Title: Removal of Cationic Heavy Metals from Drinking Water Supplies through the Ion Exchange Membrane Bioreactor
1Removal of Cationic Heavy Metals from Drinking
Water Supplies through the Ion Exchange Membrane
Bioreactor
- Adrian Oehmen
- Universidade Nova de Lisboa
- Portugal
2Heavy Metal Pollution in Waterways
- Mercury is the heavy metal with the highest known
toxicity. - Mercury is a bioaccumulative toxin that attacks
the central nervous and endocrine systems. - Can cause brain damage
- Mercury pollution enters water systems mainly
through rainfall and effluents from industrial
processes. - In water supplies, mercury exists primarily in
the cationic form (Hg2). - Maximum contaminant level for mercury in drinking
water - 1-2 ppb (WHO, US EPA)
3Ion Exchange Membrane Bioreactor (IEMB)
- Combines the transport of an ionic pollutant
(e.g. Hg2) with its simultaneous bioconversion.
- Hg2 is transported through a cation exchange
membrane at the expense of a harmless counterion
(Na). - Hg2 is then converted to Hg0 via biological
reduction, stripped from the liquid phase and
recovered in the gas phase. - The IEMB concept has successfully been applied
for the removal of anionic pollutants such as
nitrate, perchlorate and arsenate from drinking
water.
4Hg2 Transport and Bioreduction through the IEMB
Stripping to Gas phase
Hg0
Oxygen, carbon source, nutrients
Biocompartment
Water compartment
Cation Exchange Membrane
Biofilm
5Advantages of the IEMB System
- Promotes selective and efficient pollutant
removal - The associated brine solution from membrane
transport is treated - Provides a physical barrier between the polluted
water and microbial cells, carbon sources. The
initial water matrix is otherwise maintained
largely intact. - Thus, prevents secondary contamination of
drinking water - The treated water production rate does not depend
on the hydraulic retention time of the
biocompartment
6Objectives of this Study
- Selection of a suitable cation exchange membrane
- Evaluate Hg2 transport through 11 different
commercially available cation exchange membranes
by Donnan dialysis. - Biological Hg2 removal using mixed microbial
cultures - Investigate the effect of carbon source on the
process performance and Hg2 reduction kinetics. - Integrate these 2 processes in the ion exchange
membrane bioreactor to achieve Hg2 removal from
drinking water
7Cation Exchange Membrane Selection Hg2 Flux
- Fumatech FKE membrane exhibited high flux, good
mechanical stability and reasonable price
8Microbial Hg Resistance Mechanism
(Wagner-Döbler et al., 2003)
- Hg2 is converted to Hg0, via the MerA enzyme
- Hg0 is then stripped from the liquid to the gas
phase, and recovered through e.g. adsorption onto
various materials
9Mercury Measurement Methodology
Carbon source, nutrients, biomass, Hg2
Gas-phase measurement
N2 gas
Gas Flow (with Hg0)
Liquid-phase measurement
10Biological mercury reduction
Glucose culture
Acetate culture
- Two mixed cultures were enriched with Hg2
reducing organisms using different carbon sources - Glucose
- Acetate
- Most of the Hg2 was reduced to Hg0 and stripped
to the gas phase
11Biomass Growth of the Mixed Cultures
Glucose culture
Acetate culture
- Hg2 bioreduction and biomass growth were not
simultaneous - Biomass growth commenced only after Hg was
completely removed - Delay in growth of acetate culture
- Glucose was partially converted to acetate and
tended to accumulate
12Carbon Source Swap
Glucose culture
Acetate culture
- Glucose culture
- Hg2 reduction rate much slower with acetate as
carbon source - Acetate culture
- Half-saturation coefficient (KHg) is
substantially higher with acetate - Mercuric acetate complexes may be more difficult
to biodegrade
13Comparison of Culture/Carbon Source
- Glucose was a more effective substrate for
- Culture selection
- Bioreactor operation
- Good Hg mass balance recovery was achieved (gt85)
14IEMB Setup
Membrane
Water Effluent
Air Pump
Bio-Medium
pH Meter
Bio-Effluent
Dissolved Oxygen Meter
Water Feed
Magnetic Stirrer
Gold Trap
Filters
Water Compartment
Bio Compartment
Gas Flow (with Hg0)
15IEMB operation
- IEMB operated using the glucose mixed culture
- Hg2 removal gt98 at an F/A ratio of 1.5 l/(m2h)
- Hg also removed in the biocompartment (lt10 ppb)
F/A 15 l/(m2h)
F/A 1.5 l/(m2h)
16IEMB Effect of Membrane Pre-Treatment
- Membrane pre-treatment in HgCl2 increased Hg flux
through the membrane
17Conclusions
- A suitable cation exchange membrane (Fumatech
FKE) was selected for IEMB operation - Glucose was found to be a more favourable carbon
source for the operation of mixed microbial
cultures, in terms of - Enriching an effective microbial community for
Hg2 bioreduction - Maximising the rate of Hg2 bioreduction,
minimsing the mercury half-saturation coefficient
(KHg) - The integrated IEMB system was shown to be very
effective in removing a high level of Hg (gt98) - Experimental study is currently ongoing to
evaluate its potential at low Hg concentrations - Process applicable for the removal of other heavy
metals with optimisation of the biocompartment
(e.g. biosorption)
18Acknowledgements
- Co-authors D. Vergel, J. Fradinho, J. L. Capelo,
S. Velizarov, J. G. Crespo, M. A. M. Reis - The financial support by Fundação para a Ciência
e a Tecnologia (FCT), Portugal through Project
No. PPCDT/AMB/57356/2004 and postdoctoral
research grant SFRH/BPD/20862/2004.