CONCLUSIONS
Within the zinc concentration range used in this study (1.05 to 4.85 mg l-1), the aquatic moss Fontinalis
antipyretica can accumulate, at equilibrium, the metal ion by a factor 4531 to 1220 (Zn concentration in the
moss, mg Kg-1, dry wt. / Zn concentration in water, mg l-1).
Cw=3,49 mg l -1 ;Hardness=150 mg CaCO 3 l -1
0
1000
2000
3000
4000
5000
6000
0 50 100 150 200 250 300
Time (h)
C (
µg g-1 dry wt.)
k1=139 h-1
k2=0,103 h-1
Cmr=1648 mg l-1
6th World Congress of Chemical Engineering
Melbourne, Australia 23-27 September 2001
The metal uptake rate, for identical water hardness, tends to decrease as the Zn concentration in the water
increases, suggesting a toxic effect in mosses and a subsequent deterioration of their physiological state.
Competitive adsorption exists between zinc and calcium ions. For similar Zn concentrations the
bioaccumulation tends to decrease as the total hardness of water increases.
At the end of the decontamination stage, plants only retain on average about 20% of the metal
accumulated at the end of the uptake period.
A first-order mass transfer model adequately describes the metal uptake and release stages, then
permitting the calculation of the kinetic constants and equilibrium concentrations.
The model permits to calculate the time required to reach the metal concentration in the mosses close to
the equilibrium concentration; this parameter is useful for monitoring purposes.