29
Tableau 1: Average and standard deviation concentration for D&F in the leachate from the wood
pole yard and in the influent and effluent of the willow-CW
Leachate
Willow-CW
HSSF CW influent Influent
Effluent
TEF
1
Conc.
3
TEQ
2
Conc. TEQ
Conc. TEQ
Units
pg/L
pg TEQ/L pg/L pg TEQ/L pg/L pg TEQ/L
Furans
TCDF
0.1
81
8.1
1.5
0.15
1.1
0.11
PeCDF
0.03
764
22.9
1.2
0.04
1.2
0.04
HxCDF
0.1
790
79.0
9.1
0.91
1.6
0.16
HpCDF
0.01
1915
19.2
46.0 0.46
0.9
0.01
OCDF
0.0003 1745
0.5
48.0 0.01
2.0
6.0E-04
Sommation
5295
129.7
105.8 1.57
6.8
0.32
Dioxins
TCDD
1
34
34.0
0.7
0.70
1.5
1.50
PeCDD
1
310
310.0
1.5
1.50
1.4
1.40
HxCDD
0.1
1840
184.0
5.8
0.58
1.4
0.14
HpCDD
0.01
5640
56.4
485.0 4.85
2.1
0.02
OCDD
0.0003 13400 4.0
126.0 0.04
5.5
1.7E-03
Sommation
21224 588.4
619.0 7.67
11.9 3.06
Total D&F
26519 718.1
724.8 9.24
18.7 3.38
1 : Toxicity equivalency factors (Van den Berg et al., 1998), 2 : Toxicity equivalency, 3 : dioxins and
furans contents, TCDF/D = Tetrachlorinated dibenzo-p-furans and dioxins; PeCDF/D = Pentachlorinated
dibenzo-p-furans and dioxins; HxCDF/D = Hexachlorinated dibenzo-p-furans and dioxins; HpCDF/D =
Heptachlorinated dibenzo-p-furans and dioxins; OCDF/D = Octachlorinated dibenzo-p-furans and dioxins
According to our results, based on toxicity equivalency (TEQ), the willow-CW treatment allowed
achieving an extra 63 % D&F removal. Therefore the studied treatment chain (i.e. HSSF-CW and
willow-CW) achieved a global removal of 99.5%. Although, these important removal
efficiencies, it didn’t allow to meet the effluent criteria objectives which is about 0.0051 pg
TEQ.L
-1
for the summation of D&F calculated using the TEQ factors (WHO, 2006). Precipitation
and evapotranspiration affected the water balance and caused unpredictable flow of wastewater
through the wetland as also reported by Rash and Liehr (1999). During hot summer days of July
and August with minimal rainfall and maximum day temperatures of 35°C, no outflow was
recorded at the outlet of the willow-CW. Willows-CW could be built to ensure complete
evapotranspiration of water or to limit the water outflow of such process trains. As plant
evapotranspiration effectively concentrates the effluent the TEQ removal efficiency would be
best computed considering masses of TCDD/F removed.
Willow growth and health showed no signs of growth loss despite the added pollutants. No
metals were found in the willow tissues. Biosorption tissues analyses highlighted that willows
preferentially bioaccumulated D&F in their roots ([D&F]
root
= 0.12 ng TEQ/kg DW, [D&F]
shoot
=
0.02 ng TEQ/kg DW).
