MIL-HDBK-1005/16
maintain area BOD5 loadings in a suitable range. For this lagoon
type, allowable organic loadings are generally much higher in
summer than in winter, an advantage in areas where seasonal food
processing wastes are received during summer.
The total containment pond and the controlled discharge
pond are forms of facultative lagoons. The total containment
pond is applicable in climates where evaporative losses exceed
rainfall. Controlled discharge ponds have long hydraulic
detention times, and effluent is discharged once or twice per
year when the effluent quality is satisfactory.
7.2.2
Aerated Lagoons. In an aerated lagoon, oxygen is
supplied mainly through mechanical or diffused air aeration
rather than through photosynthesis and surface reaeration. Many
aerated ponds have evolved from overloaded facultative ponds that
required aerator installation to increase oxygenation capacity.
Aerated lagoons are generally 6 to 20 feet (2 to 6 m) deep with
detention times of 7 to 20 days. The chief advantage of aerated
ponds compared with facultative lagoons is that they require less
land area.
Aerated ponds are used in both municipal and industrial
wastewater treatment applications. For municipal wastes, aerated
ponds are often resorted to when a facultative system becomes
overloaded and minimal land is available for expansion. For
industrial wastes, they are sometimes used as a pretreatment step
before discharge to a municipal sewerage system. In both
municipal and industrial applications, aerated ponds may be
followed by facultative ponds.
7.2.3
Aerobic Lagoons. Aerobic ponds, also called high-rate
aerobic ponds, maintain DO throughout their entire depth. With
detention times averaging between 5 and 20 days, they are usually
12 to 18 inches (30 to 45 cm) deep, allowing light to penetrate
the full depth. Mixing is often provided to expose all algae to
sunlight and to prevent deposition and subsequent anaerobic
conditions. Oxygen is provided by photosynthesis and surface
reaeration, and aerobic bacteria stabilize the waste.
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