Microbial shifts and VFA production in the optimization of anaerobic digestion by thermal hydrolysis coupled with vacuum fermentation

This study investigated a novel thermal-hydrolysis combined with a vacuum fermentation system for high-grade volatile fatty acids (VFA) recovery, and the corresponding changes in the microbial community. Four systems with and without hydrothermal pre-treatment (HTP) and vacuum were mobilized; results revealed that integration of HTP with vacuum has the highest potential in terms of VFA recovery, sludge disintegration, and solid reduction. HTP and vacuum fermentation systems were associated with the highest COD solubilization (45 %), and VFA yield (0.32 g COD/g VSS added). Vacuum fermenters with and without pre-treatment have the highest specific denitrification rates of 7.6 and 7.2 mg NO₃-N/g VSS.h, respectively, compared to all other samples and control (acetate). Changes brought about by vacuum fermentation included a shift in the microbial community toward enriching fermenters, mainly Caprothermobacteria and Thermotagea, responsible for VFA production.