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<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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