Reliable Odor Control from Renewable Solar Power

Such scenarios are not limited to sludge storage ponds. Industrial storage basins that hold manufacturing effluents, and even rainwater, contain odor-producing sulfurous compounds (e.g., mercaptans/thiols) that can waft over communities unless capped effectively and reliably.

"We are concerned about maintaining an odor cap," said David Williams, project engineer at Shell Oil's Martinez, California, refinery. "Our treatment pond is about a quarter-mile from the residential community. We've got a delicate situation. Even a slight amount of odor can arouse complaints from the community."

Problems with odor control led Williams to look for a new aeration technology to replace two brush aerators installed in a refinery pond that had proved unreliable and induced odor complaints from local residents.

The Need for Reliability
Brush aerators often fail to provide a continuous odor cap to the edges of a pond, allowing putrid gases to escape into the air. The turbulent action of brush aerators can also disturb pond sediment, causing bacterial oxygen demand to rise and eat away the odor-insulating oxygen blanket, even causing the formation of sludge islands at the surface of ponds. Worse yet, brush aerators can whip up aerosols and potentially harmful bacteria that can be carried by winds into surrounding neighborhoods.

To assure reliable odor control, wastewater managers use some extraordinary methods of covering and dispersing odors from sludge storage basins and anaerobic ponds.

Some plants spray or inject deodorizers to neutralize rank vapors, or install costly blower systems to filter odorous compounds from the air. Other facilities installed multimillion-dollar windmill arrays to disperse odors upward into the air and away from the community. In other cases, chemicals such as hydrogen peroxide are poured into ponds to re-aerate surface waters and fortify odor caps.

The Circulator Solution
At the Martinez refinery, Williams found a new aeration technology that could provide the reliable odor control he needed 24 hours a day. A solar-powered water circulator called the SolarBee aerates ponds by circulating only the top two feet of the pond at rates up to 10,000 gpm. This circulation occurs with a gentle, near laminar long-distance flow pattern that provides an oxygenated odor cap across the entire surface.

"The SolarBee installation shifts the paradigm in pond aeration," Williams said, "by making us re-evaluate our way of doing business. We've moved away from expecting only a brush aeration system or fossil-fuel power-intensive method to aerate a pond." Plus, the units, which are powered by PV solar panels, provided significant cost savings.

"Because the wastewater pond is at a remote location, we used rented diesel generators to power the brush aerators," stated Williams. "Total rental costs for testing that system ran about $15,000 a month. The alternative of powering the site from the grid would cost up to $150,000 due to the remote location and electrical classification. The SolarBees save $10,000 per year in energy costs over the alternative of hard-wired aerators."

Since installing the circulator systems, the Martinez wastewater pond "has zero odor complaints due to inadequate aeration," reported Williams.

Odor and Algae Control
Similar results were achieved at another wastewater treatment plant constructed in 2003 in Discovery Bay, California, which had been equipped with two brush aerators anchored from shore in each of two lagoons.

Gregory Harris, PE, a partner at Herwit Engineering (Concord, California), said the brush aerators began to fail after a year.

"Their floats became corroded and began leaking," said Harris. "Two units sank. We were unhappy with the aerators' performance. They sprayed water everywhere and consumed lots of electrical power. We had to do something to aerate the surface of the water. Otherwise, we faced at least occasional odor problems from the sludge ponds."

Harris heard the SolarBee system could aerate pond water and control algae, and noted, "We didn't have a heavy biological load, but we thought it might be a good aeration solution for odor cap." Plus the Discovery Bay facility was able to take advantage of rebates from the California Wastewater Optimization Program, a state energy conservation program.

"We turned off the two aerators that were still operational," said Harris, "and installed two SolarBees in August 2004. They've worked well. We've taken DO samples from the water, and the lowest we've seen was 3 milligrams per liter." The algae disappeared, the district saved energy, and it is expected the units will pay for themselves within two years.

Costs Avoided
Another installation in South Carolina yielded savings as well. Myrtle Beach spent $30,000 to $50,000 per year for deodorizer that was sprayed into the air to contain wastewater odor problems. Within a few weeks of installing two of these solar-powered water circulators, an odor cap sufficiently eliminated the need for spraying. The facility turned off the bubbler system and gained additional savings on energy costs.

Applications for Other Organics
"Engineers often design a pond knowing there may be odor-capping issues," explained Joel Bleth, president of PSI.

"Other times, odor problems occur because of unforeseen conditions," said Bleth, "such as changes in manufacturing processes that produce organic effluents, or population growth that creates pond oxygen demand beyond what most aeration systems can handle with consistent reliability."

Bleth added that many industrial wastewater managers may not be aware that the effluents of their processes can cause severe odor problems that could lead to a crisis. "Wineries, pulp processors, manufacturers, food processors...all produce organic waste," he said.

"Wastewater pond managers try various sorts of systems and chemicals to prevent an odor crisis, but even an occasional failure of an odor cap can result in an air-quality citation over a very brief time -- especially in heavily populated areas," warned Bleth.

About the author

Ed Sullivan is a technical writer based in Hermosa Beach, California. This article is reprinted with permission of the president of Pump Systems, Inc. (PSI), and first appeared the October 2005 issue of PUMPS & SYSTEMS (www.pump-zone.com).