Synergistic anaerobic digestion of chicken manure: Balancing biogas and biofertilizer via microbial dynamics and multivariate analysis

Abstract

Optimizing anaerobic digestion (AD) parameters is a key factor in improving the performance of AD systems. This study investigates the synergistic effects of total solids (TS: 6, 9, 12 %), substrate-to-inoculum ratio (SIR: 1:2, 1:1, 2:1), and digestion time (10, 20, 30, 40 days) on biogas production, microbial dynamics, and digestate quality from chicken manure. Among the highest reported, the results revealed that TS 6 % coupled with SIR 2:1 achieved the highest cumulative biogas yield (780 mL/g VS) and methane content (489.7 mL CH₄/g VS, 67 %). Stabilization was achieved within 20–30 days, approximately 40 % faster than higher TS systems. Microbial community analysis revealed that the optimal configuration not only maximized biogas production but also enriched beneficial microbial consortia, including Firmicutes, Fastidiosipila, and Syntrophomonas. Moreover, optimizing TS and SIR in the current AD system created ideal conditions for syntrophic microbial consortia. The digestate from this configuration exhibited > 90 % germination index and low phytotoxicity, confirming its viability as a biofertilizer. Multivariate analysis, including principal component analysis and response surface methodology, statistically validated the interdependence of operational parameters, demonstrating strong correlations between biogas yield, microbial composition, degradation efficiency, and digestate quality. These results demonstrated that optimum TS-SIR combinations can simultaneously enhance methane production, accelerate digestion kinetics, and ensure digestate safety, which is critical for industrial AD systems. This multi-factorial approach provides a framework for designing AD systems that contribute to sustainable agricultural practices and align with circular economy principles.