Empirical characterisation and mathematical modelling of settlement in composting batch reactors

Abstract

The settlement of organic matter during composting was measured at different levels during the active biodegradation phase in forced-aerated static reactors loaded with different mixtures of organic wastes. The temperature evolution and the concentration of oxygen and carbon dioxide were also recorded in the exhaust gases. Two two-parameter equations and their generalised three-parameter form were fitted to the experimental data and their capability to predict settlement as a function of time was discussed. The settlement field inside the reactors was successfully described with a linear profile. At any given time and vertical position, mass settlement was proportional to the initial height after reactor loading. Furthermore, a relationship linking settlement to biological activity was also proposed. Under all tested experimental conditions, settlement showed a clear correlation with the cumulative oxygen consumption that was modelled with a three parameter equation.