Update on Water & Resource Recovery Center Odor Abatement EffortsCity of Dubuque
City Council Meeting
Action Items # 01.
Copyrighted
July 5, 2023
ITEM TITLE: Update on Water & Resource Recovery Center Odor Abatement Efforts
SUMMARY: City Manager 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
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TO: The Honorable Mayor and City Council Members
FROM: Michael C. Van Milligen, City Manager
SUBJECT: Update on Water & Resource Recovery Center Odor Abatement Efforts
DATE: June 29, 2023
Water & Resource Recovery 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
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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: June 29, 2023
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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 physical,
biological, and chemical processes to remove up to 98% of incoming organic pollutants.
Primary and secondary sludges produced during treatment are blended with high -strength
organic wastes and treated by anaerobic digestion. The anaerobic digestion process
stabilizes the sludge by converting volatile organic material into biogas.
The biogas produced at the Center is 68 — 70% methane, and 30% carbon dioxide, with
traces of additional gasses, such as hydrogen sulfide, mercaptans, amines and siloxanes.
While not harmful in low concentrations, hydrogen sulfide, mercaptans, and amines can
produce significant odors.
While some level of odor is to be expected in a wastewater treatment facility, odors at the
W&RRC have increased significantly over the past few years.
After investigating sources of odor, W&RRC staff identified points in the process that are
most likely the main contributors. The processes likely most responsible for the odors, listed
from most significant to least significant, are blended sludge storage, primary clarification
(sulfides produced under low oxygen conditions in long forcemains /pressurized sewers),
waste activated sludge storage, and anaerobic digestion.
Wastewater received at the W&RRC contains pollutant concentrations that are higher than
what is considered domestic strength. Due to the success of several local food
manufacturers, our system receives a higher than domestic level of sulfur, nitrogen, and
phosphorus. Sulfur is converted, under anaerobic conditions, into sulfides, 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.
The mineralization occurs in several locations, although most significantly in the heat
exchangers that are used to cool thermophilic sludge (131 °F) to the mesophilic range
(95°F). Due to the mineralization, the heat exchangers are unable to effectively cool the
sludge, resulting in a higher -than -desired sludge temperature in the mesophilic digesters.
The mesophilic digesters utilize floating covers, designed for biogas storage, and are likely
emitting a higher concentration of odorous compounds (from the exposed sludge between
the cover and tank wall) due to the warmer sludge.
W&RRC staff identified a possible solution to combat the mineralization and hydrogen
sulfide concentrations. The solution includes dosing ferric chloride (iron salt) into the
anaerobic digesters to bind sulfur and phosphorus, reducing the hydrogen sulfide level, and
mineralization.
DISCUSSION: W&RRC staff searched for vendors capable of providing both chemicals and
technical expertise necessary for the implementation of odor mitigation systems. Several
vendors were able to provide chemicals, although USP Technologies was selected based
on their ability to provide both chemicals and technical expertise necessary for the project.
The initial proposal provided by USP Technologies contained terms and conditions that
were unacceptable to the City. The City proposed amendments to the terms and conditions.
These amendments were not immediately accepted by USP Technologies. After additional
meetings and further discussion, between the City and the vendor, the vendor was able to
escalate the City proposed amendments, for final approval.
We have executed an agreement, with USP Technologies, which will provide chemicals and
technical services, for odor reduction measures at the W&RRC. The agreement provides
per gallon chemical pricing which includes technical services. Based on assumptions, from
initial testing, we are issuing a purchase order, in the amount of $50,000.00, to USP
Technologies. Data collected during initial testing will be used to refine cost projections, and
to request additional funds if necessary.
For the project, USP will provide:
• 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
• 1-12S monitoring services
• applications support through the course of the trial
• a summary report/presentation of findings with recommendations
• Chemical safety training for designated personnel
Further development of the W&RRC odor mitigation strategy will be informed by data
collected, and reductions achieved, through the initial odor reduction project.
ACTION REQUIRED: This memorandum is intended for informational purposes.
Cc: Cori Burbach, Assistant City Manager