The first stage, at left, operates as a continuous-feed, complete-mix digestion process at 53° C and about 13-day hydraulic resistance time. The second stage, center, operates at greater than 53° C in a four-tank fill/hold/hold/draw mode with a 16-hour minimum batch time.
The District of Columbia's Water and Sewer Authority facility will consist of eight 4 1/2 million-gallon egg-shaped digesters and four 2 1/2 million-gallon silo-shaped digesters, scheduled to be completed around 2012. This rendering shows how the facility will use a flow-through configuration that consists of multiple thermophilic digesters in series. Source: Model by Knoll Architectural Models Inc.; modified by Susan Sicora, Brown and Caldwell