bacteria to continue the cycle. The heavier solids settle to the bottom where they are
degraded under anaerobic conditions to produce methane, carbon dioxide, and other
gases. Some of the water is lost by percolation and, in dry weather, some is lost by
evaporation. Effluents can be used for irrigation or discharged into stream if applicable
Federal, state, and local discharge standards are met. The efficiency of a stabilization
pond is affected by the detention time, pond depth, organic loading, temperature, light,
number of units, and wind. If local pond practices call for organic loadings outside of
the standard range, Headquarters, Department of the Army, must approve them
beforehand. Stabilization ponds may be aerated by either mechanical or diffused air
systems. These devices may be designed to provide sufficient oxygen for biological
metabolism and adequate mixing. Mechanical surface aerators are commonly used for
this purpose in the southern and temperate climate areas, while diffused air systems
have been successful in severe climates where icing may prove troublesome for the
mechanical devices.
b. Uses. Stabilization ponds may be used for secondary treatment of settled
primary effluent, in which case they are called oxidation ponds; or they may be used to
treat raw wastewater. Because of the inherent possibility of disagreeable odors arising
from stabilization ponds, the ponds should be located a sufficient distance from
habitations to prevent creating a nuisance.
c. Construction. StabIization ponds are constructed by leveling the required
area and surrounding it by a dike of relatively impervious earth. The dikes should be
sown with grass or sodded to prevent excessive erosion. Outlet structures, which are
located on the windward side, will permit lowering the water level at a rate of not less
than 1 foot per week while the pond is receiving its normal flow. Three sets of baffles
will be concentrically around the outlet structure(s). The first and third baffles, which
extend 3 to 5 feet around the outlet structure, will be located at least 6 inches to 1 foot
above the highest water level. The second baffle is set on the bottom of the pond and
extends to within 6 inches in the lowest anticipated operating level. The depth may vary
from 3 to 5 feet, depending on the area and the quantity of wastewater to be treated.
The bottom of the pond will be as level as practicable with variations not exceeding 6
Inches from the designed bottom elevation. Capacity should be sufficient to provide a
30-day detention period. They may be constructed as single cells, cells in parallel, or
cells in series. Where the terrain permits, the ponds may be constructed in series at
different elevations (see Figure 2-28) connected by shallow weirs. This arrangement
permits maximum aeration and oxidation.
d. Performance. Stabilization ponds will accommodate up to 50 pounds of
BOD per acre of pond area, or roughly 1,000 persons per acre. They should remove
from 90 to 95 percent of the BOD and about 90 percent of the coliform bacteria. Ponds
with detention times of about 50 days will remove 99 percent of the coliform bacteria.
MD0161
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