Mechanism of Starch Removal in
Activated Sludge Process
SHANKHA K. BANERJI, Assistant Professor
BENJAMIN B. EWING, Professor
R. S. ENGELBRECHT, Professor
Civil Engineering Department
University of Illinois
Urbana, Illinois
RICHARD E. SPEECE, Associate Professor
Department of Civil Engineering
New Mexico State University
University Park, New Mexico
INTRODUCTION
Although significant advances have been made toward explaining the removal
behavior of dissolved organic matter in wastewaters, similar information on colloidal and particulate organic matter in biological waste treatment is still very
limited. This shortcoming assumes more importance when one realizes that a significant fraction of domestic and some industrial wastes is colloidal in nature. It
has been estimated by Balmat (1) that colloids in domestic sewage represent as
much as 52 per cent of the biochemical oxygen demand (BOD) and 54 per cent by
weight of the suspended solids. Industrial wastes from textile desizing processes,
paper and pulp mills, dairy plants and food processing industries are likely to have
a high percentage of colloids.
LITERATURE REVIEW
It has been demonstrated by several investigators (2, 3, 4) that, the removal
of simple soluble organic matter occurs by enzymatic assimilation and that physico-
chemical processes, like adsorption, play no part. The simple organic molecule
is transported by a specific enzymatic process involving permeation across the cell
membrane. The utilization of the substrate occurs inside the cell and involves the
synthesis of new protoplasm and production of energy for cell maintenance.
On the other hand, the mechanism of removal of colloidal components of
wastes in activated sludge systems has not been clarified. It has been suggested by
Eckenfelder and Gloyna (5) that colloidal matter in wastes is removed on contact
by adsorption on the activated sludge surface. Smallwood (3) experimentally
showed that adsorption was the predominant phenomenon in the removal of a colloid, C^-tagged chlorella algae, in an activated sludge system. However, the
substrate was quite unusual and perhaps not representative of colloidal wastes.
Furthermore, the presence of 40 per cent of the radioactivity in the supernatant
liquid after six hrs of aeration did not necessarily mean that the balance of the
radioactivity had been adsorbed on the cell surface. There was a good possibility
that the balance of the radioactivity could have been incorporated into the cell
protoplasm.
The large size of the colloidal molecules prohibits their direct entry into
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