The effects of aerobic digestion on centrifugation

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Virginia Polytechnic Institute and State University

The purpose of this investigation was to study the effects of activated sludge aerobic digestion on the subsequent performance of a centrifuge. Two runs, utilizing two, 55 gallon barrels as digesters per run, were conducted using detention periods of 15 and 14 days, for run #1 and #2, respectively. Besides centrifugation, various water quality parameters were monitored during the two digestion runs.

Results of this investigation indicated that the aerobic digestion process is suitable for waste activated sludge stabilization. Significant total and volatile solids reductions in conjunction with consistent supernatant COD and BOD₅ reductions were noted. However, prolonged periods of aeration caused a decrease in both the filterability and the centrifugation performances. Both reached their optimum peaks within the first 5 days of aeration and then gradually declined. This seems to indicate that once a sludge reaches the endogenous respiration state that sludge handling becomes much more difficult. The improvement in centrifugation efficiency that occurred during the early stages of aerobic digestion was not enough to justify the expense of aerobic digestion prior to centrifugation.