Design And Application Of Spiral Aerobic Composting Reactor

With the rapid development of animal husbandry in China,there are about 118 million livestock and poultry in China every year,which leads to a large increase in the emission of livestock and poultry manure.According to the Ministry of Agriculture,the current annual output of livestock and poultry manure is about 3.8 billion tons.Aerobic composting is one of the economical and effective ways to treat and recycle livestock and poultry waste.However,the traditional aerobic composting method has some problems,such as low composting quality,long composting time and significant greenhouse gas emission such as methane and nitrous oxide.Adding exogenous additives（such as biochar,wood vinegar,etc.）in aerobic composting can improve the composting efficiency and reduce the negative effects of traditional composting.In addition,the existing composting reactors in the society have some problems such as poor tightness and mixing uniformity,which is not conducive to the theoretical research of aerobic composting technology and the promotion and practical application of organic solid waste utilization.Therefore,aiming at the above problems,a spiral-type aerobic composting reactor was designed and made,which was used for composting experiments to further study the action mechanism of exogenous additives on greenhouse gas emission reduction and nitrogen retention in aerobic composting,and optimize the composting process.Specific research contents and results are as follows:（1）Design of spiral aerobic composting reactor.The whole structure of spiral aerobic composting reactor was established according to the actual production requirements and relevant theoretical knowledge.The volume of the composting reactor,the basic size of the reactor,the structure and parameters of the agitator,the ventilation system,the leachate filter layer and other auxiliary control devices were analyzed and designed.The three-dimensional modeling of aerobic composting reactor was completed and the static stress of spiral agitator was analyzed.（2）Simulation analysis of material mixing process in compost reactor.Through EDEM simulation software,the apple tree sawdust accumulation Angle was simulated,the apple tree sawdust particle model was calibrated,and the optimal parameters of the discrete element model were obtained:the Poisson ratio of apple tree sawdust was 0.5,the rolling friction coefficient of apple tree sawdust to apple tree sawdust particles was 0.2,and the collision recovery coefficient of apple tree sawdust to apple tree sawdust particles was 0.2.The spiral aerobic compost reactor was optimized by orthogonal test with calibrated parameters.The optimal working parameter combination of spiral aerobic compost reactor was C1B3A3,that is,the spiral diameter was 350mm,the spiral rise Angle was 10°,and the rotation speed was 90r/min.（3）Manufacture and experimental study of spiral aerobic composting reactor.After the processing and production of spiral-type aerobic compost reactor was completed,the experiment was carried out with the compost reactor as the experimental device,pig manure and apple tree sawdust as the raw materials.The changes of temperature,water content,p H,conductivity,germination index and C/N ratio during the prototype test were studied.The results showed that the high temperature lasted for more than 10 days in the composting process.The moisture content continues to decrease,dropping to about 35%after composting.After composting,the p H of the material is stable at about 8.3,indicating that the compost product is more suitable for acidic soil.After composting,the material C/N is less than 20 and the germination index is more than 80%,indicating that the material is fully mature.The above indexes indicate that the spiral aerobic compost reactor has good mixing effect on compost materials and meets the requirements.（4）Effects of exogenous additives on greenhouse gas emission reduction and nitrogen retention in aerobic composting of pig manure.The results showed that adding biochar（B）could accelerate the composting process of pig manure and apple tree sawdust.The addition of B and wood vinegar（PY）reduced the emission of NH₃,CO₂,CH₄ and N₂O by 18.82-35.88%,1.38-15.39%,16.98-62.73%and 4.47-19.91%,respectively.B+1.0%PY treatment had the lowest nitrogen loss（2.12%）,and B+0.5%PY treatment had the lowest greenhouse gas emission（11.62 g/kg）.The bacterial community analysis showed that PY and B synergistic application could increase the relative abundance of Proteobacteria,and contribute to nitrogen fixation and reduce nitrogen loss.