Ponds


Photo Credit:  Virginia Department of Health

Ponds are probably one of nature's most economical ways of treating sewage and producing a highly purified effluent.  The degree of treatment provided by ponds depends upon the type and number of ponds used.  Ponds can be used as the sole type of water treatment or can be used in conjunction with other forms of wastewater treatment.  Sewage ponds have many advantages and disadvantages compared to packaged plants.  

Both ponds and packaged plants have to deal with aeration of the water being treated.  In the sewage pond, oxygen is transferred directly into the water across the surface area without the need for any equipment.  A package plant, in contrast, must install an aerator to add oxygen to the water.  

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.