Stoichiometric and kinetic model parameters for microbial transformations of suspended solids in combined sewer systems

Biotransformation of wastewater particles with different settling velocities has been investigated based on analysis of long term oxygen uptake rate (OUR) measurements and a conceptual model describing aerobic transformations of organic matter has been used for interpretation. No significant changes in the biodegradability of wastewater particles with different settling velocities were found. In this respect wastewater particles differed from earlier findings for sewer sediments. Methods for determination of model parameters describing aerobic heterotrophic biomass growth and wastewater substrate transformations have been derived and values estimated by adding readily biodegradable substrate to wastewater particles and sewer sediments. The validity of modeling results was subsequently tested. The model was capable of predicting biomass growth for long term measurements correctly and to simulate the OUR satisfactorily, however, peaks in OUR were difficult to simulate, probably because of a simplified description of hydrolysis used in the concept. Generally, it can be recommended to use OUR measurements, interpreted by a conceptual model describing aerobic transformations of organic matter, as a valuable methodology for characterization of wastewater particles as well as suspended sewer sediments in terms of COD-fractions and related biotransformations.