Bacteria and Virus Removal

The removal of both bacteria and viruses in multiple-cell pond systems is very effective for both the aerated and unaerated types, as shown in Table 3.7 and Table 3.8. The effluent in all three of the cases in Table 3.8 was undisinfected. The viruses measured were the naturally occurring enteric types and not seeded viruses or bacteriophage. Table 3.8 presents seasonal averages; see Bausum (1983) for full details. The viral concentrations in the effluent were consistently low at all times, although, as shown in the table, the removal efficiency did drop slightly in the winter at all three locations.

Numerous studies have shown that the removal of fecal coliforms in ponds depends on detention time and temperature. Equation 3.25 can be used to estimate the removal of fecal coliforms in pond systems. The detention time used in the equation is the actual detention time in the system as measured by dye studies. The actual detention time in a pond can be as little as 45% of the theoretical design detention time due to short-circuiting of flow. If dye studies are not practical or possible, it would be conservative to assume for Equation 3.26 that the "actual" detention time is 50% of the design residence time:

TABLE 3.7

Fecal Coliform Removal in Pond Systems

Fecal Coliforms (No./100 mL)

TABLE 3.7

Fecal Coliform Removal in Pond Systems

Fecal Coliforms (No./100 mL)

Location

of Cells

Time (d)

Influent

Effluent

Facultative ponds

Peterborough, New Hampshire

3

5l

4.3 x 106

3.6 x 105

Eudora, Kansas

3

4l

2.4 x 106

2.0 x 102

Kilmichael, Mississippi

3

l9

12.8 x 106

2.3 x 104

Corinne, Utah

l

180

1.0 x 106

l.O x 100

Partial-mix aerated ponds

Windber, Pennsylvania

3

30

1 x 106

3.0 x 102

Edgerton, Wisconsin

3

30

1 x 106

3.0 x 101

Pawnee, Illinois

3

60

1 x 106

3.3 x 101

Gulfport, Mississippi

2

26

1 x 106

1.0 x 105

Source: USEPA, Design Manual Municipal Wastewater Stabilization Ponds, EPA 625/1-83015, U.S. Environmental Protection Agency, Center for Environmental Research Information, Cincinnati, OH, 1983.

Source: USEPA, Design Manual Municipal Wastewater Stabilization Ponds, EPA 625/1-83015, U.S. Environmental Protection Agency, Center for Environmental Research Information, Cincinnati, OH, 1983.

Ct 1

Cf = Effluent fecal coli concentration (number/100 mL). Ci = Influent fecal coli concentration (number/100 mL). t = Actual detention time in the cell (d).

kT = Temperature-dependent rate constant (d-1), equal to (2.6)(1.19)(Tw-20). Tw = Mean water temperature in pond (°C). n = Number of cells in series.

See Chapter 4 for a method of determining the temperature in the pond; for the general case, it is safe to assume that the water temperature will be about equal to the mean monthly air temperature, down to a minimum of 2°C.

Equation 3.26 in the form presented assumes that all cells in the system are the same size. See Chapter 4 for the general form of the equation when the cells are different sizes. The equation can be rearranged and solved to determine the

0 0

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