Water & Resource Recovery Center Odor Reduction Update Copyrighted
February 6, 2023
City of Dubuque Action Items # 010.
City Council Meeting
ITEM TITLE: Water& Resource Recovery Center Odor Reduction Update
SUM MARY: City Manager providing an update on odor reduction efforts at the Water
& Resource Recovery Center.
SUGGESTED Receive and File; Presentation Suggested Disposition:
DISPOSITION:
ATTACHMENTS:
Description Type
MVM Memo City Manager Memo
Staff Memo Staff Memo
Dubuque
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TO: The Honorable Mayor and City Council Members
FROM: Michael C. Van Milligen, City Manager
SUBJECT: Update on Odor Reduction Efforts
DATE: February 1, 2023
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
Dubuque
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TO: Michael C. Van Milligen, City Manager
FROM: William O'Brien, W&RRC Manager
SUBJECT: Update on Odor Reduction Efforts
DATE: January 31, 2023
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 residential, commercial, and industrial
growth through the year 2030.
The project updated virtually every part of the existing 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.
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.
Anaerobic digestion (a natural, biological process) has been used for decades to
stabilize solids prior to land application. In addition to the stabilization of solids, this
process produces biogas. The biogas is either collected and burned to heat process
water, supplied to microturbines for the cogeneration of electricity and heat, or is
upgraded to renewable natural gas, and injected into the local natural gas pipeline.
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 through wastewater treatment), the City investigated
opportunities to capitalize on the recent investment in anaerobic digestion by providing
a local disposal point for high-strength organic waste. After reaching out to several local
industries, the City soon discovered that some locally produced high-strength organic
wastes were being transported up to several hundred miles from Dubuque, at significant
financial and environmental costs.
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 nearly $2 million, in revenue, to the sanitary sewer fund. In addition to
providing a revenue stream, co-digestion has reduced waste disposal costs for local
industries, and has allowed the city to produce additional biogas that can further reduce
the overall cost of wastewater treatment.
DISCUSSION: The anaerobic digestion process provides financial and environmental
benefits, and unfortunately provides conditions to produce odorous compounds such as
hydrogen sulfide. In the anaerobic digestion process, sulfur reducing bacteria break
down sulfur compounds (mainly sulfate) in wastewater, and produce hydrogen sulfide,
and other odorous sulfur compounds, in the process. 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:
• 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. The opinion
of probable construction costs (OPCC) will be presented at the 90% design
review meeting (February 2023).
• Investigating the sources of sulfur (which can be broken down into hydrogen
sulfide), including contributions from domestic wastewater, industrial wastewater,
hauled wastes, and sulfur that naturally occurs in the drinking water supply.
• Investigating the impact of physical sewer infrastructure on the conversion of
oxidized sulfur compounds (e.g., sulfate) to reduced sulfur compounds such as
hydrogen sulfide.
• In Summer 2022, we 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 sulfides). Unfortunately, commodity level iron salts (a
byproduct of steel pickling) were not accessible at that time, although the City
may have been able to access a manufactured iron salt at a cost of around
$600,000 per year (cost could be more or less depending on observed reduction
in sulfides).
• In December 2022, a vendor conducted on-site "jar testing" of several odor
reduction chemicals, for the reduction of purgeable (gases releasing from liquid)
hydrogen sulfide. Tests were conducted on raw wastewater influent, primary
wastewater effluent, and blended sludge. Chemicals tested included ferric
chloride, ferrous chloride, hydrogen peroxide, potassium permanganate, and
magnesium hydroxide. Initial testing indicated both ferrous chloride and hydrogen
peroxide may provide the most cost-effective reduction of hydrogen sulfide in
both the raw wastewater influent, and blended sludge.
• We continue to work with consultants to further expand our understanding of
odor production and to provide continued guidance on odor mitigation.
Ongoing odor mitigation efforts will include the following actions:
• Completion of design for high-strength waste improvements this spring. Bid
project in late spring/summer 2023. Construction of project could begin as early
as fall of 2023 (project completion dependent on lead time for critical
components).
• Continuation of work with consultants to further develop understanding of odor
production and odor mitigation options.
• Pilot testing of hydrogen peroxide, and/or ferrous chloride in raw wastewater
influent, and blended sludge.
• Identification of odor reduction expenses (operating and capital improvement) for
inclusion in future budget requests.
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: Odor reduction efforts will be implemented within the existing FY23,
and proposed FY24 sanitary sewer budgets.
Cc: Crenna Brumwell, City Attorney
Cori Burbach, Assistant City Manager