A team of engineers developed a novel, chemical-free method to remove arsenic from groundwater in West Bengal, India. The method uses bacteria to oxidize arsenic in an underground aquifer treatment system. Six such plants are now operating and supplying over 6,000 liters of safe drinking water per day at a low cost of $1 per 10 cubic meters. This subterranean arsenic removal process could provide an affordable solution to arsenic-contaminated groundwater used by millions of people worldwide.

1. 22 MAY 2010 Asian Water
SPECIAL FEATURE
Arsenic is a naturally occurring
and highly toxic element found
in groundwater in many parts of the
world. Wikipedia has reported that
137 million people are affected in
70 countries by consuming arsenic-
contaminated water. In most affected
countries, groundwater is the main
sourceofwaterfortheruralpopulation.
These communities urgently require
a simple and affordable solution to
remove arsenic from groundwater for
both drinking and irrigation purposes.
Therefore a chemical and waste free
treatment method could provide long
term solution to this pressing problem.
This report describes a novel chemi-
cal free method that was successfully
developed by a team of engineers to
remove arsenic (As) from groundwater
in a village in West Bengal, India. Six
such plants are now in operation in
rural locations and are being used to
supply water to the local population.
Each plant produces up to 6000 litres of
Getting
bacteria
to remove
arsenic from
groundwater
A low-cost, chemical free
method to remove arsenic from
groundwater has been suc-
cessfully developed by a team
of engineers. This could help
millions of people exposed to
the dreaded mineral in large
swathes of the world.
safe drinking water depending on the
demand (arsenic concentration <10
ppb) with a typical production cost of
US$1 for every 10m3.
The initial study was conducted at
Kasimpore, a village in North 24 Parga-
nas District, approximately 25km from
Kolkata during the period April 2005
to March 2008. The main sources of
water in the village were shallow wells
and tube wells. Kasimpore was chosen
as the model village in this study since
fielddatarevealedthat70%ofthetube
wells inthisvillagehadarsenicconcen-
trations above 100 µg.L-1, as compared
to the WHO guideline value of 10 µg.L-1.
The village is located in the lower
Gangetic plains of West Bengal, where
arseniccontaminationhasreachedan
alarming level. The first trial plant was
set up with the following aims.
1. To develop a new technology
based on ‘in-situ arsenic removal’
method from groundwater without
the aid of any chemicals;
2. To produce safe water at a very low
cost that is affordable to margina-
lised rural communities;
3. To keep the plant cost below
US$2,000 and cost of supplying po-
table water to each family to about
US$2 a month.
4. Thetreatmentsystemcouldbeused
for irrigation if required, to supple-
ment canal water supply.
Though arsenic in groundwater is of
geological origin, the global nature of
contamination became apparent in
the last decade as the use of ground-
water for drinking as well as irrigation
has increased many folds. In terms of
the population affected, it is the one
ofthemostseriousenvironmentalprob-
lems in the world. Following the clinical
evidence for the chronic toxicological
effects of arsenic in drinking water, the
WHO guideline value for As in drinking
waterwasprovisionallyreducedin1993
from 50 μg l-1 to 10 μg l-1.
Installing the pump
By Bhaskar Sen Gupta,
Suvabrata Chatterjee,
Praphawadee Otarawanna and
Soumyadeep Mukhopadhyay

2. Asian Water MAY 2010 23
SPECIAL FEATURE
Localised groundwater arsenic
problems are now being reported
fromanincreasingnumberofcountries
around the world and many new cases
are likely to be discovered. A significant
amount of research has been carried
out over the last decade on charac-
terising and occurrence of arsenic in
affected region across the world.
While many of these areas are
related to the areas of mineralisation
and mining activities (such as in USA,
Canada, India and Thailand), there
are areas in Japan and New Zealand
where the arsenic contamination of
groundwater is due to geothermal flu-
ids. However, the areas of high arsenic
occurrence are located in the uncon-
solidated sediments such as inland
closedbasinsinaridorsemiaridregions
such as Argentina, Mexico and South
West America or large alluvial and del-
taic plains like the Bengal delta.
One of the world’s most significant
arsenic poisoning from exposure to
groundwater occurs in the Bengal
delta. Very high arsenic concentration
in groundwater is found in areas where
the concentration in the sediments
ranges from 2000-10000 μg/kg. The
high levels of arsenic probably occur
due to three separate factors; (i) arse-
nic is present in the aquifer sediments,
(ii) mobilisation of arsenic from the soil
to the groundwater and, (iii) transport
by groundwater movement.
However, common anthropogenic
hypotheses cannot explain large
scale groundwater contamination in
the deltaic plain of Bangladesh and
West Bengal. Most researchers concur
on the following phenomena as key
contributing factors for high arsenic
mobility in groundwater.
• Change in pH;
• Change from oxidising condition to
reducing condition or vice versa;
• Biological activity
The conventional technologies
used in India and elsewhere for ar-
senic removal are based on ‘pump
and treat’ method involving either
adsorption or membrane processes.
Such plants are expensive to run and
have problems associated with waste
disposal and maintenance. In contrast,
Subterranean Arsenic Removal (SAR)
or ‘In-situ treatment’ plants neither use
any chemicals, nor produce a waste
stream. Their installation is similar to a
tube-well; all parts are easily available
in most parts of the world and can be
installed by village technicians.
The SAR Process (www.insituarsenic.org)
High concentration of As in ground-
water in the Gangetic plains of West
Bengal and Bangladesh is due to the
presence of bacteria in the groundwa-
ter that use arsenic bearing minerals
as a source of energy among one of
the available sources, turning insoluble
As(V) to soluble As(III).
Inspecting works
Figure 1: Schematic diagram
of the SAR Process

3. 24 MAY 2010 Asian Water
SPECIAL FEATURE
The process was reversed by re-
charging aerated water (DO > 4 mg/L)
in the treatment zone of aquifer which
suppressed the growth of arsenic re-
ducing bacteria and promoted the
growth of chemoautotrophic arsenic
oxidising bacteria (CAOs) over a pe-
riod of six to eight weeks.
Subterranean groundwater treat-
ment is in a way similar to oxidation
andfiltrationprocessesofconventional
surface treatment plants for removal
of Fe and Mn from water but has: (i)
the added benefit of huge adsorption
space of more than 3000 m3 in the
aquifer zone for a small plant and, (II)
theadvantageofenzymaticoxidation
of As (III) to insoluble AS (V).
The process is unique on account
of the following features:
1. The underground aquifer is turned
into a natural biochemical reactor
andadsorber,thatremoves soluble
As along with Fe and Mn at an el-
evatedredoxvalueofgroundwater
(Eh> 300 mV in the oxidation zone),
when dissolved oxygen concentra-
tion in the groundwater is raised
above 4 mg/L.
2. The oxidation processes are ac-
celerated by the autocatalytic
effect of the oxidation products
and by the autotrophic microor-
ganisms. No chemicals are used
and no sludge is produced in the
process, thus maintaining normal
permeability of the aquifer. Every
single component used in the plant
is available from local hardware
shops.
A simple layout of the plant is il-
lustrated in Figure 1. In order to create
anoxygen-richzonethatpromotesthe
growth of arsenic oxidising bacteria,
water was aerated in a tank by pump-
ing the water through plastic shower
heads, and a measured quantity was
returned to the aquifer at the same
depth in a predetermined time gap.
Groundwater generally has low
oxygen content and the shower-
ing process increased the dissolved
oxygen up to 6 mg/L. The operating
sequence comprised delivery, inter-
mission (rest) and infiltration (Figure 2).
The basic design of a subterranean
treatment plant consists of an aeration
chamber containing a spray nozzle or
Constructing the treatment plant
Figure 2: A sample operating programme for an in-situ treatment plant
Figure 3: Adsorption phenomenon
in the aquifer

4. 26 MAY 2010 Asian Water
SPECIAL FEATURE
water jet air pump, a storage tank and
pipelines for delivery from the aquifer
to the overhead tank and back. All
plant components are available from
local DIY shops. T
The success of the process also
depends on controlled precipitation
of iron (Fe) on the aquifer sand so that
the precipitate has a dense goethite
or lepidocrocite type structure. Con-
trolled precipitation of Fe also ensures
that it traps arsenic as it is adsorbed
on the aquifer sand and is subse-
quently oxidised to form a dense and
compact structure, without affecting
the permeability of the aquifer sand.
During the groundwater delivery, Fe
(II) is adsorbed to the surface of the
soil grains, while oxygen rich water
oxidises Fe(II) deposits into insoluble
ferric hydroxide that remove arsenic
as co-precipitation product.
The oxidation processes are ac-
celerated by the autocatalytic effect
of the oxidation products and by the
autotrophic micro organisms. Ferrous
oxide could serve as an energy source
for iron oxidising bacteria. The process
is explained in Figure 3. The method
is very effective in reducing the con-
centration of As below 10 µg.L-1. The
main advantage of this process is
that there is no sludge handling cost.
The oxidation processes are acceler-
ated by the autocatalytic effect of
the oxidation products and by the
autotrophic micro organisms. Ferrous
oxide could serve as an energy source
for iron oxidising bacteria. The process
is explained in Figure 3. The method is
very effective in reducing the concen-
tration of As below 10 µg.L-1
. The main
advantage of this process is that there
is no sludge handling cost. Figure 4 in-
dicates the change in iron and arsenic
concentration at the well outlet in the
first two months of operation. The plant
produces water with arsenic concen-
tration lower than 5 µg.L-1
.
Conclusion
The SAR technology could transform
the way arsenic will be removed from
groundwaterinEasternIndiaandother
parts of the world. It is appropriate for
the Ganga and Mekong delta where
the arsenic is of arsenopyrite origin.
An estimated 70 million people are
affected in India and Bangladesh by
arsenic exposure and another 30 mil-
lion in other ASEAN countries. The tech-
nology holds the promise of achieving
the following goals:
1. Providing safe drinking and irriga-
tion water to millions at an afford-
able price in arsenic affected
areas.
2. Prevention of arsenic related dis-
eases such as cancer of liver, lungs
and bladder as well skin lesions.
3. Reducingarsenicexposurethrough
the food chain
4. Using the enormous water re-
sources of shallow aquifers in South
and South-East Asia, which may be
unsuitable for drinking and irriga-
tion purposes due to high arsenic
content.
Note: Readers can view plant data and
results at www.insituarsenic.org
Fig 4: Change in arsenic and iron concentration in groundwater at Nilgunj Plant in West Bengal
26 MAY 2010 Asian Water
Bhaskar Sen Gupta is a Senior Lecturer
in Environmental Engineering in the
School of Planning, Architecture
and Civil Engineering at the Queen’s
University,Belfast,Ireland.Priortojoining
Queen’s University in 2000, he was an
Associate Professor of Environmental
Management in University of Malaya
and Reader in Chemical Engineering
in Jadavpur University, Calcutta.
Suvabrata Chatterjee is a Senior
Engineer in Aker Solutions’ Process
Department in the UK. Praphawadee
Otarawanna is a PhD student at the
School of Planning, Architecture and
Civil Engineering, Queen’s University
Belfast. Soumyadeep Mukhopadhyay
will be joining the PhD programme at
the University of Malaya from June
2010.