ADSORPTION OF HEAVY METALS WITH INERT BIOLOGICAL
SLUDGES AT NEUTRAL PH'S
Roque A. Roman-Seda, Assistant Professor
Department of Civil Engineering
University of Puerto Rico
Mayaguez, Puerto Rico 00708
INTRODUCTION
This work tried to ascertain what ordinary secondary sludges can do to remove dissolved heavy
metals from wastewaters at neutral pH's.
The long range goal of the study was to assess the feasibility of developing a new technology for
the removal of heavy metals from wastewaters utilizing biological sludges as adsorbers. A secondary
but nonetheless important motivation was to create a useful application for an unwanted by-product
of wastewater treatment.
The short term goal of the project was to estimate the potential of inert biological sludges for
the removal of heavy metals at neutral pH's under batch conditions. It is important that the adsorber
perform well at or near the pH region at which it would be used in order to avoid the costly addition
of chemicals, thus making the new technology cost attractive.
PREVIOUS WORK
Microorganisms have been shown to concentrate cations from their aquatic environment and,
specifically, to concentrate heavy metal ions. Beveridge et al [1] has shown this phenomenon for
Bacillus subtilis in particular and for bacterial cell walls in general [2]. Chio [3] documented the
uptake of heavy metals by microbes. Elsabee et al [4] illustrated the relationship between cupric
complexes and cell wall related structures. Paskins-Hurlburt et al [5] documented the relationship
between biosorption of lead and a specific kind of microorganism.
Volesky et al [6] showed that biosorbent activity is not associated exclusively with living organisms
but that it is present in dead biomass as well to perhaps an even greater degree. Biosorption has been
specifically linked to the cell wall.
Volesky [7] and other workers [8,9,10] have gone beyond and demonstrated the feasibility of
concentrating uranium, thorium, actinides and other valuable heavy metals from dilute radioactive
wastes or seawater by using pure cultures of microorganisms that selectively remove these metals.
The work done so far suggests that this biosorption property should be present in wastewater
sludges and that, therefore, these may be useful in sequestering heavy metals from wastewaters. It
is the intent of this work to investigate such a connection and to elucidate some of the parameters
that enhance the biosorption phenomenon.
OBJECTIVES
The objectives of this study were: 1) To determine whether there exists in biological sludges a
significant biosorption capacity for the removal of cadmium, lead, nickel, and chromium; and 2) To
determine the effects of the operational parameters of contact time, sludge concentration, and initial
metal concentration on overall removal.
EXPERIMENTAL PROCEDURE
A source of dried, stabilized sludge was selected from a municipal wastewater treatment plant.
Information was collected on the operational characteristics of the plant and on the wet sludge
characteristics before it was dried.
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