Solar Powered Circulators Help Cap Odor Problems

Controlling odors that emanate from storage basins and anaerobic ponds is an ongoing challenge for wastewater managers. Solar powered circulation has emerged as one means for achieving ongoing odor control at municipal facilities.

When deployed for odor control, SolarBee™ water circulators are set for a shallow water intake. Only the top two or three feet of the pond is circulated – at rates of up to 10,000 gallons/minute. This constant re-circulation occurs with a gentle, near-laminar radial flow that emanates from the unit. There’s no turbulence, so BOD from deeper water is not brought to the surface. The result is surface absorption of atmospheric oxygen, and the creation of an oxygenated “odor cap” that effectively covers the entire pond surface.

Any sulfide gases, which would ordinarily waft from the pond and cause odor problems, are destroyed by the dissolved oxygen that forms the odor cap.

In creating an effective odor cap it is critical to ensure that influent BOD does not mix into the top 2-3 feet of the pond – because that BOD could use up all of the dissolved oxygen there. Therefore, influent water must enter the pond horizontally – and below the odor cap at the top of the pond.

In some ponds, the influent pipe brings in water vertically from the bottom of the pond. In those cases, a deflector must be lowered over the inlet pipe. A metal table, about the size of a standard card table, works well at deflecting incoming water into a horizontal pattern, keeping that water from traveling to the top of the pond.

Likewise, the pond effluent pipe should also be below the 2-3 foot odor cap. That way, the high-DO water that comprises the odor cap is not constantly drained off the pond. In some situations, the effluent pipe is positioned at the top of the pond so it can remove surface water in a skimming fashion. In those cases, an elbow or an anti-skimming deflector can often be constructed, allowing water that leaves the pond to come from below the odor cap.

Case History

Faced with a recurring odor problem, in January 2005 Myrtle Beach, SC, installed six SolarBee water circulators in the first three cells of a 48-acre raw sewage pond. At the same time, an existing bubble aeration system was shut off. In August 2005, DO measurements showed significant improvement over results from the prior year. Specifically, DO was 4.5 mg/L in the top three feet of the pond, compared to 1.8 mg/L in 2004. At the same time, ambient H₂S levels dropped from 100 mg/L to zero in all points but one (and that one was much lower than it had been, recording a new level of just 2.7 ppm).

Now, four years later, SolarBee is still keeping odor under control, according to Perry Shelley, Superintendent at the Myrtle Beach water reclamation facility. There are no complaints from the community. And Myrtle Beach continues to save some $50,000 per year in reduced energy and chemical costs, compared to use of the bubble aeration system and air deodorizers. WW