CLASSIFICATION OF BIODEGRADABILITY BY GROWTH KINETIC-PARAMETERS

On the basis of classical Monod equations for microbial growth, kineti c parameter values are assessed to enable the characterization of biod egradability as a substance property. Although growth is a microbial p roperty, the substance selects those species from a mixed inoculum tha t can profit at most under the prevailing conditions. Hence it is conc luded that the combination of observed cell yield Y approximate to 0.5 g solids/g COD, maximum growth rate mu(max) > 0.3/day, and half-satur ation constant K-s < 0.6 mg COD/liter provides a suitable set of borde rline criteria for classification of chemicals as readily biodegradabl e. Of these parameters mu(max) is suitable for differentiating chemica ls, whereas Y seems more or less equal for all readily degradable subs tances and K,is not easily measurable with existing standard test meth ods. In this approach the density of specific microbes in the inoculum or during the test is excluded from the substance characterization an d thus adaptation phenomena have no influence. From correlation studie s and model calculations it can be expected that if the above paramete rs are estimated on the basis of standard tests for ready biodegradabi lity, these tests will not produce false positives. Provided that the above parameters can be estimated, any other method than just the stan dard methods can be used to classify a substance as readily biodegrada ble. (C) 1994 Academic Press, Inc.