Preparation and Mechanisms of Core-Shell Hierarchical Porous Composites for Targeted Enrichment and Protection of AnAOB

Abstract

To achieve both efficient enrichment of anaerobic ammonium-oxidising bacteria (AnAOB) and protection under inhibitory stress, a core-shell hierarchical porous molecular sieve composite (BFMS) was developed using a Fe-modified biochar core (BC/Fe) and a surface-loaded NaY-type molecular sieve shell (MS). Through stepwise optimisation of KOH dosage, pore-forming temperature, Fe(III) loading, and molecular sieve coating ratio, the optimal synthesis conditions were determined as m(BC):m(KOH) = 1:1.2, 850 °C, BC: FeCl3 = 1 g:20 mL, and 60% MS loading. Under the optimal conditions, BFMS significantly enhanced AnAOB enrichment and metabolic activity, achieving a denitrification rate constant of 0.159 h-1, which was 4.2 times that of the control, with a maximum denitrification efficiency of 93.33%. Under Cu(II) (5 mg·L-1) and tetracycline (TCE) (1 mg·L-1) stress, BFMS maintained 57.50% denitrification performance, whereas the control retained only 18.70%. Structural characterization showed that BFMS possessed a hierarchical porous structure favourable for microbial colonisation, while Fe species were stably anchored at the BC/Fe interface through Fe-O coordination, and a large number of MS are distributed on the material surface. Mechanism-verification experiments combined with DFT calculations revealed that the enhanced performance of BFMS originated from the synergistic roles of the core-shell structure. The Fe-O coordinated BC/Fe interface exhibited electron-rich and strongly coupled electronic characteristics, which promoted AnAOB enrichment and activity and enabled local interfacial interactions with Cu(II) and TCE, while the molecular sieve shell reduced the accessibility of inhibitory compounds to the biologically active region, thereby achieving the protective effect on AnAOB.