By Robert Jeyaseelan
A new odor control technology was applied to hydrogen sulfide odors in a sludge thickener at the Figueroa Avenue Water Pollution Control Facility in Yuma, AZ. In a recent 24-hour field test, H2S levels as high as 70 parts per million were essentially eliminated during the test period.
"This is the most malodorous part of the plant," said Jeremy McCall, supervisor of the Figueroa Avenue WPCF. "The technology operated as designed, and the test documented that the fogging system was effective in removing H2S."
The Figueroa Avenue WPCF is the largest and oldest of three treatment plants serving Yuma, population about 100,000, located in the Southwest corner of Arizona near the Mexican and California borders.
The facility is designed for 12 mgd and currently treats about 7 mgd, primarily from residential customers, although several industries contribute flow as well. Connected population is about 75,000.
Two influent streams feed the plant through a common interceptor. One, consisting of about 65 percent of the plant's throughput, is treated with ferrous chloride some 30 miles upstream of the plant to counter odors. The second stream enters the plant without any pre-treatment for odors.
The treatment process train consists of a headworks, grit removal, primary basins, activated sludge with fine bubble diffusion, and secondary clarification. After disinfection with sodium hypochlorite and de-chlorination with sodium bisulfate, the treated effluent is discharge to the Colorado River.
Primary and waste activated solids are digested in a pair of anaerobic digesters, and then hauled as a liquid to area farm fields for sub-surface injection. Prior to digestion, the primary solids are thickened in an enclosed gravity sludge thickener, which was the site of the odor control demonstration. The thickener is 40 feet in diameter, and the dome cover height is 10 feet above the concrete wall.