Design and experiments of a vertical aerobic composting reactor based on EDEM

Aerobic composting has been one of the fastest ways to fertilize soil products via organic decomposition under an oxygen-rich environment. Among them, the aerobic composting reactor can be one of the most important facilities during aerobic composting in recent years. However, some challenges are still remained in the aerobic composting reactor, including the long duration, low maturity homogenization, and utilization efficiency. In this study, an optimal vertical reactor of aerobic composting was designed with three independent layers using E-Discrete Element Method (EDEM) and Fluent simulation. An effective volume of 120 L was also obtained in the developed reactor. A series of simulations and experiments was implemented to verify the structural parameters. Each stage was also controlled to shorten the duration of the composting process in this reactor. The continuous process of feeding in and out of feedstocks was established, according to the actual requirement of the reactor during aerobic composting. ANSYS platform was finally used to verify the mixing system of the reactor. The results showed the maximum stress and deformation of the reactor were 75.288 MPa and 3.680 mm during aerobic composting, respectively, fully meeting the high requirements of standard design. At the same time, the EDEM and Fluent simulation were then used to analyze the movement of materials during aeration and discharging. The results showed that the discharge rate of the reactor was 98.14% at the string speed of 20 r/min, and the gas volume fraction was above 90% during aeration. Better performance of the reactor was achieved in the discharge and aeration system during this time. A series of experiments was carried out on aerobic composting, particularly with the chicken manure and corn straw that were mixed at a ratio of 1:4 (dry weight basis). It was found that there was no significant difference in the temperature of the same layer during composting of the three batches (P>0.05). Specifically, the duration of the high-temperature period (higher than 50 °C) was maintained 9, 7 and 5 days, respectively, for the three raw materials. It infers that the composting fully met the ecological demand of harmless in this case. More importantly, the pH values were between 8.0 and 9.0, whereas, the electrical conductivity (EC) values were between 2.0 and 3.0 mS/cm during composting of three batches. There was a significant difference in the pH and EC values of each layer (P<0.05). However, there was no significance (P>0.05) at the same layer during the three batches. Moreover, the seed germination rates were also all above 100%. In addition, the degradation rates of volatile solid (VS) were 14.99%, 16.03%, and 13.24%, respectively, in the three batches. Hence, the stable properties of composting were achieved in the excellent performance of the developed reactor. Therefore, the improved composting reactor can be expected to serve as the aerobic composting reactor in the utilization of agricultural wastes.