Enhancing and unlocking faster start‐up anaerobic granulation <i>via</i> bioadditives

Abstract The prolonged start‐up period of high‐rate anaerobic anaerobic reactors represents a critical techno‐economic bottleneck, and this study demonstrates that targeted bioadditive conditioning offers an effective strategy to accelerate granulation while simultaneously enhancing methane yields at laboratory and pilot scales in two 2 L lab‐scale upflow anaerobic sludge blanket reactors (R1: multivalent cation addition, R2: chitosan addition) and subsequently, a 20 L pilot‐scale reactor, respectively. Laboratory‐scale experiments demonstrated that chitosan‐based conditioning shortened granulation time by approximately 15 days compared with conventional operation, whereas multivalent cations primarily improved microbial diversity and structural stability. When these strategies were combined and evaluated in a 20 L pilot‐scale reactor, biomass concentration increased by 126% and methane content reached 74.5% within 52 days, indicating accelerated commissioning and earlier energy recovery. The confirmation of this hypothesis is economically relevant, as reduced start‐up periods directly translate into faster cash‐flow generation, lower financial risk during early operation, and improved feasibility of capital‐intensive anaerobic treatment facilities. Beyond process intensification, the results reveal an overlooked interdisciplinary connection between polymer‐assisted microbial aggregation, granule‐scale ecology, and reactor‐scale techno‐economic performance. Metagenomic analysis revealed that chitosan favored the dominance of extracellular polymeric substance‐producing genera such as Methanobacterium and Clostridium , while multivalent ions supported greater microbial diversity. Overall, this work provides a scalable and cost‐effective framework for improving anaerobic digester start‐up performance, offering clear industrial relevance and a basis for future integration with digital twin‐based optimization and investment decision‐support tools. Last but not least, this study highlights the synergistic impact of bioadditives and reactor scale on anaerobic sludge granulation and system performance.