Abstract:
Biogas engineering based on anaerobic digestion is an important engineering way for the resource utilization of agricultural wastes (i.e. straws, livestock and poultry manure) and plays an important role in promoting the circulative agriculture. How to achieve the effective resource utilization of the digested biogas residue is important for the operation of biogas engineering. Composting is a crucial way to accomplish the harmless, reduced and resourceful utilization of biogas residues and widely applied to the treatment of manure and wastewater in concentrated animal feeding operations (CAFOs). Reactor composting, with the advantages of shorter composting period, smaller area, easier automation control and lower secondary pollution, has been widely used for the waste treatment in large-scale CAFOs. However, the technique of reactor composting still needs to be improved, for its remaining defects that may cause insufficient aeration, difficult water removal and low degree of intensification of composting stuff, which restricts its application for biogas residue composting. In this study, a pilot aerobic fermentation rotary reactor with the volume of 500 L for the integrated biogas residue composting was designed to meet the demand of rapid composting treatment of biogas residue. The aerobic fermentation rotary reactor for biogas residue was mainly composed of raw material pretreatment, aerobic fermentation, biological deodorization and reactor control unit. The rotary copying board was improved, including pushing material copy board, parallel copy board, and blocking material copy board. The ventilation system was improved by “frequency conversion air supply-controllable heating-fan-shaped cloth gas-sectional aeration” technologies. An automatic control system for the designed reactor has been developed; the biogas residue pretreatment and biological deodorization technology were integrated in the designed reactor. Based on the organic matter degradation model and the moisture removal model, the ventilation rate and frequency were optimized. The optimal process parameters of the aerobic fermentation rotary reactor were obtained, the rotary filling rate was 0.6.The rotary rotation speed was 3 r/min. The aeration frequency was aeration 12 min, interval 18 min. The aeration rates during the warming-up, thermophilic and cooling periods were 112, 114 and 110 L/min, respectively. The performance tests were carried out with biogas residue, pig manure and straw as raw materials for 15 days of composting, the ratio of biogas residue, pig manure and straw was 8.75:6.25:4, the moisture content of the mixed materials was 55%-60%, C/N was 20-25. The results showed that the reactor has the function of real-time monitoring the temperature and oxygen data of different gradients. The temperature of composting piles higher than 50 ℃ could last for 7 days during the composting process. The germination index of composted pile was more than 80% after 15 days of composting. The moisture content of composted pile was less than 30% after 15 days of composting. This study could provide technique and equipment support for the rapid composting of biogas residue.