57    ADVANCED MEASUREMENT CELLS FOR AUTOMATED
QUANTIFICATION OF BIODEGRADATIVE MICROBIAL
OXYGEN UPTAKE IN FLUID, SEMI-SOLID AND SOLID
MEDIA
J. B. Hill, Research Chemist
R. D. Bleam, Manager of Technical Services
T. G. Zitrides, President
Bioscience Management, Inc.
Bethlehem, Pennsylvania 18017
C. S. McDowell, President
Tri Bio, Inc.
Allentown, Pennsylvania 18013
INTRODUCTION
In the late nineteenth century, scientists first noticed that microorganisms consumed oxygen while
decomposing organic wastes. Since then, oxygen uptake measurements have been used as a measure
of the treatment of wastewaters.
One of the most popular oxygen uptake measurement techniques was the biochemical oxygen
demand (BOD) test, from which has been derived the standardized five-day BOD test.1 Although
many newer and more sophisticated experimental procedures have been developed, including chemical oxygen demand (COD) and total organic carbon (TOC) analyses, the BOD test maintains its
usefulness today. An increasingly popular experimental procedure used to measure oxygen uptake,
which is closely related to the BOD test, is respirometry. This method is designed to monitor the
progression of biodegradation reactions in terms of oxygen uptake.2,3 There are two types of respirometry, electrolytic and manometric. Manometric respirometry measures oxygen uptake by monitoring pressure reduction in a closed system. Commercial manometric systems use either air or oxygen to
provide the oxygen requirements to the system. The principle of both manometric oxygen and electrolytic respirometry systems, is to maintain the dissolved oxygen level in the biodegrading sample during
oxygen demand by continuous replacement of the oxygen consumed with oxygen from the headspace
of the sample reactor. In electrolytic systems, oxygen is generated by electrolytic dissociation of water
to oxygen and hydrogen. In manometric oxygen systems, oxygen is supplied as a pure gas from
cylinders. Electrolytic instruments hydrolyze either copper sulfate or sulfuric acid. The sample oxygen
demand is determined by converting the power required (to generate oxygen and reestablish the initial
oxygen composition in the headspace) into oxygen equivalents.
The remaining discussion and results will focus on electrolytic respirometric instruments. Electrolytic respirometry was initially developed to test wastewaters. It automates the labor intensive five-day
BOD test.4 It can measure the biodegradability of a wastewater without dilution of the sample, unlike
the standard BOD test. The technique was designed to more closely simulate the environment of a
wastewater treatment plant, and therefore give a better indication or measurement of its state of
operation. Commercial instruments were originally developed in the 1970's primarily for wastewater
samples of moderate strength.
However, due to its versatility, electrolytic respirometry found its way into an increasingly wide
range of applications for water borne contaminants of both high and low strength. Larson and Perry3
have shown that the rate and extent of biodegradation of organic compounds in low strength natural
waters can be assessed with electrolytic respirometry. Other researchers have used electrolytic respirometry to determine biodegradation kinetics. Grady, Dang et al. used this technique to determine
kinetics for single organic compounds in dilute aqueous solutions in batch reactors, and found it to be
much less labor intensive than other techniques.5 Still others demonstrated that respirometry and
chemical oxygen demand analyses are sufficient to characterize kinetic constants for wastewaters,
45lh Purdue Industrial Waste Conference Proceedings, © 1991 Lewis Publishers, Inc., Chelsea, Michigan 48118.
Primed in U.S.A.
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