Synergy in Nano-Fe3O4 and MOF-808 composites enriches their applications in sludge anaerobic fermentation

Waste activated sludge is an important resource rich in carbon and phosphorus. While volatile fatty acids (VFAs) and phosphate can be produced or released into the aqueous phase during anaerobic fermentation, increasing the yield of VFAs and simultaneously recovering phosphate in a fast and economical manner has proven to be challenging. This study demonstrates a possible approach to address this challenge using a magnetic composite material named Fe3O4@MOF-8081.5. The introduction of Fe3O4@MOF-8081.5 into anaerobic fermenters increased the VFAs concentration by 1.68 times due to its highly defective structure, unsaturated Zr active sites, proton-electron conductivity, and inhibition of methanogenesis by acting as an electron competitor. Moreover, the defective structure as well as the synergistic effect between the two components endow Fe3O4@MOF-8081.5 excellent phosphate adsorption capacity and efficiency. The main forces between MOF-808 and phosphate are ligand exchange and weak interactions according to the molecular dynamic simulation results. Although the magnetic recovery rate of Fe3O4@MOF-8081.5 in the absence of biosolids is perfect, how to improve its performance with biosolids should be further explored in the future.