Trace Elements in Biological Waste Treatment With
Specific Reference to the Activated Sludge Process
DENNIS K. WOOD, Graduate Student
GEORGE TCHOBANOGLOUS, Associate Professor
University of California, Davis
Davis, California 95616
INTRODUCTION
The role of nitrogen and phosphorus as essential nutrients for the proper operation of
biological treatment processes is well documented. The role of trace elements as
micronutrients, however, is not well defined. Due to the difficulty in measurement and the
complex chemistry and biochemistry involved, the requirements for trace elements have not
been determined.
The purpose of this paper is to deliniate the significance of trace elements in biological
waste treatment with specific reference to the activated sludge process. To do this, the
material to be presented has been divided into sections dealing with 1) a review of the role of
trace elements in biological systems, 2) a review of the sources of trace elements in
wastewater and the mechanisms that may be responsible for their removal before
utilization, 3) an analysis of the role of trace elements in the activated sludge process, and 4)
the implications of the presence of absence of trace elements in the design and operation of
biological treatment systems.
TRACE ELEMENTS IN BIOLOGICAL SYSTEMS
To understand the role of trace elements in biological waste treatment it will be useful
to review 1) the importance of trace elements in microbial growth and metabolism, 2) their
effects on population dynamics, and 3) trace element requirements in biological systems.
Growth and Metabolism
Trace elements are a requirement for the growth and metabolism of microorganisms.
Essential and other trace elements are listed in Table I. Not all organisms require every
essential element, though each element is required for the growth of at least one common
organism. The other elements shown in Table I have been found in the ash of organisms, but
their requirement for growth has not been established (1).
Trace elements are required for two basic functions. First, they are required as metallic
enzyme activators (2). An enzyme activator is a small molecule that stimulates growth, but
unlike a coenzyme, is not an explicit part of the reaction. Second, they are required for the
electron transfer in oxidation-reduction reactions.
Iron is essential for aerobic bacterial growth, and it may be a universal requirement for
all organisms (2, 3). It is responsible for the electron transport in cytochromes, a group of
proteins whose prosthetic group prophyrin contains iron. A series of cytochromes is stepwise reduced and oxidized following the oxidation of flavoproteins. Iron is also required for
the synthesis of certain enzymes including catalase, peroxidase, and aconitase which is
required in the isomerization of citric acid to isocitric acid in the tricarboxylic acid cycle.
Zinc and cobalt serve as metallic enzyme activators (2). These metals may be
dissociable ions on the active sight of the enzyme. Zinc is required for the activities of
carbonic anhydrase and carboxypeptidase A, an enzyme that exhibits both peptidase and
estarase activity. Cobalt is required for the activity of carboxypeptidase and the synthesis of
vitamin B-12.
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