MEASUREMENT AND VALIDATION OF KINETIC PARAMETER VALUES FOR PREDICTIONOF BIODEGRADATION RATES IN SEWAGE-TREATMENT

Analysis of about 140 oxygen uptake curves from standard biodegradatio n tests with the electrolytic respirometer yielded growth kinetic para meter values. The maximum observed growth rate, mu(max), On the 52 dif ferent substances varied between 1 and 6/day, The measurement of the h alf-saturation constant K-s at the depletion phase of the oxygen uptak e curves appeared problematic. For 24 substances the values were below 1 mg ThOD/liter, Apparently high K-s values of several tenth mg ThOD/ liter for the other 28 substances are explained by retarded mineraliza tion of intermediates due to the relatively high initial test concentr ations of up to 300 mg ThOD/liter. At lower test concentrations (down to 15 mg ThOD/liter) the measured K, values for these substances were also typically below or around 1 mg ThOD/liter, Based on the above-men tioned maximum growth rates and the low values for K-s, the predicted steady-state residual concentration of these substances in the effluen t of completely mixed sewage treatment plants is between 10 and 100 mu g/liter. This level is in accordance with the range of measured value s taken from literature, Based on this research and additional data fr om literature, the separation between readily and inherently degradabl e can be made at the critical values of mu(max) approximate to 1.5/day and K-s approximate to 1 mg ThOD/liter. (C) 1996 Academic Press, Inc.