45    DETERMINATION OF BIODEGRADABILITY KINETICS OF
RCRA COMPOUNDS
USING RESPIROMETRY FOR STRUCTURE-ACTIVITY
RELATIONSHIPS
Henry H. Tabak, Research Chemist
U.S. Environmental Protection Agency
Office of Research and Development
Risk Reduction Engineering Laboratory
Cincinnati, Ohio 45268
Sanjay Desai, Graduate Student
Rakesh Govind, Associate Professor
Department of Chemical and Nuclear Engineering
University of Cincinnati
Cincinnati, Ohio 45221
INTRODUCTION
Electrolytic respirometry is attaining prominence in biodegradation studies and is becoming one of
the more suitable experimental methods for measuring the biodegradability and the kinetics of biodegradation of toxic organic compounds by the sewage, sludge and soil microbiota and for determining
substrate inhibitory effects to microorganisms in wastewater treatment systems.
Biodegradation of toxic and hazardous organic compounds holds a great promise as an important
fate mechanism in wastewater treatment and in soil detoxification. Information about the extent and
rate of biodegradation is a prerequisite for informed decision making on the applicability of the
biodegradation approach. Unfortunately, relatively little quantitative data are available from which
engineering judgement can be made, because of the large effort required to assess biodegradation
kinetics.
The ongoing biodegradation studies are concerned with the prediction of the biological fate of toxic
organic compounds using electrolytic respirometry as an approach to measure the biodegradation of
selected organic compounds and generate biokinetic data so that these can be ultimately used to
establish a possible correlation between molecular substrate configuration (physical/chemical characteristics) and biomass activity (kinetic parameters) as an index of biodegradation. The experimental
respirometry testing is also providing data on the concentration levels of toxic organics inhibitory to
microbial activity.
Initially, the inter-laboratory, ring test, Organization of Economic Cooperation and Development
(OECD) studies at the EPA laboratory, Cincinnati, Ohio, were undertaken to develop confirmatory
respirometric biodegradability testing procedure. Respirometric biodegradability and biokinetic data
were provided for the selected non-inhibitory and nonadsorbing compounds, tetrahydrofuran, hex-
amine, pentaerythritol, 1-naphthol, sodium benzene sulphinate, thioglycolic acid and the biodegradable reference compound, aniline.
Subsequently, similar electrolytic respirometry studies were initiated to determine biodegradation
kinetic parameters for selected representative toxic compounds of varied classes of organics included
in the Priority Pollutant, RCRA and Superfund CERCLA lists, and to demonstrate presence of any
inhibitory effects of these organics of specified concentration levels on the sludge biomass and on the
metabolism of biogenic compounds.
The objectives of the present study were to utilize the electrolytic respirometry oxygen uptake data
to: 1) determine the biodegradability of selected RCRA alkyl, chloro and nitrobenzenes, phenols,
phthalates, and ketones and representative CERCLA leachate toxic organics; 2) generate information
on their acclimated times (t„) and the initiation and termination time values for the declining growth
44th Purdue Industrial Waste Conference Proceedings, © 1990 Lewis Publishers, Inc., Chelsea, Michigan 48118.
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