Long-Term Biodegradability Tests of Organic
Industrial Wastes
JAMES C YOUNG, Associate Professor
Department of Civil Engineering
STEPHEN B. AFFLECK, Research Associate
Department of Agronomy
Iowa State University
Ames, Iowa 50010
INTRODUCTION
Some organic industrial wastes are difficult to treat biologically because they are either
toxic, non-biodegradable, or only slowly degraded so that they are not removed at the
normal operating conditions of a biological treatment plant. Therefore, before designing
biological treatment plants to receive such wastes, biodegradability tests must be
conducted. If a chemical inhibits biological growth, its maximum permissible
concentration must be determined. If it is biodegradable, the characteristics of the
biodegradation reaction should be known. Those reaction characteristics most important
are reaction rates, lag times in biological growth, concentration and temperature effects,
and the production of by-products.
Biodegradability tests are not new, and many investigators have reported the results of
biodegradability studies. However, most of these studies have been relatively short-term,
usually on the order of several days or less. The purpose of this paper is to report the results
of biodegradability tests, extending over 180 days, designed to determine the treatability of
various components of a pharmaceutical waste.
This project came about because of difficulties which occurred when attempting to
treat a pharmaceutical waste which contained a complex mixture of raw process chemicals
and production products. Lack of treatment was evident by the inability to obtain efficient
organic carbon removal in bench-scale and pilot-scale biological treatment plants. A
persistent yellow-orange color suggested that one of the problem chemicals was one or more
isomers of nitroaniline, a raw material used in the manufacturing process. Also, since
nitroanilines are known to be poisonous to humans (I, 2, 3) it was suspected that these
compounds were a likely cause of the treatability problems in the waste treatment system.
Therefore, studies were conducted to: 1) Determine the relative biodegradability of the
isomers of nitroaniline; and 2) To determine if one or more of the isomers of nitroaniline
was toxic to the microorganisms occurring in biological treatment plants.
Identification of such toxic or non-biodegradable wastes would permit the
manufacturing process to be modified so that these compounds could be prevented from
entering the wastewater stream. Information on reaction rates for organic materials
resistant to degradation, but not toxic, would permit the treatment plant operation to be
modified so that the removal of these compounds could be optimized.
BIODEGRADABILITY TESTS
A comprehensive summary of chemical structures resistant to aerobic biochemical
stabilization was presented by Ludzack and Ettinger (4). This report categorized chemicals
by homologous series and reported biodegradability, or resistance to biodegradability, in
terms of days of acclimation, ratio of observed oxygen demand to the oxygen demand
theoretically required to convert the chemicals to carbon dioxide, water and ammonia, and
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