Aerobic microbial growth in semisolid matrices: Heat and mass transfer limitation

Abstract

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.

Laboratory-scale Experiment for an Active-stage Composting Process under the Same Material and Operating Conditions

“…Two good examples are the use of compost as an excellent soil amendment and the use of heat generated in the composting process. Several papers on composting process modeling have been published (Finger et al, 1976;Fujita, 1980;Seki and Komori, 1984;Bach et al, 1987Hamelers, 1993;Keener et al, 1993;Kaizer, 1996;Stombaugh and Nokes, 1996;Das and Keener, 1997;VanderGheynst et al, 1997;Seki, 2002). Since composting is a complicated phenomenon involving simultaneous heat and moisture transfer with microbial reactions in dispersed phases of solid, liquid, and gas, effective models directly related to the practical application of composting are yet to be proposed.…”

Development and validation of mathematical model for aerobic composting process

“…The aims of this work were the following: (1) to develop the new dynamic and structured model for aerobic composting process by connecting the reaction kinetics with mass and heat transfer between three phases of the system, (2) to evaluate the kinetic parameters in suggested kinetics of the model by using the experimental results from laboratory reactor, (3) to validate the model with several experimentally measured dynamic state variables, (4) to show the efficiency of the validated model through the determination of the effects of the main process factors on the degradation of organic waste and evaluations of their optimum values.…”

Overall Heat Transfer Coefficients in Organic Substrates Composting

“…This approach has the advantage of allowing bulk fluid, or solid, temperatures to be used in heat transfer calculations for designing large-scale composting reactors. However, the wide research conducted to date to model the heat transfer processes (Andrews and Kambhu, 1973;Finger et al, 1976;Hamelers, 1993;Hogan et al, 1989;Stombaugh and Nokes, 1996;Richard, 1997;VanderGheynst et al, 1997;Higgins and Walker, 2001;Mohee et al, 1998;Sangsurasak and Mitchell, 1998;Nielsen and Berthelsen 2002;Ekinci et al, 2004;Xi et al, 2005;Richard and Walker, 2006) of the composting process has not comprehensively addressed the variations of the overall heat transfer coefficient during the composting process stages. The work presented in this paper addresses this specific research need.…”