3. Results and discussion
Mercury transport is illustrated in Fig. 2a for
the case of the Nafion 112 (Dupont, USA) membrane,
and clearly display the good permeability of
this membrane for Hg2+ transport. Similarly, As (in
the form of H2AsO4
–) was transported well through
an Ionac MA3475 membrane (Sybron Chemicals
Inc, USA), as shown in Fig. 2b. The flux of ionic
mercury and arsenate through the respective membranes
were calculated as 2.5 ´ 10–8 mmol cm–2 s–1
(0.18 g m–2 h–1) and 2.7 ´ 10–8 mmol cm–2 s–1
(0.14 g m–2 h–1), respectively, under the test conditions.
The optimal membranes for the transport of
ionic mercury and arsenate will be determined
from further testing.
Additionally, a strain of Pseudomonas putida
has been shown to biologically convert mercurial
compounds such as Hg2+ to Hg0, while arsenic can
be precipitated by sulphate-reducing bacteria and
removed using conventional solid–liquid separation
techniques. The capacity of these bacteria to
convert mercury and arsenic compounds will be
clearly displayed in future studies.
In conclusion, the IEMB system appears to
be a promising technology for ionic mercury
and arsenate removal from drinking water without
the risk of secondary contamination by bacteria
or metabolic by-products. We will clearly demonstrate
the IEMB capacity for Hg and As removal
to achieve very low target limits for these toxic
compounds, while optimisation of the integrated
process will be performed using experimental
and modelling techniques.
Acknowledgements
The financial support by Fundação para a
Ciência e a Tecnologia (FCT), Portugal through
Project POCI/AMB/57356/2004 is gratefully
acknowledged. Adrian Oehmen acknowledges
FCT for the post-doctoral grant SFRH/BPD/
20862/2004.