Impact of substrate feed patterns on solids reduction by the Cannibal process.

A biological solids reduction process that uses a side-stream anaerobic reactor (Cannibal process) was investigated to better understand why variations in solids reduction occur in field installations. Field observations indicated that single stage, high sludge age processes would frequently not provide a low solids yield. To study this, laboratory sequencing batch reactors were operated, one as a conventional activated sludge system and the other two with a side-stream anaerobic reactors. The control and one anaerobic side-stream system were operated with a 5-minute feed cycle to mimic a plug flow system. The other anaerobic side-stream system operated with a 4-hour feed cycle to simulate complete mix. The 5 minutes feed Cannibal system generated up to 80%. less biological solids than the control. The 4 hours feed Cannibal system produced less biological solids than the conventional activated sludge system but remained higher than for system with a 5-minute feed time.