Sustainable anaerobic co-digestion of swine manure and animal by-products: unravelling biogas production, microbial dynamics, and nutrient-rich digestate potential

This study investigates the anaerobic co-digestion of swine manure and animal by-products to enhance biogas production and nutrient-rich digestate, compared with mono-digestion of swine manure. The co-digestion performance was assessed in different reactor configurations at different mixing ratios. Swine manure and carcasses were collected and pre-treated, then submitted to tests to determine biogas production potential. The co-digestion performance was assessed in different reactor configurations (CLB and CSTR) changing carcasses/manure ratios. Results demonstrated that co-digestion improved gas productivity. In the CSTR, biogas productivity increased from 0.41-1.63 L_Nbiogas L_reactor^-1 d^-1, while methane productivity increased from 0.24-1.03 L_NCH4 L_reactor^-1 d^-1. In the CLB, biogas productivity rose from 0.19-0.61 L_Nbiogas L_reactor^-1 d^-1, with methane productivity increasing from 0.12-0.38 L_NCH4 L_reactor^-1 d^-1. Stability was maintained throughout the experiment, with a notable rise in total ammonia nitrogen (TAN) and a stable pH due to effective buffering capacity. In the CSTR, TAN reached 3.8 gN·L⁻¹ with free ammonia concentrations of approximately 500 mgN·L⁻¹, while in the CLB TAN stabilised at 2.5g N·L⁻¹ with free ammonia consistently below 50 mgN·L⁻¹. Microbial analysis revealed differences between mono-digestion and co-digestion. Co-digestion favoured a diverse community, which significantly contributed to biogas production. Co-digestion also resulted in higher nitrogen and phosphorus concentrations in the digestate compared with mono-digestion, due to the nutrient content of the added carcass material. The study confirms that co-digestion not only enhances biogas production but also produces nutrient-rich digestate, making it a viable and environmentally friendly waste management solution.