Denitrification Performance and Mechanism of Permeable Reactive Barrier Technology with a Sulfur Autotrophic Denitrification Composite Filler in Rare Earth Mine Engineering Applications

Sulfur autotrophic denitrification (SAD) is an economical, rapid, and efficient wastewater denitrification process. In this study, based on previous studies on SAD fillers, permeable reactive barrier technology with a SAD composite filler as a substrate was created to treat the groundwater of rare earth mines. The feasibility of this permeable reactive barrier technology with a SAD composite filler in rare earth mine engineering applications was demonstrated, with a maximum nitrate removal efficiency of 100%, an average nitrate removal efficiency of 92.68% on days 40-47 (the influent water was 100% rare earth mine groundwater), and a low accumulation of nitrite and ammonium. In addition, the reactor had a good removal effect on 16 rare earth elements (La, Ce, Pr, Nd, Sm, Eu, Sc, Y, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu); except for that of Sc, the removal effects were over 98%. Moreover, scanning electron microscopy (SEM), confocal laser scanning microscopy (CLSM), and Fourier transform infrared spectroscopy (FTIR) confirmed that extracellular polymeric substances (EPSs), especially polysaccharides, had a facilitative effect on the removal of rare earth elements. Furthermore, 16S rRNA gene sequencing demonstrated that Sulfurovum (18.11%), Ferritrophicum (15.55%), Thiobacillus (13.35%), and Sulfurimonas (8.51%) were the main denitrification genera of the reactor. Overall, the results of this study provide a case reference for permeable reactive barrier technologies with SAD composite fillers in rare earth mine engineering applications.