Water & Resource Recovery Center - Nutrient Reduction Plan Copyright 2014
City of Dubuque Action Items # 5.
ITEM TITLE: Water & Resource Recovery Center - Nutrient Reduction Plan
SUMMARY: City Manager recommending approval of the draft Nutrient Reduction
Strategy for the Water & Resource Recovery Center prepared by Strand
Engineers and Associates and to recommend authorization for Strand to
submit the plan to Iowa Department of Natural Resources (I DNR).
Staff will make a brief presentation.
RESOLUTION Authorizing Strand Associates of Madison, Wisconsin, to
submit to the Iowa Department of Natural Resources the Water &
Resource Recovery Center Nutrient Reduction Plan
SUGGESTED DISPOSITION: Suggested Disposition: Receive and File; Adopt Resolution(s), Staff
Presentation
ATTACHMENTS:
Description Type
❑ W&RRC Nutrient Reduction Strategy-MVM Memo City Manager Memo
❑ Staff Memo Staff Memo
❑ Resolution Resolutions
❑ Report Draft for Council Supporting Documentation
THE CITY OF Dubuque
AII11-America CiI.ty
UB E1
Masterpiece on the Mississippi 2007-2012-2013
TO: The Honorable Mayor and City Council Members
FROM: Michael C. Van Milligen, City Manager
SUBJECT: Water& Resource Recovery Center Nutrient Reduction Strategy
DATE: September 3, 2015
Water& Resource Recovery Center Manager Jonathan Brown is recommending
approval of the Draft Nutrient Reduction Strategy for the Water & Resource Recovery
Center prepared by Strand Engineers and Associates and to recommend authorization
for Strand to submit the plan to Iowa Department of Natural Resources (IDNR).
The City of Dubuque's National Pollution Discharge Elimination System (NPDES)
discharge permit required that the Water & Resource Recovery Center develop a
Nutrient Reduction Plan over a two year period and submit the plan to The Iowa
Department of Natural Resources by October 1, 2015.
The NPDES permit issued to the Water & Resource Recovery Center, effective October
2013, requires that the Water & Resource Recovery Center develop a plan for the
removal of Total Nitrogen and Total Phosphorous from its effluent under the IDNR
Nutrient Reduction Strategy Requirements. The development of the plan required at a
minimum one year of testing the influent and effluent of the Water & Resource Recovery
Center to determine Total Nitrogen and Total Phosphorous levels and any removal that
takes place and a year to develop the plan of action. Strand has prepared a draft
document for the Nutrient Removal Plan for review and comment prior to submitting the
plan by October 1, 2015. A summary of the findings and budget impacts are as follows:
A. Short-Term
1. [FY2016 - $0] investigate ability of the Water & Resource Recovery Center
to remove ammonia and partially remove nitrogen. This is currently taking
place and will continue for the next few months.
2. [FY2017 - $50,000] If task one proves promising make temporary changes
to one basin of the Water & Resource Recovery Center secondary
treatment system (activated sludge) for a full scale pilot test.
3. [FY2018 — $70,000] Assuming success in the pilot proceed with design
engineering to install similar permanent facilities for all three of the
activated sludge basins.
4. [FY2019 - $780,000] Begin three year process of installing permanent
facilities for all three basins.
5. [FY2020-$425,000] Continue installation
6. [FY2021-$425,000] Complete installation
B. Mid-Term Recommendations — Phosphorous reduction using a Struvite
Recovery system. The draft plan calls for this process to be budgeted for
FY2023 - 24 at an estimated $3.9 million dollars. Struvite is a crystal that may
form during the anaerobic digestion process. Depending upon the amount of
Struvite production it can cause operational difficulties downstream of the
digesters. The Water & Resource Recovery Center does have issues with
Struvite formation and there may be merit to implementing this removal
process earlier than the timeframe given in the report.
C. Long-Term — Implementation of the AnitaMOX process for the removal of
Total Nitrogen in FY2030 at $6.1 million dollars. The AnitaMOX process
allows for the direct conversion of ammonia to nitrogen gas bypassing the
need to go from ammonia to nitrite to nitrate to nitrogen gas. This will allow
the removal of nitrogen without increasing the need for additional costs of
providing oxygen to the process.
If this plan is approved by IDNR this would allow the Water & Resource Recovery
Center to achieve its Total Nitrogen and Total Phosphorous reduction goals over a
period of 15 years at a cost of an estimated $11 .7 million dollars with major costs out 5-
15 years.
During the facilities planning process that took place in 2007-2008 IDNR was contacted
to determine the possibility of nutrient removal requirements during the 20 year planning
period. At that time IDNR was not able to provide guidance as to when nutrient removal
would be required and to what level. For the purpose of facility planning it was assumed
that Total Nitrogen and Total Phosphorus limits would be implemented within the 20
year planning period. Based on Total Nitrogen and Total Phosphorous limits required in
other areas of the country an effluent limit of 5 mg/L Total Nitrogen and 0.5 mg/L Total
Phosphorous would be likely. Because of the uncertainties of the timing of nutrient limits
as well as the magnitude of these limits the facility plan did not include a detailed
evaluation of the treatment processes and facilities needed to construct future nutrient
removal facilities. It was considered unwise to design and build something to unknown
standards both in timing and requirements. The plan and final design did take into
account the possibility of future nutrient removal requirements and careful attention was
given to not build anything that would need to be removed later or that would interfere
with any future nutrient removal requirements. The work done on the secondary
treatment portion of the existing plant was limited to replacement of the 35 year old
mixers, coating the basins to protect the concrete and the replacement of the controls.
The design and construction of a facility to achieve an anticipated Total Nitrogen and
Total Phosphorous removal at 5 and 0.5 mg/L would have likely added an additional
$15 to 20 million dollars or more to the project. Under the proposed nutrient reduction
plan the costs for removal to 18 mg/L Total Nitrogen and 2 mg/L Total Phosphorous will
be approximately $11 .7 million dollars over a fifteen year time frame.
2
The Water & Resource Recovery Center is also taking part in a study sponsored by the
Iowa League of Cities for the feasibility of using nutrient trading to offset some of the
treatment costs for nutrient reduction. The staff of the Water & Resource Recovery
Center and Strand believe that nutrient trading can be an important tool for
improvement of watershed nutrient reductions but that the majority of the Total Nitrogen
and Total Phosphorous will need to be removed using treatment processes at the Water
& Resource Recovery Center and nutrient trading credits used for the more costly
removal of nutrients at lower permit concentrations of Total Nitrogen/Total Phosphorous
if these become a part of a future NPDES permit.
I concur with the recommendation and respectfully request Mayor and City Council
approval.
Mic ael C. Van Milligen
MCVM:jh
Attachment
cc: Barry Lindahl, City Attorney
Cindy Steinhauser, Assistant City Manager
Teri Goodmann, Assistant City Manager
Jonathan Brown, Water & Resource Recovery Center Manager
3
THE CITY OF Dubuque
AII11-America CiI.ty
UB E1
Masterpiece on the Mississippi 2007-2012-2013
TO: Michael C. Van Milligen, City Manager
FROM: Jonathan R. Brown, W&RRC Manager
SUBJECT: W&RRC Nutrient Reduction Strategy
DATE: August 4, 2015
INTRODUCTION: The purpose of this memo is to provide a copy of the Draft Nutrient
Reduction Strategy for the Water & Resource Recovery Center (W&RRC) prepared by
Strand Engineers and Associates of Madison Wisconsin and to request authorization for
Strand Associates to submit the plan to IDNR.
BACKGROUND: The City of Dubuque's Water & Resource Recovery Center (W&RRC)
NPDES discharge permit required that the W&RRC develop a Nutrient Reduction Plan
over a two year period and submit the plan to The Iowa Department of Natural
Resources (IDNR) by October 1, 2015. A copy of the draft report is attached for review.
The report also contains a copy of the W&RRC NPDES permit which includes the
Nutrient Reduction Requirements.
DISCUSSION: The NPDES permit issued to the W&RRC, effective October 2013,
requires that the W&RRC develop a plan for the removal of Total Nitrogen (TN) and
Total Phosphorous (TP) from its effluent under the IDNR Nutrient Reduction Strategy
Requirements. The development of the plan required at a minimum one year of testing
the influent and effluent of the W&RRC to determine TN and TP levels and any removal
that takes place and a year to develop the plan of action. Strand Engineers and
Associates has prepared a draft document for the Nutrient Removal Plan for review and
comment prior to submitting the plan by October 1, 2015. A summary of the findings
and budget impacts are given below. A more detailed description can be found on
pages 26 and 27 of the draft plan.
A. Short-Term ( All costs are based on 2015 dollars the budget impact will adjust
these dollars for possible inflation at 3% per year)
1. [FY2016 - $0] investigate ability of the W&RRC to remove ammonia and
partially remove nitrogen. This is currently taking place and will continue
for the next few months.
2. [FY2017 - $50,000] If task one proves promising make temporary changes
to one basin of the W&RRC secondary treatment system (activated
sludge) for a full scale pilot test.
3. [FY2018 — $ $70,000] Assuming success in the pilot proceed with design
engineering to install similar permanent facilities for all three of the
activated sludge basins.
4. [FY2019 - $780,000] Begin three year process of installing permanent
facilities for all three basins. (First year costs will be higher due to the
need to construct a pumping station along with modifications to the basin.)
5. [FY2020-$425,000] Continue installation
6. [FY2021-$425,000] Complete installation
Overall project costs may be lower if bid and constructed as one.
B. Mid-Term Recommendations — Phosphorous reduction using a Struvite
Recovery system. The draft plan calls for this process to be budgeted for
FY2023 - 24 at an estimated $3.9 million dollars. Struvite is a crystal that may
form during the anaerobic digestion process. Depending upon the amount of
Struvite production it can cause operational difficulties downstream of the
digesters. The W&RRC does have issues with Struvite formation and there
may be merit to implementing this removal process earlier than the timeframe
given in the report.
C. Long-Term — Implementation of the AnitaMOX process for the removal of
Total Nitrogen FY2030 at $6.1 million dollars. The AnitaMOX process allows
for the direct conversion of ammonia to nitrogen gas bypassing the need to
go from ammonia to nitrite to nitrate to nitrogen gas. This will allow the
removal of nitrogen without increasing the need for and additional costs of
providing oxygen to the process.
If this plan is approved by IDNR this would allow the W&RRC to achieve its TN and TP
reduction goals over a period of 15 years at a cost of an estimated $11 .7 million dollars
with major costs out 5-15 years.
Staff of the W&RRC and Strand Associates have conducted two conference calls with
IDNR staff to discuss this approach to the plan and have received favorable comments.
The City of Dubuque Nutrient Reduction Strategy Plan will be among the first to be
reviewed by IDNR and they have expressed thanks for keeping them informed about
the process and direction of planning.
During the facilities planning process that took place in 2007-2008 IDNR was contacted
to determine the possibility of nutrient removal requirements during the 20 year planning
period. At that time IDNR was not able to provide guidance as to when nutrient removal
would be required and to what level. For the purpose of facility planning it was assumed
that total nitrogen (TN) and total phosphorus (TP) limits would be implemented within
the 20 year planning period. Based on TN and TP limits required in other areas of the
country an effluent limit of 5 mg/L TN and 0.5 mg/L TP would be likely. Because of the
uncertainties of the timing of nutrient limits as well as the magnitude of these limits the
facility plan did not include a detailed evaluation of the treatment processes and
facilities needed to construct future nutrient removal facilities. It was considered unwise
2
to design and build something to unknown standards both in timing and requirements.
The plan and final design did take into account the possibility of future nutrient removal
requirements and careful attention was given to not build anything that would need to be
removed later or that would interfere with any future nutrient removal requirements. The
work done on the secondary treatment portion of the existing plant was limited to
replacement of the 35 year old mixers, coating the basins to protect the concrete and
the replacement of the controls. The design and construction of a facility to achieve an
anticipated TN and TP removal at 5 and 0.5 mg/L would have likely added an additional
$15 to 20 million dollars or more (in 2008 dollars) to the project. Under the proposed
nutrient reduction plan the costs for removal to 18 mg/L TN and 2 mg/L will be
approximately $11 .7 million dollars over a fifteen year time frame.
The W&RRC is also taking part in a study sponsored by the Iowa League of Cities for
the feasibility of using nutrient trading to offset some of the treatment costs for nutrient
reduction. The staff of the W&RRC and Strand believe that nutrient trading can be an
important tool for improvement of watershed nutrient reductions but that the majority of
the TN and TP will need to be removed using treatment processes at the W&RRC and
nutrient trading credits used for the more costly removal of nutrients at lower permit
concentrations of TN/TP if these become a part of a future NPDES permit.
BUDGET IMPACT: The short term budget impact has the following projected rate
increases, based on issuing a 10 year Iowa Finance Authority State Revolving Fund
Loan:
Fy19 1 .02%
Fy20 0.56%
Fy21 0.56%
The long term rate impacts for fy23-24 and then fy30 will need to be determined based
on upon the means developed for financing these projects.
ACTION: The purpose of his memo is to provide information regarding the development
of a Nutrient Reduction Plan as required by IDNR and to request that the City Council
authorize Strand Associates of Madison Wisconsin to submit to IDNR on behalf of the
City of Dubuque the Water & Resource Recovery Center Nutrient Reduction Plan to
IDNR.
Attachments:
3
RESOLUTION NO. 313-15
AUTHORIZING STRAND ASSOCIATES OF MADISON, WISCONSIN TO SUBMIT TO
THE IOWA DEPARTMENT OF NATURAL RESOURCES THE WATER & RESOURCE
RECOVERY CENTER NUTRIENT REDUCTION PLAN
Whereas, the NPDES permit issued to the Water & Resource Recovery Center in
October 2013 required the development of a Nutrient Reduction Plan to be submitted to
the Iowa Department of Natural Resources by October 1, 2015 and that this plan has
been developed by Strand Associates of Madison, WI.
NOW THEREFORE, BE IT RESOLVED BY THE CITY COUNCIL OF THE CITY OF
DUBUQUE, IOWA:
That Strand Associates of Madison, WI is authorized to submit a Nutrient Reduction
plan for the City of Dubuque Water & Resource Recovery Center on behalf of the City of
Dubuque Water & Resource Recovery Center.
Passed, approved and adopted this 8th day of September, 2015.
Attest:
Kevin S:Fitnstahl, City Clerk
Roy D. Buol, Mayor
June 19, 2015
Mr.Jonathan Brown, W&RRC Manager
City of Dubuque
795 Julien Dub Drive
Dubuque, IA 52001
Re: City of Dubuque Water and Resource Recovery Center Nutrient Reduction Study
Second Draft
Dear Jonathan,
Enclosed is an electronic copy of the second draft Nutrient Reduction Study report. Following your
review of the report, we anticipate meeting with City officials to present and discuss the
recommendations and direction for future compliance with the Iowa Nutrient Reduction Strategy.
Please call me with questions.
Sincerely,
STRAND ASSOCIATES, INC.®
Randall A.Wirtz, Ph.D., P.E.
Enclosure: Report
RAW plh\SA1v1AD\1100-1199A1154V046AWcd\Nuhient SwdyVReport Dcatt#2.docx
Report for
City of Dubuque Water and
Resource Recovery Center
Nutrient Reduction Study
Prepared by:
STRAND ASSOCIATES, INC
910 West Wingra Drive
Madison, WI 53715
www.strand.com
June 2015
A
STRAND
AS SOC IATE S'
TABLE OF CONTENTS
Page No.
or Following
NUTRIENT REDUCTION STUDY
Existing Treatment Facility...................................................................................................... 1
Evaluation of Operational Changes for Nutrient Removal ....................................................... 6
Nutrient Reduction Goals........................................................................................................ 9
Evaluation of Treatment Technologies to Meet Nutrient Reduction Goals............................... 10
Summary of Alternatives......................................................................................................... 22
Recommended Strategy and Budgetary Considerations......................................................... 26
TABLES
Table 1 W&RRC Design Flows and Loadings ................................................................ 3
Table 2 Influent and Effluent Nitrogen and Phosphorus Data for October 2013
ThroughDecember 2014................................................................................... 5
Table 3 Average Nitrogen and Phosphorus Concentrations of Additional W&RRC
Data Collected by the City from February 2014 to December 2014................... 6
Table 4 Effect of Two versus Three Aeration Trains in Operation................................... 9
Table 5 Effect of SRT on W&RRC Operations ............................................................... 9
Table 6 Nutrient Effluent Goals ...................................................................................... 10
Table 7 BNR Simulations for Current Flows and Loads (Existing HPO Tankage)........... 13
Table 8 BNR Simulations for Future AWW Flows and Loads ......................................... 15
Table 9 Sidestream Treatment Impacts on Effluent Nutrients (Future AWW Conditions) 19
Table 10 Alternatives Summary....................................................................................... 25
FIGURES
Figure 1 City of Dubuque W&RRC Process Schematic................................................... 4
Figure 2 City of Dubuque W&RRC BioWin Schematic..................................................... 8
Figure 3 Az/O Process Schematic ................................................................................... 11
Figure 4 MLE Process Schematic ................................................................................... 12
Figure 5 Az/O Aeration Train Schematic (Existing HPO Tankage)................................... 13
Figure 6 MLE Aeration Train Schematic (Existing HPO Tankage)................................... 14
Figure 7 Az/O Process Schematic with Fourth HPO Train ............................................... 16
Figure 8 MLE Process Schematic with Fourth HPO Train ............................................... 17
Figure 9 Alternatives Site Plan ........................................................................................ 24
APPENDICES
APPENDIX A—NPDES PERMIT
APPENDIX B—COST OPINIONS
City of Dubuque Water and Resource Recovery Center, Dubuque, Iowa Nutrient Reduction Study
This report was prepared as required to meet the October 1, 2015, compliance schedule in the City of
Dubuque's (City's) Iowa Department of Natural Resources (IDNR) National Pollutant Discharge
Elimination System (NPDES) permit(No. 3126001).The purpose of this report is to evaluate the feasibility
and reasonableness of reducing the amounts of total nitrogen (TN) and total phosphorus (TP) discharged
into the Mississippi River by the City's Water and Resource Recovery Center (W&RRC). The City's
NPDES permit is included in Appendix A.
EXISTING TREATMENT FACILITY
A. Background
The City of Dubuque W&RRC was recently upgraded in a $68 million phased project that included
modifications to nearly all of the buildings and processes, conversion from sludge incineration to
anaerobic digestion with land application, conversion from chlorination-dechlorination to UV disinfection,
replacement of much of the plant's significant equipment, implementation of cogeneration using the
digester gas, and many other upgrades and modifications. The facilities planning was completed in 2008
for this major project, and at that time, the Iowa DNR indicated to the City that nutrient removal
requirements were not imminent, but could reasonably be expected within the 20-year planning window
of the facilities plan. However, there was no indication whether this might include phosphorus, nitrogen,
or both, nor could IDNR provide any limits for planning purposes. The facilities plan considered nutrient
removal requirements at a high level, and compared the existing high purity oxygen activated sludge
process to a more conventional air activated sludge process that would be more amenable to biological
nutrient removal (BNR). Because of the significant costs associated with converting to air activated
sludge, as well as the unknowns associated with Iowa's nutrient regulations, the City made a conscience
decision not to build facilities for BNR at that time. This decision was approved by the IDNR.
B. Facility Processes and Operations
The Dubuque W&RRC serves the City of Dubuque, Iowa. The W&RRC is a secondary wastewater
treatment plant providing treatment of domestic and industrial wastewater. The plant consists of
screening, grit removal, primary treatment, biological secondary treatment, and disinfection before
discharging to the Mississippi River. Excess flow equalization facilities provide storage capacity for high
flows. The biosolids train uses temperature-phased anaerobic digestion of thickened waste activated
sludge (WAS) and primary sludge followed by centrifuge dewatering. The treatment trains are discussed
further below.
1. Screening
Wastewater generated in the City of Dubuque is conveyed to the plant through two force main
sewers. The wastewater enters the Influent Flow Meter Vault outside the Headworks Building.
The influent wastewater then flows to one of two 1/4-inch mechanical fine screens where coarse
solids are removed. Each screen discharges the removed screenings into a wash press, which
returns much of the treatable organics to the influent channels and dewaters and conveys the
remaining screenings to a dumpster for landfill disposal. After screening, the raw wastewater is
sampled.
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City of Dubuque Water and Resource Recovery Center, Dubuque, Iowa Nutrient Reduction Study
2. Grit Removal
Wastewater flows from the mechanical screens through channels to one of the two vortex-style
grit tanks, which remove heavier inorganic materials. Each grit tank has a dedicated grit pump
that is used to pump the grit from the bottom of the grit tank to one of two grit washers located in
the grit removal and screening room of the Headworks Building. The grit washers remove most
of the organics from the grit and return the organics to the influent channels for treatment. The
washed grit is dewatered and landfilled.
3. Primary Treatment
There are four primary clarifiers available to provide primary treatment. The settleable solids
removed in these clarifiers are pumped to the blended sludge storage tanks before being fed to
the anaerobic digesters for stabilization. The clarified wastewater flows to the secondary
treatment systems for biological treatment.
4. Secondary Treatment
The Dubuque W&RRC employs a high purity oxygen (HPO) activated sludge treatment system
that consists of three covered aeration trains. In the three aeration trains, the primary clarifier
effluent (PRE) is combined with return activated sludge (RAS) to form mixed liquor (ML). Each
train consists of a total of nine basins arranged in a three-pass configuration (three basins per
pass) before flowing to the final clarifiers. High pure oxygen is introduced in the first stage of each
aeration tank. The oxygen gas is injected into the headspace of the first basin in each train and
flows concurrently with the liquid ML through the aeration trains. Each stage in the aeration trains
is mixed with a mechanical surface aerator.
5. Final Clarification
ML from the HPO activated sludge basins trains flows to the Mixed Liquor Splitter Box and is split
to the four final clarifiers. Settled solids are pumped back to the activated sludge process (RAS)
or to the WAS holding tanks as biosolids. The treated water flows by gravity from the clarifiers to
the UV disinfection system.
6. Disinfection
When required by the W&RBC's permit (March-November), the effluent from the final clarifiers is
disinfected using UV light to reduce the number of active pathogens discharged from the facility,
thereby minimizing potential public health risks in the receiving water.
7. Cascade Aeration
After disinfection, the final effluent flows over a series of concrete steps to introduce additional
oxygen, as well as release dissolved carbon dioxide gas to increase the wastewater pH, before
discharge to the Mississippi River.
8. Excess Flow Equalization
The original trickling filter tanks were recently converted to provide approximately 3 million gallons
of storage downstream of the primary clarifiers. Stored PRE can be routed back into the facility
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City of Dubuque Water and Resource Recovery Center, Dubuque, Iowa Nutrient Reduction Study
for complete secondary treatment at the conclusion of the high flow event. If the wet weather
event has a long enough duration, these tanks overflow to the HPO activated sludge facilities for
biological treatment.
9. Sludge Storage and Thickening
WAS pumped from the activated sludge system can be stored in the WAS holding tanks or can
be pumped directly to the rotary drum thickeners (RDTs) for thickening. TWAS is pumped to the
blended sludge storage tanks for feeding to the anaerobic digesters.
10. Biosolids Stabilization
Combined primary and thickened WAS is stabilized through a temperature-phased anaerobic
digestion (TPAD) process to destroy volatile solids and pathogens, resulting in stable Class 1
biosolids. The four digesters are operated in series with two thermophilic stages and two
mesophilic stages. The two mesophilic stages have floating gas holder covers that allow these
tanks to serve as biosolids storage tanks ahead of the dewatering centrifuges.
11. Biosolids Dewatering and Disposal
Stabilized biosolids are dewatered with two dewatering centrifuges. Centrate is equalized before
being pumped back to the W&RRC for treatment. Dewatered biosolids are directly loaded into
trucks for off-site storage and land application disposal on farmland.
The W&RRC design flows and loadings are provided in Table 1, and a schematic of the W&RRC is
provided in Figure 1.
Design Flows(mgd)
Average Dry Weather 9.14
Average Annual Flow 10.64
Average Wet Weather 13.47
Maximum Wet Weather 15.83
Maximum Day Flow 24.50
Peak Hourly Flow 40.86
Design Loadings (Ib/day)
Average Annual BODS 36,900
Maximum Month BODS 41,200
Maximum Week BODS 49,000
Average Annual TSS 29,400
Maximum Month TSS 37,100
Table 1 W&RRC Design Flows and Loadings
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Dubuque Water and Resource Recovery Center, Dubuque, Iowa Nutrient Reduction Study
Cake Polymer
LEGEND
Anaerobic EF=excess flow
Digesters FE=final effluent
Centrifuges MLSS=mixed liquor suspended solids
PRE=primary clarifier effluent
Centrate PRI=primary clarifier influent
Storage Tanks RDTs and TWAS PRS=primary clarifier sludge
Storage Tanks RAS=return activated sludge
Blended RDT=rotary drum thickener
Sludge Tank RW=raw wastewater
TWAS=thickened waste activated sludge
WAS Storage Tank UV=ultraviolet
Polymer WAS=waste activated sludge
PRS j
M
RAS Splitter Box Mississippi
LL WAS River
PRI RAS MLSS
L
Splitter Box Splitter Box
�
Primary Aeration Final
Clarifiers Tanks Clarifiers FE
PRE UV Disinfection
Grit Splitter Box and Cascade
Removal
Aeration
RAS
Screening \
RW Aeration Tank
Excess Flow EF Splitter Box
Equalizatio
To
Landfill
Figure 1 City of Dubuque W&RRC Process Schematic
Prepared by Strand Associates, Inc.® 4
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Dubuque Water and Resource Recovery Center, Dubuque, Iowa Nutrient Reduction Study
C. Baseline Nitrogen and Phosphorus Data
Influent and effluent total Kjeldahl nitrogen (TKN), TN, and TP concentrations are measured weekly. The
City also measures influent and effluent nitrate concentrations several times each month. The monthly
average influent and effluent nitrogen and phosphorus concentrations for October 2013 through
December 2014 are provided in Table 2. Note that the W&RRC was only operating two of the three
aeration trains during the majority of this time period.
Influent Effluent
Flow TKN Nitrate TN TP TKN Nitrate TN TP
Month m d) m /L) m /L) m /L) m /L) m /L) m /L) (mg/ m /L)
Oct-13 6.08 41.3 0.8 41.7 5.0 32.7 25.2 55.2 3.31
Nov-13 6.06 90.6 ND 89.8 11.0 35.1 27.5 62.6 5.41
Dec-13 5.92 76.0 ND 75.4 9.8 47.4 17.2 64.2 4.23
Jan-14 6.20 83.0 ND 82.3 8.3 49.6 16.0 66.8 4.96
Feb-14 6.40 65.6 0.1 56.2 5.8 58.2 22.7 67.6 3.52
Mar-14 7.17 42.9 0.4 42.9 5.4 34.0 24.7 58.7 4.76
Apr-14 9.24 34.3 1.9 35.9 6.2 34.5 30.7 54.1 4.65
May-14 8.98 43.7 1.4 44.6 5.3 25.3 27.1 53.7 4.14
June-14 10.71 43.6 0.7 43.9 10.3 32.5 20.3 50.1 3.18
July-14 11.18 45.3 1.2 43.4 7.3 8.7 25.4 36.6 3.06
Aug-14 7.59 47.5 1.4 48.0 8.2 19.5 29.1 52.4 5.37
Sept-14 7.56 56.0 1.0 56.5 10.4 8.2 25.4 51.4 6.61
Oct-14 7.44 78.9 No Data 78.4 10.1 No Data No Data 55.5 5.04
Nov-14 6.94 No Data No Data No Data No Data No Data No Data 52.9 3.99
Dec-14 7.67 No Data No Data No Data No Data No Data No Data 49.8 2.27
Average 7.73 55.0 1.0 54.2 7.9 32.6 24.7 55.4 4.30
Notes:
Influent measurements do not include process return flows or hauled waste.
ND= no detect.
Table 2 Influent and Effluent Nitrogen and Phosphorus Data for October 2013 Through
December 2014
To assist in evaluating the options for nutrient removal, the City also periodically measured ammonia,
TKN, nitrate, TN, TP, and soluble phosphorus concentrations in the PRE, hauled wastes, rotary drum
thickener filtrate, and centrifuge centrate. The average nutrient data from these locations are included in
Table 3.
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Dubuque Water and Resource Recovery Center, Dubuque, Iowa Nutrient Reduction Study
Soluble
Ammonia TKN Nitrate TN TP Phosphorus
Sample Location (m /L (mg/L (mg/L (mg/L (mg/L (mg/L)
Primary Clarifier Effluent 45 65 1.8 68 8.8 7.3
Hauled Wastes 175 2,640 91 2,750 184 108
Rotary Drum Thickener 106 95 3.8 98 121 104
Filtrate
Centrifuge Centrate 1,950 2,200 21 2,300 262 144
Table 3 Average Nitrogen and Phosphorus Concentrations of Additional W&RRC Data
Collected by the City from February 2014 to December 2014
The W&RRC was designed primarily to remove biochemical oxygen demand (BOD) and total suspended
solids (TSS) and was not designed to nitrify or to remove TP or TN. The HPO activated sludge process
is a high-rate process with relatively small aeration tanks and high dissolved oxygen (DO) levels, both of
which reduce the ability to convert the system to BNR processes. In addition, the low pH that the HPO
system operates at also inhibits nitrification reactions.
The average influent and effluent data presented in Table 2 indicate the W&RRC is currently removing
minimal amounts of TN. Some nitrification does occur, and under current conditions, the plant achieves
partial nitrification with two of the HPO trains in services. With all three train in service, the plant can
effectively nitrify under existing loading conditions. However, overall TN removal is minimal through the
plant. The data in Table 2 does suggest that the W&RRC is currently removing approximately 45 percent
of the influent TP. This is likely attributable to biological uptake and the relatively high percentage of
influent TP being in the particulate form (approximately 35 percent).
EVALUATION OF OPERATIONAL CHANGES FOR NUTRIENT REMOVAL
Because the W&RRC facility uses a HPO activated sludge system with covered tanks, it is unlikely that
implementing operational changes will significantly reduce the amount of TN and TP discharged in the
final effluent. In HPO systems, nitrification ability is typically limited because of a short solids retention
time (SRT), short hydraulic retention time (HRT), and because of the accumulation of carbon dioxide in
the gas headspace, which causes low pH in the ML. To achieve substantial nutrient removal, the W&RRC
will likely need to construct additional biological reactor volume and/or tertiary or sidestream treatment
technologies.
Even though nutrient reductions attributable to operational changes are expected to be minimal, two
relatively simple operational changes were evaluated to determine how the system may be optimized for
TN and TP removal. The operational changes evaluated as part of this study include:
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1 . Running all three aeration trains in parallel (current operation is two trains in parallel) to
increase SRT, HRT, and nitrification. While this may not improve nutrient removal, the
ability to nitrify is important to future denitrification for TN removal.
2. Modifying RAS and WAS rates. This is also related to increasing SRT to improve
nitrification.
To aid in evaluating the implementation of the operational changes, a BioWin computer model was
developed. The model was calibrated using the data collected for this study under current operating
conditions, though it is acknowledged that significantly more data collection would be required to fully
calibrate the model. The model was then modified to simulate the different operational changes being
evaluated. A BioWin schematic of the existing W&RRC is provided in Figure 2, and Tables 3 and 4
present the BioWin model outputs for these scenarios.
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Influent Primary Clarifiers
r rainA-#1 Train A-#2 Train A-#3
` ' } Final Clarifiers Effluent
TrainA-# Train A-#6 Train A-
Centrate Storage Tank
rain A-#7 Train A-#8 Train A-#9
rain B-#1 Train B-#2 Train B-#3
Cei trifuges Meso Dig Thermo Dig Blended Sludge Tank - -- -�--
Train B- Train B 46 Train B-
DTs rain B-#7 Train B-#8 Train B 49
Cake
W -�
rain C-#1 Train C-#2 Train C-#3
Hauled Waste
Train C-# Train C-#6 Train C-#
WAS Storage Tanks
rain C-#7 Train C-#8 Train C-#9
Figure 2 City of Dubuque W&RRC BioWin Schematic
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BOD COD TSS Ammonia TKN Nitrate TN TP
SRT Conc. Conc. Conc. Conc. Conc. Conc. Conc. Conc.
Scenario' (days) (mg/L (mg/L (mg/L (mg/L (mg/L (mg/L (mg/L m /L
Two Trains in
Parallel (Existing 6.2 6.4 35.5 12.9 29.2 32.5 8.8 41.3 5.5
W&RRC
Three Trains in 8.3 5.2 33.8 11.8 3.0 6.1 31.6 37.7 5.5
Parallel
'These results were obtained using the existing average flow rate of 7.7 mgd.
Table 4 Effect of Two versus Three Aeration Trains in Operation
BOD COD TSS Ammonia TKN Nitrate TN TP
SRT Conc. Conc. Conc. Conc. Conc. Conc. Conc. Conc.
Scenario' days) (mg/L) (mg/L) (mg/L) (mg/L) (mg/L) mg/L) (mg/L) (mg/L)
RAS = 0.32Q
WAS = 0.075 mgd 6.2 6.4 35.5 12.9 29.2 32.5 8.8 41.3 5.5
(Existing W&RRC)
RAS = 0.64Q 7.8 9.6 46.4 22.4 28.5 32.3 6.3 38.6 5.6
WAS = 0.075 mgd
RAS = 0.64Q 11.1 11.2 54.4 29.7 29.6 33.8 4.5 38.3 5.7
WAS = 0.05 mgd
RAS = 0.32Q 3.0 4.7 29.6 7.4 44.6 47.6 1.03 48.6 5.3
WAS = 0.15 mgd
RAS = 0.64Q 4.1 6.9 36.3 13.3 31.1 34.3 8.2 42.6 5.4
WAS = 0.15 mgd
'These results were obtained by modeling two trains in parallel at the existing average flow rate of 7.7 mgd.
Table 5 Effect of SRT on W&RRC Operations
As expected, the model predicted no significant change in TN or TP concentration in the wastewater
effluent from implementing these operational changes. However, the model did predict that the change
to a three-train operation (Table 4) would be expected to reduce effluent ammonia concentrations, which
has generally been the experience at the W&RRC when three trains have been operated. This appears
to be a function of HRT rather than SRT, as is evidenced by the lower ammonia levels with three trains
in service (Table 4, row 2) compared to a longer SRT with only two trains in service (Table 5, row 3).
NUTRIENT REDUCTION GOALS
As stated in the City's NPDES permit, the TN and TP effluent discharge limits will be based on one full
year of operating data after implementation of the operational changes or completion of plant
modifications, as well as a six-month optimization period, and will be incorporated into the NPDES permit
by amendment. For the purposes of this evaluation, the permit states the reduction goals shall be based
on average wet weather (AWW) design flow equivalent to concentrations of 10 milligrams per liter (mg/L)
TN and 1 mg/L TP for plants treating typical domestic strength sewage. Typical domestic strength sewage
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Dubuque Water and Resource Recovery Center, Dubuque, Iowa Nutrient Reduction Study
is considered to contain approximately 25 to 35 mg/L TN and 4 to 8 mg/L TP. For plants treating
wastewater with TN and/or TP concentrations greater than typical domestic strength, the permit states
the reduction goals should be based on achieving at least a 66 percent reduction in TN and a 75 percent
reduction in TP.
The data collected from October 2013 through December 2014 indicate the average influent TN
concentration was approximately 54 mg/L, and the average influent TP concentration was approximately
7.9 mg/L (Table 2). Based on these results and the language in the Nutrient Reduction Strategy
documents, the effluent nutrient reduction targets would include a 66 percent reduction goal for TN and
a 1 mg/L goal for TP. However, through discussion with IDNR and considering that, if the influent average
TP concentration was only 0.2 mg/L higher, the effluent target TP would more than double to above 2
mg/L (75 percent reduction), we believe a reasonable effluent TP target for the Dubuque W&RRC is 2
mg/L with a goal of ultimately being closer to 1 mg/L. The load reduction goals for TN and TP are provided
in Table 6.
Average Influent Effluent Goal Effluent Goala
Parameter (m /L) Reduction Goal (mg/L lbs/da
TN 54 66%of influent 18.4 2,067
TP 7.9 75%of influent 2.0 224
aAWW flow= 13.47 mgd. Goal is stated as an annual average.
Table 6 Nutrient Effluent Goals
EVALUATION OF TREATMENT TECHNOLOGIES TO MEET NUTRIENT REDUCTION GOALS
As previously discussed, operational changes alone at the W&RRC will not be sufficient to achieve
significant nutrient reductions, and a major capital upgrade will be required to achieve the target
reductions in TN and TP. The treatment alternatives considered as part of this study include:
■ Activated sludge MLE process for TN removal—within existing basins as well as construction of
additional volume.
■ Activated sludge A2/O process for both TP and TN removal—within existing basins as well as
construction of additional volume.
■ Sidestream nitrogen removal with Anammox processes.
■ Sidestream phosphorus removal with struvite harvesting.
■ Chemical phosphorus removal.
■ Tertiary fixed film denitrification.
■ Sidestream/mainstream bioaugmentation to promote nitrification
■ Combinations of these technologies.
Opinions of cost summaries for capital and annual operation and maintenance (O&M) costs are
presented in the following sections. The development of those cost summaries is included in Appendix B.
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A. Incorporate Biological Nutrient Removal Into Existing HPO Activated Sludge
1. Introduction
BNR can be incorporated into the W&RRC to help meet the proposed effluent limits. For this
study, two processes were evaluated—the A2/O process for both TN and TP removal and the
Modified Ludzack Ettinger (MLE) process for TN removal only. The latter process would need to
be combined with chemical phosphorus removal or sidestream phosphorus removal to meet TP
target reductions.
The A2/O process involves an anaerobic zone, anoxic zone, and aerobic zone. ML is recycled
from the end of the aerobic stage to the anoxic stage for denitrification at a typical rate of 100 to
300 percent of the influent flow. RAS is returned to the anaerobic zone. Assuming adequate
carbon is available, this process can normally attain effluent TP concentrations less than 1 and
TN concentrations below 10 mg/L. Figure 3 presents a schematic of the A2/O process.
Internal Recycle
Influent Effluent
Anaerobic Anoxic Aerobic Clarifier
RAS
V
WAS
Figure 3 A2/O Process Schematic
The MLE process is used for TN removal and involves an anoxic zone and an aerobic zone. In
this process, there is an internal recycle from the aerobic to anoxic zone, which provides nitrate
as an oxygen source at the head of the tank. RAS is recycled to the anoxic zone. Figure 4 presents
a schematic of the MLE process.
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Dubuque Water and Resource Recovery Center, Dubuque, Iowa Nutrient Reduction Study
Internal Recycle
Influent Effluent
Anoxic Aerobic Clarifier
I
RAS
V
WAS
Figure 4 MILE Process Schematic
2. Modeling Results
a. Existing Conditions
Reconfiguration of the W&RRC's existing HPO basins into the A2/O and MLE processes
was evaluated using a BioWin model. Each process was modeled for current AWW flows
and loadings assuming all three of the existing trains were in operation. For the A2/O
process model, existing Basins 1, 2, and 3 in each train were anaerobic, Basins 4 and 5
were anoxic, and Basins 6 through 9 were aerobic. The internal recycle was set as 250
percent of influent flow, and RAS was set as 62.5 percent of influent flow. For the MLE
process, Basin 1 was anoxic, and the internal recycle and RAS recycle were set as
150 percent and 75 percent of influent flow, respectively. Figures 5 and 6 show one
aeration train layout modeled for the A2/O process and MLE process, respectively. Note
that in the aerobic zones, the DO was not allowed to drop below 2.0 mg/L in the model. In
practice, this would require new mixers in some of the aerobic basins.
Results for the current flows and loading conditions are presented in Table 7. Based on
these results, the A2/O process will not be effective in reducing TN or TP to target levels if
only the existing aeration tankage is used, even at current flows and loads. The results
indicated that adequate nitrification did not occur to achieve TN removal. To determine
whether this was the result of suppressed pH, low HRT, or low SRT,we modeled the same
process maintaining a neutral pH in the aerobic basins, as well as variable SRTs. The
model predicted the same effluent nutrient concentrations under all scenarios, which
indicates that the HRT in the system is not adequate to effectively nitrify the wastewater.
As a point of addition proof, in a latter phase of the modeling, a fourth train of activated
sludge was modeled, and the longer HRT resulted in improved nitrification.
The MLE process model indicated that if the first basin were converted to an anoxic zone,
a TN reduction of about 34 percent could be expected. This level does not meet the target
effluent TN concentration of about 18 mg/L, however.
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Effluent Effluent Effluent Effluent Effluent Effluent Effluent
BOD TSS NI-13 TKN Nitrate TN TP
Scenarios (mg/L (mg/L (mg/L (mg/L (mg/L (mg/L m /L
Existing Process 5.1 12 0.2 3.2 46 50 5.5
A2/0 Process
see Figure 5 6.4 13 38 41 0.1 44 3.5
A2/0 Process
with pH Control
see Figur 5) 7.1 13 38 41 0.1 43 3.5
MLE Process
(See Figure 6) 6.3 14 0.1 3.3 29 33 5.5
'All scenarios use all three trains of the existing HPO tankage only; no new volume was assumed.
Table 7 BNR Simulations for Current Flows and Loads (Existing HPO Tankage)
Primaryi
Effluent i RAS
i
i
W
7 6 Basin 1 LEGEND
Anaerobic
Anoxic
8 5 2 Aerobic
I Forward Flow
WI I >
J� — Recycle
9 - - > 4 3
Recycle
Mixed
Liquor
Figure 5 A2/O Aeration Train Schematic (Existing HPO Tankage)
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Primary i
Recycle
Effluent i RAS
Y
- - - - - - - - - - - - - - - - i
i W
i
i
7 6 Basin 1 LEGEND
Anoxic
i Aerobic
i
8 5 2 Forward Flow
i — Recycled
i 9 4 3
i
Mixed
Liquor
Figure 6 MILE Aeration Train Schematic (Existing HPO Tankage)
b. Future AWW Conditions
Based on the modeling results of the existing flow and loading conditions presented
previously, it is clear that the current plant HPO volume is not adequate to allow conversion
of the existing tankage to BNR process configurations (A 2/0 or MLE) to meet target
effluent TN and TP limits at future AWW design flows and loading conditions. Therefore,
additional activated sludge system reactor volume will be needed. We modeled several
plant configurations and potential additions to determine the impact on effluent nutrients:
■ Existing three trains.
■ Existing three trains with MLE integral to each tank.
■ Existing three trains with construction of MLE tankage upstream.
■ Existing three train with construction of A2/O tankage upstream.
■ Construction of a fourth train.
■ Construction of a fourth train with MLE integral to each train.
■ Construction of a fourth train with construction of MLE tankage upstream.
■ Construction of a fourth train with construction of A2/O tankage upstream.
Table 8 presents the modeling results. Based on these results, the target effluent TN
concentration (18 mg/L) could be met with the construction of a fourth activated sludge
train along with the construction of upstream A2/O tankage. However, the effluent TP
concentration was not impacted significantly under this modeling scenario, which was
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likely the result of carbon limitation in the process. The MLE process configurations
resulted in slightly higher effluent TN concentrations (21 mg/L with four trains and 23 mg/L
with three trains). Although both concentrations are marginally higher than the target, the
costs required the MLE option with only three trains would be substantially less than the
construction of a fourth train of HPO. In addition, in conjunction with sidestream treatment,
this simpler version of BNR would potentially exceed the target TN reduction goals. It is
noted that none of the process configurations modeled yielded low enough effluent TP
concentrations to meet the target of about 2 mg/L.
BOD TSS NH3 TKN Nitrite Nitrate TN TP
Scenario (mg/L (mg/L (mg/L (mg/L (mg/L (mg/L (mg/L m /L
Existing 3 Trains no BNR 6.6 13 7.5 11 28 8.5 47 5.3
3 Trains with Integral MLE 8.6 17 8.8 12 21 1.1 34 5.3
3 Trains with Upstream MLE 5.9 13 4.7 7.9 15 0.5 23 4.1
3 Trains with Upstream A2/0 6.4 16 13 16 7.2 0.2 23 3.3
4 Trains no BNR 6.1 13 0.1 3.3 0.2 44 48 5.3
4 Trains with Integral MLE 6.3 13 0.1 3.3 0.7 17 21 5.4
4 Trains with Upstream MLE 5.3 12 0.1 3.2 0.1 18 21 5.4
4 Trains with Upstream A2/0 5.4 16 0.3 3.4 6.9 3.3 14 4.1
Table 8 BNR Simulations for Future AWW Flows and Loads
3. Potential BNR Construction Issues
To implement BNR at the Dubuque W&RRC, additional tankage would be constructed upstream
of the existing HPO basins. For the purposes of this report, we have assumed the existing HPO
basins would remain and serve as aerobic stages. The new tanks would serve as the anaerobic
and anoxic zones (as required) in the BNR process. Because of the significant site constraints
and the underground piping and utilities near the existing HPO basins, we have assumed that the
new anaerobic and anoxic tankage would be constructed at the same location as the North
Equalization (EQ) Basin, which would be demolished. Construction in these areas would require
pipe relocations, utility relocations, and sheeting to avoid undermining existing tanks. This
assumption requires further evaluation prior to the design of any related improvements.
Construction of a fourth train of HPO basins would be extremely difficult on the existing site. A
fourth HPO train would be difficult to construct because of Julien Dubuque Drive to the north and
the railroad/access road to the south. These site constraints would increase the cost of a potential
fourth train significantly. If a fourth train is deemed required, and given the very large costs
associated with these upgrades, it may be more desirable to invest in a more conventional air
activated sludge system well into the future and negotiate a longer compliance schedule with
IDNR.
For the purpose of developing costs for this report, a fourth HPO train was assumed to be
constructed along with new anaerobic and anoxic tankage for the A2/O configuration. Schematics
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Dubuque Water and Resource Recovery Center, Dubuque, Iowa Nutrient Reduction Study
of the A2/O and MLE processes with external anaerobic/anoxic tankage and a fourth HPO train
are shown in Figures 7 and 8, respectively.
LEGEND Primary
Anaerobic Effluent
Anaerobic Anoxic E — — Recycle—
Aerobic Zone Zone T
Forward Flow RAS
Recycle i
i
i
Tra in 4(new) Train 3 Train 2 Train 1 i
i
7 6 Basin Z 6 Basin Z 6 Basin Z 6 Basin
i
i
8 5 2 8 5 2 8 5 2 8 5 2
i
i
9 4 3 9 4 3 9 4 3 9 4 3 i
i
- - - - - - - - - I - - - - - - - - - - I - - - - - - - - - - -Y- - - - - - - - - - - - y
Ne W Ne
Mixed Mixed Mixed Mixed
Liquor Liquor Liquor Liquor
Figure 7 A2/O Process Schematic with Fourth HPO Train
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Dubuque Water and Resource Recovery Center, Dubuque, Iowa Nutrient Reduction Study
LEGEND Primary
[ Anoxic Effluent Recycle
Aerobic 30 Anoxic Zone E — — — — — — — T
I
Forward Flow — — — —
RAS
Recycle
- - - -
I
I
I
Train 4(new) Train 3 Train 2 Train 1
I
6 Basin 7 6 Basin 7 6 Basin 7 6 Basin
1 � T 1 � T 1
I8 5 I2 I8 5 2I I8 5 I2 I8 5 I2
9 4 3 9 4 3 9 4 3 9 4 3
I
I I I I
- - - - - - - - - -- -
-YI - - - - - - - - - - - - - - - - - - - - - - -
Mixed Mixed Mixed Mixed
Liquor Liquor Liquor Liquor
Figure 8 MILE Process Schematic with Fourth HPO Train
B. Sidestream Nutrient Removal
Because of the significant recycle loadings at the Dubuque W&RRC, as well as the extreme difficulty in
expanding the activated sludge system for BNR operations, sidestream treatment for TN removal and TP
removal was evaluated. For the Dubuque W&RRC, sidestream treatment would involve removing TN
and/or TP from the dewatering centrate return flows. If successful, this nutrient load reduction to the
activated sludge operations would result in reduced oxygen requirements, reduced sludge production,
and lower effluent TN and TP concentrations. In addition, sidestream TP recovery could benefit the
digestion process by reducing soluble phosphorus and struvite formation within the digesters and
downstream of the digesters.
1. Sidestream Nitrogen Removal
For this option, the dewatering centrate would be treated in a two-step biological process
(Anammox). The first step is nitritation, which typically results in approximately 55 percent of the
influent ammonia being oxidized to nitrite by ammonia oxidizing bacteria (AOB). The second step
converts remaining ammonia and nitrite directly to nitrogen gas by anammox bacteria .
Two anammox technologies were evaluated for sidestream nitrogen treatment—ANITATI MOX and
DEMON. ANITATM MOX is a mixed bed biofilm reactor (MBBR) that uses plastic media on which
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the biofilm grows. The biofilm has two layers that contain each type of bacteria, and media is
retained in the reactor by screens. The DEMON system is a suspended growth sequencing batch
reactor (SBR) process that includes a cyclone separation system to concentrate anammox
bacteria for return to the reactor.
The existing centrate equalization tanks and centrate recycle pumps would be used to feed
centrate to the anammox process, and one of the existing WAS holding tanks would be converted
to the anammox reactor for both technologies. The aeration blowers and pumps would be housed
in Structure 75 adjacent to the anammox reactor. Alternatively, the existing blowers serving the
WAS storage tanks could potentially be used for the anammox process. Modifications to the WAS
holding tanks would be needed to separate the tanks and allow one of the tanks to continue
serving as a WAS storage tank while converting the other tank to the anammox process tank.
Covering the reactor tank is recommended for both processes to retain heat.
The process would be expected to remove approximately 80 percent of the total nitrogen from
the centrate return flow, which not only reduces the effluent TN concentrations, but also reduces
the oxygen demand required for nitrification in the HPO systems and results in marginally less
sludge.
2. Sidestream Phosphorus Removal
Sidestream P removal is based on harvesting struvite (magnesium ammonium phosphate) to
remove P from the centrate or from the digested sludge directly. Two systems were evaluated for
this report—Multiform Harvest, Inc. (MHI) and AirPrex. The MHI process includes treatment of the
dewatering centrate, while the AirPrex process includes treatment of the digested sludge itself.
The MHI process uses a fluidized bed reactor to achieve TP reductions. Caustic is used to
increase pH and magnesium chloride is added to form struvite pellets. Struvite pellets are
harvested from the reactor, screened, and discharged to a dewatering sack. MHI will pick up wet,
drained product and handle distribution and ultimate disposal. The reactor for this project is
approximately 8 feet in diameter and 20 feet tall, and additional space is required for the screen,
dewatering bag, and chemical storage tanks. It is recommended that the reactor be installed in a
building. The reactor may be able to be installed in the existing connector building between
Structure 75 and the Biosolids Loadout Building. Alternatively, a new building or building addition
may be needed to house the system, and this will be assumed for costing purposes in this report.
The AirPrex reactor is physically larger than the MHI reactor (13 feet in diameter and 40 feet tall)
and is typically installed outside. AirPrex uses air stripping to increase pH (no caustic) and then
adds magnesium chloride to form struvite. The struvite extracted from the reactor is then cleaned
and dewatered on-site using a sludge washing unit. The reported advantages to removing struvite
from digested sludge with the AirPrex process, compared to removing struvite from dewatering
centrate, include the following:
a. Struvite is removed prior to dewatering, which will reduce current struvite issues
with the centrifuges and downstream processes.
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b. AirPrex claims a 2 to 5 percent improvement in dewatered cake and provides a
process guarantee of 2 percent improvement.
c AirPrex claims a 15 to 30 percent reduction in polymer needed for dewatering and
provides a process guarantee of 15 percent reduction.
A small building is recommended to house the sludge extraction system, sludge washing unit,
blower, and auxiliary piping, and this building is often constructed around the bottom third of the
AirPrex reactor. On a conceptual basis, to avoid construction of additional storage tanks, the
AirPrex system could receive digested sludge from Digester No. 3 and then discharge the sludge
to Digester No. 4, which would act as storage prior to dewatering. Alternatively, it may also may
be possible to install the AirPrex system between Digester No. 2 (thermophilic) and Digester No.
3 (mesophilic), which would remove struvite from the sludge prior to the heat recovery heat
exchangers and improve the operation/reduce maintenance of the heat recovery system.
3. Modeling Results
Table 9 presents the modeling output for sidestream treatment for future AWW design flows.
Based on the model simulations, sidestream TN removal would reduce effluent TN concentrations
by approximately 20 percent and would also reduce effluent ammonia concentrations. Struvite
recovery would have a more significant impact on effluent TP concentrations and would be
expected to meet the target effluent TP concentration of less than 2 mg/L.
BOD TSS Ammonia TKN Nitrite Nitrate TN TP
Scenario (mg/L m /L) (mg/L (mg/L (mg/L (mg/L (mg/L (mg/L)
Existing 3-Train
HPO; No 6.6 13 7.5 11 28 8.5 47 5.3
Sidestream
Treatment
Existing 3-Train
HPO Plant with 6.6 12 0.2 3.3 4.6 30 38 5.2
Sidestream TN
Removal
Existing 3-Train
HPO Plant with 7.2 13 0.2 3.5 2 41 46 1.3
Sidestream TP
Removal
Table 9 Sidestream Treatment Impacts on Effluent Nutrients (Future AWW Conditions)
C. Chemical Phosphorus Removal (CPR)
CPR involves the addition of a metal salt(commonly an iron or aluminum salt) to flocculate and precipitate
soluble phosphorus in wastewater. The precipitated phosphorus is then removed during clarification
and/or filtration. CPR is a relatively simple and predictable process, especially for effluent targets in the
1 to 2 mg/L range. Jar testing with multiple CPR chemicals is often performed to determine the required
chemical dosages.
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There are several possible application points for CPR. At the W&RRC, the phosphorus removal chemical
could be added to the primary influent, aeration tanks, or final clarifier influent. Application upstream of
the primary clarifiers can provide additional primary removal of suspended solids and organic matter in
addition to phosphorus removal, which would reduce loadings to the activated sludge system, reduce
HPO and power costs, and result in additional digester gas production because of higher primary clarifier
TSS and BOD removal rates. However, because of the complex nature of the raw wastewater, higher
chemical dosages are typically required when added to the primary clarifier influent, and sludge
production can increase by more than 20 percent in such systems. Typically more than one application
point is provided for optimization and flexibility.
Several chemicals are available for CPR, but aluminum sulfate (alum) and ferric chloride are two of the
most commonly used. Alum is typically favored in soft water applications, while ferric chloride is used
more in hard water applications. Both chemicals can affect sludge thickening and dewaterability and can
also lower the pH of the wastewater. Sodium aluminate is also sometimes used for CPR and can be
useful when pH or alkalinity is low because it is a basic chemical. Other chemicals that may be used
include ferrous chloride, ferric or ferrous sulfate, polyaluminum chloride, and rare earth metals. For this
report, it was assumed that ferric chloride would be used for CPR. Jar tests and/or full scale tests should
be performed if the City elects to implement CPR to meet future effluent phosphorus limits.
D. Tertiary Denitrification
Denitrification filters convert nitrate to nitrogen gas with the addition of a carbon source. The filters
evaluated for this study are Blue NITE filters by Blue Water Technologies, which are continuous
backwash, upflow sand filters. A carbon source is dosed to the wastewater influent prior to entering the
sand filters. In this system,fixed-film heterotrophic bacteria convert nitrates to nitrogen gas. The proposed
location of the filters is downstream of the secondary clarifiers.
Additional changes in the W&RRC are required for this technology to be feasible. Specifically, the plant
would consistently need to nitrify in the upstream activated sludge process, which would require a fourth
HPO train to be constructed as noted previously. Given this significant requirement, and because the
anticipated cost of the tertiary denitrification filters is very high, it is more feasible to construct BNR
tankage upstream of the existing HPO basins than to construct denitrification filters at the end of the
W&RRC. This option would require CPR in addition to the nitrogen removal facilities, as well as a
secondary effluent pumping station to deliver wastewater to the filters, further increasing costs. For these
reasons, this alternative will not be considered further.
E. Sidestream/Mai nstream Bioaugmentation Processes
Bioaugmentation is a generic term that refers to several biological process modifications that are
designed to enhance the population of specific groups of bacteria to improve treatment. With reference
to wastewater treatment, and more specifically for this report, bioaugmentation refers to processed that
enhance nitrifier populations to improve nitrification, which can then provide improved TN removal. At the
Dubuque W&RRC, the likely bioaugmentation process would be a form of the BAR, AT#3, or BABE
processes. All of these processes would include separate aerobic treatment of centrate from the
dewatering operations. A portion or all of the RAS is directed to the centrate treatment tanks, resulting in
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higher populations of nitrifying bacteria in the mixed liquor of the centrate treatment tanks, which then
flow to the mainstream activated sludge tanks to improve nitrification rates.
Modeling of a modified BAR process at the Dubuque W&RRC indicated that nitrification efficiency could
be improved by converting one of the trains (actually less than one of the trains) to a bioaugmentation
process tank. However, because of the very high ammonia concentrations in the centrate, a significant
amount of alkalinity addition maybe required. Likewise if denitrification is included in the bioaugmentation
process to recover alkalinity, an external carbon source would be required to provide reasonable kinetics.
Bioaugmentation processes are not further reviewed within this high-level planning report. If future
nitrification limitations become apparent in the existing activated sludge process, bioaugmentation should
be considered for potential application.
F. Conventional Air Activated Sludge BNR Facilities
The 2008 Facilities Plan identified nutrient removal requirements as being likely within the 20-year
planning period. The plan also evaluated air activated sludge as an option to the existing HPO activated
sludge, in part because of the future requirements for nutrient removal. The decision was made to
continue with HPO and hauling liquid oxygen to the site, in part because of the high cost of constructing
conventional facilities as well as the unknown direction of nutrient removal requirement in the State of
Iowa at that time. The facilities plan cost opinion indicated that conventional air activated sludge facilities
for secondary treatment (no nutrient removal) would cost at least $6 million more than maintaining the
existing HPO facilities and operations.
The Dubuque W&RRC has some significant site constraints, which limit the ability to construct additional
processes and configurations on the site without expanding in a significant manner to the east of the
plant in the location of the City's existing softball fields (see Figure 9). Expansion into that area would
likely require additional pumping, and potentially completely revised secondary treatment facilities
because of the location of the existing aeration basins and final clarifiers on the existing site. Because of
constructability concerns and the need to maintain treatment during construction, one concept for
conventional air activated sludge BNR facilities is presented below:
1. The existing HPO basins would be converted to anaerobic and anoxic basins as they are
relatively shallow (- 12-foot SWD). These basins would have excess capacity for such
purposes.
2. A new ML pumping station would be constructed within one of the existing HPO basins to
pump ML to new aeration basins.
3. New aeration basins would be constructed on the new site (existing softball field area).
4. ML would flowfrom the newfacilities backto the existing site by gravityfor final clarification
and disinfection.
There is some potential that new conventional air activated sludge tankage could be constructed on the
existing site in a staged manner to maintain treatment. However, such a construction project would be
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Dubuque Water and Resource Recovery Center, Dubuque, Iowa Nutrient Reduction Study
extremely difficult, and we believe it is more prudent to assume construction on a new site for the
purposes of this report.
SUMMARY OF ALTERNATIVES
The preceding evaluations, with the exception of tertiary denitrification and bioaugmentation processes
(for the reasons previously indicated), are summarized in Table 10 and are shown generally on Figure 9.
No single alternative is anticipated to meet the effluent nutrient reduction goals alone. However, some of
the alternatives taken together would be expected to meet the long-term nutrient targets proposed by the
IDNR Nutrient Reduction Strategy(Table 10). In particular, sidestream TP and TN removal in conjunction
with the MLE process shows the potential to not only meet the nutrient targets but also to reduce
operating costs and maintenance concerns related to struvite formation in and downstream from the
digesters.
All costs were developed at a conceptual level for the purposes of this report, and a more detailed facilities
planning study would be required to fully define the specific aspects, components, capital costs, and
impact on O&M costs for all of the selected projects. Following is a list of our major assumptions and
alternative-specific considerations.
1. New BNR tankage would be constructed within the footprint of the existing north EQ tank,
which would be demolished.
2. A fourth HPO train would be constructed either in the footprint of the existing north EQ
tank or south of the existing HPO basins.
3. A new anammox process would use one of the existing WAS storage tanks as the
anammox reactor. The blowers, pumps, and controls associated with the process would
be housed in Structure 75. There is some potential that the existing Structure 10 blowers
could be used, but this was not assumed.
4. For both TN and TP sidestream removal processes, the existing centrate storage tank
would be used as the feed tank, and the existing centrate recycle pumps would be used
to feed the sidestream treatment process.
5. For the sidestream TN removal alternatives (anammox), a significant credit for future
avoided aeration costs would be realized. To achieve future TN targets using BNR
activated sludge, the W&RRC will need to nitrify and then denitrify. Implementing an
anammox process would reduce the ammonia loadings to the activated sludge facilities
and reduce overall oxygen demand.
6. For the AirPrex sidestream TP recovery system, it was assumed that the system would
be installed hydraulically between Digesters No. 2 (thermophilic) and No. 3 (mesophilic)
to reduce struvite concerns within the heat recovery system and in downstream digesters
and processes.
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Dubuque Water and Resource Recovery Center, Dubuque, Iowa Nutrient Reduction Study
7. For the AirPrex sidestream TP recovery system, annual O&M cost savings would be
realized for biosolids dewatering, polymer use, and disposal costs. In addition, no value
of the struvite was assumed in this analysis for the AirPrex system. The struvite crystals
would likely be mixed in with the dewatered cake and land-applied.
8. For the CPR alternative, the chemical storage and feed equipment would be housed in
the existing EQ recycle pump station building.
9. For the CPR alternative, sludge production was increased by approximately 20 percent
over existing quantities to account for the anticipated increase in chemical sludge.
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Dubuque Water and Resource Recovery Center, Dubuque, Iowa Nutrient Reduction Study
Figure 9 Alternatives Site Plan
:z Centrate Storage
:y Converted to
► • ► :~. Sidestream P or N Demolish North ED
• ► • ► s1. Removal ED Tank and Add External
' a[ ► Anaerobic/Anoxic
' ► ► Tankage
70 } 80 • ► • ► • Add Denitrification .
► • ► Filters and Secondary _
j 96 Effluent Pumping '
Install i Station ".
Airprex $
Reactor '' Y 93
20 20 38
13
Install MHI .x O 35 37 .
Reactor in
Passageway90 + 20 20 a 32 45 40 48 55 53 62
78 # 50 50 60
Install Blowers r
for Sidestream N
Removal +r` 10 92 47
Convert 1 WAS ' . . . . . . . . . I '
:+ Storage TanktoN
}: Removal Reactor `' ' Chemical Add Chemical
Chemical
Addition Point Storageand Addition Point g g 10—Screening Building and Grit Facilities
Pumpingto 20—Primary Clarifiers&Primary Sludge Pump Station
Existing Building 28—Primary Effluent Splitter Box
ALTERNATIVES 30—Excess Flow Equalization
32—Excess Flow Junction Box
Sidestream PRemoval 35—Excess Flow Drainage Pump Station
37—Aeration Tank Splitter Box
................................................................... 38—RAS Splitter Box
f Sidestream NRemoval 40—Aeration Tanks
45—HPO Control Building
Biolo ical Nutrient Removal 47—Liquid Oxygen Storage Tanks
48—Mixed Liquor Splitter Box
50—Final Clarifiers
:. Denitrification Filters 53—Final Clarifier Effluent Junction Box
'"""' """"' """"' S5—RAS Pump Station
Chemical Phosphorus Removal 60—Disinfection
62—UV Building
70—Anaerobic Digestion
75—Solids Processing Building
78—WAS Storage Tanks
80—Administration Building
90—Maintenance Building
92—Septage/Hauled Waste Receiving Station
93—Cold Storage Building
96—Transformer Containment
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Table 10 Alternatives Summary
Meet TN Meet TP Effluent Effluent Magnitude of Order
Goal? Goal? TN TP Capital Costs
Alternative (Y/N) (Y/N) ((m/L (m/L millions Notes
1. HPO Activated Sludge BNR
A. 3 Trains with Internal MLE Tankage N N 34 5.3 $1 .7
B. 3 Trains with External MLE Tankage N N 23 4.1 $3.9 Significant TN improvement over 3-train with internal MLE.
C. 3 Trains with External A2/0 Tankage N N 23 3.3 $4.8 Improved TP removal.
D. 4 Trains with Internal MLE Tankage N N 21 5.4 $6.7 Close to meeting TN target.
E. 4 Trains with External MLE Tankage N N 21 5.4 $8.5 No improvement over 4-train w/internal MLE.
F. 4 Trains with External A2/0 Tankage Y N 14 4.1 $9.7 Meets TN target; not TP target.
2. Sidestream TN Removal (Anammox)-Stand Alone N N 38 5.2 $6.1 About 20 percent TN reduction.
3. Sidestream TP removal (Struvite Recovery)-Stand Alone N Y 45 1.3 $3.9 Meets TP target; also improves struvite issues at W&RRC.
4. Chemical Phosphorus Removal N Y >50 < 1.0 $0.6 Only for TP removal.
5. Combined HPO Processes
A. 3 Trains with Internal MLE +Anammox Y N 17 5.0 $8.6 Reduced recycle NH3 loads allows existing HPO volume to meet TN target.
B. 3 Trains with External MLE +Anammox Y N 18 4.2 $10.9 No real benefit over using existing HPO basins only.
C. 3 Trains with External A2/0 + Struvite Recovery N Y 29 0.5 $8.7 Could meet < 1.0 mg/L TP target.
D. 3 Trains with Internal MLE +Anammox + Struvite Recovery Y Y 15 0.5 $12.5 Meets both targets.
E. 4 Trains with External A2/0 + Struvite Recovery Y Y 13 0.6 $13.5 Meets both targets.
6. Conventional Air-Activated Sludge Y Y < 18 < 2 >$20 Would be designed to meet both targets; requires pump station and new site
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Dubuque Water and Resource Recovery Center, Dubuque, Iowa Nutrient Reduction Study
RECOMMENDED STRATEGY AND BUDGETARY CONSIDERATIONS
Because of the site constraints and difficulty and cost of constructing new conventional air activated
sludge facilities while maintaining current operations, the strategy developed for the City focuses on a
phased approach to meeting the nutrient targets over time. In addition, the City has committed significant
funds towards water quantity and quality projects as noted below:
• W&RRC Upgrades: $68 million (completed 2015)
• Lower Bee Branch: $22 million (completed 2011)
• Upper Bee Branch: $65 million (anticipated completion 2016)
• Sanitary Sewer I/I Reduction: $10 million (next five years)
• Green Alley Infiltration Projects: $33 million (through 2033)
Because of the significant capital funds already planned and committed towards improving water quality,
a phased approach is appropriate to reduce the financial burden on the City's rate payers in the near
future. The following approach is presented for the Department's consideration. This approach includes
a phased approach to implement Alternative 5.D (refer to Table 10) over an approximate 15-year period.
The projects are included as short-term (<3 years), mid-term (within 6 years), and long-term (within
15 years) projects. The City's fiscal year (FY) runs from July 1 through June 30, and the date noted is
the end of the fiscal year (i.e., FY 2017 ends on June 30, 2017).
A. Short-Term Recommendations—Demonstrate and Implement MILE
Short-term recommendations could be initiated soon and should be completed within 5 years as these
recommendations will assist in evaluating the modeling assumptions and actual field performance of the
existing HPO facilities. It is critical that some of the assumptions associated with the HPO system be
verified:
1. [FY 2016 - $0] Investigate the ability of the existing HPO system to nitrify and partially
denitrify under current flows and loadings. This would include operating all three HPO
trains to improve nitrification and then significantly reduce the speed of (or completely shut
off)the first-stage mixer in one of the HPO trains to mimic an anoxic zone for denitrification
of the RAS only. This would also require the relocation of the oxygen feed line from basin 1
to basin 2 in that HPO train. If this test appeared to be successful, the top surface mixer
blades could be removed from the first-stage mixer to improve anoxic zone mixing. In
addition, the basin 1 mixer could potentially be moved to basin 2 in each train to provide
additional aeration horsepower, and the mixer from basin 2 could be moved to basin 1 to
serve as the anoxic mixer.
2. [FY 2017-$50,000]Assuming Task 1 is successful and significant nitrification is achieved,
install a ML recycle pump at the end of the same HPO train to return nitrate to the anoxic
zone to achieve additional denitrification. A temporary pumping and force main system
could be installed to investigate the viability of this process modification.
3. [FY 2018-$70,000] Assuming success in Tasks 1 and 2, proceed with design engineering
to install similar permanent facilities for all three of the activated sludge basins.
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4. [FY 2019 - $780,0001 Begin three year process of installing permanent facilities for all
three basins.
5. [FY 2020-$425,000] Continue MLE process installation.
6. [FY 2021-$425,000] Complete MLE process installation.
B. Mid-Term Recommendations-Implement Struvite Recovery
These recommendations have a relatively high cost to implement at the plant and are therefore moved
further into the future. However, the recommendations are also expected to have a net benefit beyond
simply nutrient reductions, especially related to struvite concerns at the W&RRC. It is anticipated that this
major task will achieve the target effluent TP concentration of < 2.0 mg/L. The opinion of capital costs
associated with the struvite recovery system is $3.9 million (2015 dollars) and is recommended to be
budgeted in FY 2023 - 2024.
C. Long-Term Recommendations-Implement Sidestream Annamox
The last phase required to meet the target effluent nutrient concentrations would be to implement
anammox treatment of the centrate recycle flows to achieve additional TN reductions. This process would
have the added benefit of reducing aeration demands and associated power and oxygen purchase costs
related to ammonia oxidation in the HPO facilities. The opinion of capital costs associated with the
anammox system installation is $6.1 million (2015 dollars) and is recommended to be budgeted in about
FY 2030.
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Water & Resource Recovery Center
Nutrient Reduction Strategy
City of Dubuque Council Meeting
September 8, 2015
Wastewater Treatment & Watershed Approaches
Source: Alexander et al. 2008
Dubuque’s Nutrient Reduction Planning
Dubuque W&RRC Recent History
2007 - Planning Started
- Iowa DNR contacted to determine direction and
timing related to nutrient regulations
- Decision made – do not include
nutrient removal
2008 - Facilities Plan Approved
2010 - Design Complete (Main Upgrade)
2010 - 2013 Construction of Main Upgrade
2013 - 2014 Construction of Cogeneration
October 2013: New NPDES Permit with Nutrient Requirements
Dubuque Nutrient Decision (2008)
Why wasn’t nutrient removal part of the recent upgrades?
1.In 2007-2008, DNR’s timing and direction
was unknown; no plans to develop rules;
likely 15-20 years before upgrades would
be needed.
2.Specific processes at the existing W&RRC
were not simple to upgrade for nutrient
removal; nutrient removal would have
added >$15 million to the project.
3.Decision was made to spend as little as
possible on the activated sludge facilities.
NPDES Permit Begins the Nutrient Journey
Nutrient Study (2 Yrs)
Planning & Budgeting
(0-10 Yrs, or more)
Design & Construction (1-2 Years)
Start-Up and Optimization
(18 months)
NPDES Permit Issued
October 1, 2013 Final Limits
Established
To Be Proposed by Permittee
& Negotiated with DNR
Study Deadline is
October 1, 2015
Nutrient Reduction Study Followed
a Logical Progression
Facility Characterization
Operation Evaluation
Technology Evaluation
Watershed Considerations
Recommendations and Implementation
Nutrient Concentration Targets
Phosphorus
(mg/L)
Nitrogen
(mg/L)
Average Influent 8.0 55
Current Avg.
Effluent 4.4 54
Calculated Target 2.0 18
“Standard” Limit 1.0 10
Modeling Results – 3 vs. 4 Trains
Scenario NH3
(mg/L)
TN
(mg/L)
TP
(mg/L)
Existing 3 Trains (no BNR) 7.5 47 5.3
3 Trains w/ Integral MLE 8.8 34 5.3
3 Trains w/ Upstream MLE 4.7 23 4.1
3 Trains w/ Upstream A2 /O 13 23 3.3
Scenario NH3
(mg/L)
TN
(mg/L)
TP
(mg/L)
4 Trains (no BNR) 0.1 48 5.3
4 Trains w/ Integral MLE 0.1 21 5.4
4 Trains w/ Upstream MLE 0.1 21 5.4
4 Trains w/ Upstream A2 /O 0.3 14 4.1
Combinations of BNR + Sidestream
Scenario TN
(mg/L)
TP
(mg/L)
3-Train Integral MLE + Anammox
17
5.0
3-Train External MLE + Anammox
18
4.2
3-Train Integral MLE + Anammox + Struvite
15
0.5
3-Train External A2/O + Struvite Recovery
29
0.5
4-Train External A2/O + Struvite Recovery
13
0.6
Combinations of BNR + Sidestream
Scenario Capital Cost
(millions)
3-Train Integral MLE + Anammox
$7.2
3-Train External MLE + Anammox
$8.5
3-Train Integral MLE + Anammox + Struvite Recovery
$10.8
3-Train External A2/O + Struvite Recovery
$7.2
4-Train External A2/O + Struvite Recovery
$12.5
Note: Converting to BNR Air Activated Sludge ~ $15-$20 million
Phased Implementation Plan Will Need to
be Negotiated with DNR
Nutrient Removal Step
Cost
($)
Preliminary
Timing
Test MLE Concept (Actually A/O Process) ~$0 FY16
Implement MLE - Full-Scale Pilot on 1 Train $50,000 FY17
Full-Scale MLE -Design $70,000 FY18
Full-Scale MLE, Year 1 Construction $780,000 FY19
Full-Scale MLE, Year 2 Construction $425,000 FY20
Full-Scale MLE, Year 3 Construction (complete) $425,000 FY21
Struvite Recovery Facilities $3.9 million FY23-24
Anammox Facilities $6.1 million FY30 (+/-)
Implementation
Anammox
Tankage
Struvite Recovery
Modify Existing
Tanks for MLE
Questions and Answers