MIL-HDBK-1005/16
cover through winter.
Greater distance is recommended if
possible.
7.3.3
Exposure.
Choose a site which provides maximum sun and
wind exposure.
7.3.4
Inlets and Outlets. For circular or square lagoons,
the inlet should be near the center. For rectangular lagoons,
place the inlet at one-third the distance from the influent end.
Locate the outlet so that short-circuiting is minimized. Provide
the outlet with the capability of being drawn off at multiple
depths.
7.3.5
Construction. Provide levees with a minimum top width
of 6 to 8 feet (1.8 to 2.4 m) and an interior and exterior slope
ratio of 2:1 to 6:1. Provide natural impervious soil liner
(bentonite clay) if required to minimize exfiltration to
groundwater. Use of synthetic material lining will probably make
this treatment process uneconomical but may be required by local
regulations. See Figure 22 for details about facultative
lagoons. Refer to par. 7.7 for lagoon sealing requirements.
7.3.6
Layout. Use square, rectangular, or circular basins.
For small installations (5,000 gpd [19,000 Lpd]), single lagoons
are acceptable. Use multiple lagoons for larger installations
and arrange for series or parallel operation. See Figure 23 for
alternative lagoon flow schematics. Recirculation can be used to
increase operational flexibility and treatment efficiency.
Recirculation returns active algae cells, increases oxygenation
capacity, and dilutes influent biochemical oxygen demand (BOD)
load. The recirculation ratio should be ≤2.
7.3.7
Performance. Effluent TSS will vary seasonally
(especially in cold climates) between 50 and 150 mg/L or more and
contain 10 to 100 mg/L of algae cells. BOD removal efficiency
will vary seasonally between 70 and 95 percent. Odors may be a
transient problem during spring in cold climates where lagoon
surfaces freeze over.
7.4
Aerated Lagoon Design. Aerated lagoons are oxygenated
through the action of surface or diffused air aeration.
Because
the solids are maintained in suspension in an aerated lagoon, the
detention time required for BOD removal will be less than for a
facultative lagoon. The power requirement, however, will be
greater than for a facultative or aerobic pond, and a separate
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