MIL-HDBK-1005/16
High-rate aerobic lagoons are limited to warm,
sunny climates. They are used where a high degree of BOD5
removal is desired but land area is limited. The chief advantage
of the high-rate aerobic pond is that it produces a stable
effluent with low land and energy requirements and short
detention times. However, operation is somewhat more complex
than for a facultative pond and, unless an algae removal step is
provided, the effluent will contain high suspended solids. Short
detention times also mean that very little coliform die-off will
result. Because of their shallow depths, paving or covering the
bottom of the ponds is required to prevent weed growth.
7.2.4 Anaerobic Lagoons.
Anaerobic lagoons receive such a heavy
organic loading that there is no aerobic zone. They are usually
8 to 16 feet (2.5 to 5 m) deep and have detention times of 20 to
50 days.
An important disadvantage of anaerobic ponds is the
production of odorous compounds. Sodium nitrate has been used to
combat odors, but it is expensive and in some cases has not
proven effective. Another common approach is to recirculate
water from a downstream facultative or aerobic pond to maintain a
thin aerobic layer at the surface of the anaerobic pond,
preventing transfer of odors to the air. Crusts have also proven
effective, either naturally formed, as with grease, or formed
from Styrofoam balls. A further disadvantage of the anaerobic
pond is that the effluent usually requires additional treatment
prior to discharge.
Anaerobic ponds are usually used for treatment of
strong industrial and agricultural wastes, or as a pretreatment
step where an industry is a significant contributor to a
municipal system. Because they do not have wide application to
the treatment of municipal wastewaters, anaerobic lagoons are not
discussed further in this manual.
7.3
Facultative Lagoon Design. The facultative lagoon
should be strongly considered for those installations that have
no significant industrial wastewater component but that have
available land area. This lagoon type is simple to operate,
stable to flow and load variations, and has low capital and
operating costs.
7.3.1
Sizing Basis: Loadings for Raw Sewage. Using Table 13,
select values between the maximum and minimum values provided.
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