Effects of Aspergillus niger on the maturity and cellulose degradation of cow manure composting using EEM-FRI method

A large number of cow dung can cause the severe environmental pollution if not properly disposed of, particularly for the large-scale intensive cattle farm. A clean and sustainable treatment, composting has been commonly applied to the organic wastes in recent years. However, the traditional composting process cannot fully meet the requirement of industrial production in modern livestock farming, due to the low cellulose degradation and product maturity. Previous studies show that Aspergillus niger can be utilized to accelerate the degradation of organic matter for better composting maturity. However, a systematic understanding is still lacking on the application of Aspergillus niger on cow dung composting at present. In this study, a systematic optimization was performed on the fermentation process in composting using a combination of fluorescence excitation–emission matrix (EEM) spectroscopy and fluorescence regional integration (FRI). An attempt was also made to clarify the effects of Aspergillus niger on cow manure compost maturity and cellulose degradation. Cow manure was mixed to the moisture content of about 60%, with the wheat straw as an auxiliary material. With no Aspergillus niger as the control treatment, 1%, 2%, and 3% Aspergillus niger were added for the aerobic composting. A composting experiment was carried out in 60L composting reactors for 40 days. The compost maturity was evaluated to determine the maturity index, nutrient content, humus composition, and cellulose degradation. The results showed that the inoculation of 2% Aspergillus niger rapidly increased the temperature, where the thermophilic phase appeared 1 day ahead of time, compared with the control treatment. The content of humic acid increased by 49.94 g/kg, but the fulvic acid decreased by 37.51 g/kg, compared with the initial stage, indicating the improved humification. Once the inoculation with Aspergillus niger was 3%, the seed germination index and the total phosphorus content increased by 2.38%, and 22.3%, respectively, whereas, the degradation rates of cellulose and hemicellulose were 1.36 and 1.42 times higher than those of the control treatment, indicating more conducive to compost maturity. The EEM-FRI demonstrated that a high maturity of compost was achieved with the inoculation of Aspergillus niger, indicating the high degradation of organic matter, and the formation of humus. A correlation analysis also showed that there was a significant correlation between the total phosphorus content and cellulose, humic acid, and fulvic acid after adding Aspergillus niger. Consequently, the high compost maturity and cellulose degradation can be achieved to enhance the quality and nutrients of the products. The cow manure compost with 2%-3% Aspergillus niger can also be inoculated to efficiently promote the resource utilization of cow manure in cattle farms.