Update on Odor Reduction EffortsCopyrighted
October 17, 2022
City of Dubuque Action Items # 02.
City Council Meeting
ITEM TITLE: Update on Odor Reduction Efforts
SUMMARY: City Manager providing an update on order reduction efforts at the Water
& Resource Recovery Center.
SUGGESTED Suggested Disposition: Receive and File
DISPOSITION:
ATTACHMENTS:
Description Type
Water & Resource Recovery Center Odor Reduction City Manager Memo
Update-MVM Memo
Staff Memo Staff Memo
THE C
DUjIBQTE
Masterpiece on the Mississippi
TO: The Honorable Mayor and City Council Members
FROM: Michael C. Van Milligen, City Manager
SUBJECT: Update on Odor Reduction Efforts
DATE: October 12, 2022
Dubuque
WAWca 914
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2007-2012.2013
2017*2019
Water & Resource Recovery Center Manager William O'Brien is providing an update on
odor reduction efforts at the Water & Resource Recovery Center.
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Mic ael C. Van Milligen
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Attachment
CC' Crenna Brumwell, City Attorney
Cori Burbach, Assistant City Manager
William O'Brien, Water & Resource Recovery Center Manager
THE CITYF
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Masterpiece on the Mississippi
TO: Michael C. Van Milligen, City Manager
FROM: William O'Brien, W&RRC Manager
SUBJECT: Update on Odor Reduction Efforts
DATE: October 13, 2022
Dubuque
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2007-2012.2013
2017*2019
INTRODUCTION: The purpose of this memo is to provide an update on odor reduction
efforts at the Water & Resource Recovery Center.
BACKGROUND: Dubuque's Water & Resource Recovery Center (WRRC), the City's
wastewater treatment facility located on Julien Dubuque Drive, underwent a nearly $70
million facility upgrade that was completed in 2013. Planning efforts, for the
improvement, began in the early to mid-2000s, culminating with the completion of a
Facility Plan, in May of 2008. This major overhaul was needed to bring the aging facility
up to current standards, and to accommodate projected residential, commercial, and
industrial growth through the year 2030.
The renovation modernized nearly every segment of the facility and included several
major process changes. Following global trends toward resource recovery, the City
chose to approach wastewater treatment obligations as an opportunity to reduce energy
use, and to harvest valuable resources such as water, nutrients, and biogas.
During the planning phase, the City examined seven different solids management
alternatives, including the continuation of solids incineration. Based on the economic,
nonmonetary, and environmental comparisons of the residuals management
alternatives, the City selected anaerobic digestion with agricultural land application.
With the move away from incineration, the facility was reclassified from a major source
of air emissions to a minor source of air emissions.
Anaerobic digestion has been used for decades to stabilize solids prior to land
application. In addition to the stabilization of solids, this process produces biogas, which
can be collected and burned to provide heat for boilers, fuel for the cogeneration of
electricity and heat, or, with some additional processing, can be upgraded to renewable
natural gas.
After the City's anaerobic digesters became operational in 2012, it soon became
apparent that the system was performing quite well and retained significant digestion
capacity for future growth. After gaining some experience with the digestion process
and following industry trends toward co -digestion (digestion of high -strength organic
wastes with solids recovered during wastewater treatment), the City began identifying
opportunities to capitalize on the recent facility investment by providing a local disposal
point for high -strength organic waste. After reaching out to several local industries, the
City discovered some locally produced, high -strength organic wastes were transported
up to several hundred miles from Dubuque, for disposal, diverting financial resources
from the local economy, and increasing air emissions produced during the transport of
these wastes.
In 2013 the Water & Resource Recovery Center began co -digesting locally produced,
high -strength organic wastes, with wastewater treatment solids. To date, this service
has provided over $1.9 million, in revenue, to the sanitary sewer fund. In addition to
providing a revenue stream from tipping fees, co -digestion has reduced waste disposal
costs for local industries, and has increased biogas production, both of which reduce
the overall cost of wastewater treatment.
DISCUSSION: The anaerobic digestion process provides financial and environmental
benefits and provides conditions that can allow the production of odorous compounds.
In the digestion process, sulfur reducing bacteria can break down sulfur compounds
(mainly sulfate) in wastewater, and produce hydrogen sulfide (rotten egg odor), and
other odorous sulfur compounds. The production of sulfur compounds can vary over
time, with changes in wastewater characteristics, and can occur anywhere in the
treatment process where low or zero oxygen conditions exist.
Over the past few years, the Water & Resource Recovery Center has received an
increasing number of odor complaints. To address the increase in odors emanating
from the Water & Resource Recovery Center, the City has taken, and continues to take
the following actions:
We are currently working with consulting engineers to design improved high -
strength waste receiving and handling facilities. This project will provide
dedicated storage tanks, which will reduce the production of odorous compounds
by isolating high- strength waste from wastewater treatment solids prior to
digestion. This project will also allow high -strength waste to be routed to any of
the four existing digesters, resulting in improved digestion process control.
• We are working with our land application contractor and state regulators to
assess the potential impacts of a transition from temperature phased anaerobic
digestion (TPAD) to pure mesophilic digestion. Reduced digestion temperatures
can reduce the production of odorous compounds and may result in additional
improvements in dewatering efficiency and reduced mineral scale.
We have investigated adding iron salts (ferrous chloride or ferric chloride) to the
digestion process. The addition of iron salts would bind sulfur and reduce the
production of odorous sulfides. Unfortunately, commodity level iron salts (a
byproduct of steel pickling) are currently in short supply. The City may be able to
access a manufactured iron salt at a cost of around $600,000 per year (cost
could be more or less depending on necessary dosing required to achieve the
desired reduction in sulfides).
• We are working with Blackstone Environmental (the City's on -call environmental
consultants selected through the City's RFP process), and Strand Associates
(designers of the facility upgrade) to refine the scope of services for an
assessment of odors in and around the facility, which will then be used to
prepare a report summarizing the data, concerns, and recommended solutions.
The sanitary sewer fund budget does not explicitly identify funding, in the current fiscal
year, for odor assessment consulting fees, or for the addition of iron salts. As the City
works to close out fiscal year 2022, we are examining the availability of unspent
operating funds that may be allocated toward odor mitigation efforts.
Ongoing odor mitigation efforts include:
• Completion of design for high -strength waste improvements this winter. Bid
project in late winter/spring 2023. Construction of project expected to begin in fall
of 2023 (project completion dependent on lead time for critical components).
• Working with consultants to further develop understanding of odor production
and odor mitigation options.
• Identify odor reduction expenses (operating and capital improvement) for
inclusion in the Fiscal Year 2024 budget request.
• Continue monitoring the availability of iron salts for chemical dosing once
affordable and acquirable.
The City is working toward finalizing a request for proposals (RFP), for a Sanitary Sewer
Asset Master Plan, which will examine the condition of current sanitary sewer collection,
conveyance, and treatment infrastructure. Information gathered in this planning effort
will be used to inform future improvements to the City's sanitary sewer infrastructure,
including the Water & Resource Recovery Center.
BUDGET IMPACT: City staff are reviewing the availability of unspent FY22 Operating
Expense Funds for allocation toward odor mitigation efforts. Sanitary sewer fund
operating expenses must conform with bond covenant requirements.
Cc: Crenna Brumwell, City Attorney
Cori Burbach, Assistant City Manager