Simultaneous recovery of ammonia and volatile fatty acids from dark fermentation effluents via gas-liquid membrane contactor

The increasing interest in sustainable waste management has spurred the development of innovative technologies for resource recovery. In this context, organic waste fermentation generates effluents rich in ammonium and volatile fatty acids (VFAs), both of which represent valuable precursors for the fertilizer and chemical industries. This study introduces and evaluates an innovative membrane-based methodology enabling the simultaneous recovery of ammonia (NH3) and VFAs from synthetic and real dark fermentation broths. The experimental setup employed a gas–liquid membrane contactor consisting of a 44 cm2 hydrophobic polytetrafluoroethylene (PTFE) membrane (0.22 μm pore size) housed in a flat-plate module. The effects of different extraction solutions (HCl, H2SO4, NaOH, and ionic liquids), their concentrations, and the flow rates of both the fermentation effluent (500 mL min−1) and the extracting solution (250 mL min−1) were systematically investigated, along with the influence of the broth pH (7.0 and 5.5). Among the tested conditions, 2 M NaOH was identified as the most effective extraction medium, achieving simultaneous recoveries of 24.5 % for NH3, 50 % for propionic, butyric, and valeric acids, and 42 % for acetic acid after 168 h of operation in an acidogenic broth at pH 5.5. Furthermore, higher solvent concentrations and increased recirculation velocities were positively correlated with improved NH3 and VFA recovery, regardless of the solvent type. Overall, the results highlight the potential of the proposed membrane contactor-based approach as a promising and scalable technology for integrated resource recovery from fermentation effluents.