Moderate intensity of ventilation can significantly reduce nitrogen loss during aerobic composting of chicken manure

Objectives The study was focused on effects of different ventilation intensities on nitrogen transformation in chicken manure composting. The objectives were to optimize the operating parameters of ventilation, reduce the loss of nitrogen, and improve the quality of the final chicken manure.

Methods The experiment was conducted at the composting site of an organic fertilizer factory in Shandong Province, with the chicken manure and rice husks mixed at 1∶1 as the initial material. Under the condition of forced aeration and turning, aerobic fermentation of composting was carried out for a period of 28 days. Mild, moderate and strong ventilation intensities of 0.1, 0.2 and 0.3 m³/(m³·min) were setup during the composting. Samples were taken at different time during the process of composting.Temperature, pH and moisture content were monitored, and the contents of total nitrogen, NH₄⁺-N and NO₃^–-N were determined throughout the overall period. The germination index of the compost products was tested using rape seeds at last.

Results During composting, the windrow temperature under mild, moderate and high ventilation intensities rapidly reached up to 68.3℃, 71.8℃ and 68.6℃ respectively. The temperature of ≥ 50℃ lasted over12 days, and then declined to the environment temperature. The moisture content of windrow reduced from the initial 63.2%, 62.1%, and 64.5% to 32.4%, 30.1% and 29.2%, respectively. The pH of the windrow varied from 7.5–8.0 under all the ventilation treatments. At the end of the composting process, the seeds germination index (GI) was more than 80% in all the treatments. The content of NH₄⁺-N decreased gradually after the slight increasing at early period. The content of NO₃^–-N kept increasing significantly. The content of total N showed a trend of decreasing and then increasing gradually during entire composting. The nitrogen loss in mild, moderate and strong ventilation were 19.8%, 20.2%, and 29.6% respectively. The rates of nitrogen losses were not significantly different between mild and moderate ventilation, but both of them were significantly lower than that of strong ventilation (P ≤ 0.05).

Conclusions During the chicken manure composting, ventilation intensity does not affect the process, and all could produce qualified products that meet the safety and hygiene requirements of manure. Among three ventilation intensities, moderate intensity of 0.2 m³/(m³·min) of the material leads to the least nitrogen loss and high germination index, making it the recommended ventilation for chicken manure composting.