Development of a Biologically Based Aerobic Composting Simulation Model

Abstract

A relatively simple dynamic model based on microbial process kinetics has been developed for aerobic composting. Differential equations describing microbial, substrate, and oxygen concentrations, as well as moisture and temperature profiles have been derived as a function of vessel size and aeration rate. Microbial biomass growth was described using Monod growth kinetics as a function of degradable substrate concentration, oxygen concentration, moisture content, and compost temperature. Facility and fan operating costs have been included to permit economic optimization of the process. Predicted results demonstrated the ability of the model to quantify and describe the influence of multiple interacting factors (temperature, oxygen, moisture, and substrate availability) on the process driving the composting: microbial growth kinetics. Future development of the approach should be undertaken to provide a robust engineering model that can be used to evaluate and design environmentally sound composting facilities. An example application is presented along with data from a laboratory scale composter.

Application of validated mathematical model of composting process for study the effect of air flow rate on process performance

“…The microbial maintenance coefficient of microbial population i can be written as [5]: (5) where: mIM -mass of inorganic matter (kg). Correction factor for oxygen is described by the following equation [6]:…”

“…This process consumes oxygen and emits carbon dioxide, water vapor and heat resulting in a volume reduction of the waste and pathogen destruction when a good control is performed [3]. Growth of biomass is described as complex kinetics, usually Monod type, in regard to substrate [4][5][6][7] and oxygen [4]. Oxygen is necessary for microbial activity because the composting is aerobic process.…”

“…Only a few composting models are based on microbial kinetics. Some models consider only one substrate and only one microbial population [5,9], while the other models consider several substrates and several microbial populations [8,10]. Taking into account the disadvantages of these models, there is a need to develop a new model that can help to improve prediction and optimization of the process performance.…”

Sensitivity Analysis and Parameter Optimization of a Heat Loss Model for a Composting System

“…This technique has been employed elsewhere to assess emissions from sewer systems (Hornberger and Spear, 1980;Chang and Delleur, 1992;Corsi and Birkett, 1995;Choi et al, 1998;Choi, 1998) for determining the relative importance of factors influencing the natural attenuation of mining contaminants (Choi et al, 1999) and in quantifying the importance of the parameters in models developed to describe the fate of volatile organic compounds in trickling filters (Parker, 1997). The MPSA approach allows an assessment of the importance of each input parameter at a variety of settings of the other input parameters (Rabinowitz and Steinberg, 1991;Parker, 1997;Choi et al, 1999) and thus provides a more realistic picture than the standard analyses (Deshusses, 1994;Stombaugh and Nokes, 1996;Liang et al, 2004;Xi et al, 2005;Baquerizo et al, 2005). Standard analyses assess each input parameter only at the default values of the other parameters (Rabinowitz and Steinberg, 1991;Hamby, 1994) while in MPSA; a pairwise evaluation of the parameters is performed to allow for the development of three-dimensional response curves.…”

“…The composting process has been extensively studied and numerous mathematical models have been developed to de-scribe the heat dynamics and heat loss mechanisms by Hogan et al (1989), Stombaugh and Nokes (1996), VanderGheynst et al (1997), Mohee et al (1998), Bari et al (2000), Vining (2002), Ekinci et al (2004a), Xi et al (2005) and Ghaly et al (2006). However, no data on a combined sensitivity analysis and optimization of numerous parameters involved in these models has been explicitly reported in compost literature.…”