Comparison of first-order and nth-order kinetic models for composting process of municipal solid waste

Abstract

The aim of this study was to propose six first-order kinetic models and then compare with nth-order kinetic model for composting process of municipal solid waste. Kinetic parameters for kinetic models were determined using a nonlinear regression method. For the first-order kinetic models, the reaction rate constant is expressed through experimental variables (time, pH, electrical conductivity, temperature, oxygen concentration, carbon dioxide concentration and moisture content). For nth-order kinetic model, rate constant and reaction order are simultaneously determined. A comparison of simulated and experimental values was performed. Based on statistical indicators (correlation factor, adjusted correlation factor, root mean square deviation, variance and 95% confidence interval), the obtained results between kinetic models were also compared. In order to choose the kinetic model that best describes the experimental data, organic matter content for three reactors were calculated. For first-order kinetic models, maximum differences between experimental and model data based on organic matter content for the first reactor, the second reactor and the third reactor were ranged from 10.30% to 18.64%, from 4.77% to 14.51% and from 6.60% to 14.00%, respectively. Mean differences for the first reactor, the second reactor and the third reactor were ranged from 3.36% to 5.42%, from 4.77% to 14.52% and from 0.43% to 1.62%, respectively. For nth-order kinetic model, maximum differences between experimental and model based on organic matter content for the first reactor, for the second reactor and for the third reactor were 2.30%, 1.22% and 1.50%, respectively. Mean differences for the first reactor, the second reactor and the third reactor were 0.005%, 0.002% and 0.001%, respectively. The nth-order kinetic model showed better agreement with experimental data of organic matter content than first-order kinetic models proposed in this study and in the previous studies.