Wastewater Treatment 173y Bars with 1 -inch spaces
Figure 9-4. Bar screen used in wastewater treatment. The top picture shows a manu-
ally cleaned screen; the bottom picture shows a mechanically cleaned screen. (Photo
courtesy of Envirex.)
Most wastewater treatment plants have a settling tank (Figs. 9-6 and 9-7) after
the grit chamber, to settle out as much solid material as possible. Accordingly, the
retention tune is long and turbulence is kept to a minimum. Retention time is the total
time an average slug of water spends in the tank and is calculated as the time required