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Newsletter and Technical Publications
<Planning and Management of Lakes and Reservoirs:
An Integrated Approach to Eutrophication
Abridged Version- A Student's Guide>
Sources of Pollutants
The first step in lake and reservoir management of eutrophication is to
assess the inputs of nutrients and their effects. A model of eutrophication may
be helpful (for further discussion about modeling see Chapter 1). The
measurement and modeling of sources can be used to help assess the priority with
which to reduce the sources.
Ecologically sound planning considers environmental issues at an early stage
of planning and thus prevent pollution problems before they actually emerge.
Wastewater problems can be solved by "end-of-the-pipe" technology or
ecotechnology. Ecotechnology encompasses (a) ecologically sound planning, (b)
use of natural or constructed ecosystems to reduce inputs, and (c) restoration
of ecosystems. Natural or constructed wetlands are being used to treat
wastewater and drainage water from non-point sources including agriculture.
Restoration methods can improve lakes and reservoirs faster than otherwise would
be the case, but they cannot be used alone. If the inputs are not reduced
simultaneously, the restoration methods will have only short-term effects.
| Table 1. |
Generally applied wastewater treatment methods for
reduction in organic matter and nutrients. BOD5 means biological oxygen demand
over 5 days. |
|
| Method |
Goal |
Efficiency %
with good practice |
Costs (year 2000)
($/100m3) |
|
| Mechanical treatment |
BOD5 reduction |
20-35 |
3-8
|
| Biological treatment |
BOD5 reduction |
70-90 |
25-40
|
| Flocculation |
Phosphorus removal
BOD5 reduction |
30-60
40-60 |
6-9
|
Chemical precipitation
Al2(SO4)3
or FeCl3 |
Phosphorus removal
BOD5 reduction |
65-95
50-65 |
10-18
|
Chemical precipitation
Ca(OH)2 |
Phosphorus removal
BOD5 reduction |
85-95
50-70 |
12-18
|
| Ammonia stripping |
Ammonia removal |
70-95 |
25-40
|
| Nitrification |
Ammonium => nitrate |
80-95 |
20-30
|
| Denitrification |
Nitrogen removal |
70-90 |
15-25
|
| Ion exchange |
Phosphorus removal
Nitrogen removal |
80-95
80-95 |
70-100
45-60
|
| Waste stabilization ponds |
Reduction of BOD5
Nitrogen removal |
70-90
50-70 |
2-8
|
| Constructed wetland |
Reduction of BOD5
Nitrogen removal
Phosphorus removal |
20-50*
70-90
0-80** |
5-15
|
| Activated carbon adsorption |
Reduction of organic toxic compounds , BOD5
|
40-95 |
60-90 |
|
* Presumes a pretreatment (BOD5<
about 75 mg/l)
** The removal is dependent on the adsorption capacity of the soil applied and
whether harvest of the plants is foreseen. |
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