Environmental Engineering Reference
In-Depth Information
8.7 aCTivaTed sludge
PerforManCe-ConTrolling faCTors
To maintain the working organisms in the activated sludge pro-
cess, the operator must be sure that a suitable environment is main-
tained by being aware of the many factors influencing the process and
by monitoring them repeatedly.
Control
is defined as maintaining the
proper solids (floc mass) concentration in the aerator for the incoming
water (food) flow by adjusting the return and waste sludge pumping rate
and regulating the oxygen supply to maintain a satisfactory level of dis-
solved oxygen in the process.
8.7.1 aeration
The activated sludge process must receive sufficient aeration to
keep the activated sludge in suspension and to satisfy the organism
oxygen requirements. Insufficient mixing results in dead spots, septic
conditions, and a loss of activated sludge.
8.7.2 alkalinity
The activated sludge process requires sufficient alkalinity to ensure
that the pH remains in the acceptable range of 6.5 to 9.0. If organic nitro-
gen and ammonia are being converted to nitrate (nitrification), sufficient
alkalinity must be available to support this process, as well.
8.7.3 nutrients
The microorganisms of the activated sludge process require nutri-
ents (nitrogen, phosphorus, iron, and other trace metals) to function.
If sufficient nutrients are not available, the process will not perform as
expected. The accepted minimum ratio of carbon to nitrogen, phospho-
rus, and iron is 100 parts carbon to 5 parts nitrogen, 1 part phosphorus,
and 0.5 parts iron.
8.7.4 ph
The pH of the mixed liquor should be maintained within the range
of 6.5 to 9.0 (6.0 to 8.0 is ideal). Gradual fluctuations within this range
will normally not upset the process. Rapid fluctuations or fluctuations
outside this range can reduce organism activity.
8.7.5 Temperature
As temperature decreases, activity of the organisms will also
decrease. Cold temperatures also require longer recovery time for sys-
tems that have been upset. Warm temperatures tend to favor denitrifica-
tion and filamentous growth.
