Effects of Heavy Metals on Microorganisms.
Application to Process Design
ROBERT P. HECK, III, Research Assistant
DONALD J. SCHAEZLER, Assistant Professor
Civil Engineering Department
Texas A & M University
College Station, Texas
GARY R. KRAMER, Manager
Environics Division
Civil Engineering Research Facility
University of New Mexico
Albuquerque, New Mexico
INTRODUCTION
The major objectives of this research are: 1) to demonstrate that the effects of heavy
metals on microorganisms can be monitored using laboratory techniques currently
available and without the use of complex mathematical models; and 2) to suggest how these
effects could be applied to process design.
The following observations are thought to be important for the design of aerobic
biological waste treatment units: I) prediction of the functional rate form for biological
growth; 2) rate as a function of metal, biomass, and substrate concentrations and pH; 3)
effect of total metal concentration on growth rates and stoichiometry of acclimated and
unacclimated cultures; and 4) metal solubility as a function of biomass concentration and
pH. This information fulfills the second requirement for the formulation of design
parameters as presented by Irvine and Schaezler (1) (i.e., reaction rates specific for waste
and biomass). Use of such data for design of biological treatment of organic wastes
containing metals can optimize treatment facilities.
LITERATURE REVIEW
Heavy metal pollution arises from the effluent discharges of such industries as metal
plating, rayon cord manufacturing, tanneries, electrorefining plants, and cooling tower
blowdown (2.3,4,5,6). These discharges quite often reach a biological treatment system
which is likely to be affected by the metals.
Most of the research which has been performed with respect to heavy metals has been
directed toward suggestion of minimum concentrations to be allowed and maximum
concentrations which can be tolerated. This has been particularly true up to 1965 and is
illustrated in the Public Health Service publication of May, 1965(7). Some researchers have
attempted to use BOD or oxygen uptake (with Warburg respirometer) as a parameter for
measuring metallic effects on biological waste treatment (8,9,10,11,12,13,14). Very seldom
have investigators used similar experimental procedures regarding batch reactor
conditions, bacterial inocula, or substrate.
Some studies have brought to light many important factors which should receive
attention. Metal solubility has been reported to be a function of pH, alkalinity and various
organic complexing agents (5,7,8,11) and to be responsible for the effects of metallic
inhibition (5,8). Pettet (5) displayed manometric data showing the effects of initial pH with
a copper concentration of 25 mg/1 to relative values of 5 day biochemical oxygen demand
(BOD) for the control. However, control data were not presented to show effects of pH
alone, which may have accounted for a large portion of the effects observed (15).
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