HomeMy WebLinkAbout2023-10-23 Odor Control Study Presentation CITY OF
TWIN IFALIS Date: Monday, October 23, 2023
_ To: Honorable Mayor and City Council
°4 oQv From: Nathan Erickson, Environmental Manager
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PRESENTATION
Request:
Odor control study update.
Time Estimate:
Staff estimates 30 minutes to make the presentation.
Background:
On April 3, 2023, the Council was presented with the results from the 2022 odor control study for which
the City had contracted Consor Engineering. That study identified the next steps to be taken along with a
request for continued funding to work with Consor Engineering and money to fund a mobile odor
scrubber with associated expenses. It has been almost seven months since the April 2023 presentation to
the Council, and we would like to share a current update on the data collected during the summer,
improvements from the previous year, and information on potential options to mitigate odors.
The next steps identified in the 2022 odor control study included the following:
1. Point source management: As point sources that contribute hydrogen sulfide (H2S) to the system
have been identified, the City meets monthly with each point source to review the most current
H2S data. These meetings provide an opportunity to discuss the current odor situation and
suspected impacts traced back to the specific point source and efforts made by both parties to
address odor issues.
2. Local limit: In May of 2023, the City received a violation from the Idaho Department of
Environmental Quality stating that the City "must take immediate action to reduce concentrations
of H2S in the sewer system to levels that are protective of worker and public safety and health"
and "must develop local limits to control H2S generation in the sewer". The City has been keeping
IDEA apprised of the efforts underway with the odor control study. The measurement of H2S in
the sewer as a gas is variable and problematic, and the City has concerns about setting a local limit
when the ability to measure is so inconsistent. However, in August 2023, a new sensor became
available from the Hach Company that will measure H2S in the liquid phase (see attached Hach
Brochure). City staff are optimistic that collecting H2S data in the liquid phase will help further
pinpoint sources of H2S and lead to resolving point source contributions. With some of the money
approved in April, the City was able to purchase five sensors that should be here in the first part of
November.
3. Vapor phase treatment: With the funding approved by the Council in April 2022, the City
purchased a trailer-mounted mobile odor scrubber and started using it on July 11, 2023. The odor
scrubber has been used at two different locations in the City, and overall, the results and feedback
from the community have been very positive. With the H2S data that has been collected and the
odor reports from the community, the conclusion is that the carbon-based odor scrubber is
successful at removing H2S and significantly reducing odor reports.
4. Engineering, design, and construction next steps: With the positive results of the mobile odor
scrubber, City staff are exploring options available to install a permanent odor scrubber. The odor
scrubber would be designed to pull odorous air from the sewer collection system, treat it similarly
to the mobile odor scrubber, and discharge treated air to the surrounding atmosphere.
5. Rehabilitation of manholes: In 2022, wastewater collections applied a protective lining to eight
manholes. Wastewater collections will have future requests to fund projects to line manholes.
Approval Process:
No approval is requested at this time.
Budget Impact:
Regulatory Impact:
The odor control study allows the City to continue to partner with point sources to understand better the
causes and options available to address the odor problems. They will also help meet Strategic Plan
Objectives EC1.4.3 "The City will continue to monitor collection systems for odors and mitigate through
infrastructure improvements..." and EC1.4.4 "The City will explore creating standards for monitoring air
quality particulate saturation and associated enforcement policies."
History:
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Analysis:
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Conclusion:
Based on the findings of the odor control study, City Staff is confident that the City, together with point
sources, has successfully decreased the amount of H2S in the sewer. The study suggests that the City can
take further steps to mitigate odors, which are crucial for safeguarding the health and safety of the
community and protecting the sewer system from H2S-induced damage.
Attachments:
1. Hach Brochure
Gas vs. Liquid H2S Measurement
Be RightTm New sensor provides better
H2S insights in sewer networks
Problem Solution Benefits
In order to properly manage their By continuously measuring H,S Complete and dynamic overview of
assets and operations, water utilities directly in orjust above untreated H,S challenge.
need to fully understand how H,S wastewater with Hach H2S sensors, Proactive and data-driven approach
impacts their sewer network. This operators can make decisions on the to H2S management.
requires a precise understanding of basis of real-time data throughout the Real-time data in SCADA& cloud.
how H2S behaves across different collection system. Reliable monitoring unaffected by
locations for extended periods of time. external factors.
• Uninterrupted measurements.
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Background Corrosion 25+202 H2504
The toxic,foul-smelling,and highly corrosive gas hydrogen sulfide R
(H,S)poses a major challenge to wastewater utilities. HZS is oAg)
formed when wastewater is pumped through force mains,and H2S
induced odor and corrosion issues are commonly found in
hotspots right after the discharge into the gravitational sewer Acidic H,s„
system. Here, part of the dissolved H,S is released into the air, F Biofilm
while another part remains in the sewage,where it is transported Air
further downstream in the network if left untreated.
Challenge Water H,s„a,-HS-+H'
g Organic
Wastewater utilities typically use gas loggers to monitor H2S Carbon
concentration changes in the diluted air below manhole covers. SOa co, Anerobic Biofilm
However,seeing as H2S is produced and transported in the Concrete Pipe and Sediment
wastewater and not in the air,wouldn't it make more sense to
measure it in liquid? H2S is formed in the sewage by the reduction of sulfate.Part of the
This case study investigates if continuous, liquid-phase dissolved H2S may be released to the air where it can cause corrosion
measurements provide a better approach to H2S monitoring than after being transformed into sulfuric acid.*
gas-phase measurements and thereby deliver better insights into *Model adapted from Hvitved-Jacobsen,Vollertsen,and Nielsen(2013)-Sewer Pro-
how H2S Impacts sewer hotspots. cesses:Microbial and Chemical Process Engineering of Sewer Networks&Li,Kappler,
Jiang,and Bond(2017)-The Ecology of Acidophilic Microorganisms in the Corroding
Concrete Sewer Environment.
2 Gas vs. Liquid HZS Measurement
The HdLn r 2S sensor measures HZS directly in
wastewater and in the air above.
Setup
To analyze the benefits of measuring HzS directly in wastewater,
3 Hach HzS sensors were installed in the same 3-meter deep force
main discharge well at a Danish wastewater utility.Capable of
continuously measuring H,S in both gas and liquid phase,the
Hach H,S sensors were installed in the raw wastewater(A), in the O
headspace just above the wastewater(B),and in the headspace
just below the manhole cover(C).
Results
As seen on the graph,the liquid-phase measurements(A)provide Measurement Locations
a full overview of how H.,S impacts the sewer hotspot.The gas
phase measurements in the air above the sewage(B)were A In the wastewater(liquid)
correlated with the liquid-phase measurements,while the gas- B Above the wastewater
phase measurements in the diluted air just below the manhole
cover(C)were unable to reveal the severity of the H,S challenge. C Below the manhole cover
The major deviation in the gas-phase data(C)suggests these
measurements were heavily affected by external factors such as
turbulence,ventilation,and pumping rhythms.
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Time[hours]
3 Gas vs. Liquid HZS Measurement
A data-driven approach to HZS management
The Hach H,S sensor's liquid-phase measurements reveal the true scope of a utility's H,S challenge.This knowledge enables a data-
driven approach to H,S management for greatly improved corrosion control,optimized chemical dosing,effective root cause analysis,
and optimized planning of new infrastructure projects. Finally,the Hach H,S sensor's unique ability to measure both in and above
wastewater makes it a flexible tool suitable for odor detection campaigns as well.
Liquid-phase H2S measurements provide
better insights that enable you to...
• Make data-driven decisions when prioritizing H,S management activities.
• Minimize H S odors by focusing odor control activities on confirmed hotspots.
• Extend the lifespan of assets and prevent critical infrastructure collapse.
• Optimize chemical dosing stations using direct H,S sensor-controlled dosing—or by
verifying the effect of your dosing efforts with downstream control measurements.
• Solve H,S problems at the source by mapping individual sewer lines.
• Prevent planning errors caused by a lack of knowledge or underestimation of the
H2S challenge.
World Headquarters: Loveland, Colorado USA I hach.com
United States 800-227-4224 fax:970-669-2932 email:orders@hach.com
® Outside United States 970-669-3050 fax:970-461-3939 email:int@hach.com
�DHach Company,2021.All rights reserved.
In the interest of improving and updating its equipment,Hach Company reserves the right to a lterspecificationsto equipment atanytime. D00043.53.30730.Dec21