Update on Water & Resource Recovery Center (W&RRC) Odor Abatement Efforts Copyrighted
August 7, 2023
City of Dubuque Action Items # 05.
City Council Meeting
ITEM TITLE: Update on Water& Resource Recovery Center(W&RRC) Odor
Abatement Efforts
SUM MARY: City Manager is providing an update on odor abatement efforts at the
Water& Resource Recovery Center.
SUGGESTED Suggested Disposition: Receive and File
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 W&RRC Odor Abatement Efforts
DATE: August 2, 2023
Water & Resource Recover Center Manager William O'Brien is providing an update on
odor abatement 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 W&RRC Odor Abatement Efforts
DATE: August 2, 2023
INTRODUCTION: The purpose of this memo is to provide an update on odor abatement
efforts at the Water & Resource Recovery Center.
BACKGROUND: The Water & Resource Recovery Center (W&RRC) uses numerous
processes to treat raw wastewater, resulting in treated effluent that is then safely released
to the environment. Some of the treatment processes used, unfortunately, can produce
undesirable odors. While some level of odor is to be expected in a wastewater treatment
facility, odors at the W&RRC have increased notably over the past few years.
W&RRC staff investigated the sources of the odors and identified parts of the treatment
system that are likely responsible. The processes likely most responsible for the odors,
listed from most significant to least significant, are primary clarification, raw influent (sulfides
produced under low oxygen conditions in long forcemain/pressurized sewers), blended
sludge storage, waste activated sludge storage, and anaerobic digestion.
Wastewater received at the W&RRC contains pollutant concentrations that are higher than
domestic strength. Due to the success of some local food manufacturers, our system
receives an elevated concentration of sulfur, nitrogen, and phosphorus. Sulfur, under
anaerobic conditions, is converted into sulfide, and other odor-producing compounds.
Phosphorus and nitrogen combine with magnesium to create a mineralization (struvite) in
several process areas, reducing efficiencies, and resulting in additional maintenance.
W&RRC staff identified methods to reduce the hydrogen sulfide production and struvite
formation. The process includes injecting hydrogen peroxide, into the wastewater, at
strategic locations in the treatment system. Future treatment may include injecting iron salts
(ferric or ferrous chloride) into the anaerobic digesters to further reduce hydrogen sulfide
production, and the formation of struvite.
DISCUSSION: The City of Dubuque selected USP Technologies (USP) to provide
chemicals and technical expertise for odor reduction measures at the W&RRC. The
company is a leading provider of peroxygen-based technologies and full-service chemical
treatment programs for municipal and industrial water and wastewater treatment
applications and has extensive experience in liquid phase treatment for odor control. The
company provides services in their Midwest Territory (includes Dubuque) through staff in
Davenport, lowa.
The agreement, with USP, provides the following:
• bulk deliveries of iron, and bulk and/or tote deliveries of hydrogen peroxide
• the installation and use of up to three (3) dosing systems
• a bulk storage tank for hydrogen peroxide
• Hydrogen sulfide monitoring services
• applications support through the course of the project
• a summary report/presentation of findings with recommendations
• Chemical safety training for designated personnel
Odor mitigation efforts at the W&RRC began with a consultation, in which City staff met with
USP staff to discuss treatment objectives, suspected locations of odor release, treatment
facility design and wastewater characteristics. The initial consultation was followed by
bench testing of wastewater, from several process locations, to determine the extent of
sulfide removal at varying reaction times and dose ratios. Bench testing was conducted,
with multiple chemicals, to identify which chemicals would likely provide the most efficient
and cost-effective odor reduction.
Hydrogen peroxide was selected, based on cost, availability, and handling considerations,
for initial chemical dosing. On the morning of August 31, we began injecting hydrogen
peroxide, into the headworks (location where wastewater enters the facility), at a rate of 4
gallons per hour. Since initiating the chemical feed, we have experienced a considerable
reduction in the concentration of hydrogen sulfide emanating from the headworks, and from
the influent to the primary clarifier complex. USP staff will conduct a site visit tomorrow
(August, 3�d) to make any necessary chemical adjustments, collect data, and to provide staff
training on exchange of chemical totes.
Further odor reduction work will include a site visit from a USP wastewater treatment
specialist. The specialist will conduct additional, and more extensive, testing of multiple
wastewater process streams, to identify opportunities for treatment optimization, and ideal
locations for additional chemical injection. Data collected during this visit will be used to
inform further treatment decisions.
Ongoing odor reduction efforts include the following:
• Deployment of additional chemical feed systems as necessary to achieve sufficient
odor reduction
• Optimization of chemical dosing, including adjustments in feed rate and timing
(potential for flow paced chemical injection when warranted)
• Identifying opportunities for additional odor reduction in vapor phase (treatment of air
emanating from treatment processes)
• Identification of additional capital improvement funding needs (if capital needs
exceed the existing capital budget)
CONCLUSION: Additional details will be provided following USP consultation and
partnership. Our ongoing odor reduction work will include regular updates on the
effectiveness of chemical treatment, estimates of ongoing treatment costs,
recommendations for additional equipment or services, and requests for additional funding if
needed.
ACTION REQUIRED: This memorandum is intended for informational purposes.
Cc: Cori Burbach, Assistant City Manager