An Automated BOD Respirometer
ROBERT M. ARTHUR, Associate Professor of Bioengineering
Rose Polytechnic Institute
Terre Haute, Indiana
INTRODUCTION
Manometric respirometers are commonly used to measure the oxygen demand
of biological cultures. Their use as a research tool to measure oxygen demand of
nonhomogeneous cultures such as found in domestic and industrial waste is increasing. Thus far they are infrequently used to measure routine BOD of waste
cultures. The 11th edition of Standard Methods does not include this technique
as a method for measuring BOD of sewage, but does include it as a tentative
method for industrial waste. The instrument described herein provides for automatic readout of manometer data which may make the use of manometry superior
to dilution methods of measuring BOD.
The merits of the dilution and manometric techniques for determining five-
day BOD have been studied by several investigators. Gellman and Heukelekian
(1) point out that both five-day and ultimate oxygen demands are higher with
manometric methods, but that the reproducibility is about the same as that with
dilution methods. Jaeger and Niemitz (2) indicate that the reproducibility is
higher with manometric methods and that continuous observation of the effect of
phenomena is an advantage of manometric methods. Lee and Oswald (3) agree
with most of the above observations and, in addition, point out that manometric
methods are useful when a complete demand curve is desired, but would not be
suitable if a large number of separate tests of five-day BOD are required.
From the above it appears that there is little argument concerning the accuracy of either method when five-day or ultimate BOD's are to be determined.
However, it is unrealistic and uneconomical to use manometric methods to determine five-day BOD. The results as far as usefulness is concerned are not any
more valuable than those obtained by the dilution technique. It has been previously pointed out that manometric methods provide a complete graph of oxygen
demand. This advantage should be exploited and used to determine the oxygen
demand at much shorter periods than five days. The obvious advantage of short
term BOD's is well recognized and could offset the cost of manometric equipment.
Much work has been done recently by several investigators to develop a two-day
or perhaps even a one-day BOD test. Most of this work has been done using standard dilution techniques. The continuous record which is available by manometric
methods may make an even shorter test practical.
One reason for the lack of interest in using manometric methods may be the
work involved in taking data which must then be plotted to obtain a complete and
continuous record of demand. In addition, manometric equipment which is presently available commercially does not lend itself readily to waste studies. These
devices are usually designed for small amounts of pure cultures where the immediate demand, i.e., within eight hrs, is to be determined. Large volume respirometers have been constructed by several investigators as indicated by Gellman and Heukelekian (1). However, data must still be taken periodically and
then plotted, which may result in errors and a complete graph is never possible to
obtain.
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