Algal Influences on Dieoff Rates of
Indicator Bacteria
ERNST M. DAVIS, Assistant Professor
Environmental Health Engineering
EARNEST F. GLOYNA, Dean
College of Engineering
University of Texas
Austin, Texas
INTRODUCTION
One of the criteria taken into consideration for the operation of waste
stabilization lagoons is the effective decrease of coliform bacteria and an understanding of their dieoff and aftergrowth characteristics in the presence of various algal
species is desirable. This paper considers: first, the behavioral patterns of selected
species of enteric bacteria when in the presence of single axenic cultures and mixed
cultures of selected blue-green and green algae; and second, the behavior of enteric
bacteria in the presence of algae and known quantities of industrial wastes.
The destruction of coliform bacteria in waste treatment facilities is attributable
to a number of physical, biological, and chemical factors. For example, the adverse
effect of sunlight on bacterial metabolism has been documented by Gameson and
Saxon (1). Similarly, specific anti-bacterial agent production has been reported by
Caldwell (2), Pratt (3), and Spoehr, et al. (4). This mechanism is one which would be
the most complex to evaluate in a truly heterogeneous environment such as a waste
stabilization pond. Pure culture investigations would necessarily have to precede field
work. Other factors which may accelerate coliform dieoff are adverse temperature
conditions, variance in oxygen tension, pH changes (5), predation, nutrient
depletion, over- competition, and toxicity. The coliform indicator organisms all
require organic materials for their survival and reproduction. Whether these materials
are introduced in the form of waste or are produced by other organisms in the
aquatic environment is of little consequence to these bacteria. Their ability to use
metabolic exudates or protoplasm as energy sources is very well documented (6,7).
At the same time it must be remembered that very little organic material is necessary
for their survival. McGrew and Mallette (8) showed that E. coli could survive and
reproduce at glucose concentrations less than five mg/1.
Several species of algae appear to be capable of stimulating specific coliform
organisms, through algal metabolic exudates which are released during log growth
conditions and from nutrients which may be released after death of the algae
(6,9,10,11,12,13,14). In a matter of 30 hr, nutrients found in certain wastewaters
have been found to stimulate coliform reproduction as much as 10 to 40 times (15).
Only when all aspects of the behavioral characteristics of coliform bacteria are
recognized and understood can a true evaluation of the pollutional condition of an
aquatic ecosystem be described.
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