The Role of Phosphate in the Activated
Sludge Process
LORNE A. CAMPBELL, Head
Department of Applied Microbiology
The Ontario Research Foundation
Toronto, Canada
INTRODUCTION
"Biological methods for the treatment of sewage and trade effluents were developed largely empirically, but considerable attention is now being given to the
fundamental processes involved, since a proper understanding of these seems essential if further significant improvements are to be made" (1).
This statement appeared in a paper by Downing and Wheatland four years ago,
and during the passage of time the message of these workers has lost none of its
force.
Everyone who works in the field of wastewater purification probably has his
own particular list of fundamental processes the elucidation and proper understanding of which he would consider necessary before further processing improvements
could be made. My own list would give top priority to two questions: 1) Why and
how does activated sludge form? and 2) Once it is formed, Why and how does it
function?
In an attempt to answer the first of these questions, much thought has been
given, and many papers have been written (2,3,4, 5,6). Fortunately for graduate
students no unanimity of opinion exists on the subject and there is still much work
to be done before unanimity does exist.
However, I do not wish to address myself today to the problem of why activated sludge forms, but rather to the second question: once formed, why does it
function? Because the fact that it does function is an anamoly. It is an apparent
contradiction of the theory of catalysis. Activated sludge consists of clumps of
micro-organisms in varying stages of activity and decay. It is difficult to believe
that biological oxidation can be carried out more effectively by such clumps of
organisms many of which, as Wuhrmann has pointed out (5) must be inactive because of the nature of the clump, than by organisms which are completely active
and present a much more favorable surface-to-weight ratio, as is the case when
they are in the log phase of dispersed growth. Lackey and Smith (3) have pointed
out that an efficient activated sludge must be growing and we know that the only
way it can grow -- barring accretions -- is by the reproduction or proliferation of
micro-organisms. Proliferation of micro-organisms normally occurs as free or dispersed growth in the suspending environment. In order to understand more fully
how activated sludge functions it seemed pertinent to try and understand more fully
the factors which control the dispersed growth of sewage micro-organisms. Therefore, experiments were carried out by which it was hoped that some useful knowledge would be gained about this aspect of activated sludge.
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