Low Cost Design of Arsenic Removal from
Groundwater in Bangladesh
Kevin Banahan | Jeremy Kozub | Jesse AmselWentworth Institute of Technology
Environmental Engineering Capstone
Spring 2005
Overview of Arsenic problem
• Reliance on Surface Water
• Shift to Wells in early 70’s• 8-12 Million Wells• 35-77 million people in
regions where some wells are known to be contaminated
• Maximum concentration recommendation by WHO is 10ug/L
• Maximum concentrations in Bangladesh 50ug/L
Arsenic Pollution Mechanisms
• Arsenic is released by oxidation of pyrite
• Arsenic sorbed to minerals by over application of fertilizer
• Anoxic conditions allow iron oxyhydroxides release sorbed arsenic to solution
(8FeOOH + CH3COO- + 15H2CO3
→ 8Fe2+ +17HCO3- + 12H2O)
Theory of Arsenic Removal
Chemistry of arsenic removal from groundwater by sorption
• Synthetic groundwater composition =
H2O + As(III) + CaCl2 + MgCl2 + KCl
• Chloride ions will oxidize Arsenite (As III) to Arsenate (As V) in the presence of atmospheric oxygen
•H3AsO4 + Fe(OH)3 FeAsO4.2H2O + H2O
Our Design Considerations
• Low cost
• Simple to make
• Easy to use
• Constructed of local materials
• Takes advantage of native labor
Client Statement Problem Definition
Final Design
Conceptual Design
Preliminary Design
Detailed Design
Design Communication
5 Stage Model
To develop a low-cost treatment system for the removal of Arsenic from groundwater in Bangladesh
•Objectives –<50 ppb
•User Requirements–Family Scale–Easy to use
•Constraints–Transport of water
•Design Specifications–Sorption Isotherms–Retention time
•Alternatives–“Tea-bag” sorbent sack–Loose sorbent–Adapted column
•Verification of analytical method
•Refine process to synthesize groundwater
•Saturation experiments
•Regeneration experiments
•Refine chosen design
•Optimize chosen design
•Scale model construction
•Test and evaluate design
•Documentations:
–Analytical method–Synthetic groundwater creation method–Daily laboratory activities–Experimental data
•Completion of final design report
•Conclusions
•Suggestions
Conceptual Design
Sorbent Kinetics
0
20
40
60
80
100
0.1 1 10 100 1000 10000
Retention Time (min)
Arsenic Concentration (ppb)
Breakthrough Curve
0
20
40
60
80
100
120
0 300 600 900 1200 1500 1800
Cumulative Groundwater Treated (ml)
Arsenic Concentration (ppb)
Detailed Design
Rinsed Sorbent
54% Settled Solids
17% Aqueous29%
Suspended Solids
Effect of Particle Size on Sorption
Arsenic Mass Partitioning
Aqueous
Suspended Solids
Settled Solids
Sorbent w/ fines
0% Settled 10%
Aqueous
90% Suspended
Solids
mixed settled
Sorbent w/ fines 400 40
Rinsed Sorbent 185 70
Parts per Billion of Ingestible Arsenic(Initial Concentration = 400 ppb)
Column Experiments
Objective
• Determine Sorptive Capacity in a bench-scale treatment unit
Sorption
Initial Conc 0.3 mg/L
Final Conc 0.128 mg/L
Volume Treated 2 L
Mass Sorbed 0.344 mg
Mass Sorbent 38 g
mass/mass sorptive capacity
0.009 mg/g
Material Balance to Determine Sorptive Capacity
Column Breakthrough
0
50
100
150
200
250
300
0 50 100 150 200
Pore Volumes (1 pore volume = 11.4ml)
Effluent Concentration
(ppb Arsenic)
Sorption Curve for Raw Sorbent
Bangladeshi Technology Transfer
Recommendations for further work
• Full-scale pilot study
– 10-15 cm diameter about 10 kg of sorbent.
– Model everyday use for a week.
• Soaking scheme for regeneration.
• Lab studies using native materials
– Bamboo, safi cloth
Acknowledgments
• Dr. Jack Duggan (Design Advisor)
• Dr. Seth Frisbee (Stakeholder)
• Wentworth Professors Larry Decker, Francis Hopcroft and Henderson Pritchard for technical assistance
Thank you
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