Polycyclic Aromatic Hydrocarbon Accumulation in Phragmites australis Grown on Constructed Wetland for Sludge Stabilization

A pilot-scale constructed wetland was tested for the disposal and stabiliza- tion of sludge from a municipal wastewater treatment plant. The accumulation and dis- tribution of sixteen polycyclic aromatic hydrocarbons (PAHs) in the plants of Phragmites australis grown on the wetland receiving the sludge was investigated in comparison with native plants without the sludge to examine the effectiveness using P. australis as PAHs bioaccumulator. The experiment lasted for three years and divided into three phases: year 1 was adjustment phase; year 2 was operational phase; year 3 was natural stabili- zation phase. Analysis of the distribution of PAHs in native P. australis showed that the sequence of PAHs content in the plants was leaves > stems > roots at 2583, 2198 and 899 µg/kg (DW), respectively. After two year load and one year natural stabilization, the PAHs content in the loaded sludge declined by 63%; the tested plants in the constructed wetland accumulated much more PAHs than native plants. The bioconcentration fac- tor (BCF) of leaves was slightly higher than that of roots and stem i.e. 3.759, 3.518 and 3.368, respectively. The respective PAHs contents in the roots, stems and leaves of the tested P.australis were 7313, 7002 and 7814 µg/kg (DW), being 8.13, 3.19 and 3.02 times of that in the native one, respectively. The BCF of roots and stems of the low molecular weight (MW) PAHs (2-3 ring PAHs) predominated as 5.02 and 4.93 in all samples from the constructed wetland, while the BCF of middle-MW PAHs (4 ring PAHs) was 3.15 and 2.1, and that of high-MW PAHs (5-6 ring PAHs) was 2.29 and 2.63, re- spectively. In the leaves, the BCF of low-MW and middle-MW PAHs was 4.03 and 4.17, which was higher than 2.81 of high-WM PAHs. The results demonstrated that this plant can effectively remove PAHs from the sludge discharged to the wetland.