Modified PVA (polyvinyl alcohol) biomaterials as carriers for simultaneous removal of nitrate, Cd (II), and Mn (II): performance and microbial community

The ecological toxicity and potential risks of heavy metals that coexist with nitrates in wastewater have aroused public attention. This study developed an immobilized Fe3O4@Cu/PVA mixotrophic reactor (Fe3O4@Cu/PVA-IMR) to investigate the effect of different Mn (II) concentrations (10 mg L-1, 50 mg L-1, and 90 mg L-1), Cd (II) concentrations (10 mg L-1, 20 mg L-1, and 30 mg L-1), and hydraulic retention time (HRT) (6 h, 8 h, and 10 h) on simultaneous nitrate, Cd (II), and Mn (II) removal. Using the advanced modified biomaterial Fe3O4@Cu/PVA as carrier to embed bacteria, the performance of the reactor was further improved. The surface morphology of Fe3O4@Cu/PVA was characterized by SEM as a rough surface three-dimensional skeleton structure. When the HRT was 10 h, Mn (II) and Cd (II) concentrations were 40 mg L-1 and 10 mg L-1, respectively, indicating that the immobilized Pseudomonas sp. H117 with Fe3O4@Cu/PVA achieved the highest nitrate, Cd (II), and Mn (II) removal efficiencies of 100% (1.64 mg L-1 h(-1)), 98.90% (0.92 mg L-1 h(-1)), and 92.26% (3.58 mg L-1 h(-1)), respectively. Compared with a reactor without Fe3O4@Cu/PVA addition, the corresponding removal ratio increased by 22.63%, 7.09%, and 15.96%. Gas chromatography (GC) identified nitrogen as the main gaseous product. Moreover, high-throughput sequencing showed that Pseudomonas sp. H117 plays a primary role in the denitrification process.