66    RESPIROMETRIC METHODS FOR RAPID
TOXICITY / INHIBITION ASSESSMENT OF
INDUSTRIAL WASTEWATER
Martha I. Beach, President
John S. Beach, Jr., Vice President
N-CON Systems Company, Inc.
Larchmont, New York 10538
Fernando Cadena, Professor
New Mexico State University
Las Cruces, New Mexico 88003
INTRODUCTION
The failure of biological treatment processes in industrial and municipal wastewater treatment
plants is one of the major causes of toxic throughput and noncompliance with discharge permit
limits. Both operators and regulatory agencies are placing increased emphasis on controlling
toxic or inhibitory discharges. Monitoring the oxygen uptake rate (OUR) of industrial wastes or
mixed influent and prompt determination of their treatment inhibition potential (TIP) to the
plant's biomass (RAS) can prevent costly upsets. Rapid monitoring techniques using respirometry are valuable for both industries and municipalities because they make data available in a preventive, rather than historical, time frame.
The methods described in this paper use respirometric monitoring of oxygen uptake rate following the addition of increments of wastewater to a reactor containing microorganisms. Because they use a treatment plant's own biomass (RAS) as the reference organism, they provide a
rapid indication of the plant's ability to process specific industrial wastes. When a series of dilutions is used in a batch reactor method, concentrations that may be accepted without adverse effects can be determined. The batch method can also be used to provide an EC5() profile of the
wastes. The continuous stream method provides real time indication of treatment inhibition potential (TIP) of the waste stream, as well as a record of activity.
RESPIROMETRY: AN HISTORICAL PERSPECTIVE
Manometric devices have a long history in the field of biochemistry, beginning with instruments developed by Haldane in the late 1880s for the determination of blood gases. In 1890,
Adney made the earliest attempt to use direct absorption to measure oxygen demand of sewage.
Using a constant pressure type of manometric apparatus, he observed the rate of oxygen absorption by polluted water. At a constant pressure, the decrease in volume due to oxygen absorption
was indicated by the distance which a column of water traveled up the vertical, graduated limb
of a U-tube connecting two vessels, one partially filled with the sample, and the other containing
an equal volume of water. The entire apparatus was kept at a constant temperature in a waterbath
and shaken periodically to maintain an excess of dissolved oxygen in the sample. Although
Adney found this method was accurate, he concluded it was not suitable for routine work. Rideal
and Burgess (1909) attempted to use this apparatus, but found it unsatisfactory due to leaks
which developed in the course of shaking. They suggested that a dilution method, with incubation in closed bottles and measurement of dissolved oxygen both before and after incubation by a
modified Winkler method, was more accurate. This method was the forerunner of the standard
BOD5 test. Sierp (1928) and others revived and modified Adney's direct-aeration apparatus "to
reduce the cumbersomeness of the dilution method and afford quick, direct, and frequent readings."
50th Purdue Industrial Waste Conference Proceedings, 1995, Ann Arbor Press, Inc., Chelsea, Michigan 48118.
Printed in U.S.A.
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