DESARROLLO DE UN MODELO MATEMÁTICO PARA EL BIOSECADO DE RESIDUOS SÓLIDOS ORGÁNICOS EN PILAS

Abstract

A deterministic mathematical model was developed for biodrying a pile of organic solid waste inside a structure of glasshouse. The model included mass transfer, heat transfer, microbial growth and degradation of organic matter. The mathematical formulation is integrated by a system of four differential equations, obtained from a balance of mass and heat in the center of the pile, which are used to calculate: (1) water evaporation, (2) microbial growth, 3) consumption of organic matter, and 4) temperature. The first equation determined the moisture loss through the mass transfer coefficient and the air humidity gradient; the second one used the logistic model of microbial growth; the third one used the organic matter consumption model, and the fourth equation considered the heats of microbial metabolism, natural convection cooling-heating and the enthalpy for evaporation. The model is a useful tool for predicting microbial activity times and drying, as well as the degree of degradation of organic matter. In the particular case of this study, the model shows that the microbial activity only degraded 13 % of the organic matter, had a period of duration of 30 days during which 73% of the humidity of the pile was lost; raised the temperature of the pile to 65o C, and increased five times the rate of evaporation, but only contributed 13% of the heat for evaporation and the rest was contributed by solar radiation.