Analytical Determination of Metals
Affecting Sewage Treatment
M. L. Riehl and E. G. Will
Ohio Department of Health
Columbus, Ohio
It has been known for a number of years that certain metals, even
if present in very small amounts, can seriously affect the biological processes involved in sewage treatment. It should not be necessary to take
the time to go into any lengthy discussion of the history of this difficulty
since there are numerous reports and papers citing specific troubles.
Several Ohio sewage plants, particularly at Fostoria, London, and
Elyria, have reported difficulties which have been attributed to iron.
copper and/or zinc. More recently chromium has been blamed as a
factor inhibiting sludge digestion.
A comparison of the copper and zinc content of sewages and sludges
from plants where treatment was seriously affected, as compared to
analyses of samples from plants where no problems of this nature were
encountered, has shown that these two metals were present in much
larger quantities in the troublesome plants.
Because of the problems which have been encountered, and because
of the additional troubles anticipated from the increasing number of
electroplating plants being put into operation in the state, the Division
of Engineering of the Ohio Department of Health inaugurated plans
to make a study to determine the actual tolerance of sewages and sludges
for various metals. To make this study, it was evident that in addition
to the operating records of those plants selected for study, comprehensive
analytical data for these plants must be made available. The Chemistry
Section of the Division of Laboratories, which handles the analytical
work for the Engineering Division, was then called upon to cooperate
in this study.
It was decided to concentrate on the determination of the quantity
of a few more commonly-occurring metals, especially iron, copper, zinc,
chromium, nickel, and cadmium, and possibly investigate others such as
mercury, tin, and cobalt at a later date. Also, while cyanide is not in
the "metal" classification, it almost invariably is present in metal processing work and is considered quite toxic. Hence cyanide was included
in the study.
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