Extrapolation of Biodegradability Test Data by Use of Growth Kinetic Parameters

Formulas for extrapolation of test data on biodegradability to percentage removal in treatment plants and biological half-life time in surface water are derived from growth kinetics. A pseudo-first-order rate constant can be used provided that substance properties and microbial density in the environment are assessed independently. For comparison of kinetics at different concentration levels an extrapolation factor can be used that is based on the ratio between maximum growth rate and sludge age in a treatment plant. The specific microbial density is estimated on the basis of proportional growth on all degradable substances in a state of equilibrium after adaptation. As a consequence the percentage removal can be predicted on the basis of sludge age and influent concentration in combination with the substance properties. The formulas predict that the combination of sewage treatment and surface water gives an almost equal biological half-life time for all readily biodegradable substances in the surface water. The predicted removal percentages and biological half-life times are in agreement with observations.