| With the development of China's agriculture,excessive agricultural waste has been produced,which has posed great threat to the ecological environment.Traditionally,the management methods of residual biomass include burning,dumping,landfilling,etc.These methods have low effective utilization rates for recovering nutrients and trace elements,and the decoupling of nutrient cycling between crop and livestock systems has led to environmental pollution of air,soil and water.Through fertilizer utilization of biomass,the straw and manure will be taken to land and used in land to improve soil fertility,which is currently advocated.However,it is difficult to popularize and meet the basic requirements of crop growth by using the conventional incorporation.Aerobic composting is a way to safely and efficiently indirectly manage agricultural waste,reduce environmental pollution,and realize the recycling of biomass resources.In this paper,the multi-field reaction mechanism of aerobic composting has been studied.The key parameters of aerobic compost was simulated by establishing a mathematical model.The helical ribbon and screw impeller aerobic compost bioreactor was designed to promote homogenization for the internal temperature and the heterogeneity of oxygen content,in order to improve the efficiency of aerobic composting reaction.This topic is derived from Jiangsu Provincial Key Research and Development Program(Modem Agriculture).According to the "mass-heat-momentum" coupling characteristics of aerobic composting reaction,the the influence of temperature,oxygen content and mass on the microbial activity was taken into consideration.By analyzing the heat transfer and oxygen diffusion of the materials in the reactor under the cylindrical coordinate system,the expressions of the partial differential equations of temperature,oxygen content,substrate concentration and aerobic microorganism concentration in the two-dimensional coordinate system were obtained.After determining the boundary conditions,the mathematical model of aerobic composting reaction under multi-field coupling was established,and simulations were carried out by Matlab to obtain the curves of temperature and oxygen content at different heights.In this paper,in order to solve the problem of the axial difference of environmental parameters such as temperature and oxygen content in the aerobic composting reactor which lead to the unevenness of product,the helical ribbon and screw impeller aerobic compost bioreactor was designed based on the thermodynamics and kinetics of composting reaction.According to the computational fluid dynamics theory,the internal flow field of the bioreactor was established by using the finite element model.The internal flow field at 20,40,60,80r/min were simulated by the professional CFD simulation software Fluent.The flow field pressure,flow rate and fluid trace were obtained to determine the reactor speed.In this paper,the apparent phenomenon,temperature,pH,oxygen concentration,total carbon content,total nitrogen content,total phosphorus content,total potassium content and seed germination index of the upper,middle and lower layers of the aerobic composting reactor have been measured as key parameters of quality.The results show that the trend of temperature and oxygen content were basically the same as the mathematical model.The ribbon-screw type was able to promote the axial flow of the material and reduce the axial difference of temperature and oxygen content.The time above 50?of the upper,middle and lower layers were 7.3,6.8,5.5 d,respectively.The volume fraction of oxygen content during the reaction was more than 8%.The final carbon to nitrogen ratio of each layer was between 15 and 20.The seed germination index was greater than 88%.Thus,the reactor can achieve harmless and homogenization of aerobic compost.Moreover,,the scanning electron microscopy analysis of compost materials in different periods was carried out to obtain the variation of cow dung and straw granules. |
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