30    THE EFFECT OF INTERSPECIES COMPETITION ON
BACTERIAL SUPPLEMENTATION EFFICACY
Robert M. Cowan, Graduate Student
Kevin J. Shanahan, Graduate Student
A. Scott Weber, Associate Professor
Department of Civil Engineering
State University of New York at Buffalo
Buffalo, New York 14260
INTRODUCTION
Bacterial supplementation, or bioaugmentation, is a technique in which bacterial strains are added
to a biological waste treatment process as a means of enhancing process performance. The bacterial
culture used as the supplement may consist of specially selected naturally occurring strains, mutated
strains, or even bioengineered organisms. These cultures usually are purchased from commercial
supplement manufacturers but could be produced on site. Supplementation has been suggested for
reducing process start-up time through the addition of large quantities of organisms, recovery from
process upsets, enhancement of treatment rates, and/or for the addition of unique degradative
abilities such as the breakdown of some of the more recalcitrant priority pollutants.
For bacterial supplementation to have a significant effect on a biological treatment process, the
supplement must be capable of: 1) metabolizing the waste constituent of interest; and 2) effectively
competing for a niche in the bioreactor. Often the supplements recommended by their manufacturers
are not useful within the context of these two requirements. For example, Lange, et al1 tested several
commercial supplements suggested by their manufacturers' for treatment of a multicomponent hazardous waste and found most to be incapable of initiating degradation of the waste constituents
without a period of acclimation. They also noted significant losses of the supplemented cultures from
the reactors indicating competition effects.
For a supplement to maintain an effective niche in a biological reactor, it must compete with the
indigenous population for limiting nutrients or be added to the reactor on a continuous basis. This
competition is multifaceted; it is the combined effect of many interactions which occur between all the
organisms in a reactor and cannot be explained solely on the basis of pure culture growth rates of the
individual populations.
The interspecies interactions which can occur between two organisms have been classified by
population biologists into the six categories listed in Table I 2. Each axis of the table is labeled as the
effect the presence of one organism has on the growth of the other. A positive sign (+) indicates that
the presence of one organism benefits the other, a negative sign (-) indicates a harmful effect, and a
zero (0) indicates no effect. Most mathematical models developed to date for describing bioaugmentation have been formulated assuming either neutralism or simple competition as the only interspecies
interactions. Neutralism, where the presence of the indigenous population has no effect on the
supplement and vise-versa is rare. Simple competition is the case where the two populations compete
for the same limiting substrate but in no other way affect each others growth. The use of these
simplifications may severely limit model utility.
The objective of this paper is to present the findings of a study conducted to demonstrate that
interspecies interactions, other than simple competition, can affect the outcome of supplementation
and should be considered in modeling efforts.
BACKGROUND
To date, few attempts have been made to mathematically model supplementation processes. Where
these attempts have been made, the effects of interspecies interactions were largely ignored. The only
study in which experimental data were directly compared to model simulations was performed by
Kennedy et al3. The model used was based on an assumption of neutralism. The model provided
45th Purdue Industrial Waste Conference Proceedings, © 1991 Lewis Publishers, Inc., Chelsea, Michigan 48118.
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