Solar-powered circulators provide pond odour cap

Unique solar-powered circulators offer reliable odour control at industrial and municipal wastewater storage facilities, preventing health hazards, plus providing major savings on chemicals and energy

Unique solar-powered circulators offer reliable odour control at industrial and municipal wastewater storage facilities, preventing health hazards, public outrage and air quality citations, plus providing major savings on chemicals, deodorisers and energy.

One of the most critical requirements of wastewater management - the prevention of odours escaping from storage ponds - is so problematic that it is a disaster-waiting-to-happen for many facilities.

Even occasional lapses in maintaining an effective odour cap can have dire consequences.

For example, when the turbulence caused by brush aerators releases aerosols and bacteria-laden mist into neighbourhoods, the risks can be dreadful: serious health hazards, public outrage, and even shutdowns.

Such scenarios are not limited to sludge storage ponds.

Industrial storage basins holding manufacturing effluents, and even rainwater, contain odour-producing sulphurous compounds (e.g mercaptans/thiols) that can waft over communities unless capped effectively.

"We are very concerned about maintaining an odour cap," says David Williams, Project Engineer at Shell Oil (Shell Manufacturing) in the Martinez, California refinery.

"Our treatment pond is about 1/4 mile from the residential community.

We've got a delicate situation where even just a slight amount of odour could arouse complaints from the community.

So, we keep a close eye on it".

William's concern about odour control led him to looking for a new aeration technology to replace two brush aerators that had been installed in the Martinez refinery pond.

These rental units were unreliable and were attributed to incidents that produced odour complaints from local residents.

The need for a reliable technology.

Although in wide use, the failure of brush aerators to provide a continuous odour cap is unfortunately not a rare situation.

Brush aerators often do not provide an odour cap to the edges of a pond, in which cases putrid gases can escape into the air.

Moreover, the turbulent action of brush aerators can disturb pond sediment, causing BOD (bacterial oxygen demand) to rise and eat away the odour-insulating oxygen blanket, and even cause 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 neighbourhoods.

The need for a technology that assures reliable odour control has led wastewater managers to use some extraordinary methods of covering and dispersing odours from sludge storage basins and anaerobic ponds.

Some plants are spraying or injecting deodorisers to "neutralise" rank vapours, or installing costly blower systems to filter odourous compounds from the air.

A few facilities have installed multimillion-dollar windmill arrays to disperse odours upward into the air and (hopefully) away from the community.

In other cases chemicals such as hydrogen peroxide have been poured into ponds in order to re-aerate surface waters and fortify odour caps.

Such dramatic investments and exceptional methods demonstrate the unquestionable need for odour control at wastewater storage ponds, whether industrial or municipal.

The "circulator" solution.

At Shell's Martinez Refinery, David Williams found a new technology that could provide the reliable odour control he was looking for.

The solution was SolarBee, solar-powered water "circulators" that aerate ponds by circulating just the top two feet of the pond at the rate of up to 10,000 gallons per minute.

This circulation occurs with a gentle, "near laminar" long-distance flow pattern that provides an oxygenated odour cap across the entire surface 24 hours a day.

"The SolarBee installation gave us a good opportunity to shift the paradigm in pond aeration," Williams says.

"In a bigger sense it gave us an opportunity to take a look at the way we do business, and we've really shifted from having an expectation that to aerate a pond you need this brush aeration system, or to use a fossil-fuel, power-intensive method." In a sense, Williams found the new aeration solution in his own back yard.

Engineered as a self-contained system by Pump Systems (PSI) of Dickinson, ND, SolarBee units are powered by solar panels manufactured by Shell Solar, Royal Dutch Shell's global photovoltaics division.

This "circulator solution" also provides impressive cost savings for the Martinez facility.

"Because the wastewater pond is at a remote location, we had been using rented diesel generators to power the brush aerators," Williams explains.

The total rental costs for testing that system was about $15,000 a month.

The alternative of powering the site from the grid would have cost up to $150,000 due to the remote location and electrical classification.

The Solar Bees have the additional bonus of saving $10,000/year in energy costs over the alternative of hard-wired aerators.

"What we have today, at about half the cost of the electrical motors alone, is an environmentally-friendly system that avoids the use of hard power and provides a working relationship between Shell Solar and Shell Manufacturing, plus significant dollar savings," explains Williams.

Effective odour control for all types of ponds.

Williams reports that since the installation of the circulator systems, the Shell Manufacturing Martinez wastewater pond "has had zero odour complaints due to inadequate aeration".

And equally impressive results have been achieved using this approach at numerous industrial and municipal ponds.

In Discovery Bay, California, a wastewater treatment plant constructed in 2003 was equipped with two brush aerators that were anchored from shore in each of two lagoons.

Gregory Harris, PE, a partner at Herwit Engineering (Concord, CA), designer of the facility, says the brush aerators began to fail after a year.

"The floats on them became corroded and began to leak," Harris says".

Then two of the units sank.

Naturally, we were pretty unhappy with the aerator performance.

Plus they sprayed water all over the place and consumed a lot of electric power.

But we had to do something to aerate the surface of the water, or we would have at least occasional odour problems from the sludge ponds".

Harris looked at the SolarBee circulation system, which he had heard was effective at aerating pond water and controlling algae.

"We did not have a heavy biological load, but thought it might be a good aeration solution for odour cap," he says.

Also, the Discovery Bay facility was able to take advantage of rebates from a state energy conservation programme, the California Wastewater Optimisation Programme.

"We were able to turn off the two aerators that were still operational," Harris says.

"We installed two SolarBees in August 2004, and they have worked well ever since.

We've taken DO samples from the water and the lowest we've seen has been 3 milligrams per litre.

Also, the pond was saturated with algae after the two brush aerators sank.

Now there is no algae in the water.

Based on performance that we have seen, from the combination of the energy that the District is saving plus the rebates we're receiving from the state, the payback on the SolarBee units will be less than two years".

In another case, the City of Myrtle Beach, SC, was spending $30,000 to $50,000 per year for deodoriser, which was sprayed into the air in an effort to contain wastewater odour problems that had residents were up in arms.

"This raw sewage pond was originally equipped with a bubble (diffuser) aeration system at the bottom of the 48-acre pond," explains Michael Lipparelli, SolarBee Regional Sales Manager, "That aeration was supposed to keep everything suspended so that sludge would not build.

But sometimes that doesn't work.

So, suddenly they found themselves in a situation where the diffuser aerators were throwing the sludge and odours up toward the surface of the pond, where it would gas-off and waft over the city".

A few months ago the Myrtle Beach facility had two SolarBee units installed.

Within a few weeks these circulators had built an odour cap that was sufficient to eliminate the need for spraying and allowed the facility to turn the bubbler system off, thereby gaining additional savings on energy costs.

"Many times engineers design a pond where it is known that there may be odour capping issues," says Joel Bleth, President of PSI.

"Other times, odor problems occur because of unforeseen conditions, 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 adds that many industrial wastewater managers may not be aware that the effluents of their processes may cause severe odour problems that could lead to a crisis.

"Wineries, pulp processors, manufacturers, food processors - all produce organic waste," Bleth explains.

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

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