Sedimentation Tank Drainage
Originally the sludge blanket height was adjusted by draining through the sludge hopper that was set at the desired height for the sludge blanket. Slow draining through the main tank drain at the bottom of the tank was also used for sludge blanket draining. The preferred method of sludge draining to maintain a stable blanket was drainage from the bottom of the tank. When the sludge is drained the blanket rolls over on it self as it re-stabilizes. The blanket was less disrupted when drainage was done from the bottom. When samples of the blanket were taken the bottom portion was found to be darker in color and denser than the upper portions of the blanket. This darker color and the anaerobic septic smell that was found during total tank drain lead to the conclusion the bottom of the blanket is older and susceptible to anaerobic digestion. Draining from the bottom would also help to remove this septic sludge from the bottom of the blanket.