2-Bromoethanesulfonate-enhanced fermentation of iron-enriched sludge for short-chain fatty acid production and phosphorus transformation

Iron-enriched sludge generated from A-stage chemical capture in two-stage adsorption/bio-oxidation (A/B) wastewater treatment contains concentrated particulate organics, iron and phosphorus, yet its acidogenic conversion behavior and phosphorus speciation remain poorly understood. This work investigated semi-continuous anaerobic fermentation of this sludge under 2-bromoethanesulfonate (BES)-assisted conditions, and calcined fermentation residuals to characterize phosphorus/iron-bearing phases and evaluate their utilization potential. BES significantly enhanced organic solubilization and acidogenesis: the maximum short-chain fatty acid (SCFA) yield reached 373.2 ± 5.0 mg COD/g VS at 4-day sludge retention time, 26.6% higher than the control, with acetic acid dominating (>70% of total SCFAs). Activities of α-glucosidase, protease and phosphotransacetylase increased by 23%–80%. Phosphorus was predominantly retained in the solid phase, with iron-bound phosphorus (Fe-P) accounting for 49.8%–78.3% (elevated to 78.3% by BES) and total phosphorus recovery exceeding 89.1%. XRD and FTIR analyses confirmed iron oxide and inorganic phosphate structures in calcined residues. These findings support simultaneous liquid-phase SCFA recovery and high-value utilization of phosphorus/iron-rich residual solids.