Contact parameters calibration of mixtures in different aerobic composting period: Focusing on establishment of particle model and its flow properties

In order to calibrate the contact parameters, particle models for mixtures of each period were established by simulation of repose angle using combined models in EDEM software, and then the flow properties of mixtures in different aerobic composting periods were clarified. Results showed that compared with the six-sphere model, the use of the double-sphere model to represent the compost mixtures of each period was not only closer to the ellipsoid of the actual particles but also simplified the calculation process. The contact parameters that mostly affected the repose angle were Poisson's ratio and shear modulus of mixture in the mesophilic period and JKR surface energy in thermophilic and cooling periods. The relative errors between the simulated repose angle using the optimal parameter combination and the actual measured value were less than 2.5% indicating the reliability of the regression models at each period representing the relationship among the repose angle and significant contact parameters. In addition, the flow properties of mixtures at the mesophilic period were better than those at the thermophilic and the cooling period of its smaller repose angle, the larger mass transformation, and the smaller Ek max value. Meanwhile, mixtures in thermophilic and cooling periods had similar flow properties. Hence, these could provide information for the further application of simulation to optimize the composting process (e.g., stirring frequency and ventilation time) to promote compost maturity.