Economics of Aeration in
Waste Treatment
A. A. KALINSKE, Director of Sanitary Engineering R&D
Eimco Corporation
Salt Lake City, Utah
INTRODUCTION
Biological aerobic oxidation of organics in liquid wastes has, to date, proved
to be the most effective and economical means that we have for removing pollutants, to a high degree, which otherwise would cause depletion of oxygen in our
streams and lakes, create odors, and other undesirable conditions. In any waste
treatment system where aerobic organisms are oxidizing and stabilizing the organic
matter, it is necessary, if we are to obtain the maximum oxidizing rate that these
organisms are capable of producing, to continuously provide oxygen so it is readily
available to the organisms. Also, of course, we must simultaneously bring the
food that is dissolved or suspended in the liquid waste to the surfaces of the organisms. Thus any aeration, or oxygenation, system that we use, must perform
these two basic functions of supplying oxygen and food to the surfaces of the organisms in an efficient manner so far as first cost and operating cost, primarily
power,  are concerned
This paper will be confined to the discussion of the economics of aeration for
those aerobic processes where the organisms are kept in suspension in the liquid
waste; primarily the activated sludge process and all its modifications, and so-
called aerated lagoons.
The three principal oxygenation methods presently in use in liquid waste
treatment are: diffusion of compressed air, diffused air with submerged turbine
dispersers, and mechanical surface entrainment aerators. There are, in addition, two or three miscellaneous methods which will be briefly discussed.
DIFFUSED AIR
For many years the sole and most widely used method of supplying O2 to
liquids, into order to obtain aerobic oxidation of organic matter biologically,
was to diffuse compressed air into the liquids through various types of so-called
"spargers" or porous type of diffusers. These were installed, usually in rectangular basins, so the rising air bubbles would create a strong liquid movement
and turbulence. Many types of "diffusers" have been developed, primarily to reduce the problems of clogging of the small openings by chemical deposition and
biological growths. The rate of O2 transfer is basically influenced by the total
air-water interfacial area produced,   and the mixing and turbulence generated.
In order to obtain quantative information relating to this method of oxygenation it is not necessary that we discuss all the various types of spargers and diffusers that have been developed. It is sufficient to set down the basic criteria
on which the power requirements depend, and the factors influencing the installation costs.    The basic unit that is used to evaluate all oxygenation equipment
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