.g.,
,
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a
,_
.
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_
new municipal funding. And, nally, the problem of disposing of the ex—
tracted nutrients would still remain.
The second major problem is the extent to which chemical or other ad—
vanced treatment can prevent phosphates from entering the water. As we
have already seen, municipal wastes contribute a large portion of the total
phosphates entering surface waters. However, large amounts also enter the
water from other sources such as industrial activities, agriculture, Urban run—
off, and private sewage
treatment systems. Removal of phosphates in major
metropolitan treatment plants therefore would take care of only part of the
total problem. Furthermore, the amount of phosphates removed by processes
varies. The preceding cost estimates for the use of lime and iron salts assume
removal of at least 90 percent of the total phosphorus in municipal waste—
‘
water. Such a high removal rate has been achieved in pilot projects and in
some small advanced plants now in operation, but the rate has been lower
elsewhere. An average
of 72—84 percent total phosphorus was removed by
chemical treatment at two plants in Grayling, Michigan, and Mentor, Ohio,
respectively [51]. The current goal in the Lake Michigan Basin is 80 percent
removal.
Under sOme circumstances, removal of 80 percent of the total phosphoms
load in the waste water may still leave enough of the nutrients in the waste
eluent to perpetuate local eutrophic conditions, particularly in lakes already
overburdened with inorganic nutrients. In sum, the strategy to remove phosphates in the waste treatment plant, rather than to eliminate or limit their use
at the source in_products such as detergents, fertilizers, and industrial waste
liquids, leaves many loopholes which permit phosphate discharge to con—
tinue. In addition, the large expenditures required for this strategy places a
Pteventive Measures?
143
,
ff}? »
a
,_
.
_î'
,
_
*!
|
l
_
new municipal funding. And, nally, the problem of disposing of the ex—
tracted nutrients would still remain.
The second major problem is the extent to which chemical or other ad—
vanced treatment can prevent phosphates from entering the water. As we
have already seen, municipal wastes contribute a large portion of the total
phosphates entering surface waters. However, large amounts also enter the
water from other sources such as industrial activities, agriculture, Urban run—
off, and private sewage
treatment systems. Removal of phosphates in major
metropolitan treatment plants therefore would take care of only part of the
total problem. Furthermore, the amount of phosphates removed by processes
varies. The preceding cost estimates for the use of lime and iron salts assume
removal of at least 90 percent of the total phosphorus in municipal waste—
‘
water. Such a high removal rate has been achieved in pilot projects and in
some small advanced plants now in operation, but the rate has been lower
elsewhere. An average
of 72—84 percent total phosphorus was removed by
chemical treatment at two plants in Grayling, Michigan, and Mentor, Ohio,
respectively [51]. The current goal in the Lake Michigan Basin is 80 percent
removal.
Under sOme circumstances, removal of 80 percent of the total phosphoms
load in the waste water may still leave enough of the nutrients in the waste
eluent to perpetuate local eutrophic conditions, particularly in lakes already
overburdened with inorganic nutrients. In sum, the strategy to remove phosphates in the waste treatment plant, rather than to eliminate or limit their use
at the source in_products such as detergents, fertilizers, and industrial waste
liquids, leaves many loopholes which permit phosphate discharge to con—
tinue. In addition, the large expenditures required for this strategy places a
Pteventive Measures?
143