August 2009, Vol. 21, No.8

Problem Solvers

Hydroxyl Ion Foggers Solve Odor Problems

Problem: Hydrogen sulfide odors from lift stations overpowered existing odor-abatement technology.
Solution: Installation of a hydroxyl ion fogging system.

Chandler, Ariz., located near Phoenix, is one of the fastest growing communities in the nation. The city’s population swelled to more than 240,000 in 2006, from 29,000 in 1980, and is still rising, according to census data.

The city’s wastewater collection and treatment systems have had to keep pace. The extension of sanitary sewers and lift stations into newly developed areas created hydrogen sulfide odor “hot spots,” which resulted in a number of citizen complaints.

“We get phone calls, you bet,” said Alvin Robertson, Chandler collection systems superintendent. “And some of them from some pretty important people in the community.” Currently, the Chandler Municipal Utility maintains more than 1380 km (857 mi) of sanitary sewers, 18,000 manholes, 70,000 sewer taps, and eight pump stations throughout its 180-km2 (70-mi2) area.

Initially, the city used several carbon odor scrubbers and sodium hypochlorite for odor control to try to mitigate the situation. But while the applications were effective at first, they did not perform successfully over time, Robertson said. The hydrogen sulfide odors would return and so would the phone calls from unhappy ratepayers. Robertson estimates that previous odor-control applications cost more than $450,000.

Approximately 4 years ago, the city became aware of new O-MEGA hydroxyl ion fogging technology available from Vapex Inc. (Orlando, Fla.). “The local Vapex representative suggested we try one of the fogging units,” Robertson explained. “We did, and it worked out very well. In fact, it was like a hallelujah moment for me.”

In O-MEGA units, an atomizing nozzle generates hydroxyl ion fog and sprays it into odorous spaces, filling the headspace and chemically reacting with the vapor-phase hydrogen sulfide. Lift stations are a suitable enclosure for the fog, because they act as reaction chambers, and the reacted mist condenses back into the water stream. There is no need to withdraw odorous air from the structure and pass it through a separate odor-control scrubbing process. The odorous compounds are destroyed at a faster rate than possible with chlorine or carbon.

In addition to relatively low capital and operating costs, these units are compact and use no scrubbing chemicals. The hydroxyl ion fog reduces hydrogen sulfide corrosion within the structure and helps break down grease and kill biofilm. The units are available in a variety of sizes with a range of nozzle output rates and coverage areas.

Chandler has been applying these units to “worst-first” situations, Robertson explained. The first application was at the golf course lift station, which handles 3785 to 5700 m3/d (1.0 to 1.5 mgd) and has both a wet and a dry side with submersible dry-pit pumps located in a vault alongside the wet well. “We have a lot of turbulence at that site,” Robertson said, “and it’s right on a main thoroughfare that runs through Chandler.” The hydroxyl ion fog technology yielded positive results, Robertson explained. Odor issues have essentially been eliminated.

At another site on Kyrene Road, hydroxyl ion fogging technology destroys odors in both the lift station and a group of nearby manholes. “This is a high-flow site, with about 5 mgd [19,000 m3/d] coming into the structure through 30- and 36-in. [750- and 900-mm] pipes,” Robertson said. He explained that the fogging unit has been treating nine manholes that surround the lift station, as well as the lift station itself. “We cored through the sidewalls for 2- to 3-inch [50- to 75-mm] PVC [polyvinyl chloride] pipe connections so the PVC fogging pipes can be inserted.” A single unit produces fog, which is distributed to each chamber.

Odors from the Manganero lift station were a problem at a nearby shopping center. Another fogging system installed there has eliminated odors and stopped the complaints. The technology also has eliminated odors at the diversion structure vault near a major highway interchange.

To date, Chandler has purchased six fogging units, and the technology is now part of the city’s design specification for new lift stations.

Robertson says maintenance of the units is minimal, and operating costs are negligible, since each unit needs only a conventional 110-V electrical connection and a potable water line. “Every Wednesday, we clean the nozzles, and that’s it,” Robertson said.

While Chandler has not compiled a detailed cost evaluation of odor-control options, a recent engineering study for another city indicated that the hydroxyl ion foggers were lower in both capital and operating costs than alternatives, such as scrubbers and biofilters. In terms of present costs, the study found the foggers to be from 36% to 46% lower than the alternative odor-control systems.

And while costs are important, Robertson enjoys the side benefit of fewer odor complaints. “They have gone down,” he said. “And that’s good, because our main purpose here is to serve the public.” 

For more information, see www.vapex.com/odorcontrol.aspx, or contact Vapex at (888) 907-0004 or info@vapex.com.


©2009 Water Environment Federation. All rights reserved.