7    DETERMINATION OF TOXICITY THRESHOLDS OF
INDUSTRIAL WASTESTREAMS TO ACTIVATED
SLUDGE PROCESS USING FED BATCH REACTOR
Jerzy Patoczka, Senior Engineer
Gregory W. Pulliam, Vice President
Gary L. Chowning, Senior Engineer
AWARE Incorporated
Nashville, Tennessee 37228
INTRODUCTION
Upsets of activated sludge processes at Publicly Owned Treatment Works (POTWs) can be caused
by toxic wastestreams discharged by industrial users. A mild case of toxicity can manifest itself in
depression of nitrification rates (if applicable) or in killing the protozoan population with a resulting
increase in the effluent turbidity. These two classes of the activated sludge population (i.e., nitrifiers
and protozoa) are more vulnerable to toxins than are chemoorganotrophic bacteria. In more serious
toxicity cases, POTWs can suffer loss of treatment capacity leading to a prolonged recovery period
and, in extreme cases, causing need for reseeding the plant. Toxic upsets are sometimes followed by a
filamentous bulking episode. A POTW upset may result in failure to meet discharge permit limits and
can have a detrimental effect on the receiving stream.
In order to reduce the chances of a toxic upset, some POTWs with the voluntary cooperation of
major industrial users, have implemented a program of screening industrial wastestreams for potential toxicity to the activated sludge. Such programs are particularly desirable and effective when
industrial discharges contribute a significant part of the POTW's load and when the characteristics of
the industrial discharges change significantly and frequently (such as those associated with specialty
organic chemical plants).
If the composition of a wastestream is known, its potential impact on a biological treatment process
can be evaluated from literature data or by using toxicity estimation methods based on molecular
structure of the subject compounds. The lack of an adequate data base and the potential presence of
synergistic/antagonistic effects limit application of this method, however.
Experimental methods of assessing toxicity to biological treatment can be divided into three categories: 1) respirometric methods, 2) methods based on measurement of specific bacterial cell constituents, 3) methods measuring inhibition of substrate removal.
Respirometric methods include direct, short-term measurement of oxygen uptake rate inhibition;1-2
inhibition of BOD5 measurement;} and cumulative measurements of oxygen consumption in the
Warburg apparatus or modifications thereof.4-5 The major problem with the respirometric methods is
that interpretation of the results is difficult for streams containing biodegradable constituents. In
addition, some classes of organic toxicants (i.e., substituted phenols) have been found to stimulate
oxygen consumption without an accompanying substrate removal at less than the threshold toxicant
concentration. This effect has been attributed to uncoupling of oxidative phosphorylation, resulting
in loss of respiratory control and oxidation of intracellular constituents with loss of biomass.6-7
Several methods for evaluating toxic effects by measurement of specific intracellular constituents
have been developed. Determination of the energy storing compound, adenosine triphosphate (ATP),
has been shown to be sensitive to the effects of uncouplers, but not to heavy metals.8 Another method
in this category is measurement of dehydrogenase activity.'
Assays using cultures or organisms other than heterogenous activated sludge are sometimes used to
evaluate potential toxicity to activated sludge. The Microtox* test, during which inhibition of Photo-
bacterium phosphoreum light production is measured, is perhaps the best known of these surrogate
toxicity assays.10 While this specific strain of bacteria has been found to be a sensitive toxicity
43rd Purdue Industrial Waste Conference Proceedings. ■£ 1989 Lewis Publishers, Inc., Chelsea. Michigan 48118.
Printed in U.S.A.
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