54    A NOVEL APPROACH TO SIMPLIFIED RESPIROMETRIC
OXYGEN DEMAND DETERMINATIONS
Fernando Cadena, Associate Professor
Civil Engineering Department
New Mexico State University
Las Cruces, New Mexico 88003
Aleksander Drohobyczer, Staff Engineer
Jones and Henry Engineers
Toledo, Ohio 43606
Martha I. Beach, Vice-President
N-CON Systems, Co., Inc.
Larchmont, New York 10538
David Barnes, Staff Engineer
Geoscience Consultants, Ltd.
Albuquerque, New Mexico 87103
BACKGROUND
Several accurate manometric devices capable of measuring gas consumption or production by
microbial activity were used in the biological sciences laboratories since the turn of the century. Some
of these manometers were designed to measure oxygen demand (i.e., respirometers) during microbial
respiration. These early instruments required manual introduction of fresh air into the reactor (i.e.,
reactor venting) at frequent intervals in order to replenish oxygen consumed.' Skilled analysts were
needed to operate manually and to monitor visually manometric devices. Many of these labor intensive instruments continue to be used in biological science research.
Employment of respirometers designed for biological sciences laboratories has had limited success
in the environmental sciences. Main reasons for opposition for using such equipment in environmental applications include operational difficulty, unrepresentativeness of sample sizes (these units are
capable of analyzing only a few milliliters of sample), expense, and fragility of equipment.2
Instruments specifically designed for environmental work have gained wider acceptance. Development of instruments designed primarily for environmental applications, such as the electrolytic respi-
rometer (EBOD) and others,3 are widely used in engineering research. These devices combine relative
operational simplicity with ruggedness and sample representativeness.
Montgomery2 describes several respirometers used for environmental work before 1967. Most of
these instruments operate under the same techniques used by more refined biological science instruments. However, respirometers designed for environmental work are typically easier to use than their
biological science counterparts while permitting an increase in sample size. This increment in sample
size permits a more representative analysis of heterogeneous samples, such as domestic and industrial
wastewaters.
One of the greatest setbacks to environmental manometry occurred after Standard Methods eliminated (without explanation) the respirometric protocol for BOD determinations from the twelfth
edition, after being published in the tenth and eleventh editions.2 Consequently, the advent of laboratory computers in the 1970's brought about few changes in the area of environmental respirometry.
Use of various mechanical recorders or printers simplified data collection in environmental science
respirometers. For example, development of the electrolytic biochemical oxygen demand apparatus
(EBOD) at New Mexico State University (NMSU) by Clark4 greatly facilitated data collection. Recent
modifications to this instrument eliminate interferences due to barometric pressure variations, and
reduce errors created by electrolyte evaporation.
43rd Purdue Industrial Waste Conference Proceedings, © 1989 Lewis Publishers, Inc., Chelsea, Michigan 48118.
Printed in U.S.A.
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