Design of Sludge Digestion Tanks

Recent innovations and improvements in the design of sludge digestion tanks, not yet widely known among engineers, are considered. These include: (1) Essentially flat bottoms with multiple sludge withdrawal pipes; (2) open-ended pipes laid on the floor for the injection of compressed gas, needed for efficient mixing; (3) openings of ample size in the wall at floor level to facilitate emptying and access; (4) sampling pipes from different elevations, of ample diameter, and with discharges designed to avoid splashing; (5) a membrane cover (tried on one digester); (6) Gas piping from a single digester, large enough to carry gas displaced by pumping sludge into the tank plus about eight times the estimated average gas production; and (7) in a trickling filter plant, gas from the digester may be disposed of by blowing it through the filter.