Aerated Stabilization Basin
Treatment of White Water
THOMAS P. QUIRK, Partner
FELIX E. MATUSKY, Partner
Quirk, Lawler & Matusky, Engineers
New York, New York
PROCESS DESCRIPTION
The Aerated Stabilization Basin (ASB) process utilizes the basic unit of the
activated sludge process, i.e., aeration and clarification, in a manner designed to substitute land area for operating complexity and high capital cost.
Figure 1 illustrates the flow sheet and the type of BOD and suspended solids
removal performance expected in ASB application.
The detention time of the ASB usually ranges upwards from 1.0 days as compared with a four - six hr period for activated sludge. Because an active biological
population is not maintained, artificially, by sludge recirculation, BOD removal is
dependent upon basin temperature, mixing, and detention time. The concentration
of dissolved solids in white water and their inherent biological activity is such that
significant BOD removal can be obtained within detention periods as low as 1.0 days.
Utilization of these characteristics requires that sufficient oxygen be transferred to
the basin and that the bio-sludge produced be maintained in intimate contact with
basin contents. Both of these requirements can be provided through the use of
mechanical aeration equipment. The mixing characteristics of this equipment can
result in a hydraulic regimen approaching, for practical purposes, a totally mixed condition. Because of the short circuiting aspect of total mixing, increased detention
time will be required to achieve a given removal when compared with a non-mixed
or plug flow regimen.
BOD removal in the ASB, as illustrated in Figure 1, is limited to the oxidation
of a portion of the influent dissolved BOD which has been metabolized by biological
action. The remainder of the metabolized BOD is synthesized to bio-solids which,
themselves, exert a BOD. ASB effluent is then composed of a mixture of suspended
BOD and a residual dissolved BOD.
A clarifier may be placed in the flow sheet to increase system performance by
removal of a portion of the suspended BOD. The use of a clarifier, especially when
settling aids are employed, can significantly reduce basin volume. The cost of the
clarifier option, exclusive of sludge disposal, may be compared with the capitalized
cost of increased detention time and aeration power to achieve a comparable removal.
Basin configuration can be made suitable for a future conversion to an activated
sludge modification as mill production increases and economics preclude continued
use of the ASB process.
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