Per Capita Basis

Empirical loading criteria have traditionally been used for determining anaerobic digester volume. The oldest and simplest of these criteria is the per capita volume allowance, that is, based on population served by the treatment plant. Table 5.3 lists typical per capita design values along with other design

TABLE 5.3 Typical Design Criteria for Mesophilic Anaerobic Sludge Digesters

SI Units U.S. Customary Units

TABLE 5.3 Typical Design Criteria for Mesophilic Anaerobic Sludge Digesters

SI Units U.S. Customary Units

Parameter

Units

Value

Units

Value

Volume criteria

Primary sludge

m3/capita m3/capita

0.03-0.06

ft3/capita

1.3-2.0

Primary sludge +

0.07-0.09

ft3/capita

2.6-3.3

trickling filter sludge

Primary sludge + waste

m3/capita

0.07-0.11

ft3/capita

2.6-4.0

activated sludge

Solids loading rate

kg VSS/m3 • d

1.6-3.2

lb VSS/ft3-d

0.1-0.02

Solids retention time

d

15-20

d

15-20

Sludge concentration

Primary sludge +

%

4-7

%

4-7

biological sludge feed

Digested sludge draw-offa

%

4-7

%

4-7

Source: Adapted from U.S. EPA, 1979 and WEF, 1998. a Lower values for single-stage digesters (no supernatant draw-off).

Source: Adapted from U.S. EPA, 1979 and WEF, 1998. a Lower values for single-stage digesters (no supernatant draw-off).

criteria. Per capita loading factors should be used only for initial sizing estimates because it implicitly assumes a value for such important parameters as per capita waste load, solids removal efficiency in treatment, and digestibility of the sludge. These parameters vary widely from one community to another and cannot be predicted accurately. The values for per capita design criteria shown in Table 5.3 should be increased on a population-equivalent basis if the plant influent includes considerable industrial waste loads.

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