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

Abstract

We conducted a laboratory-scale composting experiment with forced aeration using two fermenters with the same shape and geometry under the same material and operating conditions to certify the reproducibility and construct a mathematical model for the proposed composting process as an ecosystem phenomenon. Overall, the reproducibility of the composting process was relatively good, although small differences in the temperature and heat generation rate between the two fermenters occurred after 100 h, and these differences gradually increased toward the end of the experiment. Based on these results, it seems feasible to simulate the composting process with a deterministic model to examine the behavior of the entire system for the purposes of basic system design. We propose a deterministic model for heat and mass transfer in the composting process, emphasizing that the transformation process of released biochemical energy to heat involves an "energy dissipation mechanism" as a successive substrate decomposition process. The simulated model results of the temperature, moisture content, weight, oxygen concentration, and heat generation rate were in fairly good agreement with the experimental results. However, the course of the heat generation rate over time, that is, the reaction rate at any height in the vertical direction, somewhat differed from those estimated by the measured temperature profile.

Thermodynamic interpretation of composting process using approximate integral functional

“…1 as comparative control results. These results correspond to the laboratory-scale experiment performed by Shishido and Seki (2015), and have been found to show good agreement with the experimental results. Table 1 lists the physical properties of the compost mass and the main operating conditions set for computer simulation.…”

“…There are two reasons to supposition of this model. One is that one-dimensional treatment is easier mathematically than the multi-dimensional model, and the other is that this model is equivalent to the previous model that has been already certified experimentally (Shisido and Seki, 2015) and useful to verify a newly introduced integral functional model. In this case, the enthalpy balance equation of Seki (2016) can be rewritten with some changes by sorting several terms on the right-hand side as follows:…”

“…There have been thus far many mathematical models reported on composting process even if we confine the partial differential equation type models considering spatial and temporary change of state variables, such as Bongochgetsakul and Ishida (2008), Zambra et al (2011), and Shishido and Seki (2015). Among them, the first article used finite volume method for solving the differential equations, the second used finite element method, and the third used finite difference method.…”

Exergy analysis and the dissipation function of the composting process

“…The proportion of the dissipation function to the total released exergy in the entire fermenter is given by Using the experimental results of Shishido and Seki (2015), we calculated this value ε and plotted the results against time ( Figure 4). In the calculation, Eq.…”

“…Time course of the proportion of the dissipation function to the total released exergy in the entire fermenter. The values were estimated from the experimental data of Shishido and Seki (2015); the experiment was conducted in an acrylic resin container under the aeration condition using the mixture of rice bran, chicken manure, and sawdust as feedstock. About 90% of the released exergy is estimated to be dissipated throughout the experimental duration.…”