STUDIES OF THE UPTAKE OF HEAVY METALS
BY ACTIVATED SLUDGE
Gilbert Elenbogen, Research Chemist II
Bernard Sawyer, Research Chemist III
Cecil Lue-Hing, Director of Research and Development
K. C. Rao, Biostatistician
David R. Zenz, Coordinator of Research
Research and Development Department
The Metropolitan Sanitary District of Greater Chicago
Chicago, Illinois 60611
INTRODUCTION
At present, the Metropolitan Sanitary District of Greater Chicago (District) is employing a number
of sludge management options which allow the nutrient and soil building properties of sludge to be
beneficially recycled to the environment. One drawback of these programs has been the concern, by
some, regarding the effects of heavy metals, particularly cadmium (Cd), on the land to which the
sludge is applied, and the uptake of Cd by crops grown on this land. Some investigators and regulatory agencies have indicated that the Cd content of the sludge is the limiting factor governing the
amount of sludge which can be applied at a given site.
Since the majority of sludge produced at District treatment facilities is composed of waste-activated sludge from the activated sludge process, it is clear that any reduction in the metal concentrations in waste-activated sludge would have a significant impact on metal concentrations in the digested
sludges used for land application.
Several basic approaches have been proposed for reducing waste-activated sludge metal concentrations. These include:
1. Reducing influent metal loadings to the treatment facilities;
2. Reducing sludge metal concentrations by physical or chemical treatment of the sludge;
3. Reducing sludge metal concentrations by operational changes to the wastewater treatment process.
Of the approaches listed, the District has directed its efforts to the first approach through its
Industrial Waste Control Ordinance. This approach has reduced raw sewage metal loadings to District
treatment facilities by limiting industrial discharges of heavy metals and other pollutants to the District's sewer system [1]. The second approach does not appear feasible at this time, due to the fact
that high capital and operating costs would be required to treat the large volumes of sludge produced
at the District. In the present study, the third approach was explored; namely, reducing sludge metal
concentrations by operational changes to the wastewater treatment process.
DISCLAIMER
The mention of trade names or commercial products does not constitute endorsement or recommendation for use by the Metropolitan Sanitary District of Greater Chicago.
LITERATURE REVIEW
The removal (the difference between the influent and effluent concentration) of heavy metals from
wastewater by the activated sludge process has been reported by a number of investigators. Lester
et al. [2[ reported that the removals of copper (Cu), cadmium (Cd), and lead (Pb) were 79, 63, and
73%, respectively, through the activated sludge system. Oliver and Cosgrove [3[ reported 71, 78, and
91% removal efficiencies for Cu, Cd, and Pb, respectively, at a Canadian sewage treatment facility.
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