Image adapted from www.water4people.org
Arsenic Remediation in
Bangladesh/Nepal:
The 3-kalshi Method vs.
The Arsenic BioSand Filter vs.
Well head removal
Stephanie Arbelovsky
Andrea Hektor
Christina Hynes
(team typhoidfun)
Overview
• Arsenic in Bangladesh
• 3-kalshi Method
• Arsenic Biosand Filter
(ABF)
• Well-head removal
• Pteris vittata
• Conclusion
Contamination: Timeline
• Pre-1970: Microbial contaminated
surface water
• 1970: 2.5 million tubewells drilled
• 1990: 95% of population dependant
on groundwater
• 1993: Widespread arsenic
contamination
– 60% of wells above WHO
guideline (10 ppb)
– 30% of wells above Bangladesh
guideline (50 ppb)
THE 3-KALSHI METHOD
Construction
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3 kalshis
Stand (steel or bamboo)
Course/Fine sand
Wood charcoal
Iron filings
Synthetic fabric
Photo courtesy Susan Murcott
Removal processes
• Zero-valent iron
– Arsenate (V) / Iron Oxides
• Precipitation
– Arsenite (III) / Fe (II)
FeAsO4 , also AlAsO4
• Adsorption
– Arsenate (V) / Fe(OH) 3
• Filtration
Computer image courtesy Sandia National
Laboratories
Effectiveness
• Khan’s Study:
– As(III) removal from 800 ppb to less than 2 ppb
– Final As(total) concentration less than 10 ppb
• Hurd’s Study:
– As(total) removal from 215 ppb to 4 ppb
Flow rate
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3 L water/day for adults recommended
3-kalshi provided 42-148 L/day (Khan)
Efficiency decreases with increased flow rate
Inconsistencies in the literature
Flow Rate vs Final Arsenic Content
Filtered Arsenic Content
(ppb)
Coal 754 gm
Coal 606 gm
Coal 757 gm
300
250
200
150
100
50
0
0
5
10
15
Flow Rate (L/hr)
20
25
Advantages
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Inexpensive, locally manufactured materials
Point-of-use technology
Uses existing tubewell infrastructure
Easy to construct and operate
ARSENIC BIOSAND FILTER
Arsenic BioSand Filter (ABF)
• A household-level drinking
water filter developed at MIT
to simultaneously remove
arsenic & pathogens from
tubewell water.
• 3-month pilot study (Sep
2002 to Jan 2003) conducted
in Nepal
– Evaluated performance of filter
under various conditions
– Investigated long-term removal
efficiencies
– Improved filter design
– Implemented filters in arsenicaffected villages
http://ceemeng.mit.edu/~water/Docs/Other%20Documents/NgaiWa
lewijk-%20ABF%20Report2003.pdf
Integration of 2 Removal Units
Arsenic Removal Unit
• Metal Diffuser Box, Iron Nails,
and Polyester Cloth
Pathogen Removal Unit
• Sand and Gravel Layers
. . . So, Why Iron Nails??
• Ferrous hydroxide (iron rust) is
an excellent absorbent for
arsenic
• Surface complexion reaction
occurs when aqueous arsenic
species come into contact with
ferrous hydroxide
How Does Arsenic Removal
Work??
• Iron nails rust when exposed to air and water
• Arsenic absorbed to ferrous hydroxide (FH) particles
• Some arsenic loaded FH particles trapped by polyester
cloth
• Most settle on top of fine sand layer
ABF Manufacturing
•Can be entirely constructed with locally available
materials and local labor
Concrete ABF’s were
constructed by
International Buddhist
Society
Metal diffuser boxes
manufactured in a metal
shop in Kathmandu
ABF Installation
Materials needed:
• A concrete ABF (including metal box
and lid
• 2 bottles of Piyush
– A locally manufactured calcium hypochlorite
solution used initially to disinfect the filter
• 2.5 L gravel (above 6-15 mm grain size)
– Can be collected from local river
• 2.5 L sand (1-6 mm grain size)
• ~30 L of fine sand (less than 1 mm grain
size)
• 1 piece of polyester cloth (30 by 30 cm)
• 5 kg iron nails
ABF Cleaning
• Remove metal box
• Scrape top 2 cm of fine sand layer
by hand
• Remove top layer of water with
small container
• Replace with arsenic-free water
• Repeat process several times
• Replace metal box and lid
Results
• AFB found to be effective removing:
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Arsenic: 85 – 96%, mean 93%
Total Coliform: 0 - >99%, mean 58%
E. coli: 0 - >99%, mean 64%
Iron: >90 - >97%, mean >93%
Users Liked. . .
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High flow rates (~14 L/hr)
Simple operation
Minimal maintenance
Clean-looking, good tasting water
Think that the ABF is a durable, permanent
solution to their drinking water problems!!
WELL HEAD REMOVAL
Larger Scale Treatment
• Starting in 1998, Bengal
Engineering College has installed
in the Parganas and Nadia regions.
• Initial installation costs Rs.
50,000 ($1250), but can
provide water for two to
three hundred households.
• Utilizes activated alumina
to adsorb arsenic.
• Column lasts 10 to 15
years, but must be
regenerated with caustic
soda every 4 months.
• Alumina found to be most effective,
cost-efficient method of removing
arsenic.
• Arsenic sludge generated in a 4-month
period amounts to less than 2 liters of
sludge.
• Requires no electricity.
• Villagers understand basic operating
principles of the units, and collectively
help with day-to-day operations.
• Tradition/routine of pumping water is
not disturbed.
• In all 8 locations, families pay approximately Rs. 50 per
month for maintenance and operating costs. The poor are
exempt.
Pteris vittata: Plant Technology?
• Fern native to Asia and Africa.
Commonly called Chinese Brake
Fern.
• Can remove arsenic directly
from water in a process called
phytofiltration.
• Also able to hyperaccumulate arsenic from the soil.
Generally around 22,630 mg of arsenic per kilogram of
dry fern shoots/fronds.
• In phytofiltration, arsenic water concentrations of 200
micrograms/liter by 100-fold in 24 hours.
• Squeezing sap from the plants in a press removes ¾ of
the arsenic in the plant. This arsenic can then be used for
industrial purposes.
• Researchers determining feasibility/safety of burning
plants for fuel.
Further Research
• Further study on flow rate / efficiency
relationship
• Lifetime of the system
• Cheaper
• Increased arsenic removal
Final Thoughts
• Tubewell
investment
• Perception of threat
• Cost
• Testing capability
• Few researchers,
extrapolated ideas
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http://www.annieappleseedproject.org/ptervitfersu.html
http://ceemeng.mit.edu/~water
www.who.org
www.undp.org
www.unicef.org
http://www.irc.nl/content/view/full/10354
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid
=166674
• http://www.genomenewsnetwork.org/articles/2004/08/06/f
ern.php
• http://pubs.acs.org/subscribe/journals/esthagw/2001/may/science/kc_fern.html
• http://www.science-writer.co.uk/award_winners/2028_years/2004/winner.html