Background Concentrations

A successful wetland treatment system is also a successful living ecosystem containing vegetation and related biota. The life and death cycles of this natural biota produce residuals that can then be measured as BOD5, TSS, nitrogen, phosphorus, and fecal coliforms. It is, therefore, not possible for these wetland systems to produce a zero effluent concentration of these materials; some residual background concentration will always be present. Typical concentrations of these constituents are presented in Table 6.9. These background concentrations are not composed of wastewater constituents, but their concentrations may be indirectly

TABLE 6.9

Background Concentrations of Constituents in Typical Wetlands Effluent

TABLE 6.9

Background Concentrations of Constituents in Typical Wetlands Effluent

Constituent

Range

Typical

TSS (mg/L)

2-5

3

BODa (mg/L)

2-8

5

Total nitrogen (mg/L)

1-3

2

Nitrate nitrogen (mg/L)

<0.1

<0.1

Ammonia nitrogen (mg/L)

0.2-1.5

1

Organic nitrogen (mg/L)

1-3

<2

Total phosphorus (mg/L)

0.1-0.5

0.3

Fecal coliform (cfu/100 mL)

50-5000

200

a A range from 5 to 12 has been reported for fully covered with emergent vegetation.

Note: TSS, total suspended solids; BOD, biochemical oxygen demand. Source: Data from USEPA (1999, 2000).

a A range from 5 to 12 has been reported for fully covered with emergent vegetation.

Note: TSS, total suspended solids; BOD, biochemical oxygen demand. Source: Data from USEPA (1999, 2000).

related to the system loadings. A wetland system receiving a nutrient rich wastewater is likely to produce a higher background level than a natural wetland receiving clean water. The background concentrations can also vary on a seasonal basis because of the seasonal occurrence of plant decomposition and the variability in bird and wildlife activity.

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