MIL-HDBK-1005/16
resulting in a certain amount of confusion. Wastewater lagoon
systems can be classified by dominant type of biological
reaction, duration and frequency of discharge, extent of
treatment ahead of the pond, or arrangement among cells (if more
than one cell is used). The most basic classification describes
the dominant biological reactions that occur in the lagoon, and
that classification has been adopted here. The four types of
lagoon systems are:
a)
Facultative (aerobic-anaerobic)
b)
Aerated
c)
Aerobic
d)
Anaerobic
Table 12 summarizes information on pond application,
loading, and size for each of the pond types discussed in this
section.
7.2.1
Facultative Lagoons. The most common type of pond is
the facultative pond. Other terms commonly applied are oxidation
pond, stabilization pond, sewage (or wastewater treatment)
lagoon, and photosynthetic pond. Facultative ponds are usually
4 to 8 feet (1.2 to 2.5 m) deep, with an aerobic layer overlying
an anaerobic layer, often containing solids deposits. Usual
detention time is very long, ranging from 25 to 180 days.
Anaerobic fermentation occurs in the lower layer and aerobic
stabilization occurs in the upper layer. The key to facultative
operation is oxygen production by photosynthetic algae and
surface reaeration. The oxygen is used by the aerobic bacteria
in stabilizing the organic material in the upper layer. Algae
present in pond effluent represents one of the most serious
performance problems associated with facultative ponds.
Facultative lagoons have widespread application. They
are used to treat raw municipal wastewater (usually for small
communities) and primary or secondary effluent (for small
cities). They are also used in industrial applications,
following aerated ponds or anaerobic ponds to provide additional
stabilization prior to discharge. The facultative pond is the
easiest to operate and maintain, but there are definite limits to
its performance. Effluent BOD5 values range from 20 to 60 mg/L,
and levels of suspended solids may range from 30 to 150 mg/L or
more. The facultative lagoon also requires a large land area to
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