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).
