The municipal digester for Troy, Ohio was having problems with settling as well as experiencing a odor problem. When they decided they needed to replace their coarse bubble diffuser ring, they chose a jet mixer/aerator from Mixing Systems, Inc.
The 65 ft (19.8 meter) diameter aerobic digester is designed to digest primary and secondary sludge. The tank has a 18.5 ft (5.6 meter) average side water depth with a conical bottom and the liquid level varies. The design sludge concentration is 3.5%.
Mixing Systems, Inc. solved their settling and odor problems by installing a single jet mixer/aerator near the bottom of the tank in the cone section. This directs the mixing plumes along the tank floor where the solids settled. One screw pump provides the mixing energy for the jet mixer/aerator. One positive displacement blower provides the air for oxidation of the volatile solids in the digester. The pump is run on a continual basis to provide mixing in the digester. The blower is set on a timer to run intermittently to provide oxygen when needed. As a result, there are no odors such as hydrogen sulfide and methane.
The new system also has no in-basin moving parts and easily handles fluctuating liquid conditions. In addition, a backflush system was supplied so the nozzles could be cleaned without draining the tank.