Document Type


Date of Award


Degree Name

Master of Science in Chemical Engineering - (M.S.)


Chemical Engineering, Chemistry and Environmental Science

First Advisor

Basil Baltzis

Second Advisor

Gordon Lewandowski

Third Advisor

Theodore Petroulas


It is known that two microbial populations competing purely and simply for a common substrate cannot coexist in a steady state in an environment which is spatially homogeneous. Hence they cannot coexist in a chemostat something which implies that a mixed culture of two pure and simple competitors cannot be maintained in a single ideal reactor in a steady state. The present study investigates theoretically pure and simple competition between two populations in two interconnected chemostats. Three reactor configurations are considered and analyzed. It is proved that two pure and simple competitors can coexist in a steady state in both reactors in cases where the conditions are such that they favor the growth of one species in one reactor and the growth of its competitor in the other vessel. It is then concluded that spatial inhomogeneities can lead to steady state coexistence of pure and simple competitors. The results of this study have been derived analytically and numerically. The dynamic behavior of the system at all possible steady states has been studied analytically. A number of conditions sufficient and/or necessary for the existence of each one of the possible steady states have been derived also analytically. The numerical studies have shown that one can always find a range in the operating parameters space where coexistence occurs, that the steady states are mutually exclusive and that no steady state exhibits multiplicity. The results are presented in series of two-dimensional operating diagrams and the effect of all parameters on the behavior of the system is studied and discussed in detail. It has been also proved that it is not necessary for coexistence to externally feed both vessels with nutrient medium and that there is a design configuration which makes the environment always homogeneous in which case coexistence is impossible.



To view the content in your browser, please download Adobe Reader or, alternately,
you may Download the file to your hard drive.

NOTE: The latest versions of Adobe Reader do not support viewing PDF files within Firefox on Mac OS and if you are using a modern (Intel) Mac, there is no official plugin for viewing PDF files within the browser window.