Odor Control: Air. Water. Ozone.

July 22, 2020

Hydroxyl radical misting units eliminate odor complaints in Illinois

About the author:

Tony Conn is water distribution and collections manager for Naperville, Illinois. Conn can be reached at [email protected]. Patrick Resch is director of technical sales for Vapex Environmental Technologies. Resch can be reached at [email protected].


Odors emanating from two pumping stations in Naperville, Illinois, have been eliminated through the use of hydroxyl radical misting units. 

As a result, the phone does not ring as much as before in the city of Naperville Water Service Center. And that is a good thing. 

In the past, neighbors called to complain about hydrogen sulfide odors at the North and Northwest pumping stations, even though both were equipped with carbon scrubbing systems.

Now, both stations are using hydroxyl radical misting units from Vapex Environmental Technologies, which eliminate hydrogen sulfide through a combination of air, water and ozone. The mist is directed into the odorous areas through a patented three-fluid nozzle.

Hydrogen Sulfide AKA H2S

As wastewater operators and managers well know, hydrogen sulfide is produced naturally from decaying organic matter. It can be released from sewage sludge and wastewater collection systems. It is poisonous, corrosive and flammable. It can cause a wide range of health effects. 

Workers are primarily exposed to hydrogen sulfide by breathing it. The effects depend on how much hydrogen sulfide one breathes and for how long. 

Typical background concentrations of H2S are in the 0.01 to 1.5 ppm range. The odor becomes more offensive at 3 to 5 ppm.

Above 30 ppm, H2S odor is often described as sweet or sickeningly sweet. Higher concentrations can lead to marked conjunctivitis and respiratory tract irritation, pulmonary edema, unconsciousness and death (at 1,000 to 2,000 ppm).

At Naperville’s Northwest pumping station, odor complaints averaged 15 annually; at the North station, complaints averaged four per year. H2S concentrations at both stations measured about 150 ppm.

Since the Vapex units went on line, odor complaints have been zero.

Large Utility

With more than 43,000 customers, the Naperville water and wastewater utility is one of the largest in the state and collects and treats approximately 19.7 million gallons per day (mgd) of wastewater at its Springbrook Water Reclamation Center.

The North and Northwest pumping stations—both indoors at covered wet wells—are important components in the city’s 564-mile long sewer system.

The North station measures 28 feet long by 14 feet wide and 33.5 feet deep (13,132 cubic feet of volume). Average flow is 3.2 mgd with a peak of 19.7 mgd. The Northwest station is 18 feet by 16 feet by 48 feet deep (12,384 cubic feet of volume). Average flow is 3.6 mgd with a peak of 12 mgd. 

In the past, carbon scrubbers were used to control odors, but the cost and maintenance of each carbon unit were giving the collections staff problems. Maintenance included fan motor shaft alignment, replacement of bearings, carbon replacement at breakthrough and time and equipment associated with carbon change out. 

To change out the carbon, staff had to wear hazmat suits, and the carbon change out was difficult for the workers to perform.

The city heard of Vapex odor control technology through a treatment plant in Indiana. It did not pilot test the units but based on references and reported experiences with the technology at other sites, installed a Vapex Micro unit at the North pumping station in the winter of 2017.

The next spring another unit was installed at the Northwest station, located at a busy intersection and the site of the larger share of odor complaints. 

Hydroxyl Radical Misting Technology

More than 350 Vapex odor control systems have been installed since the company introduced its hydroxyl radical misting technology some 15 years ago. The hydroxyl radical is created by combining micron-sized particles of water with ozone using the patented nozzle. This powerful oxidant attacks H2S, stripping out the hydrogens, leaving only water and a sulfur molecule. 

This vapor phase technology has been successfully applied to pump stations, wet wells, influent channels and other structures where hydrogen sulfide odors and corrosion are problems  or where fats, oils, and grease build up on the surface of the influent. The odorous air is treated in the space where it is generated. The need to transport air via ducts or large blowers is thereby eliminated, keeping energy consumption to a minimum.

The units are relatively small, use no chemicals, and operate on electricity and water, which Naperville supplies from its water distribution system. 

At Naperville, a Zipper Cable Sheath, or heavy-duty PVC extruded pressure track, provides a strong closure for all submersible pump and grinder pump power cables. This design makes the closure practical and economical. It installs and removes easily, while keeping oxidants from contacting the pump cables. 

Cost Effective

In addition to the elimination of odors at Naperville, costs have also decreased significantly. As presented at the Illinois WEA Collections Systems Conference, annual operating costs for carbon, carbon regeneration, and associated parts and labor were over $18,000 at the North pumping station, and over $19,000 at the Northwest station. By comparison, annual operating costs have come to $7,940 for each Vapex unit—a total savings of over $22,000 a year.

In contrast to the scrubbers, maintenance on the Vapex units is relatively simple. After initial startup, the nozzle should be checked weekly to ensure proper operation and evaluate condition of the nozzle face. Quarterly cleaning is a minimum requirement. Greater frequency of nozzle cleaning may be required based on water supply chemistry.

The air filter may require more frequent cleaning depending on the environment. 



With three years of successful results, the odor control systems have been visited frequently by professionals from other water utilities interested in the odor control systems and their results.

The neighbors are curious, too, often contacting the plant—not to complain—but to ask what was done to eliminate the odors.