ABSTRACT
Lagoons, or stabilization ponds, treat wastewater through the use of sunlight, wind, algae, and oxygen.
In stabilization ponds, wastewater enters the pond at a single point, either in the middle or at the edge. Algae grow in the pond by taking energy from the sunlight and using up the carbon dioxide and inorganics released by bacteria. The algae releases oxygen for use by the bacteria.
Lagoons are usually deeper than the ponds. An unaerated or facultative lagoon is usually 3 to 5 feet deep and uses aerobic and facultative bacteria to break down the organic material in the wastewater. Oxygen is furnished by algae and wind action. A facultative pond generally has an aerobic zone near the surface, an aerobic and anaerobic zone in the middle depth, and an anaerobic zone at the bottom.
In an aerated lagoon, aeration equipment is installed to provide additional oxygen. Air may be supplied by a compressor through tubes installed in the lagoon bottom or by mechanical aerators installed at the surface. Aerated ponds are deeper (10 to 18 feet) and smaller than facultative or unaerated lagoons.
Key factors in lagoon/pond operation include the following concepts40:
– Area, acres = ( width, feet ) ( length, feet ) 43, 560 square feet per acre https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9780203734216/4406a4e1-8626-47b2-b2d2-ea441a87fc3d/content/eq5.tif"/>
– Volume, acre-feet = ( area, acres ) ( depth, feet ) https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9780203734216/4406a4e1-8626-47b2-b2d2-ea441a87fc3d/content/eq6.tif"/>
– Flow rate, acre-feet day = Flow into pond, gallons per day ( 7 .48 gal/cu ft ) ( 43, 560 sq ft/acre ) https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9780203734216/4406a4e1-8626-47b2-b2d2-ea441a87fc3d/content/eq7.tif"/>
– Detention time, days = ( Volume, acre-feet ) flow, acre-feet/day https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9780203734216/4406a4e1-8626-47b2-b2d2-ea441a87fc3d/content/eq8.tif"/>
– Organic loading rate, lbs/day acre = BOD into pond, lbs/day pond area, acres https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9780203734216/4406a4e1-8626-47b2-b2d2-ea441a87fc3d/content/eq9.tif"/>