Maximizing volatile fatty acid yields from sewage sludge: Electrodialysis with bipolar membranes enhanced...

The recovery of volatile fatty acids (VFAs) from waste-activated sludge (WAS) is crucial for sustainable bio-based systems; however, low substrate degradability limits this process. This study combines heat-alkali pretreatment, Na₂SiO₃ buffering for pH stabilization, and electrodialysis with bipolar membranes (EDBM) to enhance VFAs production and alkali recovery. Semi-continuous fermentation with ultrafiltration pretreatment achieved a maximum VFAs yield of 8.20 ± 0.32 g/L at an optimal current density of 30 mA/cm², balancing hydroxide ion generation and energy consumption. The hydraulic retention time (HRT) was 2 h, with continuous 24 h operation. Microbial analysis, conducted via 16S rRNA sequencing, revealed the presence of Clostridium spp. dominated the early stages, correlating with peak VFAs production, while Shewanella spp. emerged later, indicating stress adaptation. Functional profiling showed enhanced carbohydrate and energy metabolism. This integrated approach improves VFA yield, stability, and sustainability, offering a scalable method for bioresource valorization within circular bioeconomy frameworks.