(643b) Sustainable Arsenic Removal Using Hybrid Anion Exchange Resins (ArsenXnp) In Remote Villages of West Bengal, India

Community level
arsenic removal devices in remote villages of West Bengal, India, now use hybrid
anion exchange resins (HAIX) which are essentially spherical anion exchange
resin beads containing dispersed nanoparticles of hydrated ferric oxide (HFO).
HAIX, now commercially available in the US as ArsenX^np, is a highly
selective media for removal of oxyanions of arsenic. The high selectivity of
HAIX towards arsenic oxyanions is attributed to the Donnan membrane effect. The
sorption columns used in the field for removal of arsenic are either single
column or split column design. The sorption columns are designed to allow flow
of atmospheric oxygen dissolution of which in arsenic-contaminated raw water
promotes oxidation of dissolved Fe(II) species to insoluble Fe(III) oxides or
HFO particulates. Apart from the usual role played by the sorbents like ArsenX^np
or activated alumina towards arsenic removal, the HFO particulates formed
inside the column also aid in the treatment process. Each unit is attached to a
hand-pump driven well and capable of providing arsenic-safe water to three
hundred (300) households or approximately one thousand villagers. No chemical
addition, pH adjustment or electricity is required to run these units. On the
average, every unit runs for more than 20,000 bed volumes before a breakthrough
of 50 mg/L of arsenic, the maximum
contaminant level in drinking water in India, is reached. In addition to
arsenic removal, significant iron removal is also achieved throughout the run.
Upon exhaustion, the media is withdrawn and taken to a central regeneration
facility where 2% NaCl and 2% NaOH solution is used for regeneration.
Subsequently, the regenerated resin is reloaded into the well-head sorption
column. Laboratory investigations confirmed that the regenerated ArsenX^np
is amenable to reuse for multiple cycles without any significant loss in
capacity. Field studies are under way to supplement the laboratory observation.
The process of regeneration and subsequent sludge formation reduce the volume
of disposable arsenic-laden solids by nearly two orders of magnitude. Finally,
the arsenic-laden solids are contained on well-aerated coarse-sand filters with
minimum arsenic leaching. This disposal technique is scientifically more
appropriate than dumping arsenic-loaded adsorbents in the reducing environment
of landfills as currently practiced in developed countries.