,
and a hybrid suspended and attached growth process.
Figure 6-2. Nitrogen Transformations (WERF, 2014)
Deammonification can result in significant savings compared to conventional nitrification-
denitrification (NdN) biological nitrogen removal since only a portion of the ammonium is
aerobically oxidized by ammonia oxidizing bacteria (AOB) to nitrite and without the need for
nitratation, and the subsequent step of anoxic ammonium oxidation (annamox) takes place
without the need for costly external carbon addition. This can theoretically amount to 60 percent
or more reduction in oxygen demand and associated aeration energy and near complete
eliminationof costly supplemental carbon addition. Savings in overall capital and operations and
maintenance costs for sidestream deammonification have been reported as high as 65 percent
compared to costs for a mainstream BNR system (Farina, 2012); however, actual savings will
6-5
-------
vary depending on the process used, existing facility infrastructure, influent characteristics,
process control efficiency, and other factors.
6.5 ANITA Mox® Sidestream .Deammonification Process at SDWRF
The ANITA™ Mox MB BR deammonification process is an ammonia and TN removal biofilm
process which combines nitritation with anaerobic ammonia oxidation (Annamox) in a single
stage two-step process. The two steps of the process occur in different layers of the biofilm with
aerobic nitritation occurring in the outer layer and anammox (anoxic) in the inner layer. This
takes place in a Moving-Bed Biofilm Reactor (MBBR) equipped with specially designed plastic
carriers for biofilm growth (Figure 6-3), typically retained in the reactor by screens.
Approximately 50 percent of the influent ammonia is oxidized to Nitrite (NO2") in the first step
and the nitrite produced, and the remaining ammonia, are utilized by the anammox bacteria and
converted to nitrogen gas (N?) and a small amount of Nitrate (NO3) in the second step. Both
steps occur concurrently in the biofilm.
Operational variables in the reactor such as dissolved oxygen, pH, and temperature are
maintained to favor the desired microorganisms (AOB, Annamox) in the biofilm and prevent
their washout. Biofilm processes can be limited by diffusion with the limiting factor depending
on concentration and diffusivity. In the Anita Mox MBBR process, the energy source for
nitritation and annamox is ammonium and the electron acceptors are oxygen and nitrite,
respectively. As such, the oxygen concentration in the liquid is critical. A high DO
concentration may inhibit the annamox reaction and favor the undesirable oxidation of nitrite to
nitrate by NOB while a low concentration will limit nitritation. Other important factorsare pH
and nitrite concentrations. Ensuring that nitrite is consumed at about the same rate of its
production will limit the inhibition of the annamox process by nitrite (Plaza et al., 2009).
As mentioned in Section 6.2, anaerobically digested sludge at SDWRF is dewatered with belt
filter presses. An abandoned aerobic digester was repurposed to provide approximately three
days of equalization and two 95,000-gallon deammonification reactors. Dewatering filtrate is fed
to a sidestream ANITA Mox® Deammonification facility for total nitrogen removal. The Anita
nh4+
Figure 6-3. ANITA Mox® MBBR Model (Source: Kruger/Veolia)
6-6
-------
Mox process was in full-scale operation starting in December 2015. The effluent from the
deammonification facility is returned to the head of the plant. Main system components include a
filtrate equalization tank, two parallel MBBR reactors, reactor feed pumps, and an aeration
system with coarse bubble aeration grids in the reactors and independent airflow control in each
reactor. Two submersible mixers in the equalization tank provide mixing, and a heat loop
provides supplementary heat if needed during winter months. Both reactors and the equalization
tank are provided with insulated covers to retain heat. Reactor mixing during anoxic or low DO
periods is provided by a vertical mixer. Both reactors contain airlift pumps to control excessive
foaming. MBBR media is retained in the reactor by virtue of a stainless-steel screen over the
outlet ports and a screen is placed over a sump in each reactor to allow draining when needed.
Process influent design parameters are shown in Table 6-3.
Table 6-3. Influent Design Values for the Anita Mox MBBR Process at SDWRF (Bilyk et
al., 2017)
Influent Design Values
Parameter
Units
Value
Flow. Current Average
MOD
0.04
Flow, Design
MOD
0.08
Flow. Peak
MOD
0.16
Flow. Max Hydraulic Flush
MOD
0.6-0.7
BOD. Design Flow
mg/L
85
COD. Design Flow
mg/L
500
TSS, Design Flow
mg/L
250-500
NH3-N. Design Flow
mg/L
1000
TKN. Design Flow
mg/L
1100
Alkalinity Design Flow
mg/L
2500
PH
SU
7.4
Min Temperature
C
24
6.6 Detailed Statistical Analysis - Plant Effluent Concentrations
Facility operating data from January 2015 to December 2017 were analyzed. Figures 6-5 through
6-7 and Tables 6-4 through 6-7 provide a summary of the statistical analysis performed for the
SDWRF facility.
During the entire analysis period, the data shows that the facility met its final effluent treatment
objectives shown in Table 6-2 for total nitrogen and ammonia. SDWRF's discharge permit
includes annual effluent TN loading limits of 334,705 lb/yr. Actual discharged TN loads were
217,075, 170,903 and 171,927 lb/yr in 2015, 2016, and 2017, respectively, all well within their
discharge limits.
6-7
-------
For Ammonia, SDWRF's permit includes monthly and weekly ammonia concentrations of 1 mg/1
and 3 mg/1, respectively from April to October, and 2 mg/1 and 6 mg/1, respectively from November
to March. Calculated actual average monthly and weekly effluent ammonia concentrations are as
shown below. They were found to be the same when rounded off to 2 decimal points.
Monthly
November 2014 - March 2015: 0.24 mg/1;
November 2015 - March 2016: 0.23 mg/1;
November 2016-March 2017: 0.13 mg/1;
April 2015 - October 2015
April 2016 - October 2016
April 2017 - October 2017
0.22 mg/1;
0.03 mg/1;
0.07 mg/1.
Weekly
November 2014 - March 2015: 0.24 mg/1;
November 2015 - March 2016: 0.23 mg/1;
November 2016-March 2017: 0.13 mg/1,
April 2015 - October 2015
April 2016 - October 2016
April 2017 - October 2017
0.22 mg/1;
0.03 mg/1;
0.07 mg/1.
Comparing the effluent concentrations to the ammonia permit limits shows that the facility
consistently met the seasonal ammonia limits throughout the 3-yr analysis period.
Figure 6-4 shows the 12-month rolling average TN concentrations and discharge loadings and
shows the plant's consistency in meeting the annual discharge loading limits from month to month.
350000
300000
250000
z >
*— £
200000
150000
100000
i im Annual Average Limit: 334/us
lb/year
A
A
4
A
~
A
,
1,
A
A
A
A
4'
la
~
A
k *
~ TN 12
month
rolling
average
(lbs/year)
¦TN Limit
12/27/2014 7/15/2015 1/31/2016 8/18/2016 3/6/2017 9/22/2017 4/10/2018
Figure 6-4.12-month Rolling Average Time Series Plot for TN
6-8
-------
euo
£
CD
Q.
00
x NHs
NHs Median
~ NOx
NOx Median
A TN
TN Median
~ TKN
TKN-Median
~ ON
ON Median
0.01
12/27/2014 7/15/2015 1/31/2016 8/18/2016 3/6/2017 9/22/2017 4/10/2018
Figure 6-5. 30-Day Rolling Average Time Series Plot
Figure 6-5 shows the 30-day rolling average time series plot for nutrient species effluent
concentrations at SDWRF. For the 3-year analysis period, the median 30-day rolling average TN
concentration was 6.79 mg/1 with a maximum value of 10.38 mg/1. The median 30-day rolling
average concentration was 0.05 mg/1 for ammonia and 5.60 mg/1 for NOx-N, with maximum 30-
day rolling values of 1.06 mg/1 NFb-N and 9.23 mg/1 NOx-N.
Figures 6-6 A through D include cumulative probability plots for SDWRF's daily, 30-day rolling
average, monthly average, and rolling annual average data sets. A percentile value on the x-axis
represents the probability that the value is less than or equal to the stated corresponding
concentration on the plot's y-axis. In looking at the NFb-N and TKN values on Figure 6-6A, it is
clear that for the most part, the effluent TN is comprised of nitrate nitrogen. The 95th percentile
TN daily average concentration in Figure 6-6 (A) for the 3-year analysis period is 9.36 mg/1.
6-9
-------
Daily N Species
% values less than or equal to indicated values
30 Day Rolling Avg N Species
% values less than or equal to indicated values
B
12 Month Rolling Average
nh3
NOx
~ TN
TKN
ON
Log Normal Values
I
; i iium
—zi; i' i s
•
: •
• —• *
0.2 0.5 1 2 5 10 20 30 50 70 80 90 95 98 99
% values less than or equal to indicated values
D
Figure 6-6. Probability Plots for SDWRF - (A) Daily Data; (B) 30-day Rolling Average; (C)
Monthly Average; (D) 12 Month Rolling Average
For the period of December 2015 through December 2017 corresponding to the implementation
of the Anita Mox, the 95th percentile effluent TN average concentration was lower at 8.85 mg/1.
According to SDWRF, this can mainly be attributed to the impact of the Anita Mox process in
reducing the TN load to the mainstream BNR process.
The monthly average effluent ammonia concentrations associated with the 3.84, 50, 90, 95, and
99th percentiles during the 3-year analysis period (2015-2017) are 0.02, 0.05, 0.47, 0.61, and 0.75
mg/1, respectively, all well below the discharge permit monthly average limits of 1.0 mg/1 (April
- October), and 2.0 mg/1 (November -March). Similarly, the weekly average ammonia
concentrations associated with the 3.84, 50, 90, 95, and 99 percentiles are 0.02, 0.03, 0.45, 0.76,
and 1.54 mg/1, respectively, all well below the discharge permit weekly average limits of 3.0
mg/1 (April - October) and 6.0 mg/1 (November - March).
6-10
-------
Table 6-4. Summary Statistics for Final Effluent Ammonia Nitrogen for SDWRF
NH3-N
Daily
Data
NH3-N
Weekly
Data
NH3-N
Rolling 30-
day Average
NH3-N
Monthly
Averages
NH3-N 12
Month Rolling
Average
n
753
156
1067
36
25
Mean
0.152
0.151
0.148
0.153
0.123
Geometric
Mean
0.039
0.053
0.074
0.075
0.114
Standard Dev.
0.491
0.305
0.197
0.203
0.054
CV
3.236
2.026
1.331
1.332
0.438
Skew
7.020
3.401
2.141
1.866
1.364
Minimum
0.020
0.020
0.020
0.020
0.069
Maximum
7.080
1.833
1.062
0.771
0.251
Table 6-5. Summary Statistics for Final Effluent NOx-N for SDWRF
NOx-N
Daily
Data
NOx-N
Weekly
Data
NOx-N 30-
day Rolling
Average
NOx-N
Monthly
Averages
NOx-N 12
Month Rolling
Average
n
156
156
1067
36
25
Mean
5.684
5.684
5.662
5.697
5.397
Geometric
Mean
5.038
5.038
5.513
5.518
5.354
Standard Dev.
1.785
1.785
1.260
1.345
0.716
CV
0.314
0.314
0.223
0.236
0.133
Skew
0.079
0.079
0.086
-0.373
0.731
Minimum
0.005
0.005
2.178
2.178
4.636
Maximum
11.700
11.700
9.225
8.025
6.754
Table 6-6. Summary Statistics for Final Effluent Total Nitrogen for SDWRF
TN Daily
Data
TN Weekly
Data
TN 30-day
Rolling Average
TN Monthly
Average
TN 12 Month
Rolling Average
n
156
156
1067
36
25
Mean
6.908
6.908
6.881
6.920
6.600
Geometric
Mean
6.647
6.647
6.759
6.775
6.564
Standard Dev.
1.788
1.788
1.279
1.374
0.721
CV
0.259
0.259
0.186
0.199
0.109
Skew
0.080
0.080
0.151
-0.323
0.784
Minimum
1.530
1.530
3.625
3.625
5.817
Maximum
13.030
13.030
10.378
9.303
7.990
6-11
-------
Table 6-7. Summary Statistics for Final Effluent ON for SDWRF
ON Daily
Data
ON Weekly
Data
ON 30-day
Rolling Average
ON Monthly
Average
ON 12 Month
Rolling Average
n
156
156
1067
36
25
Mean
1.098
1.098
1.100
0.934
0.921
Geometric
Mean
1.048
1.048
1.084
0.917
0.920
Standard
Dev.
0.306
0.306
0.182
0.195
0.050
CV
0.279
0.279
0.166
0.209
0.055
Skew
0.117
0.117
-0.399
1.303
0.198
Minimum
0.160
0.160
0.590
0.723
0.862
Maximum
2.190
2.190
1.525
1.514
1.009
3.0
2.5
^ 2.0
W>
-T?
I 1.0
:: ..lot
3.84 50 90 95 99
(14d)
Probability
¦ Daily
30-day Rolling
Monthly Averages
12 Month Rolling Averages
Weekly
6-12
-------
12.0
10.0
^ 8.0
£ 6.0
4.0
2.0
0.0
I
1
T
Daily
30-day Rolling
Monthly
Averages
12 Month
Rolling Averages
3.84 50
(14d)
90
95
99
Probability
Figure 6-7. Probability Summary for SDWRF
Figure 6-7 can be used to assess the process variability for TN and NH3-N. For example, the
daily data 50th percentile TN concentration for the entire 3-year period was 6.95 mg/1, and the
95th percentile was 9.61 mg/1 for TN with a ratio of 95th to 50th percentile of about 1.38.
Calculating this ratio for the periods before the Anita Mox process was in service (January 2015
- November 2015) and after it was in service (December 2015 - December 2017), the ratios
were 1.43 and 1.38, respectively, demonstrating slightly lower variability when Anita Mox® was
in service.
6.7 Process Performance - ANITA Mox® Sidestream Deammonification at SDWRF
As shown in section 6.5 above, the centrate pre-treatment facility (CPT) at SDWRF uses the
ANITA Mox® Sidestream Deammonification system to treat anaerobically digested sludge
dewatering filtrate for ammonia and total nitrogen load reduction. The Anita Mox process was in
full-scale operation starting in December 2015. The effluent from the deammonification facility
was returned to the head of the plant.
A simplified diagram of SDWRF deammonification system is shown in Figure 6-3 (Hollowed et
al„ 2018).
6-13
-------
influent
Figure 6-8. Simplified Flow Diagram of SDWRF Deammonification System
Digested sludge is typically dewatered five days a week in one shift, and the filtrate flows to the
equalization (EQ) tank. The Anita Mox reactors are normally fed at a steady rate set to ensure
that the EQ tank is not full anytime during the weekly dewatering cycle. Any excess filtrate is
returned to the head of the plant.
Aeration control can be accomplished in one of three modes: intermittent aeration, continuous
aeration, and DO control. Intermittent aeration with constant airflow is the main mode of
operation with a specified duration of aerobic and anoxic cycles. The facility indicated that this
mode results in stable operation as the filtrate ammonia concentrations are generally stable.
However, the facility has used the DO control mode on two separate occasions but decided that
intermittent mode results in more stable operation. The process is underloaded with respect to its
design loading, and therefore using DO control mode results in too many pounds of oxygen for
the system for it to operate in the optimal manner. On-line DO, ammonia, and nitrate probe
readings are used to monitor the process. Grab samples are also collected and analyzed in the
laboratory for reactor ammonia, nitrite, and nitrate nitrogen. These samples are generally
collected at a minimum of once a week with some exceptions.
6-14
-------
Figure 6-9. Monthly Average Ammonia Percent Removal for Sidestream Reactors 1 and 2
Figure 6-9 shows ammonia percent removal in reactors 1 (Rl) and 2 (R2). As shown, both
reactors were able to reach ammonia removal rates of as high as 86 percent (April 2016 for Rl
and December 2017 for R2). The rates were calculated based on reactor influent and effluent
laboratory analysis provided by the facility. However, the facility experienced periods of reduced
performance due to process imbalances requiring additional and more frequent process control to
stabilize the process.
One incident occurred in June - July 2016, when the facility experimented with the continuous
aeration mode which negatively impacted performance and likely favored NOB over anammox
based on the process control procedure used at the time, resulting in nitrate elevation. This
resulted in a reduction in ammonia removal efficiency to a monthly average of 70 percent in Rl
and 63 percent in R2 for July 2016 as shown in Figure 6-4. As a result, the intermittent aeration
mode operation was resumed, and the removal efficiency improved as shown in the August
2016 average ammonia removal of 75 percent in Rl and 80 percent in R2.
Another incident occurred in November 2016 which the facility attributed to struvite buildup in
the reactor feed piping from the equalization tank. This reduced reactor influent flow and
increased reactor HRT and was subsequently corrected by implementing pipe cleaning, flushing
the reactors with dilution water to remove excess solids and nitrite, and struvite formation
minimization procedures.
6-15
-------
Another process difficulty was experienced in R1 in August 2017, attributed to faulty high DO
probe readings while operating temporarily in the DO control mode. This resulted in an
unnecessary reduction of the DO setpoint by the process control system and an elevation in the
ammonia concentration. The operators corrected by temporarily shutting off the reactor feed
flow and switching the airflow control mode to an intermittent cycle to allow the reduction of
ammonia concentration to normal levels before restarting feed flow, and by cleaning and
calibration of the probe. A detailed assessment of the operational difficulties experienced by the
facility and the approaches taken to address them is provided by Bilyk et al. (2017).
It should be noted that the SDWRF experienced a significant improvement in plant effluent total
nitrogen concentrations with a reduction of approximately 1.5 mg/1 TN after the Anita Mox
process was in operation at full scale (December 2015 to December 2017) compared to a period
before Anita Mox was in full scale operation (January 2014 to November 2015). This
improvement was achieved notwithstanding increases in influent TKN loads in 2016 and 2017
compared to 2015. While the facility has implemented a number of other efforts to improve TN
removal (such as implementing mainstream BNR ammonia-based aeration control in 2015 and
improvement of baffle walls in the mainstream BNR reactors in 2016 to reduce air back-mixing
from the aerobic zone into the 1st anoxic zone), the implementation of the Anita Mox process and
the associated reduction in the return nitrogen load to the mainstream and its reduced variability
played an important role in the reduction in plant effluent total nitrogen concentrations
mentioned above.
6-16
-------
REFERENCES
Bilyk, K., Khunjar, W., Pace, G., Worley-Morse, T, Cocker, C., Lobdell, S., Taylor, R., Gasper,
B., Pitt, P. (2017). "Lessons Learned about Deammonification from Design, Startup and
Operation of an ANITA™ Mox System". Proceedings of the Water Environment Federation
Nutrient Symposium 2017, 253-263.
Bilyk, K. (2017). "Nutrient Removal Optimization". Presentation at the 2017 Annual Conference
of the North Carolina Section of the American Water Works Association & The North Carolina
Member Association of the Water Environment Federation, October 5, 2017.
EPRI (Electric Power Research Institute). 2013. "Electricity Use and Management in the
Municipal Water Supply and Wastewater Industries". Technical Report 3002001433. Palo Alto,
Calif.
Farina, T., 2012. "An Overview of Sidestream Treatment Alternatives Used to Increase Nutrient
Removal". Presentation at Ohio Water Environment Association Annual Conference. Aurora,
OH, June 20, 2012.
Hollowed, M., Thesing, G., Liang, S. (2018). "Tale of Two Cities: Operation of Sidestream
Anita Mox™". Proceedings of the Water Environment Federation Nutrient Symposium 2018,
747-759.
Mulder, A., Van de Graff, A.A., Robertson, L.A., and Kuenen, J.G. 1995. "Anaerobic
Ammonium Oxidation Discovered in a Denitrifying Fluidized Bed Reactor". FEMS Microbiol
Ecology 16, 177-184.
Plaza, E., Trela, J., and Hultman, B. 2009. "Swedish Experience with Deammonification Process
in Biofilm System". Joint Polish-Swedish-Ukrainian Reports, Report no. 14, Proceedings of
Research and application of new technologies in wastewater treatment and municipal solid waste
disposal in Ukraine, Sweden and Poland.
Twomey, Kelly M., and Michael E. Webber. 2011. "Evaluating the Energy Intensity of the U.S.
Public Water Supply." Proceedings of the ASME 2011 5th International Conference on Energy
Sustainability, ES2011- 54165. 1735-48.
U.S. EPA. 2009. "Clean Energy Lead by Example Guide: Strategies, Resources, and Action
Steps for State Program". Washington, DC: US Environmental Protection Agency.
WEF (1997). "Energy Conservation in Wastewater Treatment Facilities". Manual of Practice
No. MFD-2. Alexandria, VA.
6-17
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CHAPTER 7.0
Town of Hillsborough Wastewater Treatment Plant
Hillsborough, North Carolina
Modification and Enhancement of 5-Stage BNR - Case Study
7.1 Background
The Hillsborough Wastewater Treatment Plant (HWWTP) is a 3.0 MGD wastewater treatment
facility located in the Town of Hillsborough, North Carolina. As of January 2016, HWWTP's
NPDES permit annual total nitrogen (TN) discharge load was reduced to 10,422 lb/yr to comply
with the water quality standards for Falls Lake, the drinking water supply for the City of Raleigh,
NC. At the plant's annual average design flow of 2.4 MGD, the permit annual average TN
discharge load is equivalent to 1.43 mg/1.
HWWTP implemented the first phase of nutrient removal upgrades by converting the system to a
5-Stage BNR process. The facility had originally planned additional upgrades of the original
BNR system to include a reverse osmosis (RO), ion exchange (IX), or equivalent process
treatment to be added downstream of the BNR facility. However, since the facility's actual flow
is significantly lower than design flow, as shown in Table 7-1, HWWTP implemented innovative
modifications to its BNR process. It also implemented process control strategies. This allowed
the plant to meet its discharge limits without the need for the RO or IX processes and without the
need for carbon or other chemical addition. As a result, the facility reported that it expects further
upgrades will be deferred by several years.
7.2 Plant Processes
Liquid treatment processes include preliminary treatment consisting of bar screening and grit
removal. This is followed by a five-stage BNR process for removal of BOD as well as TN and
total phosphorus (TP), followed by secondary clarification where alum is added for additional
phosphorus removal if needed. Figure 7-1 shows the liquid and solids treatment trains at
HWWTP before upgrading the biological process to the five-stage BNR configuration (shown in
Figure 7-4 below). Since the upgraded BNR system was constructed by modifying two
previously existing stages of aeration and secondary clarification, the last two stages (anoxic,
reaeration) of the current 5-stage BNR system are physically separated from the previous three
stages. The system is equipped with methanol addition capability in the second anoxic zone and
alum addition capability to the secondary clarifiers to be used if needed. Denitrification filters
with alum addition are also available but are only used to remove residual suspended solids and
total phosphorus. No external carbon is added. The effluent is then disinfected by chlorination
prior to dechlorination and post aeration, and then discharged to the Eno River. Solids processing
includes aerobic digestion of waste activated sludge, digested sludge storage, gravity belt
thickening of digested sludge, storage of thickened sludge, and dewatering prior to hauling the
sludge offsite.
7-1
-------
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mm*
kww|
^ firi 1
444
T WM I
CRT f A
— "•-
Sutl i S49tl
Sbg*1 A*m>Pi Curtbr kMtJMta Gertie*
¦ ^VtefesrilHA
CM***
C«rt«l
fiKeri ft*
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-«—w
C*-)»kfcN
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r-I_
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I . PMAfflWII
\
. Ta Efl»
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¥ HhA 3d,
¦¦ '0
Figure 7-1. Solids and Liquid Treatment Process Trains at HWWTP Before BNR
Upgrades
(Adapted from Mahagan and Bilyk, 2016 - With Permission)
Table 7-1. Design and Average Raw Influent Concentrations and Percent of Design Loads
for the HWWTP from January 2015 to December 2017
Parameter
Raw Influent Design
Average
Raw
Influent
Percent
of
Design1
(Annual Average)
(Maximum Month)
Flow (MGD)
2.4
3.2
1.04
43
BOD5 (lbs/d)
4,441
6,000
1941
44
TSS (lbs/d)
4,421
5,400
2055
46
TKN (lbs/d)
697
840
NA
NA
TP (lbs/d)
121
150
NA
NA
Temperature (°C)
NA
NA
19.13
NA
Note:
1- Percent of design values, except for flow, are based on average annual values for the analysis
period for influent design loads (lbs./day) and actual influent loads (lbs./day).
N/A: Data not available or applicable.
7-2
-------
Table 7-2. NPDES Limits - January 2015 - December 2017 at HWWTP
Parameter
Monthly
Average
(mg/1)
Weekly
Average
(mg/1)
Quarterly
Average
(mg/1)
Annual Load
(lbs/yr)
Flow (MGD)
3.0
N/A
N/A
N/A
BOD5
5.0
7.5
N/A
N/A
BOD5 (Nov - Mar)
7.0
10.5
N/A
N/A
TSS
30.0
45.0
N/A
N/A
Ammonia
2.0
6.0
N/A
N/A
TN
N/A
N/A
N/A
50,228 (until 12/31/2015)
10,422 (effective 1/1/2016)
TP
N/A
N/A
2.0
1,352 (effective 1/1/2016)
Temperature (°C)
N/A
N/A
N/A
N/A
Note:
1- N/A: Data not available or applicable.
7.3 Conventional Nitrogen Removal Technology
Nitrogen removal in most wastewater treatment facilities (also known as water resource recovery
facilities - WRRFs) is achieved biologically through conventional biological nitrogen removal
(BNR) using nitrification and denitrification (NdN) processes, with nitrification consuming as
much as half the power required for aeration based on typical wastewater carbon to nitrogen
ratios (COD/TKN). NdN is a two-step process in which autotrophic and heterotrophic bacteria
sequentially convert ammonia to nitrogen gas. The first step, nitrification, is aerobic whereby
ammonium (NH4+) is oxidized to nitrite (NO2") by ammonia oxidizing bacteria (AOB), and
nitrite is converted to nitrate (NO3") by nitrite oxidizing bacteria (NOB). The second step is
anoxic whereby NO3" is converted to NCh'then to nitrogen gas by ordinary heterotrophic
organisms (OHOs). In the first step, ammonia conversion consumes oxygen and alkalinity. In the
second, no oxygen is consumed, and alkalinity is produced. Additionally, since this second step
reaction is by heterotrophic bacteria, sufficient carbon is needed from the wastewater COD or by
external chemical carbon addition to achieve a minimum COD:TKN ratio of ten or more
depending on the carbon source type.
Nitrogen removal in wastewater treatment facilities can be accomplished as an integral
component of the biological treatment system or as an add-on process to an existing treatment
plant. A variety of biological treatment configurations are used by treatment facilities to achieve
biological nitrogen removal, and the selection of a specific process depends on treatment
requirements, existing process and equipment, and other site-specific conditions. In some
systems, nitrification and denitrification can be achieved in one treatment unit while in others,
denitrification can be achieved separately in either post-anoxic or pre-anoxic units.
Suspended-growth biological nutrient removal processes can be categorized as single sludge or
two-sludge processes. Single sludge refers to systems that use only one solids separation device,
normally a secondary clarifier (Metcalf & Eddy, 2003). In such systems, the biological tank is
7-3
-------
divided into different zones of anoxic and aerobic conditions and mixed liquor can be pumped
from one zone to another as internal nitrified recycle (NRCY). These systems are generally
categorized depending on whether the anoxic zone is located before, within, or after the aerobic
nitrification zone. In the pre-anoxic configuration, initial contact of the wastewater and the
returnactivated sludge (RAS) occurs in the anoxic zone and nitrate produced in the aerobic zone
is recycled to the pre-anoxic zone. One example of such a process is the Modified Ludzack-
Ettinger (MLE) process shown in Figure 7-2.
N itrified Recycle
^
Influent.
Anoxic
Aerobic
Tank
Tank
Secondary
Clarifier
Effl uei^t
RAS
WAS
Figure 7-2. Modified Ludzack-Ettinger Process
The MLE is a two-stage process that consists of an anoxic zone upstream of an aerobic zone. An
internal recycle carries nitrate created during the nitrification process in the aerobic zone along
with mixed liquor to the anoxic zone for denitrification. RAS is mixed with the influent to the
anoxic zone (EPA, 2008). This process is generally used to meet intermediate levels of total
nitrogen concentrations (generally about 7-10 mg/1 but as high as 15 mg/1 in some cases). This
is attributed to nitrate removal being limited by the practical levels of internal recycle to the pre-
anoxic zone (Metcalf & Eddy, 2003).
Multi-stage processes are used to achieve higher levels of nitrogen removal such as the 4-Stage
Bardenpho Process. This process is essentially an MLE process with subsequent anoxic and oxic
zones, but the nitrate nitrogen leaving the last oxic zone is lower, as low as 3 to 4 mg/1 with
supplemental carbon addition. The five-stage Bardenpho process illustrated in Figure 7-3 uses
the same layout but adds an anaerobic zone in front of the four-stage system to allow for
biological phosphorus removal. In the anaerobic zone, RAS from the clarifiers and influent
wastewater are mixed but not aerated. Both processes (4 and 5-stage Bardenpho) have a
relatively longer SRT (10 to 20 days) and enhance nitrifier growth as well as carbon oxidation
capability. The second anoxic zone provides additional denitrification using nitrate produced in
the aerobic zone as the electron acceptor and the endogenous organic carbon as the electron
donor (Metcalf & Eddy, 2003).
7-4
-------
Nitrified Recycle
Anaerobic
Tank
Influent
(Optional)
Methanol
Addition
i
Aerobic
Tank
\
Anoxic
Aerobic
Anoxic
1
Tank
Tank
Tank
Secondary
Clarifier
Effluent.
RAS
WAS
Figure 7-3. 5-Stage Bardenpho Process
7.4 Five-Stage BNR Modifications at HWWTP
In 2010 the North Carolina Division of Water Quality revised the nutrient standards for Falls
Lake to significantly lower allowable levels of TN and TP to be implemented starting in January
2016. These standards resulted in a lower annual average TN discharge allocation of 10,422
pounds per year for HWWTP which at a design flow of 2.4 MGD is equivalent to a TN
discharge limit of 1.43 mg/1. In 2011, construction began on upgrades to HWWTP's biological
treatment system and included reconfiguring existing basins to a conventional 5-stage BNR
treatment facility based on a design annual average TN effluent criterion of 3 mg/1. The upgrades
included reconfiguring the existing aeration tanks based on a 5-stage Bardenpho system, new
surface mixers, baffle walls, and process instrumentation. This was the first part of a three-stage
upgrade with an anticipated second stage future upgrade to include either reverse osmosis, ion
exchange, or equivalent process treatment to be added downstream of the upgraded BNR system.
7-5
-------
HKET
¦r!i; L
AH
+>
41
MR
T
t
JUC
4
f
*
AH
- w. ^
A3
r m
*
AX
riiJ p.
i. tnif ijUHif
FiHm*
IrorntdJH
Punp
£rjutii
Figure 7-4. HWWTP 5-Stage BNR Configuration (Source: Mahagan and Bilyk, 2016, with
permission)
The new 5-stage BNR system was put in service in October 2013. The facility reported that
system sizing criteria for each BNR stage were based on a calibrated BioWin model. As
explained in section 7.6 below, the facility was able to meet the design criteria for a TN of
approximately 3 mg/1 starting in mid-May 2014, with effluent concentrations consistently around
or below 3 mg/1 TN. In addition, HWWTP operations staff took the initiative to further optimize
the process and were able to meet further performance improvements while addressing a number
of operational challenges explained in section 7.6.
7.5 Detailed Statistical Analysis - Plant Effluent Concentrations
Facility operating data from January 2015 to December 2017, reflecting a period of optimized
operations after the improvements were in place, were analyzed. Figures 7-6 through 7-9 and
Tables 7-3 through 7-6 provide a summary of the statistical analysis performed for the HWWTP
facility in Hillsborough, NC. As explained below, the data shows that the facility consistently
met the final effluent permit requirements for total nitrogen shown in Table 7-2 throughout the
analysis period.
Figure 7-5 shows the 12-month rolling average TN discharge loadings and shows the plant's
consistency in meeting the annual discharge loading limits from month to month. The annual TN
discharge loading limit for 2015 was 50,228 Ib/yr while for 2016 and 2017, the annual limit was
10,422 Ib/yr. At the design flow of 2.4 MGD, these loads correspond to annual average effluent
TN concentrations of 6.9 mg/1 TN (2015) and 1.4 mg/1 TN (2016 and 2017). Actual annual
discharged TN loads were 6,535 lb/yr, 4,711 Ib/yr, and 5,533 lb/yr in 2015, 2016, and 2017,
respectively, all well below their discharge loading limits. The annual average influent flows for
2015, 2016, and 2017 were 1.07, 1.10, and 0.95 MGD, respectively.
For ammonia, HWWTP's permit includes monthly and weekly ammonia concentrations of 2 mg/1
and 6 mg/1, respectively. As shown in Figure 7-7 below, all effluent ammonia concentrations were
well below limits throughout the 3-year period.
7-6
-------
~ TN 12 month rolling average discharge (lbs/year)
TN Annual Average Permit Limits (1/1/16-12/31/17)
TN Annual Average Permit Limit (1/1/15 -12/31/15)
60,000
50,000
40,000
(O
CD
^ 30,000
20,000
10,000
0
TN Annual Average Limit before 12/31/15:
CI HOC 1 Ur /1 //-» r
*->
TN Annual Average Limit after 1/1/16:10,422
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A
A
i A
12/27/2014 7/15/2015
1/31/2016
8/18/2016
3/6/2017
9/22/2017
Figure 7-5. 12-Month Rolling Average Time Series Plot for TN
Figure 7-6 shows the 30-day rolling average time series plot for effluent nitrogen species
concentrations at HWWTP. For the 3-year analysis period, the median 30-day rolling average
TN concentration was 1.57 mg/1 with a maximum value of 5.34 mg/1.
7-7
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Figure 7-6. 30-Day Rolling Average Time Series Plot
Figure 7-7 shows the individual sample time series plot for effluent nitrogen species
concentrations at HWWTP. Samples are generally collected once a week. The chart shows some
variability in total nitrogen concentrations. For the 3-year analysis period, the median TN
concentration was 1.53 mg/1 with a maximum value of 8.33 mg/1.
x NH3-N
NOx-N
TN
• TKN
• ON
Figure 7-7. Effluent TN Individual Sample Time Series Plot
7-8
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Figures 7-8 A through D include cumulative probability plots for HWWTP's daily, 30-day
rolling average, monthly average, and rolling annual average data sets. A percentile value on the
x-axis represents the probability that the value is less than or equal to the stated corresponding
concentration on the plot's y-axis. In looking at the nitrogen species values on Figure 7-8A, it is
clear that for the most part, the effluent TN is comprised of nitrate nitrogen and organic nitrogen
(organic nitrogen values were calculated as the difference between TKN and NFb-N). The 95th
percentile TN daily average concentration for the 3-year analysis period is 2.97 mg/1.
C D
Figure 7-8. Probability Plots for HWWTP - (A) Daily Data; (B) 30-day Rolling Average;
(C) Monthly Average; (D) 12-Month Rolling Average
Figure 7-9 below show the various cumulative probability percentiles for the nitrogen species.
The graph can also be used to highlight the process variability for TN and NFb. For example, the
daily TN 50th percentile effluent concentration was 1.53 mg/1 and the 95th percentile was 2.96
7-9
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mg/1 for TN, with a 95 percent/50 percent of about 1.93 demonstrating significant
variability typical offacilities meeting very low TN limits.
Table 7-3. Summary Statistics for Final Effluent Ammonia Nitrogen for HWWTP
nh3-n
Daily Data
NH3-N Rolling
30-day
Average
NH3-N Weekly
Averages
nh3-n
Monthly
Averages
NH3-N 12-
Month Rolling
Average
n
319
1,067
156
36
25
Mean
0.12
0.11
0.11
0.10
0.12
Geometric
Mean
0.057
0.06
0.06
0.06
0.11
Standard Dev.
0.50
0.24
0.45
0.23
0.053
CV
4.04
2.30
4.00
2.33
0.46
Skew
8.18
5.45
8.88
5.79
0.26
Minimum
0.050
0.050
0.05
0.050
0.062
Maximum
4.80
1.85
4.65
1.45
0.18
Table 7-4. Summary Statistics for Final Effluent NOx-N for HWWTP
NOx-N
Daily Data
NOx-N Rolling
30-day
Average
NOx-N Weekly
Averages
NOx-N
Monthly
Averages
NOx-N 12-
Month Rolling
Average
n
157
1,067
146
36
25
Mean
0.73
0.73
0.73
0.74
0.79
Geometric
Mean
0.60
0.66
0.59
0.67
0.78
Standard Dev.
0.58
0.389
0.58
0.412
0.070
CV
0.79
0.53
0.80
0.56
0.09
Skew
3.24
2.27
3.24
2.66
-1.07
Minimum
0.100
0.195
0.10
0.315
0.62
Maximum
3.96
2.68
3.96
2.26
0.88
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Table 7-5. Summary Statistics for Final Effluent Total Nitrogen for HWWTP
TN Daily
Data
TN Rolling 30-
day Average
TN Weekly
Averages
TN Monthly
Averages
TN 12 month
rolling
Average
n
157
1,067
146
36
25
Mean
1.71
1.71
1.72
1.71
1.80
Geometric
Mean
1.53
1.60
1.53
1.60
1.80
Standard Dev.
1.00
0.72
1.02
0.77
0.14
CV
0.58
0.42
0.59
0.45
0.08
Skew
3.78
2.40
3.75
2.85
-1.51
Minimum
0.42
0.57
0.42
0.74
1.44
Maximum
8.33
5.34
8.33
4.95
1.96
Table 7-6. Summary Statistics for Final Effluent ON for HWWTP
ON Daily
Data
ON Rolling
30-day
Average
ON Weekly
Averages
ON Monthly
Averages
ON 12 month
rolling
Average
n
155
1,067
144
36
25
Mean
0.87
0.88
0.88
0.87
0.90
Geometric
Mean
0.75
0.83
0.76
0.82
0.88
Standard Dev.
0.40
0.28
0.40
0.28
0.15
CV
0.45
0.32
0.46
0.33
0.17
Skew
0.80
0.51
0.80
0.26
0.45
Minimum
0.03
0.22
0.03
0.27
0.74
Maximum
2.31
1.86
2.31
1.61
1.12
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¦ Daily
B 30-day average
Monthly Averages
¦ Annual Averages
Ui Weekly
(14d)
Probability
^ 3.5 1
60 3.0
3.84 50 90 95 99
(14d)
Probability
a
3.84 50 90 95 99
(14d)
Probability
Figure 7-9. Probability Summary for HWWTP
s I
I-
m 1.0
Z 0.5 ¦
0,0 —— - » *
3.84 50 90 95 99
¦ Daily
30-day Rolling
Monthly Averages
¦ Annual
¦ Weekly
¦ Daily
¦ 30-day Rolling
Monthly Averages
¦ Annual Averages
¦ Weekly
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7.6 Process Performance and Lessons Learned - Five-Stage BNR Modifications at
HWWTP
In looking at the plant's effluent TN concentrations over the 3-year analysis period as shown in
Figures 7-6 through 7-8 above and as explained in Section 7.5, it is clear that the facility
maintained exceptional performance for a 5-Stage BNR system for the entire 3-year period. As
mentioned in Section 7.4, the new 5-stage BNR system was put in service in October 2013 and
system sizing criteria for each BNR stage were based on a calibrated BioWin model. Reported
results from the first six months in 2014 plotted in Figure 7-10 below show that the system met
the design criteria for a TN of approximately 3 mg/1 starting in mid-May 2014, with effluent
concentrations consistently around or below 3 mg/1 TN.
Eff Total Nitrogen
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Figure 7-10. Initial BNR Performance in 2014
(Source: Mahagan and Bilyk, 2016, with permission)
While the facility achieved significant improvement in effluent TN concentrations, it should be
noted that the BNR system experienced initial variability in effluent TN, lower pH, poor sludge
settleability in secondary clarifiers, and higher than expected TP concentrations. As a result, the
facility initiated the addition of caustic soda at high doses to control the pH. As the pH was
raised above 6.6, TN effluent concentrations stabilized and sludge settleability improved.
Biological phosphorus removal was also being observed.
The facility then initiated an effort to evaluate additional system and process improvements to
ensure continued high performance and consistent and stable process operation. This involved
development of a simple model to determine the detention times at each stage at various flows
based on the total flow leaving each zone as an indication of the adequacy of each zone's sizing.
After reviewing the model, staff determined that at current flows, aerobic zones volume could be
significantly reduced, and the internal nitrogen recycle rates could be significantly increased,
resulting in better process control and improved effluent quality. As a result, system
modifications were completed at the end of June 2014 and in full operation by July 2014. A
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summary of the modifications is included below, and a detailed discussion of the 5-stage BNR
configuration and equipment modifications and process control strategies is reported by
Mahagan and Bilyk, 2016. In general, treatments plants may find opportunities to reconfigure
flow through existing basins and effect improvements to enhance BNR treatment allowing the
plant to achieve enhanced biological treatment (EPA, 2010). The modifications implemented by
HWWTP described below are a good example of successful process enhancements that may be
implemented by facilities that are below design capacity. The modifications further improve
performance and achieve enhanced denitrification by modifying BNR system zones and internal
mixed liquor recycle rates. The biodegradable carbon that would otherwise be oxidized
aerobically can be used instead to fuel further nitrate removal.
The modifications to the BNR zones included reallocating a portion of the first aerobic zone to
anoxic volume as shown in Table 7-7. In addition, the nitrogen recycle flow rate was increased to
900 percent to keep this new anoxic volume mixed and maximize denitrification capacity. As a
result, the facility reported that effluent TN concentrations were dramatically reduced, initially
from around 3 mg/1 to 1.5 mg/1 and averaging 1.38 mg/1 over the next 12 months. No pH
adjustment was needed during that time, and no additional carbon source or coagulant was used
to achieve these results (Mahagan and Bilyk, 2016).
Table 7-7. Comparison of Zone Volumes and Detention Times Before and After
Modifications to the Original Design
(Adapted from Mahagan and Bilyk, 2016)
Original
(Nov 2013 through June 2014)
Modified
(July 2014 through Se
p 2015)
Zone
Volume
(MG)
%of
Volume
Allocated
NRCY
%of
Inf
Volume
(MG)
%of
Volume
Allocated
NRCY
% ofInf
Anaerobic
0.125
6%
0.125
6%
1st Anoxic
0.375
17%
200%
0.875
39%
900%
Aerobic
1.5
67%
1
44%
2nd Anoxic
0.1875
8%
0.1875
8%
Reaeration
0.0625
3%
0.0625
3%
Avg Influent Flow: 1.038 MGD
Avg Influent Flow: 0.898 MGD
The facility also implemented a process control strategy that included several components. As
the first aerobic zone volume was reduced, a tapered aeration approach was implemented with
DO setpoints of 2.2 to 3.0 mg/1 at the head of the zone and 0.5-1.5 mg/1 at its end. Additionally,
in anticipation of storm events, operators implemented a procedure to pace the nitrogen recycle
pumps to maintain a desired anoxic zone detention time. This included gradually reducing the
speed of the nitrogen recycle pumps manually to reduce the possibility of recycle flow spikes
(that would cause shorter anoxic zone detention times resulting in elevated effluent TN).
Additionally, the plant modified detention time setpoints through the plant's supervisory control
and data acquisition (SCAD A) system that modulate the speed of the recycle pumps to maintain
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a desired detention time setpoint. The facility reported that this was done to allow for increasing
the first anoxic zone detention time. This was based on sampling the end of the first anoxic zone,
testing for nitrate concentrations and using the result to increase the detention time setpoint if the
nitrate concentration is above the target (usually 0.3 to 0.5 mg/1).
The facility does not fully know the exact scientific cause of the significant enhancement of
nitrogen removal to levels well below those typical to 5-Stage BNR processes. It suspects that
several causes worked together to attain this significant level of treatment. The treatment level
was attained without the addition of costly external carbon addition, except for small amounts of
methanol during short periods of time. The increase in the NRCY rate was likely an important
contributor to the success. Another potential cause of significant operational improvement was
thought to be related to conditions selecting for organisms that are more adept at hydrolyzing
slowly biodegradable influent BOD under anoxic conditions. The plant believed this was likely
aided by the splitting of the first anoxic zone into two separate compartments, the first
compartment serving as an anoxic selector and the second compartment being completely anoxic
and approaching anaerobic conditions. Anaerobic conditions are/were demonstrated by the very
low nitrate found at the end of the second compartment of the first anoxic zone. The second
anoxic zone also has separate chambers with the three chambers resulting in a plug flow and
each compartment becoming more anoxic. HWWTP staff believe this is part of the reason for the
success in removing nitrate without additional carbon added.
Finally, in considering the challenges encountered and lessons learned by the facility after
implementing the above, two brief operational incidents of reduced performance occurred around
November 2015 and February 2017 and were addressed by the facility. The first occasion in
November 2015 saw elevated TN effluent concentrations (Figure 7-6) starting on November 3rd
(3.7 mg/1) and as high as 6.5 mg/1 on November 10th before going back to typical concentrations
on November 24th (1.69 mg/1). This incident was reported to be caused by the impact of large
discharges of drinking water plant sludges which caused organic nitrogen spikes. This was
resolved by controlling these discharges, thus eliminating the spike loads.
The second incident occurred in February 2017, with higher plant effluent TN concentrations
starting on January 31 (3.7 mg/1) and peaking at 8.3 mg/1 on February 7th before subsiding on
February 21st (2.3 mg/1). The facility reported that although the specific cause was not
completely identified, they suspected that the cause was a chemical discharge to the collection
system which inhibited nitrification; ammonia nitrogen levels measured between February 7th
and February 14th were in the 7 - 8 mg/1 range with no other causes identified. The ammonia
levels started to subside gradually reaching typical levels on February 20th.
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REFERENCES
Mahagan, J., Bilyk, K. (2016). "How I've Kept Effluent TN Below 1.5 mg/L Without
Supplemental Carbon for 500 Days and Counting". Proceedings of the 2016 Water Environment
Federation's Technical Exhibition and Conference (WEFTEC), pp 3317-3328.
Metcalf and Eddy, Inc. (2003). "Wastewater Engineering Treatment and Reuse", 4th ed.;
McGraw-Hill, Inc.: New York.
U.S. EPA, 2008. "Municipal Nutrient Removal Technologies Reference Document - Volume I -
Technical Report". EPA 832-R-08-006. Washington, DC.
U.S. EPA, 2010. "Nutrient Control Design Manual". EPA EPA/600/R-10/100. Cincinnati, OH.
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