The Physical Design of
Biological Towers
THOMAS S. ALLEN, Sales Manager
ROBERT P. KINGSBURY, Sales Manager
Environmental Control Division
Ethyl Corporation
Baton Rouge, Lousiana 70801
INTRODUCTION
In the ten years from 1960 to 1970 a new process for the secondary treatment of
municipal and industrial effluents appeared on the waste treatment scene in this country
and abroad. This process, that is referred to as a biological tower, is in fact a direct
descended of the well known rock trickling filter. A number of papers have been given by
these writers (1,2,3,4) and others (5,6,7,8,9) to differentiate what they can accomplish, how
they can be expected to perform on a variety of wastes, and how they should be sized from a
process standpoint. What has been largely lacking is information relating to the translation
of the process specifications to the physical design of the tower.
This paper is intended to be a first step towards filling this need. It will not at any point
recommend a specific method of tower construction, but rather will show with specific
examples how a representative number of towers from all over the world have been
constructed. The authors have in fact functioned only to collect, organize, and present the
engineering details from consulting engineers and engineering companies throughout the
world. The authors are.indebted to the contributing consultants who have given their
permission for the use of their designs in this paper. A complete list of these consultants
together with location of their tower designs is presented in Table I.
This paper breaks down the functions of the various parts of the tower and tries to
illustrate with specific designs varying approaches to handling the different particular
functions. Thus a particular tower may be included only to show how one engineer designed
to distribute waste over the biological media.
During the paper's preparation, thought was given to summarizing the results of the
operating towers included. This proved to be an involved and lengthy presentation. As a
result no operating data on any of the towers is included. Many of the towers covered,
however, have been reported elsewhere from a process standpoint and references have been
cited.
When this paper was prepared, the number of biological towers operating on a
worldwide basis was estimated to be about 400 with over 100 in the U.S. Towers were
selected for this paper to represent the widest possible engineering and construction
variations. Following this scheme, tower design features have been included from four
countries.
This paper is limited to aerobic towers packed with rigid modules of high surface and
low density per cubic foot.
A "state of the art" paper should also cover the very latest thinking in tower design.
This has been done by including several towers which have been designed but not yet
constructed. Some of the features shown on these towers have never been used before, but
represent current solutions to biological tower design problems developed by the concerned
engineers.
Certainly most engineers involved in tower design today will recognize that the field is
rapidly changing. This paper, developed with the cooperation of many of the involved
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