Constructed wetlands for advanced treatment of wastewater with a complex matrix from a metal-processing plant: Bioconcentration and translocation factors of various metals in Acorus gramineus and Cyperus alternifolius

Abstract

A flow-through constructed wetland (CW) has provided advanced treatment of wastewater with a complex matrix from a metal-processing plant. The main CW system (length 20 m, width 46 m, depth 0.3 m) was planted with aquatic plants such as Acorus gramineus, Cyperus alternifolius L., Iris pseudacorus, Lythrum anceps, Myosotis scorpioides, Phyla nodiflora L., and Zantedeschia aethiopica. During August–November 2007, the main CW system reduced total organic carbon concentrations from 5.7 to 1.2 mg/l, total nitrogen from 23.2 to 19.0 mg/l, and NH 4 +-N from 6.8 to 4.0 mg/l, on average, in physicochemically treated wastewater. Furthermore, CW reduced Fe concentrations significantly from 60 to 33 μg/l, Cu from 77 to 40 μg/l, Zr from 5.3 to 1.5 μg/l, Ag from 43 to 14 μg/l, Sn from 54 to 16 μg/l, and Au from 5.8 to 3.2 μg/l. For quantification and assessment of metal accumulation, A. gramineus and C. alternifolius were separately cultivated for 3 months in an experimental CW (length 10 m, width 1.25 m × 2 lanes, depth 0.3 m). The experimental CW showed low removals for most metals, probably because of lower plant density and the shorter HRT than the main CW. Bioconcentration factors (BCFs) of various metals such as Mn, Ni, Cu, Zn, In, Sm, Au, Pb, and Bi for both plants were 10 3–10 4. Generally, the metal with the higher concentration in water presented higher contents in plants. Both emergent plants commonly showed BCFs higher than >10 4 for Fe but lower than <10 3 for Ag and Zr. Regarding accumulated metals, roots generally showed higher metal contents than the rhizomes, stems, or leaves. Translocation factors (TFs) of most metals from roots to rhizomes or leaves of A. gramineus were 10 −2–10 0. Neither Pb nor Zr was detected in leaves of A. gramineus. The TFs of most metals for rhizomes, stems, and leaves of C. alternifolius were, respectively, 10 −1–10 1, 10 −3–10 0 and 10 −2–10 0. No Mn, Ni, Zr, Pb, or Bi was detected in leaves and/or stems, but some were found in roots of C. alternifolius.