56    A COMPUTERIZED RESPIROMETRIC METHOD FOR
DETERMINING INHIBITION POTENTIAL OF
WASTEWATERS
Martha I. Beach, President
N-CON Systems Co.
Larchmont, New York 10530
Ricardo B. Jacquez, Professsor
Fernando Cadena, Assoc. Professor
Atul Shah, Graduate Research Assistant
New Mexico State University
Las Cruces, New Mexico 88003
INTRODUCTION
Twenty years ago, with the passage of the Clean Water Act, the federal government embarked on a
program to clean up the navigable waters of the United States. Along with restrictions, guidelines and
discharge permits, the construction grants program provided funds for the design and construction of
thousands of Publicly Owned Treatment Works (POTW). In some instances the failure of new and
sophisticated waste treatment plants to meet their effluent permit limits has been traced to toxic
wastes from industrial operations. In 1984, the Environmental Protection Agency (EPA) issued its
national "Policy for Development of Water Quality-Based Permit Limitations for Toxic Pollutants."
This Policy is being implemented by the National Pollutant Discharge Elimination System (NPDES)
and represents a major change in Federal and State pollution control strategies. Permit discharge
compliance is no longer based on specified end-of-pipe technology or specific single chemical analyses. The Environmental Protection Agency (EPA) has incorporated whole effluent toxicity tests to
their control strategy because there is now a general consensus that an evaluation of effluent toxicity,
when adequately related to instream conditions can provide a valid indication of receiving water
impacts.1
In an effort to limit the entry of toxic materials into the POTW, stringent pre-treatment regulations
have been promulgated. This in turn has resulted in increased interest in the effects of various
materials on biological treatment systems, as well as on the receiving waters.
In spite of the fact that most engineers generally refer to activated sludge or biomass in the singular,
microbiologists and bio-process engineers are quick to point out that activated sludge consists of an
innumerable and diverse population of aerobic microorganisms. These microorganisms consume the
carbonaceous material in the wastewater if they are healthy and have sufficient oxygen available.
WHAT IS TOXICITY?
Toxicity can not truly be defined as an absolute. We should think more in terms of functional
toxicity. Functional toxicity must take into account the form and concentration of the substance,
exposure time, type and condition of the exposed specie(s). Functional toxicity occurs when a substance or substances cause reduced metabolism in the subject organism(s) resulting in reduced activity
and/or food intake, inability to reproduce, or death.
In this context, a substance is considered toxic if, when taken into a POTW, it causes an upset to the
biological process(es) of the plant and allows the discharge of the toxic substance, as well as other
substances, in partially or untreated form in excess of discharge permit limits. This discharge will, in
turn, be toxic to the biota of the receiving waters.
BIOMONITORING TECHNIQUES
A wide array of biomonitoring techniques have evolved for determining the effect of treatment
plant effluent on receiving waters. The best known are those involving various species of fish and
45th Purdue Industrial Waste Conference Proceedings, © 1991 Lewis Publishers, Inc., Chelsea, Michigan 48118.
Printed in U.S.A.
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