5    A RESPIROMETRIC METHOD FOR BIOKINETIC
CHARACTERIZATION OF TOXIC WASTES
Anthony F. Gaudy, Jr., Professor
Anand Ekambaram, Graduate Research Assistant
Department of Civil Engineering
University of Delaware
Newark, Delaware 19716
Alan F. Rozich, President
Bioprocess Engineering, Inc.
Wilmington, Delaware 19808-0936
INTRODUCTION
Recent papers have described the use of kinetic models and parameters computed from the
biokinetic constants included in them to predict performance of activated sludge processes treating
either noninhibitory or toxic organic substrates.1-6 Our recent work has also suggested that the
biokinetic parameters may play a role in industrial waste pretreatment programs, since relative
numerical values of certain biokinetic parameters might be employed as one of the criteria for grading
industrial wastes and establishing sewer charges.4'6
The major impediment to more general use of kinetic models in plant operations has been the need
for periodic evaluation of the biokinetic constants and the realization that the procedures for obtaining numerical values of these constants is somewhat laborious. Numerical values of the kinetic
constants depend largely upon the nature of the waste and the biological composition of the activated
sludge which is degrading the carbon sources in the waste. Since these numerical values can be
expected to change from time to time, their determination is best accomplished on a routine basis. In a
recent paper,4 we pointed out some of the experimental difficulties in determining the values of the
constants by the generally accepted batch growth procedures, and we have shown that the accumulated oxygen uptake curve could be used to compute the growth curves from which values of n at
various concentrations of substrate, S0, could be determined. The approach, under conditions
wherein measurement of growth was by the usual method, i.e., optical density, was difficult and the
"02 surrogate" technique, as it was called, saved much labor and time in amassing the required data.
The method was shown to reproduce growth curves for heterogeneous microbial populations metabolizing noninhibitory carbon sources. Equations for calculating the concentration of either biomass or
soluble substrate remaining in the system from the 02 uptake data are given below:
X, = Xc + AO,,/R (1)
COD, = COD0 - A02 ,/RY, (2)
It should be obvious that the equations are applicable only during the substrate removal period.
Also, it should be noted that the analyst is interested mainly in the early, or exponential growth,
portion of the curve. The R term in the equation can be calculated from the cell yield, Y,, and the
oxygen equivalent (COD) of the biomass, Ox in accord with the following equation.
R =  1/Y, -Ox (3)
The R values also can be obtained directly from the growth data using the following equation.
R = A 02 ,/(X, - X0) (4)
It can be seen that R represents the amount of respiratory oxygen used in producing a unit mass of
cells.
In a previous paper,4 we mentioned that we were extending the work to a known inhibitory
substrate and to whole industrial wastes.
43rd Purdue Industrial Waste Conference Proceedings,  I   1989 Lewis Publishers, Inc., Chelsea, Michigan 48118.
Printed in U.S.A.
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