Enhanced aggregation and sedimentation of nanoscale zero-valent iron (nZVI) with polyacrylamide modification

Abstract

Nanoscale zero-valent iron (nZVI) settled slowly and incompletely in a nano-iron reactor (NIR) in wastewater treatment, and the effluent quality and processing capacity of nZVI were degenerated. Herein, three types of polyacrylamide (PAM), anionic-APAM (nZVIAPAM), cationic-CPAM (nZVICPAM), and nonionic-NPAM (nZVINPAM)) were applied to modify the nZVI (nZVIPAM), which were proved to enhance aggregation and sedimentation in the gravity settling clarifier of NIR. PAM modification lead to aggregate by forming large agglomerates. The median sizes of aggregates were 32, 194, 168 and 133 μm respectively for nZVI, nZVICPAM, nZVINPAM, and nZVIAPAM. Under quiescent conditions, bare nZVI needed 5 min to reach sedimentation equilibrium, while nZVIPAM just within 1 min nZVICPAM settled more quickly and completely than nZVINPAM and nZVIAPAM. The Fe concentration in the dynamic flow NIR effluent could keep a low level for 8 h for nZVIPAM, while bare nZVI for 6 h. Iron concentration was 3.11, 0.037, 0.93, and 1.20 mg·L−1 for nZVI, nZVICPAM, nZVINPAM, and nZVIAPAM after 8-h-reaction. Meanwhile, the reactivity of nZVIPAM was kept much longer for lead removal in the NIR. Results demonstrated PAM modifications (especially CPAM) provided a reliable solution for nZVI aggregation and sedimentation in wastewater treatment.