EVALUATION OF INTERACTION KINETICS AND
EQUILIBRIA FOR HEAVY METAL-SLUDGE SYSTEMS
Ronald D. Neufeld, Assistant Professor
Jorge Guttieriez, Graduate Student
Richard A. Novak, Graduate Student
Department of Civil Engineering
University of Pittsburgh
Pittsburgh, Pennsylvania 15261
INTRODUCTION
Certain industrial effluents have associated trace levels of potentially toxic heavy
metals.   In natural waters these metals have been documented as interacting with sediments and accumulating in fish and wildlife, thus adversely influencing man's well being
and utilization of water resources.   Federal and state guidelines and limitations have been
placed on trace metal discharges.   Considerable efforts and dollars have been expended on
the measurement of heavy metals and the development of effective and inexpensive techniques for their removal.
Biological sludges, as from an activated sludge process, are similar to organic river sediments in the sense that both have been observed to have the ability to remove heavy
metals from liquid wastes.   Indeed, a property of all living organisms is the ability to concentrate ions within the organism against a concentration gradient.   It is possible to use
the natural affinities of sludges towards heavy metals as a technique to concentrate and
accumulate aqueous-phase heavy metals.   Previous work by Neufeld [ 1 ], Neufeld and
Hermann [2], Cheng, Patterson and Minear [3] and Neufeld, Gutierrez and Novak [4]
have quantified apparent distribution coefficients and equilibrium relationships between
liquid-phase and biological-solid phase heavy metal concentrations.   These results have
demonstrated solid-liquid distribution coefficients on the order of 103 to 10 4, with resultant metal on biomass concentrations in the range of 10% to 20% by weight.   While
the chemical mechanism for such uptake is still ill-defined, it can be postulated that
metals are sorbed onto extracellular polysaccharide polymer fibrils that are excreted by
and enmesh the biological cells.   For process purposes, the kinetics of such uptake and
the expressions of equilibria thereby resulting must be determined.
OBJECTIVE OF STUDY
The objectives of this research are to use laboratory investigations to determine a suitable expression which describes the temporal accumulation of heavy metals on biological
sludge, and secondly to use that expression in mathematically determining a resultant
equilibrium relationship.   An additional objective was defined:   to expand the available
data base on the equilibria of aqueous metal extraction via biological sludge to include the
elements chromium VI, chromium III, nickel II, lead II and zinc II.
EXPERIMENTAL APPROACH
In general, the specific rate of accumulation of heavy metals on biological sludge is a
function of both the physical and chemical environment ambient to the sludge in accord
with a general expression of the form
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