37    ADAPTATION AND DEADAPTATION KINETICS OF
ACTIVATED SLUDGE
PR. Senthilnathan, Graduate Student
J. J. Ganczarczyk, Professor
Department of Civil Engineering
University of Toronto
Toronto, Ontario, M5S 1A4
INTRODUCTION
The microbial populations in the activated sludge are versatile in degrading various organic priority
pollutants, if adequate time for acclimation (adaptation) is given.1'2.3 The rate of biodegradation can
drastically vary with the extent of adaptation. When sufficient time for adaptation cannot be provided, bioaugmentation or the addition of pre-adapted cultures to activated sludge can be implemented to increase the efficiency of biodegradation.
However, in a new environment, when the favored substrates are not available, the adapted cultures
may lose their ability (deadaptation) to degrade the specific chemicals to which they were adapted.
Also, microorganisms engineered for bioaugmentation, depending on the methods of preservation,
may undergo deadaptation during storage and transportation. In fact, an additional period of acclimation was found necessary to initiate biodegradation by some biological supplements.4 The rate of
deadaptation and the length of time needed for deadaptation might be an important factor in:
1) predicting the biodegradability of organic pollutants which are discharged intermittently; 2) successful application of bioaugmentation products; and 3) determining the shelf life of such products.
This study is a preliminary attempt to determine the effect of deadaptation on phenol acclimated
activated sludge when subjected to a new environment with glucose as the sole carbon source. The rate
of adaptation of these cultures to glucose was also determined. Phenol was selected for this study
since: 1) it is a common pollutant found in many industrial wastewaters; 2) it is known to be toxic or
inhibitory to microorganisms; and 3) phenol degrading biological supplements are commercially
available.
BACKGROUND
Adaptation
Adaptation or acclimation of microorganisms is a process of physiological, morphological or
genetical adjustment to environmental conditions that makes the microorganisms more fit for existence under new habitat. Microbial populations acquire the ability to grow under conditions unfavorable to the original populations by making changes in the pattern of expression of their genes.
Microbial adaptation to high and low temperatures, increasing and decreasing salinity, increasing and
decreasing pH, ultraviolet radiation, and several toxic chemicals (including antibiotics, 2,4-D, methyl
parathion, p-nitrophenol) is well known.2-5~9 Adaptation to one chemical can induce the ability to
metabolize a host of other chemicals which are structurally similar.3'9
Adaptation can be induced in two ways: 1) by gradually increasing the intensity of the selection
pressure; and 2) by exposing the population to the extreme conditions to allow for the emergence of
the surviving organisms. The length of time required for adaptation varies with respect to the type of
inoculum (seed), the amount of inoculum, nature of the test compound, physical and chemical
conditions prevailing during the exposure, exposure concentration, and duration of exposure. The
adaptation time required by activated sludge for degrading various priority pollutants vary from few
days to 6 weeks depending on the nature of pollutant.'"
Adaptation can be either phenotypic or genotypic. In phenotypic adaptation, the genetic information content of the cells is unchanged; only the degree of expression of genes is altered. Phenotypic
adaptation may be common during short-term fluctuations in the environment. Genotypic adaptation
43rd Purdue Industrial Waste Conference Proceedings, © 1989 Lewis Publishers, Inc., Chelsea, Michigan 48118.
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