One-Stage vs. Two-Stage Anaerobic Digestion of Molasses From a Circular Economy Context: Energy Recovery and Digestate Fertilizer Value - raw data

Anaerobic digestion (AD) is widely used to recover renewable energy from organic wastes, yet efficiently processing substrates rich in readily fermentable carbon remains challenging in conventional single-stage systems. This study compared a single-stage system with a two-stage configuration separating acidogenic and methanogenic phases, using molasses as a model carbon-rich industrial substrate. The two-stage system achieved approximately 12% higher energy recovery and enabled biohydrogen production contributing about 10% of the total recovered energy, while reducing the accumulation of fermentation intermediates. The resulting digestate exhibited lower residual chemical oxygen demand, higher pH, and increased levels of plant-available nitrogen, alongside microbiome specialization and enrichment of plant growth-promoting taxa. Overall, the findings demonstrate that two-stage AD enhances both energy efficiency and fertilizer value, supporting integrated energy–nutrient recovery within circular bioeconomy systems.