Patent ID: 7169306

Claim:
A method of operating an aerobic digester sewage treatment system having two aerobic digesters and a gravity thickener basin, in varying conditions of influent flow into the system, comprising: providing the system with an influent bypass capable selectively of delivering influent either to the gravity thickener basin or to one of the aerobic digesters, bypassing the gravity thickener basin, operating the system in different modes as follows: (a) at a lower influent flow by delivering influent via said influent bypass to a first of the digesters, where aerobic digestion occurs, and then to a second of the digesters in a series relationship of the digesters, and then from the second digester into the gravity thickener basin, where the aerobically digested sludge is thickened and supernatant liquid is removed; or (b) at a higher level of flow as a pre-thickened aerobic digestion system with gravity thickening and denitrification in the gravity thickener, influent sludge being delivered to the gravity thickener where thickening occurs, and then to an in-loop digester with the other digester isolated, and with recycling from the in-loop digester back to the gravity thickener basin until a desired solids content is reached in the in-loop digester.