Section Four
PROCESSES -D. RESPIROMETRY
44    COMPARISON OF RESPIROMETRIC METHODS FOR
DETERMINATION OF BIOKINETIC
CONSTANTS FOR TOXIC AND NONTOXIC WASTES
Anthony F. Gaudy, Jr., H. Rodney Sharp Professor Emeritus
Department of Civil Engineering
University of Delaware
Newark, Delaware 19711
Anand Ekambaram, Environmental Engineer
Woodward-Clyde Consultants
Plymouth Meeting, Pennsylvania 19462
Alan F. Rozich, President
Richard J. Colvin, Engineer
Bioprocess Engineering, Inc.
Wilmington, Delaware 19808
INTRODUCTION
Respirometric techniques have been of some interest in the pollution control field for many years.
However, early attempts to use respirometry as a replacement for the BOD test did not result in
practical methodology. This and the general impracticability of the BOD test for devising control
strategies for operation of treatment facilities were probably the major factors which have deterred
adoption of respirometric methods in the field. Recent developments in equipment design as well as
urgent technological needs for biokinetic information are causing a resurgence of interest in respirometric techniques.
It is well-recognized that oxygen uptake during growth on organic carbon sources represents
exertion of carbonaceous BOD, and it has been known for over four decades that the oxygen used is
due to oxidation of a portion of the carbon source; most of the remaining portion removed from
solution is channeled into biomass. This major partition of the carbon source between respiration and
synthesis is so well established that it can serve as a basis for making material balances to check the
accuracy of experimental results during growth experiments.1 Various markers for the substrate can
be employed, but it has been shown that the chemical oxygen demand, COD, of the carbon source and
biomass, along with the biological oxygen uptake registered during growth, is the best and the most
practical basis for making the material balance; thus, the material balanced is energy as represented by
COD.2 We have often made use of this technique to check recovery of substrate COD in batch studies.
An example of some published recovery values is given by Rao and Gaudy.3
It should be realized that the major interest among workers engaged in development of kinetic
models for wastewater purification has been prediction of removal of the carbon source, but it should
also be realized that the mechanistic basis for removal of the carbon source is microbial assimilation
and growth. Thus we try to model the causative mechanism, i.e., the growth process, and treat
substrate removal as the resultant, or consequence, of this overall process in devising wastewater
purification equations. The fact that a portion of the waste is oxidized is reflected in biomass yields
less than unity (based on COD of the carbon source). Thus, in predictive modeling of system performance, oxygen uptake is accommodated but is not considered in kinetic equations predicting effluent
quality.
Our own resurgence of interest in respirometry came about because of our work on kinetic modeling and the need to simplify laboratory procedures used to obtain numerical values for the biokinetic
44th Purdue Industrial Waste Conference Proceedings, © 1990 Lewis Publishers, Inc., Chelsea, Michigan 48118.
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