achieving very low limits, in coagulation processes.
One possible means of overcoming these
problems is through the ion exchange membrane
bioreactor (IEMB) [1], illustrated in Fig. 1. This
approach allows for the isolation of the microbial
culture from the feed stream through a membrane
barrier (in the “biocompartment”), avoiding contamination
of the treated water with cells, metabolic
by-products and excess levels of carbon.
The charged ion exchange membrane excludes
similarly charged ions, while permitting the flow
of oppositely charged ions. The transport of
charged micro-pollutants to the biocompartment
can be stimulated by supplying an excess of a
harmless ion to the biocompartment for counter
transport, according to Donnan dialysis principles.
The conversion of the pollutant in the biocompartment
keeps its concentration at low
levels and consequently ensures an adequate
driving force for transport. Since Hg is often
present in the cationic form (Hg2+), a negatively
charged cation-exchange membrane is required
for pollutant transport; while arsenic is often
present as negatively charged arsenate (H2AsO4
–)
or arsenite (H2AsO3
–), thus permeable through
positively charged anion-exchange membranes.
This technology has shown excellent performance
for the removal of pollutants such as
nitrate and perchlorate from drinking water,
however, the IEMB potential for the removal of
Hg and As has not yet been investigated. This
paper explores the use of the IEMB system for
mercury and arsenic removal from drinking
water treatment systems.