Making the most of a waste water lagoon

By Anna Crickmer, PE, Project Manager, Capital Programs, Department of Corrections

Photos by Clallam Bay Corrections Center staff

The head operator of the waste water treatment facility at Clallam Bay Corrections Center.

The head operator of the waste water treatment facility at Clallam Bay Corrections Center smiles in front of the waste water “polishing” pond.

Sewage treatment at Clallam Bay Corrections Center (CBCC) is the epitome of sustainable operations. They have an aerated lagoon (very low tech) with a polishing pond of duckweed (also very low tech), but staff are so dedicated to the operation that they get contamination reduction results exceeding some very high tech operations.

The main way to measure sewage treatment performance is the reduction of Biochemical Oxygen Demand (BOD) and Total Suspended Solids (TSS). Aerated lagoons generally reduce BOD by 75-80% and TSS by 70-80%. High tech, activated Sludge plants, the gold standard of sewage treatment, usually get 85-97% reduction in BOD and 87-93% in TSS.

The plant at CBCC gets 96% reduction of BOD, and 99% reduction of TSS—even better than the gold standard! 

One reason that they get these remarkable results is that they aerate the heck out of the lagoon. The original aerators are still in operation, thanks to meticulous maintenance, and more aerators have been added. In the summer months, water stays in the lagoon for 25 1/2 days before moving to a second pond, the “polishing” pond.

The prison's waste water starts its treatment in a lagoon full of aerators.

The prison’s waste water starts its treatment in a lagoon full of aerators.

The polishing pond is covered in duckweed. The duckweed takes up nutrients such as nitrogen and phosphorus (pollutants if discharged), and shades the water so that no algae can grow. The duckweed is grown in “corrals” so that it doesn’t blow to one side of the pond. The sides of the corrals tip over so that the operators can travel across them in a small pontoon boat when they maintain the pond. Water stays in the polishing pond 24 1/2 days, and then is ready for discharge into the Strait of Juan de Fuca.

The second treatment pond, the "polishing" pond, is covered in duckweed; the grid of corrals is to keep the duckweed coverage complete (without those barriers, the floating plants would migrate with the wind).

The second treatment pond, the “polishing” pond, is covered in duckweed; the grid of corrals is to keep the duckweed coverage complete (without those barriers, the floating plants would migrate with the wind).

The staff operators of the plant are exceptionally competent, and likable characters besides. Both used to be loggers, and say that their environmental conscience has been raised considerably because of their work at DOC. One of them told me, “Why, I even want to save whales now!”

 

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