Waste Treatment—A Source of Eutrophicaon
The problem in the secondary treatment system which appeared to be associ—
ated with eutrophication in Lake Washington could not be diagnosed by
BOD measurements. Although the bacteria consume organic matter before it
reaches the receiving water, thus preventing the depletion of oxygen in the
stream or lake, this very process releases the inorganic substances which act
as plant nutrients and are discharged into the stream. There, nutrients such as
phosphates and nitrates feed the algae until they become overabundant and
die. Decaying organic masses result, reducing the dissolved oxygen content of
the stream just as much as the organic loads discharged from the older primary treatment facilities which these secondary treatment plants replaced.
In 1968, 467.1 million pounds of phosphates entered surface waters from
all types of municipal sewage treatment facilities serving 139.7 million
people [12]. In the same year, approximately 1.16—1.35 billion pounds of ni—
trogen entered U.S. surface waters from human excrement in effluents from
primary and secondary sewage
treatment plants. Human wastes are the main
source of nitrogen in domestic wastes [13]. The approximate amount of nutri—
ents removed by each type of treatment appears below:
Waste Treatment Process
Primary
Secondary
Total nitrogen [14]
15—20%
ISO—50%
Total phosphorus [15]
10%
30%
The oversight in secondary treatment strategy that promotes eutrophication is the result of utilizing one segment of the aquatic cycle and ignoring
what follows. Thus, in addition to being concerned with the balance of oxygen between oxygen—producing photosynthetic green plants and oxygen—con—
suming animals and bacteria, the closely related balance of nutrients and
other necessary growth factors must also be considered. In the process of pho—
tosynthesis, plants use carbon dioxide, water, and sunlight in order to produce
carbohydrates. Essential plant nutrients also include a number of inorganic
elements and compounds. Nitrogen is needed for the production of amino
acids—the building blocks of proteins. It is available to algae in the form of
nitrates (NO,), nitrites (NOZ), and ammonia (NH,). A limited source is nitrogen gas (N2) which may be xed (changed chemically into nitrates) and in—
corporated into the cells of certain bacteria and blue-green algae. Phosphorus
is needed in small quantities
in all living things to produce ATP (adenosine
triphosphate), an important energy molecule, and the nucleic acids DNA and
RNA which transmit genetic information. Phosphorus is supplied to plants
mainly in the form of phosphates Which, under natural conditions, are derived from phosphate—bearing rocks such as apatite.
Nitrogen and phosphorus are both found in a variety of forms in aquatic
ecosystems as the result of domestic and agricultural wastes. Untreated sew—
age contains nitrogen, usually in the form of m‘ea and ammonia, which may
_
be converted in some secondary sewage
treatment processes,
such as the actiWaste Treatment—A Source of Eutrophication
'l 29
The problem in the secondary treatment system which appeared to be associ—
ated with eutrophication in Lake Washington could not be diagnosed by
BOD measurements. Although the bacteria consume organic matter before it
reaches the receiving water, thus preventing the depletion of oxygen in the
stream or lake, this very process releases the inorganic substances which act
as plant nutrients and are discharged into the stream. There, nutrients such as
phosphates and nitrates feed the algae until they become overabundant and
die. Decaying organic masses result, reducing the dissolved oxygen content of
the stream just as much as the organic loads discharged from the older primary treatment facilities which these secondary treatment plants replaced.
In 1968, 467.1 million pounds of phosphates entered surface waters from
all types of municipal sewage treatment facilities serving 139.7 million
people [12]. In the same year, approximately 1.16—1.35 billion pounds of ni—
trogen entered U.S. surface waters from human excrement in effluents from
primary and secondary sewage
treatment plants. Human wastes are the main
source of nitrogen in domestic wastes [13]. The approximate amount of nutri—
ents removed by each type of treatment appears below:
Waste Treatment Process
Primary
Secondary
Total nitrogen [14]
15—20%
ISO—50%
Total phosphorus [15]
10%
30%
The oversight in secondary treatment strategy that promotes eutrophication is the result of utilizing one segment of the aquatic cycle and ignoring
what follows. Thus, in addition to being concerned with the balance of oxygen between oxygen—producing photosynthetic green plants and oxygen—con—
suming animals and bacteria, the closely related balance of nutrients and
other necessary growth factors must also be considered. In the process of pho—
tosynthesis, plants use carbon dioxide, water, and sunlight in order to produce
carbohydrates. Essential plant nutrients also include a number of inorganic
elements and compounds. Nitrogen is needed for the production of amino
acids—the building blocks of proteins. It is available to algae in the form of
nitrates (NO,), nitrites (NOZ), and ammonia (NH,). A limited source is nitrogen gas (N2) which may be xed (changed chemically into nitrates) and in—
corporated into the cells of certain bacteria and blue-green algae. Phosphorus
is needed in small quantities
in all living things to produce ATP (adenosine
triphosphate), an important energy molecule, and the nucleic acids DNA and
RNA which transmit genetic information. Phosphorus is supplied to plants
mainly in the form of phosphates Which, under natural conditions, are derived from phosphate—bearing rocks such as apatite.
Nitrogen and phosphorus are both found in a variety of forms in aquatic
ecosystems as the result of domestic and agricultural wastes. Untreated sew—
age contains nitrogen, usually in the form of m‘ea and ammonia, which may
_
be converted in some secondary sewage
treatment processes,
such as the actiWaste Treatment—A Source of Eutrophication
'l 29