Image adapted from www.water4people.org

Arsenic Remediation in Arsenic Remediation in Bangladesh/Nepal:Bangladesh/Nepal:

The 3-kalshi Method vs.

The Arsenic BioSand Filter vs.

Well head removal

Stephanie ArbelovskyAndrea 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

• 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

• FiltrationComputer 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

• 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

0

50

100

150

200

250

300

0 5 10 15 20 25

Flow Rate (L/hr)

Fil

tere

d A

rsen

ic C

on

ten

t (p

pb

)

Coal 754 gm Coal 606 gm Coal 757 gm

Advantages

• Inexpensive, locally manufactured materials

• Point-of-use technology

• Uses existing tubewell infrastructure

• Easy to construct and operate

ARSENIC BIOSAND FILTER

Arsenic BioSand Filter (ABF)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 arsenic-affected

villageshttp://ceemeng.mit.edu/~water/Docs/Other%20Documents/NgaiWalewijk-%20ABF%20Report2003.pdf

Arsenic Removal UnitArsenic Removal Unit• Metal Diffuser Box, Iron Nails,

and Polyester Cloth

Pathogen Removal UnitPathogen 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

Integration of 2 Removal UnitsIntegration of 2 Removal Units

How Does Arsenic Removal How Does Arsenic Removal Work??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

Concrete ABF’s were constructed by

International Buddhist Society

•Can be entirely constructed with locally available materials and local labor

Metal diffuser boxes manufactured in a metal

shop in Kathmandu

ABF InstallationABF InstallationMaterials 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 CleaningABF 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

ResultsResults

• AFB found to be effective removing:– Arsenic: 85 – 96%, mean 93%– Total Coliform: 0 - >99%, mean 58%– E. coli: 0 - >99%, mean 64%– Iron: >90 - >97%, mean >93%

Users Liked. . .Users Liked. . .

• 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.

• Utilizes activated alumina to adsorb arsenic.

• Column lasts 10 to 15 years, but must be regenerated with caustic soda every 4 months.

• Initial installation costs Rs. 50,000 ($1250), but can provide water for two to three hundred households.

• 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.

• In all 8 locations, families pay approximately Rs. 50 per month for maintenance and operating costs. The poor are exempt.

• Tradition/routine of pumping water is not disturbed.

Pteris vittata: Plant Technology?

• Can remove arsenic directly from water in a process called phytofiltration.

• Fern native to Asia and Africa. Commonly called Chinese Brake Fern.

• 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

• 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/

fern.php• http://pubs.acs.org/subscribe/journals/esthag-w/2001/

may/science/kc_fern.html• http://www.science-writer.co.uk/award_winners/20-

28_years/2004/winner.html