Microbial profiling of swine-waste digestates: implications for biofertilizer application

The search for sustainable energy sources has become more urgent due to the high level of pollution caused by petroleum-based products. Digestate, a byproduct of the digestion of organic waste generated during biomethane production, can be used as a biofertilizer. This compound enriches the soil and promotes the proliferation of nitrogen-fixing bacteria, which benefits sustainable agriculture. This study assessed the biofertilizer potential of digestates from two anaerobic digesters (pilot and laboratory scale) using swine carcasses and effluent. Physicochemical analyses and microbial diversity profiles revealed differences between the digestates. The microbial diversity was higher in the laboratory-scale digester, suggesting that the presence of swine carcasses favored the development of a more diverse community, which is essential for producing a biofertilizer. Shannon diversity indices for laboratory scale and pilot scale were 7.6 and 5.4, respectively. The most abundant genera observed in the laboratory-scale digester were Methanoculleus (25.38%), Clostridium (7.08%), and Pseudomonas (5.65%). On the other hand, at pilot scale, the greatest abundance was associated with Clostridium (20.90%), Turicibacter (14.13%), and Methanosarcina (3.78%). Beneficial genera including Bacillus, Pseudomonas and Bradyrhizobium were found in both scales, which may play roles in plant growth promotion, phosphorus solubilization, and nitrogen fixation. The abundance of Methanoculleus was higher at the laboratory scale. The results indicate that digestate from the laboratory-scale digester had a greater microbial diversity and a higher presence of beneficial taxa, including Bacillus (2.2%) and Paenibacillus (1.5%), known to stimulate plant growth through phytohormone production. However, further studies including metabolic pathways or field testing are needed to understand the variation in microbiota associated with digestates from swine waste, including animal carcasses.