Impact of thermal hydrolysis time on volatile fatty acids production from sludge fermentation: Insights into dissolved organic matter transformation and microbial succession

While thermal hydrolysis pretreatment (THP) represents a promising technology for enhancing the production of volatile fatty acids (VFAs), the specific impact mechanisms of the THP duration on the acidogenic fermentation process have yet to be fully understood. This study addresses this gap by investigating the influence of various THP times on biochemical processes, microbial components, and genetic mechanisms during the fermentation process. The results indicate that extending the THP duration from 10 to 30 min is advantageous for achieving higher VFAs production and an increased proportion of acetic acid (2876.5 and 28.9% versus 4523.8 mg COD L-1 and 44.6%). Mechanism investigations revealed that longer THP durations are particularly effective in enhancing hydrolysis and solubilization. Notably, The PN and PS concentrations at THP time of 30 min was 68.6% and 83.6% higher than that at THP time of 10 min at 2nd d. Additionally, extended THP durations led to the enrichment of VFAs-producing and hydrolysis functional microorganisms (e.g., Comamonas, Fonticella, Bacillus and Romboutsia), along with the specialized functional genes (e.g., accA, accC, accD and bccA), which are crucial for elevated VFAs production. Collectively, this study provides comprehensive insights into the impact mechanisms of varying THP durations on VFAs production and offers valuable contributions to the field of sludge management and resource recovery research.