lagoon can be a facultative stabilization pond (or facultative lagoon), a sedimentation clarifier, or a dissolved air flotation clarifier, each incorporating the recycle
of biological solids (or biosolids). The oxygen required by the aerated lagoon
process is supplied by surface or diffused aerators. As with other suspendedgrowth systems, the turbulence created is used to maintain the contents of the
basin in suspension.
Lagoon, anaerobic Anaerobic lagoons are capable of treating high strength wastewater. They are relatively deep (8–20 ft. depth; 20–50 days DT) ponds with steep
sidewalls in which anaerobic conditions are maintained by keeping wastewater
organic loading so high that complete deoxygenation is prevalent. Although some
oxygenation is possible in a shallow surface zone, once grease form an impervious surface layer, complete anaerobic conditions develop. Waste treatment or
stabilization results from thermophilic anaerobic digestion of organic wastes. The
treatment process is analogous to that occurring in single stage untreated anaerobic digestion of sludge in which acid forming bacteria break down organics. The
resultant acids are then converted to carbon dioxide methane, cells and other
products. In a typical anaerobic lagoon, raw wastewater enters near the bottom of
the pond (often at the center) and mixes with the active microbial mass in the
sludge blanket which is usually about 6 ft. deep. The effluent discharge is located
near one of the sides of the pond, submerged below the liquid surface. Excess
undigested grease floats to the top, forming a heat retaining and relatively airtight
cover. Wastewater flow equalization and heating are generally not practiced.
Excess sludge is washed out with the lagoon effluent. Recirculation of waste
sludge is not required.
Lagoon, facultative Facultative lagoons are intermediate depth (3–8 ft. depth;
20–180 days DT) ponds in which the wastewater is stratified into three zones.
These zones consist of an anaerobic bottom layer, an aerobic surface layer, and an
intermediate zone. Stratification is a result of solids settling and temperaturewater density variations. Oxygen in the surface stabilization zone is provided by
reaeration and photosynthesis. This is in contrast to aerated lagoons in which
mechanical aeration is used to create aerobic surface conditions. In general the
aerobic surface layer serves to reduce odors while providing treatment of soluble
organic by-products of the anaerobic processes operating at the bottom. Sludge at
the bottom of facultative lagoons will undergo anaerobic digestion producing
carbon dioxide, methane, and cells. The photosynthetic activity at the lagoon
surface produces oxygen diurnally, increasing the dissolved oxygen during
daylight hours, while surface oxygen is depleted at night. It is used for treating
raw, screened wastewater, or primary effluent, secondary effluent, or weak
biodegradable industrial wastewater.
Lake dredging Lake dredging helps to maintain a healthy environment for both
aquatic life and recreational activities because both natural and man-made lakes
eroding sediment, silt accumulation, and algae blooms can gradually build up
causing both depth and water quality issues.
Lake An inland body of water, fresh or salt, of considerable size usually greater
than 50 acres (200,000 square meters) and occupying a basin or hollow on the
Earth’s surface.
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M.-H. S. Wang and L. K. Wang
of biological solids (or biosolids). The oxygen required by the aerated lagoon
process is supplied by surface or diffused aerators. As with other suspendedgrowth systems, the turbulence created is used to maintain the contents of the
basin in suspension.
Lagoon, anaerobic Anaerobic lagoons are capable of treating high strength wastewater. They are relatively deep (8–20 ft. depth; 20–50 days DT) ponds with steep
sidewalls in which anaerobic conditions are maintained by keeping wastewater
organic loading so high that complete deoxygenation is prevalent. Although some
oxygenation is possible in a shallow surface zone, once grease form an impervious surface layer, complete anaerobic conditions develop. Waste treatment or
stabilization results from thermophilic anaerobic digestion of organic wastes. The
treatment process is analogous to that occurring in single stage untreated anaerobic digestion of sludge in which acid forming bacteria break down organics. The
resultant acids are then converted to carbon dioxide methane, cells and other
products. In a typical anaerobic lagoon, raw wastewater enters near the bottom of
the pond (often at the center) and mixes with the active microbial mass in the
sludge blanket which is usually about 6 ft. deep. The effluent discharge is located
near one of the sides of the pond, submerged below the liquid surface. Excess
undigested grease floats to the top, forming a heat retaining and relatively airtight
cover. Wastewater flow equalization and heating are generally not practiced.
Excess sludge is washed out with the lagoon effluent. Recirculation of waste
sludge is not required.
Lagoon, facultative Facultative lagoons are intermediate depth (3–8 ft. depth;
20–180 days DT) ponds in which the wastewater is stratified into three zones.
These zones consist of an anaerobic bottom layer, an aerobic surface layer, and an
intermediate zone. Stratification is a result of solids settling and temperaturewater density variations. Oxygen in the surface stabilization zone is provided by
reaeration and photosynthesis. This is in contrast to aerated lagoons in which
mechanical aeration is used to create aerobic surface conditions. In general the
aerobic surface layer serves to reduce odors while providing treatment of soluble
organic by-products of the anaerobic processes operating at the bottom. Sludge at
the bottom of facultative lagoons will undergo anaerobic digestion producing
carbon dioxide, methane, and cells. The photosynthetic activity at the lagoon
surface produces oxygen diurnally, increasing the dissolved oxygen during
daylight hours, while surface oxygen is depleted at night. It is used for treating
raw, screened wastewater, or primary effluent, secondary effluent, or weak
biodegradable industrial wastewater.
Lake dredging Lake dredging helps to maintain a healthy environment for both
aquatic life and recreational activities because both natural and man-made lakes
eroding sediment, silt accumulation, and algae blooms can gradually build up
causing both depth and water quality issues.
Lake An inland body of water, fresh or salt, of considerable size usually greater
than 50 acres (200,000 square meters) and occupying a basin or hollow on the
Earth’s surface.
462
M.-H. S. Wang and L. K. Wang