The correct answer is: A. Septic tanks are horizontal continuous flow type of sedimentation tanks.
Septic tanks are anaerobic, not aerobic, and therefore do not use continuous flow. Instead, they use a process called sedimentation to separate solids from liquids. The solids settle to the bottom of the tank, while the liquids flow out to the drain field.
Septic tanks are typically provided a detention period of 12 to 36 hours. This allows time for the solids to settle and for the liquids to be treated by the bacteria in the tank.
Septic tanks are completely covered and high vent shafts are provided for the escape of foul gases. This prevents the gases from building up and causing problems.
Therefore, the incorrect statement is A. Septic tanks are horizontal continuous flow type of sedimentation tanks.