Converting an aerated lagoon to an activated sludge system can be accomplished by operating the aerated lagoon as a sequencing batch reactor. A portion of the aerated lagoon is partitioned into two or more complete-mix SBR zones. SBRs operate in a sequence of fill, react, settle, and decant. In a single-train lagoon SBR, flow into the basin will continue through all four cycles. Where parallel systems exist, the SBR can be operated as a typical SBR system; however, the construction costs will be greater. As noted previously, Rich (1999) refers to this operation as a continuous-feed, intermittent discharge process, but it is the same as the commercial SBR system marketed by Austgen Biojet. In SBR mode, intermittent aeration is used, and a decanting process is used to transport the settled wastewater to downstream facultative cells or disinfection before discharge. Decant is accomplished with pumps, surface weirs, or floating decant devices. A portion of the MLSS must be wasted during the react (mixing and aeration) phase to keep the process in balance. Rich (1999) suggested adding a recycle pump station and returning the mixed liquor to the influent sewer to provide an anoxic environment for control of sludge bulking.
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