The effect of the presence of more easily degradable alternative carbon sources on the biodegradation of toxic waste components is of great practical importance. In this work, a mixed phenol/glucose waste was fed to two heterogeneous populations acclimated to different conditions: one was acclimated to phenol as a sole source of carbon and one to a mixed phenol/glucose substrate. Batch substrate utilization experiments were performed under both growth and nonproliferating (no medium nitrogen source) conditions in order to assess substrate removal patterns at the levels of enzyme production and enzyme function. The results indicated that the substrate removal pattern exhibited by the cells was significantly influenced by the acclimation characteristics of the culture. The phenol acclimated cells showed an initial preference for phenol, but the presence of glucose hindered phenol removal rate under both growth and nonproliferating conditions. The cells acclimated to the mixed phenol/glucose waste demonstrated rapid initial glucose removal with a slower concomitant utilization of phenol; acclimation to the mixed waste evidently had a significant impact on the substrate removal pattern for this mixed substrate system.

The utilization of biological processes for purification of wastewaters, particularly those containing toxic organic compounds, emphasizes the practical necessity for developing adequate mathematical models for design and operation of these processes. Microbial growth on inhibitory carbon sources, e.g. phenol, offers interesting mathematical modelling problems, but when attention is given to obtaining and analyzing experimental data for the purpose of determining the values of biokinetic constants for use in the models, the difficulties and uncertainties resulting from the nature of the substrate and the heterogeneity of the microbial populations offer even more challenging problems. There is an urgent need to develop a representative data base or a range of numerical values for kinetic constants employed in relationships between growth and substrate utilization rates which are, in turn, used in the mass balance equations for the reactor system. We have recently completed a three-year study on these aspects, and the purpose of the present communication is to present and explain the approach we evolved for obtaining and analyzing the growth data and to give some insight into the range of values for the kinetic constants relating specific growth rate p and substrate concentration S. Table I shows several of the equations which have been proposed to depict the relationship between p and S. Equation (1) is recognized as the "Haldane" equation. As Table I. Kinetic models for growth on inhibitory substrates. ANALYSIS OF GROWTH CURVES Adapted from Edwards (ref. 8).*To whom all correspondence should be addressed. However, the analysis of batch growth data and the fitting of these data to the Haldane relationship are not as straightforward as for the Monod equation. Figure 1 shows growth curves calculated according to each equation. Both equations approximate exponential growth in the early hours. Actually, in this stage, the Monod curve gradually falls away from exponential increase, whereas the Haldane equation describes an upward curve which eventually sweeps into an accelerating slope as the inhibitory substrate concentration is decreased at an increasing rate due to growth. Following this, a decelerating phase is reached as substrate concentration is further reduced. This behavior, which is due to the inhibitory function, S2/Ki, complicates the analysis of experimental growth curves, because one might easily mistake the exponential phase for a lag phase and the accelerating phase for an exponential phase.The analysis of growth curves according to eq. (1) has further complications when considering plots of p vs. S. It can be shown that eq. (1) will go through a maximum value (dp/dS = 0) and this value, p*, can be calculated as the value of p corresponding to a substrate concentration, S*:For the growth conditions used in the calculated curves shown in Figure 2, p* occurs at an S* of ca. 69 mg/L. The plots for initial substrate concentrations So = 0.5s" and So = S* give the appearance of growth on a noninhibitory subs...

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