But the natural method of aeration used
by a sewage pond takes much longer than an aerator does to add oxygen to
the water. As a result, ponds treat sewage much more slowly than packaged
plants do. The minimum detention time of a pond is 45 days.
In contrast, a packaged plant has a two to four hour detention
time. And, since ponds must hold the wastewater much longer than packaged
plants do, the ponds must also have a much larger area to retain the sewage.
If the time and area are available, sewage ponds are very economical facilities to maintain. Packaged plants require frequent monitoring for various parameters such as ammonia and B.O.D. In contrast, ponds require only one visit per day to monitor pH and D.O.