ENCYCLOPEDIA OF ENVIRONMENTAL SCIENCE AND ENGINEERING - EUTROPHICATION pdf

This chapter concerns itself with the nature of algae, the environmental factors affecting their growth, the nature of the entrophication problem sources, relative quantities of nutrient

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INTRODUCTION

For a considerable time, scientists have been aware of the

natural aging of lakes, a process so slow that it was

consid-ered immeasurable within the lifetime of human beings In

recent years, however, that portion of the nutrient enrichment

or eutrophication of these and other natural bodies of water

contributed by man-made sources have become a matter of

concern Many bodies of water of late have exhibited

biologi-cal nuisances such as dense algal and aquatic weed growths

whereas in the past they supported only incidental populations

of these plants

Excessive nutrients are most often blamed in the

scien-tiﬁ c literature for the creation of the plant nuisances Among

the nutrients, dominant roles have been assigned by most

researchers to nitrogen and phosphorus These elements can

be found in natural waters, in soils, in plants and animals, and

in precipitation Man-made sources for these nutrients are in

domestic wastes and often in industrial wastes

This chapter concerns itself with the nature of algae, the

environmental factors affecting their growth, the nature of

the entrophication problem (sources, relative quantities of

nutrients contributed by these sources, threshold limits for

the growth of aquatic plants), and various techniques for the

removal of those nutrients usually associated with the

eutro-phication problem

THE PHYSICAL NATURE OF ALGAE

Most bodies of water which can be considered eutrophic

exhibit various predominant forms of algae at different times

of the year Algae that are important to investigators concerned

with the eutrophication problem may be classiﬁ ed into four

groups which exclude all but a few miscellaneous forms The

four groups are:

1) Blue-green algae (Myxophyceae)

2) Green algae (Chlorophyceae)

3) Diatoms (Bacillariophyceae)

4) Pigmented flagellates (Chrysophyceae,

Euglenophyceae)

The basis for this classiﬁ cation is the color of the

organ-ism Blue-green and green algae are self descriptive, whereas

diatoms are brown or greenish-brown Pigmented ﬂ agellates

can be brown or green They possess whip-like appendages called ﬂ agella, which permit them to move about in the water

It is not inferred by the above list that all algae are restricted to these colors Rhodophyceae, for example, which are primarily marine algae, are brilliant red

Aquatic biologists and phytologists do not agree on the number of divisions that should be established to identify algae Some authorities use as many as nine divisions while others use seven, ﬁ ve and four Nevertheless, the four divi-sions as suggested by Palmer will be used as they are adequate for the ensuing discussions

BLUE-GREEN ALGAE Blue-green algae as a group are most abundant in the early fall at a temperature range of 70 to 80°F Data obtained from water sources in the southwestern and southcentral United States indicate that for this section of the country maximum growth occurs at the end of February and through-out much of April, May and June When blue-green algae becomes predominant, it frequently indicates that the water has been enriched with organic matter, or that previously there had been a superabundance of diatoms Blue-green algae are quite buoyant due to the oil globules and gas bubbles which they may contain For this and other reasons they live near the surface of the water often producing offensive mats or blankets Since these algae are never ﬂ agellated, they are not considered swimmers although a few, such as oscillatoria and spirulina, are able to creep or crawl by body movements Some of the common blue-green algae are anabaena, aphani-zomenon, rivularia, gomphosphaeria and desmonema

GREEN ALGAE Green algae are most abundant in mid-summer at a tem-perature range of 60 to 80°F For water bodies in the south-western and southcentral United States, maximum growth occurs during the ﬁ rst half of September with little variation throughout the remainder of the year Like the blue-green algae, green algae usually contain oil globules and gas bub-bles which contribute to the reasons why they are found near the surface of the water Green algae are distinguished by their green color which comes from the presence of chloro-phyll in their cells Many of the green algae are ﬂ agellates

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and due to their swimming ability they are frequently found

in rapidly moving streams Some of the common green algae

are chlorella, spirogyra, chlosterium, hydrodictyon, nitella,

staurastrum and tribonema

DIATOMS

Diatoms are usually most prevalent during the cooler months

but thrive over the wide temperature range of from 35 to

75°F For water bodies in the southwestern and

southcen-tral United States, diatoms thrive best in May, September

and October with the maximum growth observed in

mid-October It is generally recognized that many diatoms will

continue to ﬂ ourish during the winter months, often under

the ice The reason for the increase in growth twice a year

is due to the spring and fall overturn, in which food in the

form of carbon, nitrates, ammonia, silica and mineral matter,

is brought to the surface where there is more oxygen and a

greater intensity of light

Diatoms live most abundantly near the surface, but unlike

the buoyant green and blue-green algae, they may be found

at almost any depth and even in the bottom mud Diatoms

may grow as a brownish coating on the stems and leaves

of aquatic plants, and in some cases they grow along with

or in direct association with other algae In rapidly moving

streams they may coat the bottom rocks and debris with a

slimy brownish matrix which is extremely slippery Lastly,

diatoms are always single-celled and nonﬂ agellated

PIGMENTED FLAGELLATES

No classiﬁ cation of algae has caused more disagreement

than that of the pigmented ﬂ agellates The difﬁ culty arises

from the fact that hey possess the protozoan characteristics

of being able to swim by means of ﬂ agella, and the algae

characteristic of utilizing green chlorophyll in association

with photosynthesis Thus they could be listed either as

swimming or ﬂ agellated algae in the plant kingdom, or as

pigmented or photosynthetic protozoa in the animal

king-dom One of many attempts to resolve this problem has been

the proposal to lump together all one-celled algae and all

protozoa under the name “Protista.” This method, however,

has not met with general acceptance For the sanitary

engi-neer the motility of the organism is of lesser importance than

its ability to produce oxygen The pigmentation

character-istic associated with green chlorophyll and oxygen

produc-tion is sufﬁ cient criteria for separating these organisms into

a class by themselves Thus a distinction is made between

pigmented ﬂ agellates (algae) and nonpigmented ﬂ agellates

(protozoa)

Pigmented ﬂ agellates are more abundant in the spring

than at any time of the year although there is generally

con-siderable variation among the individual species Apparently

ﬂ agellates are dependent on more than temperature They

are found at all depths, but usually are more prevalent below

the surface of the water than at the surface

For present purposes pigmented ﬂ agellates can be divided into two groups: euglenophyceae which are grass-green in color and chrysophyceae which are golden-brown

Euglenophyceae are usually found in small pools rich in organic matter, whereas chrysophyceae are usually found in waters that are reasonably pure

Some of the more common pigmented ﬂ agellates are euglena, ceratium, mallomonas, chlamydomonas, cryptomo-nas, glenodinium, peridinium, synura and volvox

MOTILITY

Of additional value in the classiﬁ cation of algae are their means of motility Three categories have been established, namely:

Nekton—algae that move by means of flagella

Plankton—algae that have no means of motility

Benthic algae—algae that attach themselves to a fixed object

NEKTON Nekton are the most active algae and are often referred to

as “swimmers.” Due to their activity they use more energy and in turn release more oxygen during the daylight hours Their cells are supplied with one, two, or more ﬂ agella which extend outward from the front, side or back of the cell These ﬂ agella enable the organisms to move about freely in the aquatic environment and to seek food which,

in the case of turbulent water, is constantly changing in location

In general nekton have the most complex structure of the three categories and come nearest to being simple animals Nekton are the predominant algae found in swiftly moving rivers and streams

According to Lackey, results of tests performed on waters

of the Ohio River show that certain nekton are the only algae that provide reliable clear-cut responses to the presence of pollution and thus are true indicator organisms Five ﬂ ag-ellates have been singled out on the genus level as being common and easily recognized They are (1) cryptomonas, (2) mallomonas, (3) synura, (4) uroglenopsis, and (5) dino-bryon Dinobryon is perhaps the most easily recognized due to its unique shape which resembles a shaft of wheat Samples taken from several rivers indicate that these algae react adversely to the presence of sewage and are found in abundance only in clean water Unfortunately not all experts agree on what constitutes clean water and what algae serve

as indicator organisms Patrick states that the “healthy” por-tion of a stream contains primarily diatoms and green algae Rafter states that the absence of large amounts of blue-green algae is an indicator of clean water Palmer lists 46 species which have been selected as being representative of “clean-water algae,” and these consist of diatoms, ﬂ agellates, green algae, blue-green algae and red algae In addition Palmer lists

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47 species of algae condensed from a list of 500 prepared

from reports of more than 50 workers, as being representative

of “polluted-water algae.” These consist of blue-green algae,

green algae, diatoms and ﬂ agellates

PLANKTON

Plankton are free-ﬂ oating algae which are most commonly

found in lakes and ponds, although they are by no means

lim-ited to these waters Most species are unicellular; however,

they tend to become colonial when their numbers increase,

as in the formation of a heavy concentrated growth known

as a “bloom.” An arbitrary deﬁ nition of a bloom is that

con-centration of plankton that equals or exceeds 500 individual

organisms per ml of raw water Blooms usually show a

pre-dominance of blue-green algae although algae from other

classes can also form blooms

An algae bloom often becomes sufﬁ ciently dense as

to be readily visible on or near the water surface, and its

presence usually indicates that a rich supply of nutrients is

available Other environmental factors may stimulate the

formation of blooms, and a bloom of the same organism

in two bodies of water may or may not result from

identi-cal favorable environmental conditions These growths are

extremely undesirable in bodies of water, in general, and in

potential water supply sources in particular for the following

reasons:

1) They are very unsightly

2) They interfere with recreational pursuits

3) When the water becomes, turbulent, fragments of

the mat become detached and may enter a water

treatment system clogging screens and filters

4) When the algae die (as a result of seasonal changes

or the use of algicides), decomposition occurs,

resulting in foul tastes and odors

5) They may act as a barrier to the penetration of

oxygen into the water which may result in fish

kills

6) They may reduce the dissolved oxygen in the water

through decay or respiration within the bloom

7) Some blooms release toxic substances that are

capable of killing fish and wild life

8) They may cause discoloration of the water

9) They attract waterfowl which contribute to the

pollution of the water

Some of the common blue-green algae that form blooms

are anabaena, aphanizomenon, oscillatoria, chlorella and

hydrodictyon Synedra and cyclotella are common diatoms

that form blooms and synura, euglena and

chlamydomo-nas are common ﬂ agellates that form blooms Filamentous

green plankton, such as spirogyra, cladophora and

zyg-nema form a dense ﬂ oating mat or “blanket” on the surface

when the density of the bloom becomes sufﬁ cient to reduce

the intensity of solar light below the surface Like blooms,

these blankets are undesirable, and for the same reasons

cited earlier However, in addition, blankets also serve

as a breeding place for gnats and midge fl ies, and after storms they may wash up on the shores where they become offensive In many cases hydrogen sulfi de and other gases which are able to spread disagreeable odors considerable distances through the air are liberated In large amounts, hydrogen sulfi de has been known to seriously discolor the paint on lakeside dwellings

BENTHIC ALGAE Benthic algae are those algae which grow in close associa-tion with a supply of food That is, they seek out an aquatic environment where nutrients are adequate, then attach themselves to a convenient stationary object such as a sub-merged twig or rock They may be found in quiet ponds and lakes or in fast-moving rivers and streams In some cases they break away from their attachments and form unsightly surface mats, or they may re-attach themselves somewhere else Chlamydomonas is such an organism, where in one growth phase it may be found attached to a ﬁ xed object, and in another phase it may be dispersed throughout the water

Benthic algae include diatoms, blue-green algae, green algae and a few species of red fresh-water algae None of the pigmented ﬂ agellates are benthic Most attached algae grow

as a cluster of branched or unbranched ﬁ laments or tubes and are fastened at one end to some object by means of an anchoring device Others take the shape of a green felt-like mat (gomphonema), a thin green ﬁ lm or layer (phytoconis),

or a soft fragile tube (tetraspora) Some of the most common benthic algae are cladophora, chara, nitella, ulothrix, cym-bella, vaucheria and gomphonema

ENVIRONMENTAL FACTORS AFFECTING GROWTH

OF ALGAE The effects of certain environmental factors on the growth

of the aforementioned forms of algae have been fairly well deﬁ ned The most important parameters to be considered in the growth pattern are light intensity, temperature, pH and nutritional requirements

LIGHT INTENSITY Light is essential to all organisms which carry on photo-synthesis; however, requirements or tolerance levels differ greatly with the organism For example, terrestrial species

of vaucheria grow equally well in fully-illuminated soil and densely-shaded soil, while a number of blue-green algae grow only in shaded habitats In addition, some algae are unable to endure in the absence of sunlight caused by sev-eral consecutive cloudy days, whereas certain submerged algae are unable to withstand exposure to full sunlight Thus, an algae kill may be noted during a drought where

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shallow water prevents depth-dwelling algae from escaping

the intensity of the sunlight penetration Often muddy rivers

are virtually algae-free due to the lack of penetration of the

sunlight, the Missouri and the Mississippi being two such

rivers

The distribution of algae at the various depths in a

body of water is directly correlated with the intensity of

illumination at the respective depths This distribution

would be difﬁ cult to express in general terms when dealing

with algae on their species level In addition, the depths at

which these species would be found would change with

such variables as growth phase of the organism,

tempera-ture and the absorptive and reﬂ ective characteristics of the

water It can be stated, however, that certain fresh-water

red algae and blue-green algae are found only at

consid-erable depths and that some diatoms exist in the bottom

mud In the most general terms it can also be stated that

algae are found at all levels, but most commonly near the

surface

The vertical distribution may also be related to the

divi-sion of light rays into various spectral colors This dividivi-sion

varies with the concentration of dissolved color material,

plankton and particulate matter, with the seasons, and with

the depth In colored water the violet-blue end of the

spec-trum is absorbed more readily As depth increases light rays

divide differently with greater absorption occurring at the

red end of the spectrum

The depth to which light penetrates has a direct inﬂ uence

on photosynthetic activity The seasonal variation in this

light and the resulting availability of certain dominant wave

lengths may be the reason for ﬂ uctuations in the composition

of the algal population from spring to fall Much more work

is needed in this area

TEMPERATURE

In general, temperature is not the key factor in determining

the nature of the algal ﬂ ora Most species are able to grow

and reproduce if other environmental conditions are

favor-able According to Patrick, however, the above statement is

not true in the case of diatoms, where temperature changes

are more important than any other environmental factor in

inﬂ uencing their rate of growth Additional work in this area

by Cairns indicates that certain diatoms grow best only at a

speciﬁ c temperature, and that at some temperatures they will

not grow at all

Most algae are not affected by minor changes in pH

brought about by the seasonal variations, growths of

carbon-dioxide producing organisms, etc Large changes such as

would be caused by the introduction of industrial wastes or

acid mine waters, will greatly affect algae, usually causing a

decrease in population

The majority of algae thrive when the pH is near 7.0

Some blue-green algae prefer high pHs Anacystis and

coc-cochloric are found at about pH 10.0 with little or no growth

below pH 8.0 Other algae such as eugleny mutabilis,

cryp-tomonas erosa and ulothrix zonata prefer low pHs

NUTRITIONAL REQUIREMENTS AND TOXIC ELEMENTS FOR ALGAE

Calcium

Calcium is not an essential element for most algae, although some cannot develop without it

Calcium and Magnesium

As bicarbonates they are a supplemental supply of carbon dioxide for photosynthesis This accounts for the greater abundance of algae in hard-water lakes than in soft-water lakes

Iron

Most algae grow best when the ferric oxide content of the water is between 0.2 to 2.0 mg per liter Above 5 mg per liter there is a toxic effect unless it is overcome by the buffering action of organic compounds or calcium salts Certain dia-toms (eunotia and pinnularia) are found in iron-rich water Efﬂ uent from steel mills may be toxic to most algae if the resulting iron concentration exceeds the toxic limitation

Copper

Copper is extremely toxic to algae in the range of 0.1 to 3.0 ppm as copper sulfate; the sulfate form being used as an algi-cide Some algae are able to tolerate large amounts of copper ion and are considered copper-sulfate resistant Protococcus, for example, is not destroyed by 10 ppm of copper sulfate

Phenol

At a concentration of up to 1.9 mg per liter, phenol appar-ently has no toxic effect on diatoms

Nitrates, Phosphates and Ammonia

These are essential food elements necessary for growth Nitrogen may be obtained from nitrates, nitrites or simple ammonia compounds The primary source of these nutrients

is from sewage treatment plant efﬂ uents, although nitro-gen may be derived from the atmosphere, land runoff, etc (See section on EUTROPHICATION.) In general as little

as 0.3 to 0.015 ppm of nitrates and phosphates will produce blooms of certain species of algae, other conditions being favorable

Oil

Streams polluted with oil are usually low in algae One vari-ety of diatoms may be dominant in such waters

Salinity

Increases in salinity up to about one percent do not affect the algae population Signiﬁ cant increases, such as caused

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by salt-brine wastes, may destroy most of the algae present,

however Certain fresh-water algae may become adapted to

water with slowly increasing salinity

Hydrogen Sulfide

At a concentration of 3.9 ppm, hydrogen sulﬁ de is toxic to most

diatoms Some resistant species are achnanthese afﬁ nis, cymbella

ventricosa, hantzschia amphioxys and nitzschia palea

Silica

Silica is necessary for the growth of diatoms whose cell wall is

composed of silica Presently no limits have been determined

(to the author’s knowledge)

Vitamins

Several vitamins in small quantities are a requisite to growth

in certain species of algae Chief among these vitamins are

vitamin B-12, thiamine and biotin These vitamins are

sup-plied by bottom deposits, soil runoff and by the metabolites

produced by other organisms

Micronutrients

Substances such as manganese, zinc, molybdenum,

vana-dium, boron, chlorine, cobalt, etc are generally present in

water in the small concentrations sufﬁ cient for plant growth

Carbon Dioxide

Carbon dioxide is necessary for respiration If it is deﬁ cient,

algae may remove carbon dioxide from the atmosphere

Chlorine

Chlorine is toxic to most algae and is used as an algicide in

the range of 0.3 to 3.0 ppm It is used as an algicide in the

treatment plant and distribution system Some algae,

cos-marium for example, are resistant to chlorine Protococcus,

which is resistant to copper sulfate, is killed by 1 ppm of

chlorine Therefore, algae resistant to the copper ion may not

be resistant to the chlorine ion and vice versa

Calcium Hydroxide (lime)

An excess of lime in the water, as may be introduced during

pH adjustment for coagulation, results in the death of certain

algae Five ppm of lime with an exposure of 48 hours has

been lethal to melosira, nitzschia and certain protozoa and

crustacea

THE EUTROPHICATION PROBLEM

Of the factors previously discussed which promote the growth

of algae, that factor which man has altered is the nutrient

concentration in may of the natural waterways

In simplest terms, eutrophication is the enrichment of waters by nutrients from natural or man-made sources Of the many nutrients which are added to the waters by man-made sources, nitrogen and phosphorous are most often cited

by researchers as being the key nutrients responsible for the promotion of algae growth In nearly all cases when the nitrogen and phosphorus level of a body of water increases, there will be a corresponding increase in the growth of algae and aquatic plants Such growth greatly speeds up the aging process whereby organic matter invades and gradually dis-places the water until eventually a swamp or marsh is formed Unfortunately, the process of eutrophication is often difﬁ cult

to reverse in bodies of water such as large lakes where the

ﬂ ushing or replacement time for the waters can be in the order of years

The following sections provide the relative magnitude of natural and man-made sources of nutrient material associated with plant growth

SOURCES OF NUTRIENTS While it is recognized that certain algae require a number

of chemical elements for growth, it is also known that algae can absorb essential as well as superﬂ uous or even toxic elements Although every essential element must be present in algae, this does not mean that every element is essential On the other hand, the absence of certain nutrient elements will prevent growth Nutrients may be classiﬁ ed

as (1) “absolute nutrients,” which are those which cannot

be replaced by other nutrients, (2) “normal nutrients,” which are the nutrients contained in the cell during active growth, and (3) “optimum maximum growth.” It may also

be well to assign a broad meaning to the word “nutrient” and deﬁ ne it as anything that can be used as a source of energy for the promotion of growth or for the repair of tissue

In evaluating the effects of nutrients on algae, care must

be exercised to consider the interaction between nutrients and other physical, chemical or biological conditions Rapid growth of algae may be stimulated more by factors of sun-light, temperature, pH, etc., than by an abundance of nutrient material Tests performed with nitzschia chlosterium, in order

to study the interaction of environmental factors showed that two identical cultures of the organism, when supplied with a reduced nutrient level, had a lower optimum light intensity and optimum temperature for maximum growth Thus light intensity and temperature data should accompany data on nutrient concentration and growth rate

Of all the possible nutrients, only nitrogen and phosphorus have been studied in depth both in the ﬁ eld and in the labo-ratory This is because of the relative difﬁ culties associated with the study, analysis and measurement of trace elements, compounded by the minute impurities present in the regents and distilled water In addition, nitrates and phosphates have a long history of use in agricultural fertilizers where determination of their properties have been essential to their economical use

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The following are the most common sources of nitrogen

and phosphorus in bodies of water:

1) Rainfall—Based on experimental data, it has been

found that rainwater contains between 0.16 and

1.06 ppm of nitrate nitrogen and between 0.04 and

1.70 ppm of ammonia nitrogen Computations

based on the nitrogen content of rainwater show

that for Lake Mendota, Wisconsin, approximately

90,000 pounds of nitrogen are available each year

as a result of rainfall Thus it can be seen that

rainfall plays a significant role in building up the

nitrogen content of a lake or reservoir especially

if the surface area is large

An examination of the phosphorus content of rainwater

of different countries shows that a number of concentrations

may exist ranging from 0.10 ppm to as little as an

unmeasur-able trace, the latter reported in the Lake Superior region

of the United States In view of the wide variation in the

determinations, little can be stated at present regarding the

degree of phosphorus build-up in impoundments resulting

from rainwater

2) Groundwater—Studies conducted on sub-surface

inflows to Green Lake, Washington, show that this

water contains approximately 0.3 ppm of

phospho-rus Other reports, however, claim that the amount

of phosphorus in groundwater is negligible

Investigations into the nitrate content of groundwater

pro-duced variable results; however, it can be stated that 1.0 ppm

is a reasonable ﬁ gure The results of the above studies on both

nitrogen and phosphorus can be summarized by stating that

groundwater should not be discounted as a possible source of

nutrients and that quantitative values should be obtained for

the speciﬁ c locality in question

water drainage, overflow from private disposal

systems, organic and inorganic debris from paved

and grassed areas, fertilizers from lawns, leaves,

etc In view of the variable concentration of the

above material, precise figures cannot be obtained

on the phosphorus or nitrate content that would be

meaningful for all areas

Studies conducted in 1959 and 1960 by Sylvester on

storm water from Seattle street gutters shows the following

nutrients:

Organic nitrogen—up to 9.0 ppm

Nitrate nitrogen—up to 2.8 ppm

Phosphorus—up to 0.78 ppm soluble and up to 1.4 ppm

total

4) Rural Runoff—Rural runoff for the purposes

of definition may be considered as runoff from

sparsely-populated, wooded areas with little or

no land devoted to agriculture Investigations by

Sylvester showed that the phosphorus content

of drainage from three such areas in the state of

Washington contained 0.74, 0.77 and 0.32 lb./acre/

year, or a total concentration of 0.069 ppm The

corresponding nitrate nitrogen concentration and

organic nitrogen concentration amounted to 0.130 and 0.074 ppm, respectively

5) Agricultural Runoff—Agricultural runoff is one

of the largest sources of enrichment material and may be derived from two sources—wastes from farm animals and the use of nitrogen and phos-phorus-containing fertilizers

Farm-animal wastes add both large quantities and high concentrations of nutrients to adjacent streams and rivers The large concentrations are due primarily to the practice of herding animals in relatively conﬁ ned areas A comparison

on the nutrient value of animal wastes and human wastes has been made in a study by the President’s Science Advisory Committee According to the ﬁ ndings, a cow generates the waste equivalent of 16.4 humans, a hog produces as much as 1.9 humans and a chicken produces as much as 0.14 humans The use of chemical fertilizers in the United States has grown almost 250% in the decade from 1953 to 1963 In

1964 the use of phosphorus-containing fertilizers and the use

of nitrogen-containing fertilizers reached approximately 1.5 and 4.4 million tons, respectively, per year Most all of this fertilizer is distributed to soil already high in natural-occurring nitrogen When nitrogen fertilizer and natural soil nitrogen combine, there is a great increase in crop production, but also a greater opportunity for loss of this nitrogen in runoff This loss will increase if the fertilizer is not properly applied,

if it is not completely utilized by the crops, if the crops have

a short growing season (the land being non-productive for a time), if the land is irrigated, and if the land is sloped The addition of nitrogen-bearing fertilizers also increase the quantity of mineral elements in the soil runoff which are necessary for the growth of aquatic plants and algae When applied, the nitrogen in the fertilizer is converted into nitric acid which combined with the minerals in the soil, such as calcium and potassium, rendering them soluble and subject

to leaching

6) Industrial Wastes—The nutrient content of indus-trial waste effluents is variable and depends entirely upon the nature, location and size of the industry In some cases the effluents are totally free of nitrogen and phosphorus

The meat packing industry is one of the chief producers of nitrogen-bearing wastes The greatest producer of phosphate-bearing wastes is most likely the phosphate-manufacturing industry itself Most phosphate production in the United States

is concentrated in Florida and as a result many severe local-ized problems of eutrophication have resulted in that state Fuel processing industries and petroleum reﬁ neries dis-charge vast quantities of nitrogen into the atmosphere both

in the gaseous state and solid state as particulate matter This nitrogen is then washed from the atmosphere by the rain and carried back to earth In 1964, the 500 billion tons of coal used in the United States released about 7.5 million tons of nitrogen into the atmosphere, most of which has returned to

be combined with the soil This greatly exceeds the use of nitrogen in the form of fertilizers which, as previously stated, amounted to 4.4 million tons for that year Thus, through the atmosphere we are bringing more nitrogen into the soil than

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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

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-eutroeutro-phied 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 concon-tent 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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varies with the organism and with the type of nitrogen For

ammonia nitrogen the optimum range varies from 0.3 to 5.3

ppm and for nitrate nitrogen the optimum range falls between

0.3 and 0.9 ppm Below these values the growth rate decreases

as the concentration of nitrogen decreases

Apparently the use of the various forms of nitrogen by

algae is not constant throughout the year Tests conducted

at Sanctuary Lake in Pennsylvania (1965) indicate that the

order of preference for the three forms of

nitrogen—ammonia-nitrogen, nitrate-nitrogen—ammonia-nitrogen, and nitrite-nitrogen—are deﬁ ned

by three seasonal periods, which are:

(2) Nitrate nitrogen (3) Nitrite nitrogen

(2) Nitrate nitrogen (3) Nitrite nitrogen The amount of nitrogen in the aquatic environment is

important to algae because it determines the amount of

chlo-rophyll that may be formed Too much nitrogen, however,

inhibits the formation of chlorophyll and limits growth

Laboratory studies on algae conducted by Gerloff indicate

that of all the nutrients required by algae, only nitrogen,

phos-phorus and iron may be considered as limiting elements, and

of these three, nitrogen exerts the maximum limiting inﬂ

u-ence Approximately 5 mg of nitrogen and 0.08 mg of

phos-phorus were necessary for each 100 mg of algae produced

The corresponding nitrogen/phosphorus ratio is 60 to 1

Hutchinson cites phosphorus as being the more

impor-tant element since it is more likely to be deﬁ cient When

phosphorus enters a body of water, only about 10% is in the

soluble form readily available for algal consumption During

midsummer total phosphate may increase greatly during the

formation of algal blooms, while soluble phosphate is

unde-tectable due to rapid absorption by the growing algae Very

often during warm weather these blooms are stimulated by

the decomposition and release of soluble phosphates from

the bottom sediments, deposited by the expired blooms of

previous seasons Thus when phosphates are added to a

lake, only a portion of the phosphates are used in

produc-ing blooms The blooms thrive and consume phosphates for

only a short time, and a signiﬁ cant amount ﬁ nds its way to

the bottom sediments where it will be unavailable to further

growth of aquatic vegetation

Prescott examined a number of algae and concluded

that most blue-green algae are highly proteinaceous

Aphanizomenon ﬂ os-aquae, for example, was shown to

con-tain 62.8% protein Green algae were found to be less

pro-teinaceous Spirogyra and cladophora, for example, contain

23.8 and 23.6% respectively Thus it can be concluded that

the nitrogen requirement (for the elaboration of proteins)

depends on the class of algae, and that blue-green algae

would require more nitrogen than green algae

Provasoli examined 154 algal species to determine the requirements for organic micronutrients He found that although 56 species required no vitamins, 90 species were unable to live without vitamins such as B 12 , thiamin and biotin, either alone or in various combinations He concluded that these vitamins are derived from soil runoff, bottom muds, fungi and bacterial production (B 12 ), and from a natural resid-ual in the water

Ketchum and Pirson conducted a series of examina-tions on the inorganic micronutrient requirements of algae and concluded that a number of elements are necessary for growth No numerical values were assigned to the require-ment levels Those elerequire-ments shown to be essential were C,

H, O, P, H, S, Mg, Ca, Co, Fe, K and Mo Those elements which may be essential (subject to further study) were Cu,

An, B, Si, Va, Na, Sr, and Rb

In summation, absolute values and nutrient thresholds cannot be set at this time because too little is known regard-ing the requirements of individual species It might be stated

in general terms, however, that nitrogen and phosphorus are two essential nutrient elements related to the production of blooms, and that if they are present in the neighborhood

of 0.2 ppm and 0.05 ppm, respectively, algal growths will increase signiﬁ cantly

NUTRITIONAL THRESHOLDS FOR THE GROWTH

OF AQUATIC PLANTS Studies conducted by Harper and Daniel indicate that sub-merged aquative plants contain 12% dry matter of which 1.8% are nitrogen compounds and 0.18% are phosphorus compounds Hoagland indicates that when the nitrate content

of water is high, nitrates may be stored in aquatic plants to

be reduced to the usable ammonia nitrogen form as required Subsequent investigations show that ammonia nitrogen can

be substituted for nitrate nitrogen and used directly Light apparently is not a necessary factor in the reduction of the nitrogen

Muller conducted a number of experiments on both algae and submerged aquatic plants, and concludes that exces-sive growths of plants and algae can be avoided in enriched waters if the concentration of nitrate nitrogen is kept below 0.3 ppm, and if the concentration of total nitrogen remains below 0.6 ppm

OXYGEN BALANCE Recently, attention has been given to the effect of the intense growths of algae on the oxygen balance of natural water-ways It has been established that the dissolved oxygen concentrations may exhibit wide variation throughout the course of the day This variation is attributed to the ability of algae to produce oxygen during the daylight hours, whereas they require oxygen for their metabolic processes during the hours of darkness

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In addition, since algae are organic in nature, they exert

a biochemical oxygen demand (BOD) on the stream oxygen

resources as does other materials which are organic

Extensive tests were run on the Fox River in Wisconsin

by Wisniewski in 1955 and 1956 to examine the inﬂ uence

of algae on the puriﬁ cation capacity on rivers In the most

general terms, the studies indicate that algae increase the

B.O.D by adding organic matter capable of aerobic

bacte-rial decomposition and by the respiration of the live cells

which utilize oxygen during the absence of light In the

presence of light, algae produce oxygen and as a result

may cause a “negative” B.O.D for a production of oxygen

in excess of that required for the normal B.O.D

require-ments or aerobic bacterial stabilization In addition to the

above, the following speciﬁ c conclusions were drawn from

the tests:

1) The oxidation rate resulting from the respiration

of live algae was much lower than that obtained

by the biological oxidation of the dead algae

2) The ultimate B.O.D of live algae was practically

the same as for dead algae

3) A linear relationship was found to exist between the

five-day B.O.D of suspended matter and volatile

suspended solids concentration

4) The B.O.D increases with increases in suspended

solids, the latter consisting largely of algae

Additional work was done in this area and reported

in 1965 by O’Connell and Thomas They note that the

oxygen produced by photosynthetic plants is affected

greatly by changes in the availability of light due to cloud

cover, turbidity in the water, etc., and therefore it may be

too variable to be used as a reliable factor in evaluating

the oxygen resources of a river Another variable may be

the loss of oxygen to the atmosphere during the daylight

hours, caused by excess oxygen production and localized

supersaturation

An important consideration is the type of photosynthetic

plants which are prevalent in a river According to the above

authors, if benthic algae and/or rooted aquatic plants are

predominant (in lieu of phytoplankton), there will be little

beneﬁ cial effect on the oxygen balance In addition

night-time absorption of oxygen through respiration can seriously

reduce daily minimum concentrations of dissolved oxygen

Determination of the effects of the benthic algae

oscillato-ria along a ﬁ vemile stretch of the Truckee River in Nevada

indicated that on the average of the organism produced 72.5

pounds/acre/day of oxygen through photosynthesis Oxygen

uptake for these same organisms amounted to an average of

65.4 pounds/acre/day

An examination of the oxygen proﬁ les indicated that the

oxygen variation throughout the day ranged from 2 (at night)

to 13 (during daylight) parts per million

It is dissolved oxygen variations such as the above which

has been responsible for the disappearance of high quality

game ﬁ sh in many of our natural waterways

CONTROL METHODS TO PREVENT EUTROPHICATION

There are a number of methods which attempt to limit the amounts of nutrients in bodies of water once the point of eutrophy has been reached Some of these include dredging and removing bottom sediments with an inert liner, harvesting the algae, ﬁ sh, aquatic weeds, etc., and diluting the standing water with a water of lower nutrient concentration Although these methods may have their proper application, if eutrophi-cation is to be decelerated, nutrient removal must start before wastes are permitted to enter the receiving waters

Regarding the speciﬁ c nutrients necessary to be removed, most researchers have placed the blame of eutrophication in waters to the inorganic forms of phosphorus and nitrogen

A smaller number of researchers are claiming that the algae– bacteria symbiosis relationship might be responsible for the rapid growth of blooms and that the amount of algae pres-ent in natural waters is in direct balance with the amount of carbon dioxide and/or bicarbonate ions in the waters They further argue that an external supply of the above elements

is necessary for the growth of algae populations Since nei-ther theory has been proved conclusively to date, the control methods given will be for the removal of nitrogen and phos-phorus since it is these nutrients which most researchers lay

to the blame of eutrophication and which have been there-fore subsequently studied in detail

NITROGEN REMOVAL

Land Application

It has been found that nitrogen-bearing waters, when perco-lated through soil are subjected to physical adsorption and biological action which removes the nitrogen in the ammo-nium form It appears, however, that the nitrate form of nitrogen remains unaffected At present this process is only

at the theoretical stage, and to the author’s knowledge no full-scale application has been attempted Considerable land area would be involved which may prove a deterrent

Anaerobic Denitrification

In this process, the nitrate present in sewage is reduced by denitrifying bacteria to nitrogen and nitrous oxide gases which are allowed to escape into the atmosphere In order to satisfy the growth and energy requirements of the bacteria, methanol

in excess of 25 to 35% must be added as a source of carbon The removal efﬁ ciency ranges from 60 to 95% The major advantage to anaerobic denitriﬁ cation is that there are

no waste products requiring disposal This process is still primarily in the experimental stage at this date

Ammonia Stripping

Ammonia stripping is an aeration process modiﬁ ed by ﬁ rst raising the pH of the wastewater above 10.0 At this pH the

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ammonia nitrogen present is readily liberated as a gas and

is absorbed into the atmosphere Aeration is usually

accom-plished in a packed tray tower through which air is blown

This process is suited to raw sewage where most of the

nitrogen is either in the ammonia form or may be readily

converted to that form In secondary treatment processes

the conversion of ammonia nitrogen to nitrate nitrogen can

be retarded by maintaining a high organic loading rate on the

secondary process

Efﬁ ciency of nitrogen removal by ammonia stripping is

excellent with 80 to 98% reported There is also the advantage

that there are no waste materials which must be disposed of

PHOSPHORUS REMOVAL

Chemical Precipitation

Precipitation of phosphorus in wastewater may be

accom-plished by the addition of such coagulants as lime, alum,

ferric salts and polyelectrolytes either in the primary or

sec-ondary state of treatment, or as a separate operation in

ter-tiary treatment In general, large doses in the order of 200

to 400 ppm of coagulant are required However, subsequent

coagulation and sedimentation may reduce total phosphates

to as low as 0.5 ppm, as in the case of lime Doses of alum

of about 100 to 200 ppm have reportedly reduced

orthophos-phates to less than 1.0 ppm

Phosphorus removal by chemical coagulation generally

is efﬁ cient with removals in the order of 90 to 95% reported

Additional beneﬁ ts are gained in the process by a reduction

in B.O.D to a value of less than 1.0 ppm Both installation

and chemical costs are high, however, and the sludges

pro-duced are both voluminous and difﬁ cult to dewater

Sorption

Sorption is the process of passing wastewater

down-ward through a column of activated alumina whereby the

common form of phosphate are removed by ionic attraction

Regeneration of the media is accomplished by

backwash-ing with sodium hydroxide followed by acidiﬁ cation with

nitric acid

Contrary to alum treatment, this process has the advantage

in that sulfate ions are removed and thus the sulfate

concentra-tion is not increased Since no salts are added, the pH and the

calcium ion concentration remain unchanged The process is

efﬁ cient with more than 99% removal reported The process

should be limited to wastewater with a moderate amount of

solids so as not to clog the media

REMOVAL OF NITROGEN AND PHOSPHORUS

Biological (secondary) Treatment

In the secondary method of sewage treatment, bacteria

uti-lize soluble organic materials and transform them into more

stable and products In the process nitrogen and phosphorus

are removed from the wastes, utilized to build new cellular materials, and the excess is stored within the cell for future use For each pound of new cellular material produced, assuming the material to be in the form of C 5 H 7 NO 2 , about 0.13 pounds of nitrogen and about 0.026 pounds of phospho-rus would be removed from the sewage In the actual opera-tion of this process not all of this nitrogen is removed unless additional energy material in the form of carbohydrates

is added Although it may be possible to eliminate all the nitrogen, a considerable amount of soluble phosphorus may remain, possibly because of the high ratio of phosphorus

to nitrogen in sewage, attributable to synthetic detergents Much of this phosphorus can be removed by absorption on activated sludge ﬂ oc when it is later separated and removed This process offers a 30 to 50% removal of nitrogen and about a 20 to 40% removal of phosphorus without the spe-cial addition of carbohydrates

Reverse Osmosis

The process of reverse osmosis consists of passing wastewa-ter, under pressures as high as 750 psi, through a cellulose acetate membrane The result is the separation of water and all ions dissolved therein In actual practice the process has been plagued with difﬁ culties primarily due to membrane fouling

or premature failure of the membrane In addition some nitrate and phosphate ions escape through the membrane

Removal efﬁ ciency ranges from between 65 to 95% (for nitrogen)

Electrodialysis

Like reverse osmosis, electrodialysis is a non-selective demineralization process which removes all ions which would include the nitrate and phosphate ions Essentially

an electric current is used in conjunction with a membrane inserted in the line of current ﬂ ow to separate the cations and anions

The problems that have developed in the operation of this process include membrane clogging and precipitation

of low-solubility salts of the membrane Acidiﬁ cation of the water and removal of some of the solids prior to treatment has been effective in minimizing these problems, although it adds to the cost

Removal efﬁ ciency ranges from between 30 to 50% (for nitrogen)

Ion Exchange

In the ion exchange process wastewater is passed through

a media bed which removes both anionic phosphorus and anionic nitrogen ions and replaces them with another ion from the media Regeneration of ion exchangers is com-monly accomplished with inexpensive sodium chloride, and frequently the salt is salvaged by recycling the backwash water

Difﬁ culties in the process may be caused by fouling of the exchange resin due to organic material and reduction in

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