Mathematical Description of the Initial Stages of a Composting Process in a Batch Bioreactor

A mathematical model to describe a composting process in a tubularbioreactor is proposed in this work. This model considers the bioreactor as a biphasicsystem in which the gas phase provides the oxygen, whereas in the solid-liquid phase, themicroorganisms grow by consuming the substrate and dissolved oxygen. The mathematicalmodel describes temperature and oxygen and water concentration changes in both phases,as well as microorganisms, substrates, andSalmonellaconcentrations in the solid-liquidphase as a function of time and position in the bioreactor. The composting modelproposed was sensitive to changes in the maximum growth rate, substrate to biomass yield,ambient temperature, and initial concentration of water in the solid-liquid phase. A designanalysis of the bioreactor was performed, keeping the total bioreactor volume constant. The study consisted of changing (i) theinterstitial gas velocity, (ii) the initial mass fraction of water in the solid-liquid phase, and (iii) the global heat transfer coefficient. Itwas found that an increase in the bioreactor insulation was the most proper alternative to achieve an adequate sanitization of thecomposting system followed by the initial water concentration in the solid-liquid phase. Overall, the mathematical model could beused to design nonexistent composting tubular bioreactors or describe existent bioreactors to help achieving sanitizing conditions