Experimental Conditions in the Study of tl
Physiological Ecology of Activated Sludge
JOHN J. CIBULKA, Research Associate
Sanitary and Water Resources, Department of Civil Engineering
Vanderbilt University
Nashville, Tennessee
GEORGE W. MALANEY, Associate Professor of Sanitary Biology
Department of Civil Engineering
Vanderbilt University
Nashville, Tennessee
INTRODUCTION
During the past decade the people of this nation have become increasingly
aware of and alarmed over the threat of a diminishing supply of usable water.
Efficient and rapid reclamation of water for re-use is linked with the improvement of biological aerobic treatment methods to the point that they are capable
of rapid renovation of enormous quantities of waste water. The most popular
biological unit is the activated sludge system which employs a heterogeneous population of microorganisms to stabilize wastes. Many investigators have studied
the activated sludge process with a pragmatic goal of improved design and treatment, but as van Gils states, few have been concerned with the fundamental
nature of the purification process (1).
Gaudy and Gaudy (2) indicate one approach to this problem by stating, "The
challenging aspect to researchers in this field is the necessity of uncovering facts
of predictive value for natural populations rather than for a single culture. " However, they add, "Ideally, pure culture studies may form useiul tools for the investigations of heterogeneous populations."
Studies on the ability of pure cultures of activated sludge microorganisms to
clarify sewage have been made by a number of investigators. Butterfield, et al.,
(3), Ruchhoft, et al., (4), and Buck and Keefer (5), employing zoogleal species
isolated from activated sludge, found that BOD removal by pure cultures is similar
to that attained with the mixed flora of whole sludge. However, other workers
reported that no pure culture was able to clarify domestic wastes as efficiently as
sewage-seeded sludge, although some species approach 90 per cent efficiency.
When van Gils compared the oxidation of selected organic compounds by pure
cultures and by whole sludge, he found that members of the genera Pseudomonas,
Anhrobacter, Flavobacterium, and Zooglea give oxygen consumption curves
similar to those of activated sludge (1). No work comparing whole sludge oxidation patterns with those of pure and mixed cultures, employing the ratios of
microbial populations existing in an aeration tank has been reported. Knowledge
of the effect of one species upon another species or group of species is fundamental
to attaining the goal of the systems analyst, i. e., development of a picture of the
activated sludge aeration tank environment as a predictable functioning ecosystem.
Current investigations on the physiological ecology of activated sludge micro-
- 78  -