Organic Load and the Toxicity of
Copper to the Activated-Sludge Process
B. V. SALOTTO, Chemist
E. F. BARTH, Chemist
W. E. TOLLIVER, Chemist
M. B. ETTINGER, Chief, Chemistry and Physics
U. S. Department of Health, Education, and Welfare
Public Health Service
Bureau of State Services
Division of Water Supply and Pollution Control
Robert A. Taft Sanitary Engineering Center
Cincinnati, Ohio
The Robert A. Taft Sanitary Engineering Center has studied the effects of
heavy metals, singly and in combination, on the activated-sludge process. In
these studies the organic load was approximately the same. The present investigation considers the effect of organic loading on the toxicity and distribution of
copper in the activated-sludge process. Copper was chosen because its toxicity
is significant at a relatively small concentration and because preliminary work
on effect of organic loading had been reported in a previous paper (1).
PROCEDURE
The activated-sludge pilot plants used were designed for complete treatment
of sewage employing primary settling, aeration with continuous sludge return, and
secondary settling. A description of one of the plants is shown in Figure 2 of the
first paper in the series (2). Sewage was fed at a constant rate. Sludge from the
secondary settler was pumped continuously to the first chamber of the aerator at
a rate of about 35 per cent of the sewage flow. Sludge-wasting rates were adjusted to hold mixed-liquor volatile-suspended-solids concentrations between
1, 000 and 1, 200 mg/l. Total detention time was nine hrs with a flow of 100
gals/day.
The sewage used was domestic in origin and of relatively low strength because
of ground water infiltration. The sewage was fortified each day by addition of
homogenized fish meal to the main holding tank. Average COD values of the
sewage before and after additions were 200 and 380 mg/l. The nutrient character
of the fortified sewage was found to be adequate. Calculated BOD:N;P ratio was
100:6:3.
Three identical pilot plants were operated in parallel. One unit received
undiluted fortified sewage at a constant rate. Copper sulfate solution was introduced at the sewage feed inlet continuously. The other two units were fed the
same sewage diluted approximately 2:3 with tap water. Copper sulfate solution
of the same concentration was introduced continuously in the influent sewage of
one of these units; the other unit received no copper and served as a control.
Since the MLVSS in the three units were maintained at approximately the same
levels, the organic load on the units receiving diluted sewage was about one-half
that of the unit receiving the strong sewage. The effects of two copper concentrations were studied at each organic load level. The concentrations selected,
one and five mg/l,  were present continuously in the influent sewage.   The five
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