Trace Metals and
Filamentous Micro-organism Growth
JOHN T. PFEFFER, Assistant Professor
AZIZ ABU SAMRA, Research Assistant
DIANN T. SCHWEGLER,   Research Assistant
Environmental Health Research Laboratory
University of Kansas
Lawrence, Kansas
INTRODUCTION
Ever since the introduction of the activated sludge process, one of the chronic
operational problems has been sludge bulking. This is a very general term which
basically means a characteristic of the sludge which produces a light, fluffy
sludge that has poor settling properties. One of the principal causative agents of
sludge bulking is an excessive growth of filamentous micro-organisms. These
organisms are present in activated sludges but usually in small numbers, with
nonfilamentous bacteria as the predominant growth. The resulting sludge usually
has good settling properties.
The predomination of the filamentous micro-organisms can be induced by
changes in the environment. The causes of these growths are generally attributed
to such factors as low pH, low dissolved oxygen, low nitrogen or high carbohydrate
concentration. However, correcting the above factors does not always eliminate
the predomination of the filamentous micro-organisms.
Research in biological waste treatment systems being conducted at the Environmental Health Lab at the University of Kansas has been plagued with the
growths of filamentous fungi and actinomycetes. Preliminary indications were
that the problem resulted from the absence of certain key trace nutrients in the
substrate. Analysis indicated the absence of certain trace metals in the tap water
used in the substrate. Additions of the trace metals to the tap water solutions
improved the system in many cases. However, this was not always true. Additions of certain metals far in excess of trace quantities were often necessary.
These observations led to the conclusions that not only must the metals be
present in trace quantities, but that the chemical environment must be such that
these metals are soluble. This led to the investigation of the chemical environment as related to solubility and to the growth characteristics of filamentous
micro-organisms as related to the presence of the trace metals. This report is
concerned with the availability of trace metals and the growth of filamentous
fungi.
A search of the literature indicates that a considerable amount of research has
been conducted on the sludge bulking caused by filamentous micro-organisms.
The majority of this work was concentrated on Sphaerotilus. Very little research
has been conducted on other micro-organisms producing filamentous growths.
Genetelli and Heukelekian (1) indicate that fungi are rarely the cause of sludge
bulking, but the most prevalent cause is sphaerotilus. This has been the contention of many investigators. However, there are several papers which report fungi
as the cause of problems with sludge bulking (2,3,4,5).
There  can be no question that Sphaerotilus is responsible for many of the
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