Environmental Engineering FOURTH EDITION

2 12 ENVIRONMENTAL ENGINEERING

Raw

Heated to 95°F

Digested

sludge out

Raw

Heated to 95°F

Digested

sludge out

Figure 10-4. Anaerobic sludge digesters. (Photo courtesy of Dorr Oliver Inc.)

suspended solids per day per capita. The total suspended solids load entering the
wastewater treatment facility can be estimated if you know the population served by
the facility. Solids produced in secondary treatment must be added to the total load,
along. with any “special treatment” solids (e.g., phosphorus removal sludges). Once
the solids production is calculated, the digester volume is estimated by assuming a
reasonable loading factor such as 4 kg of dry solids/m3 x day (0.27 lb/ft3 x day). This
loading factor is decreased if a higher reduction of volatile solids is desired.

EXAMPLE 10.2. Raw primary and waste activated sludge containing 4% solids is to be
anaerobically digested at a loading of 3 kg/m3 x day. The total sludge produced in the