The City of Knoxville was experiencing high hydrogen sulfide gas levels of 800-1000 ppm in its force main, causing odor issues. Previous chemical treatment reduced odors but not to acceptable levels. An ECO2 SuperOxygenation system was installed to dissolve oxygen into the force main and maintain aerobic conditions, preventing hydrogen sulfide formation. Preliminary results showed hydrogen sulfide levels were reduced to near non-detectable levels. The system operates by extracting a sidestream of wastewater, bubbling in liquid oxygen to fully dissolve it, and returning it to the force main.

1. WEFTEC 2008 ABSTRACT November 30, 2007
Force Main Odor and Corrosion Control by
SuperOxygenation, Knoxville TN
by
Jeff Hooyman, Knoxville Utilities Board,
835 E Jackson Avenue, Knoxville, TN 37915
Phone: 865-594-8274 Fax: 865-594-8278
and
David A. Clidence P.E., ECO Oxygen Technologies,
3939 Priority Way South Dr. Suite 400 Indianapolis, IN 46240
Phone: 317-706-6482 Fax: 317-816-0940
City of Knoxville, TN Force Main Odor Problem
The City of Knoxille collection system is a complex system of lift stations and 1249 miles of
service mains (or pipes) which covers 108 square miles to serve 64,000 customers. Like many
cities, Knoxville has a force main that was sized ten years ago for a projected level of industrial
and residential development that has not yet been realized. Consequently, the Forks of the
River force main is oversized with wastewater velocities running less than optimal. The force
main is over 6 miles long with hydraulic retention times (HRT) of 18 – 24 hrs. This is allows
for significant anaerobic conditions to develop in the force main resulting in the generation of
malodorous hydrogen sulfide gas. The generation of hydrogen sulfide gas in this force main
has plagued the City for many years. Over the last ten years, the City has tried many methods
and spent a great deal of money to reduce the odor production. The City conducted tests to
determine the level of hydrogen sulfides released at blow-off vaults and measured H2S levels of
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2. WEFTEC 2008 ABSTRACT November 30, 2007
800 ppm to 1000 ppm. Some of the vaults were located near heavily residential and
commercial areas. The City instigated a chemical treatment program using Calcium Nitrate at
the Forks of the River pump station to reduce the odors generated in the force main. This
treatment reduced the odors but not to acceptable levels. Using this chemical treatment, the
City still measured 10 mg/L of dissolved sulfide at the force main discharge. The City sought
additional new methods for preventative, non-chemical in pipe treatment to further reduce the
odors to non detectable levels.
Root Cause of Odor in Force Mains
The root cause of most odor problems associated with wastewater collection and treatment is
the presence of naturally created malodorous gases. The gases are formed by Sulfate Reducing
Bacterial, (SRB’s) under anaerobic conditions resulting from the imbalance of high BOD
loading and the limited solubility of oxygen into wastewater. This problem is exacerbated in
long force mains and slow-cycled residential lift stations due to high microbial oxygen uptake
rates, long detention times, and low dissolved oxygen (D.O.) levels. These anaerobic conditions
produce significant amounts of hydrogen sulfide (H2S) which is both odorous and highly
corrosive. Since anaerobic conditions are precursors to H2S formation, a logical solution to H2S
control is to induce aerobic or oxic conditions. SuperOxygenation is a process to sustain
aerobic conditions by using an ECO2 “Speece” Cone (Downflow Bubble Contactor) to dissolve
pure oxygen into wastewater to prevent the formation of H2S.
Forks of the River Force Main – Knoxville, TN
An ECO2 SuperOxygenation system was designed and installed 1.0 mile upstream of the Forks
of the River force main discharge in November of 2007. Preliminary data shows the system
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3. WEFTEC 2008 ABSTRACT November 30, 2007
successfully reduced hydrogen sulfide gas at the force main discharge. This is being done at a
capital and annual operating cost resulting in a 3 - year payback versus alternative chemical
treatment.
The system operates by redirecting a side-stream flow of 700 gpm of raw, unscreened
wastewater from the force main and pumping it through an ECO2 Cone. Liquid oxygen is
delivered to site and stored in a liquid oxygen storage tank. Oxygen gas is fed at a rate of up to
1,000 lbs per day into the ECO2 Cone which has an exceptionally large oxygen/wastewater
interface generated by an intense bubble swarm to achieve rapid oxygen dissolution. The ECO2
SuperOxygenation system completely dissolves the gaseous oxygen into the wastewater side-
stream before it is blended back into the force main. Enough oxygen is dissolved into the force
main to sustain aerobic conditions through the remainder of the force main reducing the amount
of H2S generated to near non-detectable levels.
Conclusions
Generation of malodorous hydrogen sulfide gas in the Forks of the River force main has
plagued the City of Knoxville, TN for many years. In 2007, the City sought additional new
methods for preventative, non-chemical, in pipe treatment and chose ECO2 SuperOxygenation
technology to sustain aerobic conditions in the force main to further reduced H2S to acceptable
levels.
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4. WEFTEC 2008 ABSTRACT November 30, 2007
Figure 1: ECO2 SuperOxygenation System Installed on the Forks of the River Force Main
Figure 2: ECO2 SuperOxygenation System Equipment and Piping Plan
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5. WEFTEC 2008 ABSTRACT November 30, 2007
Figure 3: ECO2 SuperOxygenation System Equipment and Piping Elevation
Figure 4: Forks of the River Force Main Profile
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6. WEFTEC 2008 ABSTRACT November 30, 2007
Figure 3: ECO2 SuperOxygenation System Equipment and Piping Elevation
Figure 4: Forks of the River Force Main Profile
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