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USE OF PONDS
Shallow ponds (3 to 5 feet or 1 to 1.5 meters deep) are
often used to treat wastewater and other wastes instead of, or
in addition to, conventional waste treatment processes. (See
Figures 9.1 and 9.2 for typical plant layouts and Table 9.1 for
purpose of pond parts.) When discharged into ponds, wastes
are treated or STABILIZED^ by several natural processes
acting at the same time. Heavy solids settle to the bottom
where they are decomposed by bacteria. Lighter suspended
material is broken down by bacteria in suspension. Some
wastewater is disposed of by evaporation from the pond sur-
face.
Dissolved nutrient materials, such as nitrogen and phos-
phorus, are used by green ALGAE,2 which are actually micro-
scopic plants floating and living in the water. The algae use
carbon dioxide (COa) and bicarbonate to build body proto-
plasm. In so growing, they need nitrogen and phosphorus in
their metabolism much as land plants do. Like land plants,
they release oxygen and some carbon dioxide as waste prod-
ucts.Purpose
Ponds can serve as very effective treatment facilities. Exten-
sive studies of their performance have led to a better under-
standing of the natural processes by which ponds treat
wastes. Information is provided here on the natural processes
and ways operators can regulate pond processes for efficient
waste treatment.HISTORY OF PONDS IN WASTE TREATMENT
The first wastewater collection systems in the ancient Orient
and in ancient Europe discharged wastewater into nearby
bodies of water. These systems accomplished their intended
purpose until overloading, as in modern systems, made them
objectionable.
1 Stabilized Waste. A waste that has been treated or decomposed to the extent that, if discharged or released, its rate and state of decomposition
would be such that the waste would not cause a nuisance or odors.
2 Algae (AL-gee). Microscopic plants which contain chlorophyll and live floating or suspended in water. They also may be attached to structures,
rocks, or other submerged surfaces. Algae produce oxygen during sunlight hours and use oxygen during the night hours. Their biological activi-
ties appreciably affect the pH, alkalinity, and dissolved oxygen of the water.
In ancient times, ponds and lakes were purposefully ferti-
lized with organic wastes to encourage the growth of algae
which, in turn, greatly increased the production of fish due to
the food supply provided by the algae. This practice still con-
tinues and is a recognized art in Germany.
The first ponds constructed in the United States were built
for the purpose of keeping wastewaters from flowing into
places where they would be objectionable. Once built, these
ponds performed a treatment process that finally became rec-
ognized as such.
The tendency over the years has been to equate pond treat-
ment efficiency with the absence of odors. Actually, the oppo-
site is true as the greatest organic load destroyed per unit of
area (high treatment efficiency) may be accompanied by ob-
jectionable odors.
Since 1958, engineers have designed and constructed a
great number of ponds using research by qualified biological
consultants, current scientific knowledge of ponding, and the
experience of past successes and failures. When operated in
a knowledgeable and purposeful manner, these ponds have
successfully performed a variety of functions.
As a complete process, the ponding of wastewater offers
many advantages for smaller installations. This is true provid-
ed that land is not costly and the location is isolated from resi-
dential, commercial, and recreational areas. The advantages
are that a pond:
1. Does not require expensive equipment;
2. Does not require highly trained operating personnel;
3. Is economical to construct;
4. Provides treatment that is equal or superior to some con-
ventional processes;
5. Is a satisfactory method of treating wastewater on a tem-
porary basis;
6. Is adaptable to changing loads;
7. Is adaptable to land application;
8. Consumes little energy;
9. Serves as a wildlife habitat;
10. Has an increased potential design life;
11. Has few sludge handling and disposal problems; and
12. Is probably the most trouble-free of any treatment proc-
ess when used correctly, PROVIDED A CONSISTENTLY
HIGH-QUALITY EFFLUENT IS NOT REQUIRED.
The limitations are that a pond:
1. May produce odors;
2. Requires a large area of land;
3. Treats wastes inconsistently depending on climatic condi-
tions;
4. May contaminate groundwaters; and
5. May have high suspended solids levels in the effluent.