Pilot-scale demonstration of phytoremediation of PAH-contaminated sediments by Hydrilla verticillata and Vallisneria spiralis

The results of phytoremediation of sediments contaminated with polycyclic aromatic hydrocarbons (PAHs) by two submerged aquatic plants (Vallisneria spiralis and Hydrilla verticillata) at pilot scale were reported for the first time in this study. During a 108-day period, the plants grew well, and more PAHs were dissipated in planted sediments than in unplanted sediments. At the end, dissipation ratios of phenanthrene and pyrene were 85.9% and 79.1% in sediments planted with V. spiralis, 76.3% and 64.6% in sediments planted with H. verticillata, but only 64.8% and 55.8% in unplanted sediments. V. spiralis exhibited higher phytoremediation ability, which was significantly related to its root oxygenation as indicated by the redox potential in sediments. The remediation results at pilot scale were also compared with those previously obtained in our laboratory. The ratio of root weight to sediment weight showed a similar trend to PAH dissipation enhancement. Bioconcentration factors of PAHs in the two plants were larger in the pilot experiment than in the laboratory tests as a result of quicker increase of plant weight in the pilot experiment.