26    SORPTION CHARACTERISTICS OF
STABILIZED BIOLOGICAL SLUDGE
Noah I. Galil, Senior Lecturer
Department of Civil Engineering
Technion - Israel Institute of Technology
Technion City, Haifa 32000, Israel
Shaul Mevorah, Environmental Engineer
"Balasha - Jalon" Consulting Engineers, Ltd.
Haifa, Israel.
ABSTRACT
Cadmium was sorbed by sludge solids and had the tendency to achieve saturation at equilibrium
concentrations above 15 mg/L. Sorption of phenol was relatively low along equilibrium concentrations of up to 10 mg/L, and then sorption substantially increased. Comparing the sorption of
cadmium on sludges which have been stabilized at similar levels, a small advantage could be observed for sludge treated by anaerobic digestion. No significant differences between anaerobic and
aerobic sludges were found for phenol sorption. The stabilization level appears to be an important
factor in the sorption of cadmium and phenol on sludges originating from both aerobic and abaer-
obic digestion processes. Both contaminants have increased their sorption characteristics as the
concentration of dissolved organic matter in the aqueous solution was higher. Phenol, especially,
exerted low sorption in low organic solutions and increased significantly its sorption characteristics in the presence of dissolved organics. Soluble organics matter, originating from the sludge,
was found as an important factor controlling the sorption of cadmium and phenol by sludge,
which released dissolved organic matter proportionally to the stabilization level.
INTRODUCTION
Studies on sorption characteristics of sludges, originating from biological treatment processes
of wastewater, are based on different methods in the preparation of the biomass, before its contact with the specific compounds which are supposed to be sorbed from the solution. Selvakumar
and Hsieh,' Bell and Tzesos2 and others based their experimental work on sludge pretreatment
and its transformation into dry particles or granular structures. Kennedy et al.3 and others performed their experiments using sludge in wet form, as it could be produced by the treatment
processes.
Studies on sorption of heavy metals onto sludge and different types of biomass have been performed by Cheng et al.,4 Koers and Mavinic,5 Nelson et al.,6 Lo and Lin,7 Gourdon at al.,8-9 and
Venkobahar,l() indicated that biomass could behave as sorbing media. Other studies reported
sorption of organic matter onto biomass: phenol, chlorophenol, chlorobenzene, ethylbenzene,1"
methylchloride, chloroform, di-chloroethylene, di-nitro- o-cresol, tetrachloetylene, lindane,12
pentachlorophenol, 2-chlorobiphenol,13 trichloroethane,14 chlorophenol, di-chlorophenol,
trichlorophenol, pentachlorophenol.3
Studies reported that the Freundlich isotherm was found to be the most appropriate mathematical relationship to describe the sorption of either heavy metals or organic matter onto sludge
from suspended growth biological reactors, such as activated sludge. The process itself was characterized by a rapid phase, usually the first minutes of the exposure, followed by a slow phase,
which could last for 24 hours or more. Most of the materials, about 80%, were sorbed during the
first phase.
52nd Purdue Industrial Waste Conference Proceedings, 1997. Ann Arbor Press, Chelsea, Michigan 48118. Printed in
U.S.A.
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