PILOT PLANT STUDIES ON HYDROLYTICALLY-ASSISTED
EXTENDED AERATION PROCESSES AT HIGH ORGANIC LOADINGS
A. F. Gaudy, Jr., Professor
Oklahoma State University
Stillwater, Oklahoma 74074
D. Scott, Environmental Engineer
Exxon Company
Houston, Texas 77001
H. Saidi, Graduate Student
Oklahoma University
Norman, Oklahoma 73069
K. S. N. Murphy, Environmental Engineer
Longview, Texas 75601
INTRODUCTION
The development of the extended aeration process has been recounted many times.
The flow sheet for the process is shown in Figure 1 (see heavy line).   The process offers
various advantages, not the least of which is the absence of separate sludge disposal.   The
concept of total oxidation of organic matter synthesized during the purification process,
first proposed by Porges, et al. [ 1 ], has undergone severe criticism and refutation by previous workers and has been supported and reinforced by many studies run in the authors'
laboratories.
= f -    a.      .       -.r.r
Figure 1.  Comparison of flow diagrams for
conventional and extended-aeration activated
sludge plants.
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Briefly, it has been held that not all organic portions of the biomass can be used as
food material by microorganisms.   Thus it has been held that there will be an inert portion
of the sludge which, upon continued recycling with no wastage of sludge, will build up and
cause the system to fail [2,3].   Extracellular bacterial polysaccharide has been cited as a
major inert organic fraction of the cells [2].   However, long-term pilot plant studies (3
years) in the author's laboratory indicated no biochemical failure of this system and it
was also shown that extracellular polysaccharide served, after acclimation, as excellent
substrate for heterogeneous populations of microorganisms [4-6].   This work offered considerable support for the concept of total oxidation.   However, the balanced steady state
►etween synthesis and oxidation of the synthesized material, as envisioned by Porges, et al.
did not occur.   It was found that the autodigestive process could not always be expected
to occur at a set rate.   These were periods of solids accumulation and periods of solids
deaccumulation wherein autodigestion exceeded synthesis.   During periods when the necessary cannibalizing populations were sparse, the aeration solids concentration would
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