Supplementation of wastewater process modelling tools to enable the kinetic analysis of sewage sludge composting

This study demonstrates mathematical description of sewage sludge composting based on identification and separate characterisation of simple process parts. For a description of the microbial processes an ASM3-based mathematical model developed for autothermal thermophilic aerobic sludge digestion is used. The oxygen mass transfer was characterized in a separate way. The 2.964 center dot 10(-3) m(2)center dot d(-1) value of the oxygen diffusion coefficient in the sludge at 55 degrees C indicates the strong oxygen limitation of the microbial degradation. The model extended with the oxygen mass transfer description has been validated using results from composting experiments performed with different specific sludge-air surface areas and with the renewal of the sludge surface.