Composition Studies of Activated Sludges
CARL E. BURKHEAD, Assistant Professor
School of Civil Engineering
University of Kentucky
Lexington, Kentucky
SAMUEL L. WADDELL, Captain
U. S. Army, Medical Service Corps
Fort Sam Houston, Texas
INTRODUCTION
It is common knowledge to sanitary engineering designers and researchers that
a relationship exists between batch and continuous activated sludge systems. Theoretically, a continuous activated sludge system exists as a stationary or moving point
on the well-known growth curve (Figure 1). Many aspects of this relationship have
been the objective of research efforts. Among these are studies of reaction kinetics,
mass changes, flocculation effects, etc. Such relationships have assisted the engineer
to translate laboratory results into meaningful design information. It is the purpose
of this paper to report on a relatively unsearched area of this relationship.
Studies have been made to determine the change in chemical composition of
activated sludges grown in batch-fed units with various pure organic substrates.
Energy-synthesis data were also collected to more completely define the chemical
changes taking place throughout all phases of the growth cycle.
PREVIOUS STUDIES
There has been a limited amount of research directed toward the determination
of the chemical composition of activated sludge. Of that which has been done, the
majority deals with point or general determinations rather than a complete analysis of
how the composition varies with time.
Hoover and Allison (1) found that the composition of Rhizobium Meliloti
bacteria grown on a sucrose inorganic salts medium containing Fe and coenzyme R
with NH3 or NO3-N, remained remarkably constant, C9_4.Hi6O4.6N, over the entire
growth period. Carbon and hydrogen analyses were by the combustion technique
and nitrogen analysis was by the micro-Kjeldahl procedure.
Probably the most frequently quoted reference dealing with the composition of
activated sludge is the work done by Hoover and Porges (2). Using chromatographic
techniques, the empirical formula of the volatile portion of a single sludge sample
grown during the assimilation of dairy waste was determined to be C5H7O2N. This
formulation has subsequently been accepted as the general composition of protoplasm, and is used in stoichiometric equations dealing with aerobic degradation
reactions.
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