Aerobic microbial growth in semisolid matrices: heat and mass transfer limitation.

A conceptual model of aerobic microbial growth in semisolid matrices were developed as a first step in the prediction of the rate of breakdown in semisolid cellulosic material. The conceptual model was described by a series of equations simplified by the assumption of steady-state microbial activity, and heat and mass transfer limitation. Temperature and oxygen distribution in compost piles were measured experimentally at the Butler County Mushroom Farm, Butler County, Pennsylvania, to test the validity of these assumptions. The compost piles consisted of ground corn husks, straw, and race horse manure. The data fit with the model was excellent with deviation between model predictions (as solved by an anglog computer) and actual temperature measurements never exceeding 3 degrees C. The effects of compost pile geometry, external temperature, compost density, external oxygen concentration, and insulation at the bottom of the pile were then predicted using a digital computer to solve the model. The predicitions show that the maximum breakdown rate occurs for an optimum height (which depends upon the system), insulating the base increases the breakdown rate, increasing the external temperature increases the initial breakdown rate but decreases the pseudo-steady-state breakdown rate and the uniformity and any increase in the external oxygen concentration increases the breakdown rate but decreases the uniformity.