6.2. Concepts Involved in Planning for Water
Quality
145
oxygen required to oxidize all the material represented by the BOD plus
certain other oxidizable carbonaceous material that cannot be oxidized by
biological means. COD is much easier to measure than BOD, taking only
a few minutes for a single measurement, whereas BOD measurements take
considerably more time.
If all of the five factors listed above are in balance in the receiving water,
adequate natural purification of waste inputs can take place to maintain
an environment that supports aquatic life and is pleasing and not harmful
to man. However, if the waste loading exceeds the natural purification capacity of the stream, offensive and anerobic conditions can result in associated fish kills, sludge banks, unsightly conditions, and unpleasant odors.
Thus a systems analysis must formulate a model that represents the sources
and sinks for dissolved oxygen so that a BOD-DO balance can be maintained as wastes are introduced into streams. The complexity of the model
depends largely on how many sources and sinks for dissolved oxygen are
included in it, and the time period of interest.
Numerous methods of controlling water quality exist or have been proposed. Typical techniques include direct waste treatment, water treatment,
in-stream aeration, and flow augmentation. Incorporation of each method
adds a further dimension of complexity to an already complex planning
problem. In waste water treatment plants a certain fraction of the waste,
say 30-50%, is removed by primary treatment; up to 90-95% can be removed by secondary treatment, and an even higher percentage removed
by what is termed tertiary treatment. After treatment the purified waste
water is discharged into a receiving stream. The present design procedure
for waste treatment plants includes consideration of the characteristics of
the waste water inflows, quality requirements for the treated effluent in
terms of the receiving stream quality specifications, specific requirements
imposed by regulatory agencies, and the reliability of the waste treatment
operation. Usually the cost of waste water treatment for each specific waste
treatment facility can be expressed as a function of the quality of the raw
water, the quantity of the water to be treated, the quality requirements
for the treated water, and the treatment process alternatives considered
for the treatment plant. Regulatory agencies specify the minimum DO requirements in the stream or the maximum allowable concentration of
BOD in the treatment plant effluent.
Water treatment plants will not be specifically included in the model
developed in Section 6.3 because the waste water treatment model can be
used for water treatment plants as well. The quality requirement for the
treated water is normally specified by the usage to which the water is to be
put. Municipal water has different specifications for the dissolved and sus-
Quality
145
oxygen required to oxidize all the material represented by the BOD plus
certain other oxidizable carbonaceous material that cannot be oxidized by
biological means. COD is much easier to measure than BOD, taking only
a few minutes for a single measurement, whereas BOD measurements take
considerably more time.
If all of the five factors listed above are in balance in the receiving water,
adequate natural purification of waste inputs can take place to maintain
an environment that supports aquatic life and is pleasing and not harmful
to man. However, if the waste loading exceeds the natural purification capacity of the stream, offensive and anerobic conditions can result in associated fish kills, sludge banks, unsightly conditions, and unpleasant odors.
Thus a systems analysis must formulate a model that represents the sources
and sinks for dissolved oxygen so that a BOD-DO balance can be maintained as wastes are introduced into streams. The complexity of the model
depends largely on how many sources and sinks for dissolved oxygen are
included in it, and the time period of interest.
Numerous methods of controlling water quality exist or have been proposed. Typical techniques include direct waste treatment, water treatment,
in-stream aeration, and flow augmentation. Incorporation of each method
adds a further dimension of complexity to an already complex planning
problem. In waste water treatment plants a certain fraction of the waste,
say 30-50%, is removed by primary treatment; up to 90-95% can be removed by secondary treatment, and an even higher percentage removed
by what is termed tertiary treatment. After treatment the purified waste
water is discharged into a receiving stream. The present design procedure
for waste treatment plants includes consideration of the characteristics of
the waste water inflows, quality requirements for the treated effluent in
terms of the receiving stream quality specifications, specific requirements
imposed by regulatory agencies, and the reliability of the waste treatment
operation. Usually the cost of waste water treatment for each specific waste
treatment facility can be expressed as a function of the quality of the raw
water, the quantity of the water to be treated, the quality requirements
for the treated water, and the treatment process alternatives considered
for the treatment plant. Regulatory agencies specify the minimum DO requirements in the stream or the maximum allowable concentration of
BOD in the treatment plant effluent.
Water treatment plants will not be specifically included in the model
developed in Section 6.3 because the waste water treatment model can be
used for water treatment plants as well. The quality requirement for the
treated water is normally specified by the usage to which the water is to be
put. Municipal water has different specifications for the dissolved and sus-