Encyclopedia of Environmental Science and Engineering, Volume I and II

EUTROPHICATION 395

we are taking out, and much of this excess ultimately gets

washed out into our waterways.

7) Municipal Water Treatment—The water treatment

plants themselves are to a degree responsible for

adding to the eutrophication problem as approxi-

mately 33% of the municipal water in the United

States is treated with compounds containing

phosphorus or nitrogen. Some of the commonly

used nutrient-bearing chemicals or compounds

are ammonia (in the use of chloramines) organic

polyelectrolytes, inorganic coagulant aids, sodium

hexametaphosphate, sodium tripolyphosphate,

and sodium pyrophosphate.

8) Waterfowl—It has been estimated that wild ducks

contribute 12.8 pounds of total nitrogen/acre/year

and 5.6 pounds of total phosphorus/acre/year to

reservoirs or lakes. A number of studies have

been conducted on waterfowl, but it may be con-

cluded that, although there may be some bearing

on localized eutrophication, in general the overall

effect is negligible.

9) Domestic Sewage Effluent—Undoubtedly the

greatest contributor toward the eutrophication

of rivers and lakes is the discharge from sewage

treatment plants. Conventionally treated domestic

sewage usually contains from 15 to 35 ppm total

nitrogen and from 6 to 12 ppm total phosphorus.

In addition there are a large number of minerals

present in sewage which serve as micro-nutrients

for algae and aquatic plants.

Phosphorus in domestic sewage may be derived from

human wastes, waste food (primarily from household garbage-

disposal units), and synthetic detergents. Human wastes have

been reported in domestic sewage at the rate of 1.4 pounds

of phosphorus/capita/year. The largest source of phospho-

rus, however, is from synthetic detergents which amounts to

approximately 2.1 pounds/capita/year. Sawyer indicates that

detergent-based phosphorus represents between 50 and 75%

of the total phosphorus in domestic sewage. It should be

noted that both the use of household garbage-disposal units

and detergents is fairly recent, and accordingly they may be

considered as contributing strongly to the development of

the recently magnifi ed eutrophication problem.

Not all the phosphorus entering a sewage treatment

plant will leave the plant since chemical removal does occur

during the treatment process. Calcium and metallic salts in

large concentrations form insoluble phosphates which are

readily removed. Very often phosphate-precipitating agents

are present in waters containing industrial wastes, and when

these agents are received at the plant, removals in the neigh-

borhood of 60% may be realized.

Nitrogen in domestic sewage is derived from human

wastes and from waste food primarily from household

garbage-disposal units. Human wastes, the major source of

nitrogen, contributes an average of about 11 pounds of nitro-

gen/capita/year. Some reduction in the nitrogen also takes

place during the treatment of the sewage. Many plants treat

the sludge anerobically which permits signifi cant release of

the nitrogen. In general the removal amounts to between 20

and 50%. The higher percentage of removal occurs when

fresh wastes are given complete treatment with no return of

sludge nutrients to the effl uent.

EUTROPHICATION STUDIES

In recent years a considerable number of studies have been

made on eutrophication and related factors. Most of the studies

can be grouped into the following categories:

1) nutrient content of runoff, rainwater, sewage efflu-

ent, bottom mud, etc.

2) nutrient analysis and physical distribution of

nutrients in bodies of water before and/or after

enrichment.

3) methemoglobinemia (illness in infants due to

drinking high nitrate-content water)

4) toxicological and other effects on fish of high

nitrate/high phosphate-content water

5) the chemical composition of plants in both eutro-

phied and non-eutrophied waters

6) the nutrient values of various fertilizers, manures

and other fertilizing elements

7) the nutrient value of various soils

8) the effects of eutrophication on aquatic plants,

animals and fish

9) studies on specific algae under either controlled

laboratory conditions or in a particular body of

water, using artificial or natural environmental

conditions

10) methods for the removal or reduction of nitrogen

and phosphorus

11) nutrient thresholds for growth of algae and aquatic

weeds

12) the effects of eutrophication on the oxygen

balance.

Of the above list, only studies conducted in the areas of

(11) and (12) will be presented below. Work done in regard

to (1) has already been presented. The removal or reduction

of nitrogen and phosphorus (10) will be discussed separately

as part of the subject matter in “CONTROL METHODS.”

NUTRITIONAL THRESHOLDS FOR THE GROWTH

OF ALGAE

Studies conducted by Chu indicate that for growth on artifi cial

media most planktonic algae fl ourish if the total nitrogen con-

tent ranges from 1.0 to 7.0 ppm and the total phosphorus content

ranges from 0.1 to 2.0 ppm. If the nitrogen is reduced below

0.2 ppm and the phosphorus below 0.05 ppm, the growth of

algae appears to be inhibited. The same inhibiting effect is cre-

ated when the nitrogen or phosphorus content is raised above

20.0 ppm. The lower limit of the optimum range of nitrogen

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