Phosphorus Removal

The principal removal mechanisms for phosphorus in FWS systems are adsorption, chemical precipitation, and plant uptake. Plant uptake of inorganic phosphorus is rapid; however, as plants die, they release phosphorus so long-term removal is low. Phosphorus removal depends on soil interaction and detention time. In systems with zero discharge or very long detention times, phosphorus will be retained in the soil or root zone. In flow-through wetlands with detention times between 5 and 10 days phosphorus removal will seldom exceed 1 to 3 mg/L. Depending on environmental conditions within the wetland, phosphorus, as well as some other constituents, can be released during certain times of the year, usually in response to changed conditions within the system such as a change in the oxidation-reduction potential (ORP). Phosphorus removal in wetlands depends on the loading rate and the detention time. Because plants take up phosphorus over the growing season and then release some of it during senescence, reported removal data must be

TABLE 6.4

Phosphorus Removal in Free Water Surface Constructed Wetlands

TABLE 6.4

Phosphorus Removal in Free Water Surface Constructed Wetlands

Location

Hydraulic Loading Rate (in./d)

Total Phosphorus Influent (mg/L)

Total Phosphorus Effluent (mg/L)

Percent Removal

(%)

Listowel, Ontario

0.95

1.9

0.7

62

Pembroke, Kentucky

0.30

3.0

0.1

96

Sea Pines, South Carolina

7.95

3.9

3.4

14

Benton, Kentucky

1.86

4.5

4.1

10

Leaf River, Mississippi

4.60

5.2

4.0

23

Lakeland, Florida

2.93

6.5

5.7

13

Clermont, Florida

0.54

9.1

0.2

98

Brookhaven, New York

0.59

11.1

2.3

79

Sacramento County, California

2.45

2.38

2.07

13

Salem, Oregon

0.40

2.2

1.0

55

Average

2.26

4.98

2.36

46

examined as to when the system was sampled and how long the system had been in operation. Removal rates of phosphorus for 10 constructed wetlands are presented in Table 6.4.

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